GT27R1A1 Ventilation of Underground Works During Construction

ASSOCIATION FRANÇAISE DES TUNNELS ET DE L’ESPACE SOUTERRAIN Organization member of the AFTES www.aftes.asso.fr

AFTES Recommendations Ventilation of underground works during construction GT27R1A1

AFTES Guidelines GT27-R1A1

Ventilation of underground works during construction English translation of the AFTES Guidelines GT27-R1A1 published in French by «tunnels et Ouvrages Souterrains» n° 176, mars-avril 2003, pp. 76-106 ............... Approved by AFTES Technical Committee, 2003 The following persons contributed to the work of Working Group GT 27 "Ventilation of Tunnels during Construction phase" and to the preparation and drafting of this Recommendation and its 2 Annexes: Recommendation and its 2 Annexes: J.P. BAUD (APAS MBTP) - J.P. BARRAL (TEC INGENIERIE) - DR BOULAT (BOULAT Medical Consultant) B. BROUSSE (CETU) - R. FREANT (BORIE SAE) - D. GABAY (RATP) - J.P. GUICHARD (CRAM Rhône Alpes) P. HINGANT (SCETAUROUTE) - G. LECUYER (RAZEL) - M. LETOUBLON (OPPBTP) - A. MERCUSOT (CETU) J.P. MEYER (INRS) - M.C. MICHEL (OPPBTP) - D. PAYOT (SOTRABAS) - J. PHILIPPE* (SNCF)J. RICARD (ALPETUNNEL / SNCF) - M.O. SENCE (SEITHA) - D. VALLET (CRAM Rhône-Alpes) J.S. VILLEGAS (VINCI Construction) The following persons reread the Recommendation and its Annexes:

A. GUILLAUME (SOCATOP) - G. PIQUEREAU (CAMPENON TP) - P. LONGCHAMP (BOUYGUES) G. COLOMBET (COYNE & BELLIER) - P. FAUVEL (SNCF)

* Jean PHILIPPE contributed extensively to initiating and setting up the W.G. AFTES Welcomes comments on this paper (Translation R obert CHADWICK - Re reading Lucy REW)

CONTENTS Pages

Pages

1 - INTRODUCTION TO THE RECOMMENDATION . . . . . . . . 1.1 - Reason for existence of recommendation . . . . . . . . . . . . . . . . . 1.2 - General approach to ventilation projects . . . . . . . . . . . . . . . . .

8 8 8

1.2.1 - Three basic principles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.2.2 - Applicable regulations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.2.3 - Management process to be followed . . . . . . . . . . . . . . . . . . . . . .

8 8 9

1.3 - Area of application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

9

2 - POLLUTION PHENOMENA . . . . . . . . . . . . . . . . . . . . . . 2.1 - Risk identification procedure . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2 - Prevention rules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3 - Risk analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

10 10 11 12

2.3.1 - Atmospheric quality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3.2 - Health and safety at work stations . . . . . . . . . . . . . . . . . . . . . . . 2.3.2.1 - Pollutants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3.2.2 - Air quality and work station comfort . . . . . . . . . . . 2.3.3 - Pollutant evaluation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3.3.1 - Limiting values . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3.3.2 - Mixtures of substances . . . . . . . . . . . . . . . . . . . . . . 2.3.3.3 - Dust . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3.3.4 - Gases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3.3.5 - Heat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3.3.6 - Fire - Smoke and fumes . . . . . . . . . . . . . . . . . . . . .

12 13 13 13 14 14 14 15 16 17 19

3 - VENTILATION PROJECT . . . . . . . . . . . . . . . . . . . . . . . . 3.1 - Minimum rules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

19 19

3.1.1 - Pollution treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1.2 - Fresh air requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

19 20

3.2 - General ventilation system concepts . . . . . . . . . . . . . . . . . . . . .

20

3.2.1 - Blowing ventilation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.1.1 - Blowing ventilation advantages . . . . . . . . . . . . . . . 3.2.1.2 - Blowing ventilation disadvantages . . . . . . . . . . . . . 3.2.2 - Extraction ventilation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.2.1 - Extraction ventilation advantages . . . . . . . . . . . . . 3.2.2.2 - Extraction ventilation disadvantages . . . . . . . . . . . 3.2.2.3 - Installation recommendations . . . . . . . . . . . . . . . . 3.2.2.4 - Special case: pilot tunnel extraction . . . . . . . . . . . . 3.2.3 - Ventilation by air flow through tunnel network . . . . . . . . . . . . . . . 3.2.3.1 - Advantages of ventilation by air flow through tunnel network . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.3.2 - Disadvantages of ventilation by air flow through tunnel network . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.4 - Combination of different solutions . . . . . . . . . . . . . . . . . . . . . . . . 3.2.5 - Ventilation for open-ended structures . . . . . . . . . . . . . . . . . . . . . . 3.2.6 - Use of permanent ventilation ducts or intermediate shafts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

20 21 21 21 21 22 22 22 23

3.3 - Input data - Design assumptions . . . . . . . . . . . . . . . . . . . . . . .

25

23 23 23 24 24

…/…

Publication en français dans TUNNELS ET OUVRAGES SOUTERRAINS n° 176

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AFTES Guidelines GT27-R1A1 Ventilation of underground works during construction

Pages

Pages

2

3.3.1 - Characteristics specific to structures and ground . . . . . . . . . . . . . 3.3.2 - Construction methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3.3 - Resources implemented . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3.4 - Pollution source determination and characterisation . . . . . . . . . . . 3.3.5 - Determination of fresh air requirements . . . . . . . . . . . . . . . . . . . . 3.3.5.1 - Dilution flow rate for diesel engine exhaust fumes (QDdt) . . . . . . . . . . . . . . . . . . . . . . 3.3.5.2 - Discharge flow rate for haulage-raised non-localised dust (QEpr) . . . . . . . . . . . . . . . . . . . 3.3.5.3 - Collection flow rate for dust and fumes emitted from localized work areas (QCpa) . . . . . . . . . . . . .

3.4 - Ventilation principles retained and general measures . . . . . . . .

28

3.4.1 - Dust treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.4.1.1 - Drill and blast . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.4.1.2 - Roadheaders . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.4.1.3 - Tunnel boring machines (TBMs) . . . . . . . . . . . . . . 3.4.2 - Gas dilution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.4.3 - Air renewal / Fresh air supply . . . . . . . . . . . . . . . . . . . . . . . . . . 3.4.4 - Feasibility of solution retained . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.4.5 - Outline diagrams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.4.5.1 - Blowing ventilation example . . . . . . . . . . . . . . . . . 3.4.5.2 - Extraction ventilation example . . . . . . . . . . . . . . . 3.4.5.3 - Blowing and extraction ventilation example . . . . .

28 29 30 30 30 30 30 31 31 31 31

4 - IMPLEMENTATION . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1 - Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

32 32

4.1.1 - Fans . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1.1.1 - General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1.1.2 - Axial fans . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1.1.3 - Centrifugal fans (Figure 14) . . . . . . . . . . . . . . . . . . 4.1.1.4 - Accelerators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1.2 - Ducting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1.2.1 - Flexible synthetic ducting . . . . . . . . . . . . . . . . . . . . 4.1.2.2 - Steel ducting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1.3 - Ancillary ventilation equipment . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1.3.1 - Distribution devices . . . . . . . . . . . . . . . . . . . . . . . . 4.1.3.2 - Protection devices . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1.3.3 - Soundproofing devices . . . . . . . . . . . . . . . . . . . . . . 4.1.3.4 - Electrical equipment . . . . . . . . . . . . . . . . . . . . . . . 4.1.4 - Dust collection and treatment devices . . . . . . . . . . . . . . . . . . . . . 4.1.4.1 - Limiting dust production . . . . . . . . . . . . . . . . . . . . 4.1.4.2 - Containment systems . . . . . . . . . . . . . . . . . . . . . . . 4.1.4.3 - Dust extractors . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1.5 - Exhaust fume treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1.5.1 - Petrol engines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1.5.2 - Diesel engines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1.5.3 - Different fuels . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1.5.4 - Exhaust fume treatment devices . . . . . . . . . . . . . . . 4.1.6 - Treatment of heat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1.6.1 - Treatment of heat sources . . . . . . . . . . . . . . . . . . . . 4.1.6.2 - Air cooling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1.6.3 - Air heating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

32 32 33 34 34 35 35 36 36 36 37 37 37 38 38 38 39 39 39 39 40 40 41 41 41 41

4.2 - Implementation and installation . . . . . . . . . . . . . . . . . . . . . . . .

41

4.2.1 - Fans . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2.1.1 - At the tunnel portal . . . . . . . . . . . . . . . . . . . . . . . . 4.2.1.2 - In the tunnel driving area . . . . . . . . . . . . . . . . . . .

42 42 42


25 25 26 26 27

4.2.2 - Ventilation ducting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2.2.1 - Flexible duct erection and suspension . . . . . . . . . . 4.2.2.2 - Rigid duct erection and suspension . . . . . . . . . . . . 4.2.2.3 - Duct replacement . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2.2.4 - Passing through equipment . . . . . . . . . . . . . . . . . . 4.2.2.5 - Tunnel driving area . . . . . . . . . . . . . . . . . . . . . . . .

42 43 43 43 43 43

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4.3 - Ventilation procedures and instructions for use . . . . . . . . . . . . . 4.4 - Personnel protective equipment . . . . . . . . . . . . . . . . . . . . . . . .

44 44

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4.4.1 - Collective protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.4.2 - Personal protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

44 44

27

5 - MAINTENANCE AND INSPECTIONS . . . . . . . . . . . . . . . 5.1 - General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.2 - Maintenance and checking . . . . . . . . . . . . . . . . . . . . . . . . . . . .

44 44 45

5.2.1 - Training and information of maintenance personnel . . . . . . . . . . . 5.2.2 - The maintenance logbook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

46 46

5.3 - Inspections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

47

5.3.1 - General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.3.2 - Contractor inspections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.3.2.1 - Ventilation and electrical inspections . . . . . . . . . . . 5.3.2.2 - Atmospheric inspection . . . . . . . . . . . . . . . . . . . . . . 5.3.2.3 - Technical inspections . . . . . . . . . . . . . . . . . . . . . . . 5.3.3 - External inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.3.4 - Measuring apparatus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.3.4.1 - Flow rate measurement . . . . . . . . . . . . . . . . . . . . . 5.3.4.2 - Pressure measurement . . . . . . . . . . . . . . . . . . . . . . 5.3.4.3 - Gas content measurement . . . . . . . . . . . . . . . . . . . 5.3.5 - Inspection frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

47 47 47 48 49 53 53 53 53 54 54

6 - ORGANISATION - ADMINISTRATIVE FRAMEWORK . . . . 6.1 - General approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

55 55

6.1.1 - Level of intervention of the different players . . . . . . . . . . . . . . . . . 6.1.1.1 - Preliminary and detailed design . . . . . . . . . . . . . . 6.1.1.2 - Construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.1.2 - Parties intervening in ventilation design . . . . . . . . . . . . . . . . . . . .

55 56 56 57

6.2 - Contractor consultation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.3 - Contractor's ventilation project . . . . . . . . . . . . . . . . . . . . . . . . .

58 58

6.3.1 - Technical offer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.3.2 - Cost . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.3.3 - Construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

58 59 60

7 - STATUTORY TEXTS . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.1 - Regulations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.2 - Standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

60 60 61

APPENDIX 1 – DIMENSIONING . . . . . . . . . . . . . . . . . . . . 1.1 - Dimensioning of ventilation components . . . . . . . . . . . . . . . . . .

63 63

1.1.1 - Design assumptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.1.2 - Design principles – Basic equations . . . . . . . . . . . . . . . . . . . . . . . 1.1.2.1 - Head losses in ventilation ducting . . . . . . . . . . . . . 1.1.2.2 - Fan design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.1.2.3 - Special design case of tunnel network ventilation . 1.1.2.4 - Atmospheric data . . . . . . . . . . . . . . . . . . . . . . . . . .

63 63 64 67 68 68

1.2 - Calculation outcome - Interpretation . . . . . . . . . . . . . . . . . . . . . 1.3 - Final design - Implementation . . . . . . . . . . . . . . . . . . . . . . . . .

69 69

APPENDIX II – GLOSSARY . . . . . . . . . . . . . . . . . . . . . . . .

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1 - INTRODUCTION TO THE RECOMMENDATION 1.1 - Reason for existence of recommendation Throughout the thought process that prevailed over the drafting of this recommendation, it became clearly apparent that ventilation, whilst certainly fundamental yet insufficient in itself, is just one of the measures required to ensure a healthy atmosphere in underground works during construction. The aim of the recommendation is to serve as a guide for designing the ventilation system of an underground construction site. In other words, all measures and facilities that allow the degree of healthiness and state of purity of the atmosphere to be respected by limiting concentrations of different polluting substances, according to regulations, in view of safeguarding the health of persons in the workplace. As a result, when presenting a ventilation project, the Contractor undertakes to guarantee sufficient fresh air volumes and flow rates to comply with these regulations and to maintain them, irrespective of site configuration.

1.2 - General approach to ventilation projects 1.2.1 - Three basic principles Ventilation studies should comprise three parts, reflecting the following basic principles. • Firstly, it is of prime importance to eliminate or limit as much as possible the emission of obnoxious, even dangerous, polluting substances at different underground construction locations, by planning appropriate techniques for excavation, mucking, support, etc. • The second principle is to favour the collection of all emitted products (especially dust) as near as possible to their source to prevent them from propagating into the site atmosphere. • Finally and only at this stage, residual pollutants not collected or neutralised at source should be diluted to maintain their concentrations below allowable thresholds 1.2.2 - Applicable regulations This recommendation does not call into question Caisse Nationale d'Assurance Maladie (CNAM) [French national health insurance fund] general rules (R352) laid down in the "Recommandations aux Entreprises relevant du Comité technique national des industries du Bâtiment et des Travaux Publics" [recommendations to contractors represented by the French national technical committee for the building and civil engineering industry], adopted on 27th. June 1990. This recommendation takes up the maximum pollutant concentrations and minimum ventilation flow rates given in the above document. However, the means that are to be implemented by the Contractor to maintain atmospheric quality at the required level are not

rigidly fixed. In particular, recent technical developments (extraction ventilation, electric motors, etc.) can lead to proposing varied ventilation systems that enable maximum concentrations to be respected, whilst possibly departing from R352 air flow rates. The aim of this recommendation is precisely to provide designers with all the information required to dimension and justify a ventilation system suited to all construction phases. 1.2.3 - Management process to be followed Managing the ventilation project for underground works during construction requires examining several successive aspects, corresponding to sections 2 and 3 of this recommendation. • Basic design starts with risk assessment in relation to both pollutant emissions and personnel working conditions; this forms the subject of section 2 (Pollution). • Application of minimum rules defined by the CNAM (recommendation R352), recalled in § 3.1. (Minimum rules) provides an initial approximation to the air flow rates to be provided. • The next stage is selecting a ventilation option, following possible comparison of several alternatives. This option will partly depend on structural geometry, construction method and planned phasing of the work. The main ventilation systems currently implemented are described in § 3.2. (General ventilation concepts). • Detailed methods of calculating air flow rates to be guaranteed with respect to pollution sources are described in § 3.3. (Design assumptions). In addition, Annexe 1 (Dimensioning) recalls methods of dimensioning ducts and fans to obtain a given flow rate. • Resulting practical measures must then be detailed, based on recommendations given in § 3.4. (Ventilation principles) for both dust treatment and gas dilution. In support of these different ventilation project development phases, this recommendation provides the reader with the following information: • A detailed description of available ventilation equipment and on-site installation methods (Section 4: Implementation). • Recommendations concerning both ventilation system maintenance and processes and methods for controlling resulting atmospheric quality (Section 5: Maintenance and inspection). • A reminder of the administrative and contractual framework governing the "ventilation sub-project", including advice on the role allocated to the different participants and on the desired progression of studies and inspections, from preliminary design through to execution manuals (Section 6: Organization and administrative framework).

1.3 - Area of application This recommendation concerns the design, dimensioning, installation, routine servicing, maintenance and inspection of artificial


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ventilation installations that allow atmospheric conditions complying with current French regulations to be maintained during construction of underground works. It is intended for: • All players involved in the act of constructing: the Owner and his Health / Safety Coordinator, the Engineer, design offices, construction contractors, inspection and consulting bodies for safety and improvement of working conditions, • Public emergency services. N.B. The specific problem of smoke extraction from a tunnel,

when a fire occurs during construction, is not dealt with in this document and there is no need to consider this when dimensioning common tunnel ventilation systems (except specifications for materials to be used). In this case, the potential role of site ventilation is a difficult problem calling for specific analysis and examination of various reference scenarios. It will be examined by the AFTES "Sécurité, Santé et conditions de travail" [safety, health and working conditions] working group (GT 12). Moreover, this analysis should be coordinated with the different operators in charge of safety, including external emergency services.

2 - POLLUTION PHENOMENA This second section of the recommendation details the following information. • Construction-related pollution phenomena and thus the risks that appropriate site ventilation can prevent. • Limiting values of pollutants and dust retained by French regulations. The risks envisaged here are essentially linked to the quality of the air that employees breathe in underground works. Prevention involves ensuring control of this quality throughout the construction period.

2.1 - Risk identification procedure The risks to which personnel will be subjected should be properly assessed before designing the site ventilation system. The following operations should therefore be performed. • Conduct a general survey of existing dangers. • Evaluate pollution emitted by different equipment and, if possible, select equipment accordingly. • Estimate residual pollution risks. • Arrange and organise, as well as possible, work stations in relation to these risks. The AFTES recommendation entitled "Lutte contre les nuisances dans les travaux souterrains" [Control of pollution phenomena in underground works], published in Tunnels et Ouvrages Souterrains (TOS) journal (N° 134, March-April 1996), stimulated thinking on this subject. Moreover, it should be remembered that ventilation is an operation that falls within the advancing construction process. In addition to risk assessment, ventilation design should therefore consider many external constraints such as: • Overall design of the works, • Partial completion times, • Ponstruction phases. Finally, constraints specific to ventilation itself should be taken into account. These include the following issues.

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• The need to ensure supervision, monitoring and effective maintenance of the ventilation system. • Necessary adaptation of ventilation installations to construction progress and changes in excavated volumes. • Risks associated with the installation and removal of mechanical ventilation means.

2.2 - Prevention rules The prevention approach to health and safety (H&S) is based on the following basic rules laid down in Clause L230.2 of the French Employment Code – "Principes Généraux de Prévention" [general prevention principles]. • Avoid occupational and environmental risks. • Assess those that cannot be avoided, especially those that are exported and/or imported. • Combat risks at source in the design and layout of parts of the works and in the choice of structures and associated equipment. • Adapt the work to the man, especially concerning: - work station design, - choice of working equipment, - working and production methods to limit, in particular, monotonous and rhythmic tasks and to reduce their health effects. • Take into account technological progress in relation to equipment and methods. • Replace what is dangerous with what is safe or less dangerous. • Plan prevention by integrating the following issues into a coherent combination: - technology, - work organization, - working conditions, - employment relations and influence of prevailing factors. • Adopt collective protection measures, giving them priority over personal protection measures by integrating their installation into procedures and/or portions of the works.


• Give appropriate instructions to workers. • In all workplaces, the employer has an overall duty to ensure safety and protect the health of workers in all work-related aspects.

2.3 - Risk analysis 2.3.1 - Atmospheric quality The atmosphere in underground works features air that can contain many pollutants coming either from the surrounding ground or from construction activity. Man cannot live in an environment in which the ambient air characteristics do not suit his breathing system and he can only adapt to relatively minor variations in the chemical compounds present. Purification capacities of the human body are effectively limited. Furthermore, certain inhaled chemicals constitute poisons because of their toxic effects. These effects depend on: • The physical chemical properties of the substance, • The dose actually absorbed by the body, • Exposure time and frequency. The respiratory tract is the main entry route for toxic substances, but skin penetration should not be overlooked because it can be very significant if the skin is damaged (wound, irritation, eczema, etc.). Recently, epidemiological cancer studies have revealed that certain substances (silica, hydrocarbons, exhaust fumes, etc.) have carcinogenic or mutagenic properties and, because of the small doses likely to cause cancer in man, research may lead to major changes in prevention approach. Reference values are detailed, when they are known. Human respiratory amplitude and frequency varies with the individual, his activity and his physiological characteristics. Air supply should at least cover human respiratory needs. "Normal" air composition in a non-polluted environment is approximately: - 21% oxygen - 78% nitrogen - 0.04% carbon dioxide - 0.96% rare gases. But in underground works: • Confinement of the air in a drift or adit shaft encourages higher pollution content and lower oxygen content, • Construction activity generates various pollutants, which themselves generate specific toxicity, • The surrounding ground can cause pollution phenomena, whose control is inconsistent: toxic gases, urban pollution, bioorganisms, natural radioactivity, etc., • By emitting carbon dioxide and consuming oxygen, human breathing modifies air quality – whilst undoubtedly insignifi-

cant in large diameter tunnel excavation, this can be a determining factor in some special operations such as shaft sinking. As a result, safeguarding the health of workers under their working conditions demands: • Renewing air required for safe human breathing, especially by supplying fresh air, • Ensuring maintenance of air quality, such that its properties remain close to those of "normal" fresh air composition, • Diluting pollutants, if need be. 2.3.2 - Health and safety at work stations 2.3.2.1. - Pollutant The following pollutants are examined in underground works. • Gases, blast fumes, diesel engine exhaust fumes, natural gases (methane, radon, etc.), gases produced by ancillary activities (welding of impervious films, installation of bituminous linings, paint application, etc.). • Dust. -

2.3.2.2 - Air quality and work station comfort Construction area ventilation should also control: • Tunnel temperature to create acceptable conditions with respect to work station activity of personnel, • Tunnel humidity to prevent fog formation, • Air circulation velocity in tunnels. 2.3.3 - Pollutant evaluation 2.3.3.1 - Limiting values Limiting values given in this document are those in force at its date of publication.


5


The E.L.V. or short-term Exposure Limiting Value represents the concentration in air that a person can breathe for a determined time (15 min. max.) with respect to the type of risk, the working conditions and the technical measurement possibilities. Respecting the E.L.V. allows immediate toxic effects to be avoided. The A.E.V. or Average Exposure limiting Value is the allowable average value of concentrations to which a worker is effectively exposed during a one day shift, i.e. 8 hours. the A.E.V. can be exceeded for short periods, on condition that the E.L.V. is not exceeded. These values are expressed in terms of atmospheric concentrations, the only penetration route into the human body being the respiratory tract. Additional (especially biological) indicators should complement these concentrations when penetration is through the digestive tract or the skin. These values are expressed: • for gases and fumes, either in ppm (cm3/m3) or in milligrams per cubic meter (mg/m3), • for liquid or solid aerosols, in milligrams per cubic meter only. 2.3.3.2 - Mixtures of substances Limiting values are valid for exposure to pure substances. However, when several noxious substances mingle at the same work station, a potentiation phenomenon or mutual inhibition of the toxicity of the substances present may exist. These effects are approximated as follows. For substances acting on the same organ or whose effects grow, by applying the following toxicity formula:

In this case, the ventilation conditions should be maintained to respect the above inequality. Ci and VLi represent the concentrations and limiting values for each listed pollutant respectively. For substances acting on different organs or whose toxic effects do not potentiate, by applying the following formula:

In this case, whatever i is, if one of the above inequalities is not respected, the air quality is declared unacceptable for the work station. Certain authors consider that NO and NO2, as well as CO and CO2, embody a synergy phenomenon and a strengthening of cumulative effects. 2.3.3.3 - Dust Dust is defined as being all solid particles with a maximum aerodynamic diameter of 100 micrometres or whose maximum limiting fall velocity is 0.25 m/s, under normal temperature conditions..

6


a) Total dust This represents all dust collected in sampling devices. This measurement permits evaluation of the dust that is deposited at the three levels of the respiratory tract: nose, larynx, trachea, bronchial tree, pulmonary alveoli. The total dust A.E.V. is 10 mg/m3. b) Alveolar dust This dust arrives at the pulmonary alveoli. It penetrates the deepest into the lungs. Particles with a diameter less than 5 micrometres have a penetration rate of over 50%. They are therefore considered the most dangerous. The alveolar dust A.E.V. is 5 mg/m3. c) Toxicity of certain dusts Silica Silica dust has a potentiating effect. In addition to causing respiratory overload, this dust in fact encourages growth of fibrous tissue and nodules, which aggravate breathing difficulties. Crystalline silica is the most noxious form and three mineral components have been identified in the silicosis mechanism: - quartz - tridymite - cristobalite The cumulative noxious effect is evaluated using the following formula.

Cns represents the concentration of non silicogeneous alveolar dust particles (mg/m3), Vns is the average exposure limiting value (AEV) for alveolar dust particles, i.e. currently 5 mg/m3. Cq, Cc and Ct represent quartz, cristobalite and tridymite concentrations (mg/m3) respectively, their AEVs being 0.1, 0.05 and 0.05 mg/m3 respectively. Asbestos Asbestos is found in a natural state in old rock masses. A geological survey of asbestos presence should be conducted. The BRGM (French regional geological society) possesses accurate geological data. Analysis of ground types encountered may be advisable to characterise asbestos presence and type. During construction, dust coverage measurements should be frequently taken. For 1 hour of work, the allowable limiting value is 0.1 fibre/cm3. If in doubt or if this value is exceeded, the working method should be reviewed. Employee collective or personal protection and environmental measures should be implemented. 2.3.3.4 - Gases The following tables show the ELV and AEV reference values given either in statutory texts or in international recommenda-


tions. Original document references feature in the "references" column and refer to the bibliography at the end of this recommendation. These tables are not product restrictive, but provide concentration limits for the products most frequently encountered in underground works. a) Blast fume values Products

ppm

Carbon monoxide CO

AEV ELV mg/m3 mg/m3 ppm

50

55

References French Social Security Occupational Diseases Table

Carbon dioxide CO2

5000

Nitrogen monoxide NO

25

30

0,15*

1,5*

Fr. Dept. of Employment Circular + Directive 91/322 Fr. Dept. of Employment Circular + Directive 91/322

Nitrogen dioxide NO2

3

Nitroglycol - nitroglycerine

9000

6

Fr. Dept. of Employment Circular + Directive 91/322 Fr. Dept. of Employment Circular + Directive 91/322

* Percutaneous penetration risk: these values do not exclude appearance of cephalalgia (headaches), which do not usually subsist after acclimatization. Headaches do not appear if the concentration remains less than 0.2 mg/m3.

b) Diesel exhaust values Products

ppm

Carbon monoxide CO

AEV ELV mg/m3 mg/m3 ppm

50

55

Dioxyde de carbone CO2 Monoxyde d’azote

25

5000

9000

Fr. Dept. of Employment Circular + Directive 91/332

3

6


5

10


30


Dioxyde d'azote N02 2

Dioxyde de soufre S02

References

5

c) Values for natural substances AEV Products Methane

ppm

ELV mg/m

ppm

mg/m3

7

10

14

3

10 000

Hydrogen sulphide

5

d) Values for other activity-emitted substances Products Formic aldehyde HCHO (formol) Nitric acid HNO3 Sulphuric acid

AEV ppm

mg/m3

0,5 2

ELV ppm mg/m3

1 5 1

4

6 3

2.3.3.5 - Heat Man has a homeothermal body, i.e. its core temperature must remain constant (37 ± 0.5 °C). To control this temperature, the body exchanges heat with the external environment in the following 4 ways.

• Radiation: thermal exchanges by radiation between hot surfaces and man. • Conduction: thermal exchanges by direct contact between the skin and a solid or liquid object. • Evaporation: loss of heat due to evaporation of sweat from the skin and respiratory membranes (perspiration can be limited by very humid air). • Convection: exchange due to velocity of air in contact with the skin. Moreover, human activity produces intense internal heat within the muscles: the energy metabolism. These exchanges allow man to regulate this thermal equilibrium with respect to his external environment. Internally, specific mechanisms are brought into play to maintain a steady body core temperature. The main parameters that can cause loss of thermal equilibrium are: • physical work, • radiation average temperature, • air temperature, • air humidity, • air velocity. Depending on exposure type and time, working in a hot atmo-


7


sphere can cause: • heat stroke or hyperthermia attacks, • syncope attacks (fainting, pallor), • water deficiency or dehydration, • sodium deficiency. Consequences vary according to individual functional capacities (age, heart rate, strength) and operator acclimatisation (job familiarity, geographical origin, climatic familiarity, etc.). Three principles should therefore be remembered to encourage a return to thermal equilibrium: • facilitate sweating, • reduce energy consumption (measured by heart rate), • reduce air temperature. Assessment of thermal constraints is complex and various indicators (especially heart rate, etc.) require extensive studies. Ambient air dry temperature is taken as reference, for want of being able at present to characterise accurately simple thermal constraint indicators for underground works. Thus, in underground works, it is recommended that operators should not be exposed to a work station ambient temperature exceeding 26 °C in a humid atmosphere. This temperature should be adjusted in relation to hygrometry and for particularly arduous tasks. Consequently, the following prevention principles should be retained. • reduce heat sources or insulate them thermally, • refrigerate if necessary,

• install suitable ventilation to maintain the temperature below the limiting value (beware of discomfort due to cold air and thermal differences exceeding 6 °C), • act on air velocity to encourage thermal convection without bothering workers by excessively high local air velocities (solution: diffuse air stream to lower its velocity), • mechanise difficult or arduous tasks to reduce energy consumption, • limit exposure time if heat is significant, • create a microclimate at the worker's location, e.g. air-conditioned machine cabs, • increase water intake, • moderate drinking water temperature (10 – 15 °C), slightly sweetened and flavored, average intake 100 – 500 ml/h, • limit sweet drinks (0.5 l/day – fruit juice, fruit-flavored milk, carbonated drinks, etc.) and coffee (400 mg/day), • prohibit alcoholic drinks, • increase sodium intake through food or drinks (meat and vegetable stocks, tomato juice), • provide showers and heating cabinets for drying clothes, • keep special personal protection in certain circumstances. 2.3.3.6 - Fire - Smoke and fumes Fire risk (machine fire, oxy-acetylene cutting, plastic welding, etc.), whilst not the subject of this recommendation, should be assessed and covered by adequate prevention measures integrating not only the role of ventilation, but also of all safety systems allowing the consequences of a fire to be limited (extinction, smoke extraction, alarm, protection and evacuation facilities).

3 - VENTILATION PROJECT 3.1 - Minimum rules 3.1.1 - Pollution treatment Ventilation principles essential to treating pollution emitted by site activities are: • for dust pollutants: - reduced emission at production points, - local collection of dust produced, if possible, - discharge of dust-laden air to the exterior, - water spraying to make dust fall, - installation of extraction systems near machinery, - fitting of pressurized cabs, - seeking of best possible airtightness between TBM and surrounding ground (bored tunnels). N.B. dust does not dilute in the atmosphere, it can only be collected or discharged.

8


• for blast fumes or gases contained in the ground: - fume or gas collection at source and direct discharge to the exterior. • for diesel engine exhaust fumes: - equipment selection and engine servicing, - fume collection at source and treatment, - dilution by ventilation in the structure. 3.1.2 - Fresh air requirements Determination of fresh air requirements results from examining the pollutants generated throughout the underground system and the way in which they have to be treated. Recommended basic values for dimensioning the ventilation circuit are as follows. • For dilution of heat engine-emitted fumes: 50 l/s per developed effective horse power (h.p.).


New fresh air

Fan

Fresh air duct

Polluted air discharge Pollution concentration Fresh air duct Maximum concentration Figure 1

• For collection and discharge of dust pollutants, blast fumes and gases contained in the ground: 300 l/s minimum per m2 of the tunnel (generally excavated) cross-section. These two flows are not cumulative. The highest value should be retained. Moreover, two other important principles should be considered: • On the one hand, maintain a distance of 5 logS (distance in m, S = excavated cross-section in m2) between the face and the extraction intake. This distance has been validated by experience for pollution collection at source. • On the other hand, whatever the ventilation solution and type implemented, check tunnel air return velocity, which should remain between 0.5 m/s (min.) and 1.5 m/s (max.) to ensure work area comfort.

3.2 - General ventilation system concepts Ventilation systems installed underground are linked to a small number of basic operating principles, irrespective of the tunnel excavation and internal construction method: • Blowing ventilation • Extraction ventilation • Ventilation by air flow through the tunnel network These different forms of ventilation can be intercombined: association of blowing and extraction ventilation systems, reversible fans, etc. 3.2.1 - Blowing ventilation In blowing ventilation, the ventilation duct supplies fresh air to the face. Polluted air flows out through the tunnel itself from the face to the exterior (Figure 1). 3.2.1.1 - Blowing ventilation advantages • Most active zones of work areas at the face (and possibly at work areas located to the rear) are supplied with fresh air.

• Air ejection velocity ensures effective face sweeping. • Polluting gas dilution is properly ensured. • Usually located outside the tunnel, the fan remains fixed and independent of face advance. • Temperature of supplied air can be controlled. 3.2.1.2 - Blowing ventilation disadvantages • Dust and especially silica are dispersed. • Even though they are diluted, blast fumes or pollution generated at the face travel the whole length of the tunnel and require evacuation of all underground personnel, representing a long delay in the work cycle. • Blast fumes emitted from the spoil during mucking are not collected at source. • The pollution gradient increases from the face to the exterior. • Work areas to the rear of the face are in the air return flow which is polluted at the face. • If not preheated, cold air supplied to the face can cause discomfort in winter. • Polluted air leaving the tunnel cannot be treated. • Smoke cannot be extracted in the event of fire. 3.2.2 - Extraction ventilation In extraction ventilation, the ventilation duct extracts polluted air near the work area and fresh air arrives at the face from outside the tunnel (Figure 2). 3.2.2.1 - Extraction ventilation advantages • Allows pollutants to be extracted at source, especially dust and fumes emitted when mucking (at the face and possibly work areas located to the rear) on condition that a distance of 5 logS is maintained between the face and the extraction intake. • Ensures rapid discharge of the blast fumes without polluting the tunnel to the rear of the face.


9


Polluted air discharge

Polluted air duct

Fan

New fresh air induction

Pollution concentration New fresh air Maximum concentration Figure 2

• Causes no temperature discomfort in the face construction area. • Allows polluted air discharge to be treated at the tunnel portal. • Ensures fresh air sweeping from the exterior to the face. • Can extract smoke from a fire. 3.2.2.2 - Extraction ventilation disadvantages • Fan must be installed inside the tunnel (except if a rigid duct is used from the exterior), which requires the fan to be regularly advanced. • The pollution gradient increases from the exterior to the face. • All pollution is returned towards the most active zone at the face. • For practical reasons, if the extraction point remains far away

from the face, fresh air supply to the tunnel face ceases and the pollution level becomes uncontrollable (appearance of dead air pockets). • Effectiveness remains limited a short distance from the face. 3.2.2.3 - Installation recommendations • The extraction duct inlet should be kept very close to the face and ventilation installations, including system maintenance operations, must be very well organized. • To avoid creation of an unventilated or dead air pocket at the face, it is possible to resort to installing a mixing fan connected to a duct taking in air upstream of the extraction intake, but this solution has the disadvantage of putting muck spoil dust particles into suspension, if the dimensioning does not consider this criterion (Figure 3).


Polluted air duct

Fan

New fresh air induction Pollution concentration

Face gas and fume lift-off

New fresh air Maximum concentration Figure 3

10



Fan


New fresh air

Fan

Polluted air duct Fresh air duct

Polluted air discharge Pollution concentration New fresh air Maximum concentration Figure 4

3.2.2.4 - Special case: pilot tunnel extraction Excavation of a pilot tunnel prior to driving the main tunnel allows ventilation and other problems to be solved. • The fan is installed at the pilot tunnel portal. • The tunnel itself is used as the ventilation duct; all pollution from the face (dust, gas and fumes) is then extracted directly at source and discharged to the exterior. Extraction air can also be easily treated before being discharged to the atmosphere (Figure 4). 3.2.3 - Ventilation by air flow through tunnel network All air in the underground works is circulated between two points: the air intake and the air return. This is the most commonly adopted ventilation principle in underground mines. Most of the time, an extraction fan is installed on the air return, ensuring that air intake through a shaft or an air intake tunnel remains free. Ventilation systems for blind headings can then be connected to the ventilation circuit using one of the above two methods. 3.2.3.1 - Advantages of ventilation by air flow through tunnel network • This form of ventilation is suitable for construction of an extensive network of tunnels and cavities, such as a mine network. • It allows high air flow rates because it is the tunnels themselves that form the air circulation ducts. • Several construction areas can be supplied by secondary ventilation systems connected to the main fresh air circuit. • Head losses are low and this leads to power saving. 3.2.3.2 - Disadvantages of ventilation by air flow through tunnel network • Pollution from different construction areas is sometimes discharged into the main circuit.

• Pollution gradient increases from air intake to air outlet. • It imposes high flow rates to ensure sufficient air quality at all construction areas, but with air return velocities that can become intolerable. 3.2.4 - Combination of different solutions Different ventilation possibilities can be combined to cumulate the advantages of the individual systems. A combination of extraction ventilation as near as possible to the face and blowing ventilation supplying fresh air at the rear offers great flexibility for both fresh air scavenging of the face and extracting pollution (blast fumes, engine exhaust fumes, dust). On the other hand, this system requires installation of two parallel ducts throughout the tunnel length and both the spatial requirement and the cost (investment, operation and maintenance) are greater than for a blowing or exhaust solution. When blowing and exhaust ventilation are combined, care must be taken to ensure that the blowing air flow rate compensates the extraction air flow rate. Furthermore, implementation of such a system demands greater monitoring of operating conditions to ensure full efficiency. Reversible fans operating in blowing or exhaust mode, depending on the construction phase, can also be used as long as, of course, the network of ducts and fans is designed to accept both ventilation modes (Figure 5). 3.2.5 - Ventilation for open-ended structures This concerns the final phase of civil works, for example application of highly polluting bituminous layers and finishing work, e.g. painting of side walls. In this case, the longitudinal type ventilation principle is applied. The natural draught can be mechanically strengthened if it is insufficient or inconsistent by installing soundproofed accelerators in the tunnel or possibly by temporarily closing the tunnel with a wall incorporating a fan capable of circulating the required air flow rate (Figure 6).


11




Fan

Pollution concentration New fresh air Maximum concentration

Figure 5

Reversible accelerator

Figure 6

New fresh air

Fan Polluted air discharge

New fresh air in permanent duct Ventilation ceiling

Figure 7

12



3.2.6 - Use of permanent ventilation ducts or intermediate shafts This involves ventilation ducts for road tunnels ventilated by a permanent transverse (end-to-end) or service tunnel-type system. Numerous examples show that advantage should be taken of these tunnels, whose construction follows the face but at a distance. This solution allows temporary ducting to be removed and, in its place, to benefit from often larger sized transit cross-sections than those of temporary sections (Figure 7). Use of intermediate shafts required for the project, or possibly created during construction, may also prove advantageous.

3.3 - Input data - Design assumptions This includes all engineering data allowing calculation of ventilation flow rates required for construction, definition of all ventilation system characteristics and determination of its operating method. 3.3.1 - Characteristics specific to structures and ground These include both geometrical characteristics of the structures to be built (excavated and lined cross-sections, lengths, slabs, surface condition, etc.) and geological characteristics of the surrounding ground. In particular, these data enable the presence or absence of silica, asbestos and possible gas emissions to be determined and the temperature gradient to be considered. 3.3.2 - Construction methods The construction method for the underground works and different ancillary works – thus the potential pollution risks – has a direct impact on ventilation system design and dimensioning. For each construction phase and each work area, checking should undertaken to ensure that the ventilation design provides air quality in accordance with relevant legislation and regulations. The following issues should be specifically considered. • The tunneling method (blasting, roadheader, TBM, etc.). • The different excavation phases (full-face, crown, bench, side drifts, ancillary excavations, etc.). • Implementation of simultaneous construction areas (at the front, face excavation; at the rear, invert construction, waterproofing, steelfixing, vault lining, slab construction, equipment installation, etc.). • Effects induced by breakthrough between tunnel cross-passages, branch tunnels, and passages to the exterior in the case of a complex tunnel network. • Performance of finishing work after tunnel breakthrough. Consideration of different phases has an impact on: • flow rates to be implemented, through modification of the mechanical equipment operating and thus of the pollutants emitted, • the ventilation circuit itself, because of constraints raised by crossing several work areas, • air flows, through modifications to the ventilation circuit, especially during breakthrough between construction areas or to the exterior.

3.3.3 - Resources implemented Construction methods allow the type and number of machines used and their operating conditions, the size of work teams, operation programming, etc. to be determined. Conversely, ventilation problems can lead to specialized equipment choices or options (e.g. electric-powered pick-up or loading equipment). 3.3.4 - Pollution source determination and characterisation Studying the construction methods and resources implemented leads directly to determining the different pollution sources and the characteristics of the most common sources. For TBM excavation and for internal structure construction: • dust emission during excavation, • emission of gases contained in the ground or in implemented products, • dust emission during mucking (conveyor, etc.), • exhaust fume emission from heat engines (diesel, etc.), • dust emission during shotcreting. For excavation by blasting and internal structure construction: • blast fume emission • emission of gases contained in the ground or in implemented products, • dust emission during mucking, • exhaust fume emission from heat engines (diesel engines – machines, stand-by generators, etc.), • dust emission during shotcreting, • heat emission from machines and/or ground and/or concrete. For roadheader excavation and internal structure construction: • dust emission during excavation, • emission of gases contained in the ground or in implemented products, • dust emission during mucking • exhaust fume emission from heat engines (diesel, etc.), • dust emission during shotcreting • heat emission from machines and/or ground and/or concrete. 3.3.5 - Determination of fresh air requirements The determination of fresh air requirements results from examining the pollutants generated throughout the underground system and the way in which they have to be treated. 3.3.5.1 - Dilution flow rate for diesel engine exhaust fumes (QDdt) For both blowing and extraction ventilation, the dilution flow rate (QD) to be provided by the ventilation system is calculated based on 50 l/s/developed effective horse power, for all active diesel engines simultaneously present in the tunnel. The notion of developed effective power warrants some explanation: if we consider the nominal power stated by the manufac-


13


turer, the effectively developed power depends on: • the machine’s effective load QDdf (Face diesel dilution) QDda (Work area diesel dilution) QDdr (Haulage diesel dilution

(m3/s) = 50 (l/s/cv) x Power (cv) / 1000

QDdt (Total diesel dilution - m3/s) = QDdf + QDda + QDdr

• the slope and location at which it operates, • its general condition (maintenance, aging, etc.). Developed effective power is therefore open to interpretation and caution is recommended, although it should be considered that systematically taking machine nominal power can lead to overdimensioning. 3.3.5.2 - Discharge flow rate for haulage-raised non-localised dust (QEpr) Dust emission is not localized and in both blowing and extraction ventilation, the required discharge flow rate (QE) is calculated based on an average of 300 l/s/m2 of excavated cross-section. Spraying with water of concrete inverts can limit this pollution and consequently reduce the required ventilation flow rate. QEpr (Haulage dust discharge - m/s) = 300 (l/s/m2) x exc. cross-section (m2)/1000

3.3.5.3 - Collection flow rate for dust and fumes emitted from localized work areas (QCpa) In this case, treatment is ensured by localized extraction ventilation as near as possible to the emission source. Extracted air is discharged to the exterior after possibly passing through a dust extractor. Recirculation of treated air is not recommended, even if a dust extractor is used, because a constant quality guarantee cannot be provided. The required collection flow rate (QC) is calculated based on a minimum value of 300 l/s/m2 of excavated cross-section.

3.4 - Ventilation principles retained and general measures Site ventilation can act in several ways; it can collect, dilute, discharge or separate polluting products generated in the tunnel. The ventilation system should allow a healthy atmosphere to be maintained at all times in accordance with current regulations. The most disadvantgeous (worst case) site configuration should therefore be systematically sought and the ventilation system designed on this basis. The examination of the ventilation conditions of a site should be conducted right from design stage by the Owner and his Health and Safety Coordinator through to construction completion by the Engineer and the Contractor. We recommend adoption of the following requirements in order to deal with problems as fully as possible.

14


3.4.1 - Dust treatment Given that this problem is the most complex to deal with, it should be examined first by asking the following questions. • Are there dust emissions? • Are dust emissions laden with silica, asbestos, etc? • What are the emission points? Based on the answers to these questions, it should be possible to determine how to deal with the problems, favoring solutions that prevent dust production or eliminate dust emissions at source. These solutions include: • drilling using water or a specific fluid, wet process shotcreting, spraying with water of mucking operation (if possible automatically), • collection at source using mist propagation processes, • spraying and suction sweeping of traffic routes, • localised extraction and treatment of polluting products • general extraction. Possibly, selection of blasting, loading and haulage equipment and every combination of these different means. The following two points should be remembered. • The dilution method does not apply to dust. • To be effective, dust extraction at the face must obey the following law: maximum distance between face and exhaust duct < 5 logS. This condition is often difficult to respect but using a system of telescopic air pipes facilitates its implementation. In the light of recent examples of tunnel construction, it should be noted that some tunnel configurations or driving processes prevent the setting up of site ventilation that is efficient enough to purify correctly the atmosphere at work stations. Underground discharge filtering and recirculation never provide a satisfactory solution and should, in any case, only be used in a sufficiently large renewing air stream. These situations are referred to hereunder. 3.4.1.1 - Drill and blast In a 100 m2 cross-section tunnel, the application of the 5 logS formula allows the distance between the face and the end of the extraction air pipe to be determined, leading to the value of 10 m. When this distance cannot be respected, experience, confirmed by ventilation forecasting calculations, has shown that exposure to crystalline silica dust measured on operators exceeds systematically the allowable limiting values of average exposure. Application of the 5 logS formula is therefore strongly recommended. Examples of means implemented on some sites are given below. • Face working machines fitted with cab pressurisation/air-conditioning systems incorporating filters providing sufficient efficiency with respect to so-called alveolar dust particles. • Installation of automatic water spraying systems for blast dust. • Design and installation of remote controlled ventube (smooth


3.4.2 - Gas dilution The ventilation air flow should dilute polluting gases (if there is no methane QCpp (localized dust collection) emission – risk of explosion) and reduce [machine + gas in ground + mucking dust] (m /s) > = 300 (l/s/m ) x exc. cross-section (m ) : 1000 them to acceptable contents according QCprb (concreting robot dust collection) to current regulations. [shotcreting] It should always be borne in mind that QCpbr (rockbreaker dust collection) resorting to electrically powered machi[machine + gas in ground + mucking dust] nery reduces significantly the production of polluting gases. Furthermore, QCpa (work area dust collection - m3/s) = Max (QCpt, QCpp, QCprb, QCpbr) there are many systems for reducing machine-generated pollutants: we desflexible duct) advance systems bringing ventubes to the face cribe them in this recommendation. after blasting. 3.4.3 - Air renewal / Fresh air supply 3.4.1.2 - Roadheaders Based on examination of the preceding two issues, it is possible to To respect average (AEV) or short-term (ELV) exposure limiting determine how to ensure air renewal and fresh air supply. values, a remote controlled system could be adopted allowing the However, it should be noted that it is a mechanical blowing ventioperator to steer his machine, whilst remaining far enough away lation system that best enables fresh air supply to be controlled in from the attack area. This method of working has proved to be active tunnel sections. wholly conclusive. 3.4.4 - Feasibility of solution retained In parallel, experiments have been conducted to improve the After deciding on an overall solution, it must be imperatively subreliability of systems for identifying on-screen rotary cutter posi- jected to critical examination of its feasibility and of its impletions with respect to the optimum profile of the tunnel excavated mentation problems. cross-section. This system, whose initial purpose was to limit • Are the structural characteristics suitable? excavation overbreak, can prove very useful in complementing the approach described in the above paragraph. Tests associating these • Are the positioning and spatial requirement of the various units compatible with site operation, machine maneuvering, work two techniques that allow the operator to use a remote control sequencing, etc? box and screen for controlling rotary cutter displacement are • Can the whole system operate at all times? currently in progress. • Is passing of the ducts through work areas permanently ensured 3.4.1.3 - Tunnel boring machines (TBMs) under conditions considered in the design calculations? On open face TBMs, samples taken to measure exposure levels to • Are the determined flow rates compatible with working comfort crystalline silica reveal frequently that allowable limiting values of in the considered areas? average exposure are significantly exceeded. Some construction areas are however equipped with an extraction 3.4.5 - Outline diagrams air pipe connected to a dust extractor, but the efficiency of this 3.4.5.1 - Blowing ventilation example system with respect to alveolar dust content of the face air cannot Retained flow rate QS is calculated based on dilution of fumes be guaranteed, insofar as the outlet from this dust extractor is not emitted by all diesel engines (50 l/s/h.p.) because this is higher connected to a duct discharging to the exterior and treated air is than the flow rates required for discharging or collecting dust raised in work areas (>= 300 l/s/m2) (Figure 8). recirculated in the tunnel. QCpt (blasting dust collection) [blast fumes + gas in ground + mucking dust]

3

New fresh air

Fan QS

2

2

Blowing fan flow rate (QS) = QDdt (Total diesel dilution) = QDdf (Face diesel dilution) + QDda Work area diesel dilution + QDdr (Haulage diesel dilution) > QEpr (Haulage dust discharge) > QCpa (Work area dust collection) > QCpt (Blasting dust collection)

Fresh air duct


Figure 8


15


3.4.5.2 - Extraction ventilation example Retained flow rate QA is calculated based on collection of dust raised during blasting and loading of muck spoil (300 l/s/m2) at the face because this is higher than the flow rates required for discharging dust raised by haulage (<< 300 l/s/m2 due to spraying of invert) and dilution of fumes emitted by diesel engines (50 l/s/m2) (Figure 9).

3.4.5.3 - Blowing and extraction ventilation example Retained flow rate QA is only calculated based on collection of dust raised during blasting and loading of muck spoil (300 l/s/m2). Retained flow QS is calculated based on dilution of fumes emitted by diesel engines (50 l/s/m2) used at the face (loading) and haulage (muck spoil transportation) (Figure 10).

Polluted air discharge Fan QA

Polluted air duct

New fresh air induction Extraction fan flow rate (QA) = QCpt (Blasting dust collection) = QCpa (Face work area dust collection) > QEpr (Haulage dust discharge) > QDdt (Total diesel dilution) = QDdf (Face diesel dilution) = QDdr (Haulage diesel dilution)

Figure 9

Fan QA



Fan QS

QCpt Polluted air duct QDdf New fresh air induction

Diluted air discharge

Blowing fan flow rate (QS) = QDdf (Face diesel dilution) + QDdr (Haulage diesel dilution) Extraction fan flow rate (QA) = QCpt (Blasting dust collection)

Figure 10

4 - IMPLEMENTATION 4.1 - Equipment 4.1.1. Fans 4.1.1.1 - General By analogy with blood circulation, fans represent the heart of the ventilation circuit, whilst fresh air ducts, shafts and tunnels correspond to arteries and the polluted air return circuit to veins. A fan is generally defined as a turbo machine creating: • a continuous (non-pulsating) air flow,

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• a limited pressure difference between its inlet and outlet (above a pressure ratio of 1.25, it is a compressor). The essential ventilation characteristics of a fan are shown on a flow/pressure diagram, on which the operating point of the machine, connected to its circuit, can be checked. This point should fall within the correct range and avoid, in particular, the behavior zone which is unsteady and dangerous for machine preservation, called the surge zone (Figure 11). Fans can be streamlined (housed within a fairing), driven by


Power Pressure Efficiency (dimensionless) Total head loss in circuit Braking power

Surge zone Operating point Total pressure

Ventilation efficiency Dynamic pressure in discharge louver Static pressure Fan flow rate (m3/s)

Figure 11 - Example of helical fan characteristic curves

electric motors and generally mounted virtually airtight on a ventilation duct (all the ventilation flow therefore passes through the fan). 4.1.1.2 - Axial fans Their main characteristics provide conventionally (Figures 12 and 13): • high efficiency over a wide flow range, • high rotational speed possibilities, • possibility of adjusting blade inclination, usually when stopped, but sometimes when operating, depending on available power (the latter system proves to be technologically complex and should only be used in and for circuits whose justification is highly exceptional), • an impeller (propeller) usually mounted directly on the shaft of an electric motor, • compactness, preventing wastage of space,

Figures 12 Diagram of axial-type fan

Motor

Outlet

Protection grille Blowing direction

▲

Flare Impeller Upstream fairing

Motor mounting Downstream fairing Impeller

• flow variation acting through inclusion of an electronic variable speed control, which offers many advantages (power limitation at start-up, flow adjustment flexibility, etc.). Flow gyration downstream of the impeller can be rectified by guide vanes, which enable both fan pressure rise and efficiency to be enhanced. Downstream guide vanes are more efficient than upstream guide vanes, the latter also tend to increase the noise level. Flow gyration should be considered when installing two fans in series (associating two counter-rotating fans is advisable). Flow reversal Flow direction can be reversed by changing the fan direction of rotation. Flow performance characteristics for fans with guide vanes will then be very poor and between 60% and 70%, for fans without guide vanes. On the other hand, a reversible fan can be obtained by: • either reversing every other blade, giving a flow performance in one direction or the other of approximately 85% of that of the initial fan, • or altering the blade pitch setting by 180° (variable pitch fan), thereby conserving 100% of the flow performance of the initial fan. Efficiency Total efficiency is nearly 80% at the nominal operating point and can be raised to 90% (high efficiency fans designed for a specific operating point). 4.1.1.3 - Centrifugal fans (Figure 14) Pressure rise is mainly due to centrifugal force. Generally, the principal characteristics of these fans are as follows: • poor performance characteristics if the outlet is not connected to a duct, • an external motor drive often through a belt (flexibility of rotational speed selection), • possibility of an outlet with 1 or 2 louvers, • 3 or 4 possible types of vane (shape and inclination with respect to direction of rotation), • one unique operating curve per fan – the only possible adjustment being the rotational speed, except if the fan is fitted with adjustable pitch vanes that generate pre-rotation of the incident flow, • efficiency, limited to 60 - 70% for some units, can reach 90% for the most efficient fans, but the high efficiency zone remains relatively narrow, • possibility of higher pressures than with helical fans operating at the same speed, • centrifugal fan operating curves are generally flatter than those of axial fans, • a smaller surge risk than for a helical (axial) fan. 4.1.1.4 - Accelerators In general, these are axial-type fans mounted at the crown of road tunnels or galleries and whose function is to induce a longitudinal draught by generating dynamic pressure due to the high air velocity within the air mass contained in the underground structure.

Figures 13


17


Fan casing

Extraction intake flare

Outlet

Extraction intake connection sleeve

Figure 14 - Typical diagram of centrifugal fan

be interconnected by means of various systems specific to each supplier. They are suitable for all diameters from 300 to Impeller and blades Flare + grating 3000 mm. They are fitted with 1 - 3 lines of suspension devices. Muffler Ventubes can sometimes incorporate Central body regularly spaced reinforcing hoops, allowing them to stay open when the Perforated sheet-metal ventilation is stopped, as well as radial air Soundproof lining internal walls Motor mounting outlets. Motor Spiraducts: Figure 15 : Accelerator Spiraducts are made from the same materials as ventubes but they are reinforced During the final construction phase after tunnel breakthrough, with a continuous helical coil. They can therefore be used under this system offers the advantage of compensating for natural ven- low positive pressure, but their high friction coefficient limits tilation, which alone is often insufficient or inconsistent. In some their use to short sections or special zones such as elbows. cases, this type of ventilation can lead to a dust problem. b) Characteristic values Dimensioning of accelerators is based on free field delivered These are as follows: thrust and not on flow rate, unlike fans connected to a duct. Free field thrust is derived from the formula F = ρ.Q.V, where ρ is the - allowable pressure - ultimate strength density, Q the fan flow rate and V the jet velocity (Figure 15). - tear strength 4.1.2 - Ducting - dynamic perforation strength - flame resistance 4.1.2.1 - Flexible synthetic ducting - electrical resistance of both faces a) Types of ducting - rotting resistance Flexible ducting is made of fabric coated with synthetic material, which must be flame resistant and subjected, before use, to heat - hydrocarbon and chemical resistance conduction tests according to a standard stated by the manufac- c) Storage systems turer/supplier. Storage cassettes are commonly used for smooth ventubes; these Materials used should have a certain number of physical characte- allow the ventilation ducting to be released in step with tunnel ristics to be suitable for use in a tunnel. advance, whilst keeping it in tension. They can be divided into two main types: 4.1.2.2 - Steel ducting • smooth flexible ducts or ventubes, which only operate under a) Types of ducting positive pressure, Light sheet-steel tubes, which can be used for both blowing and • spiral flexible ducts or spiraducts, which can be used under extraction ventilation. They are commonly called air pipes. positive or low negative pressure. We distinguish: Ventubes: Ventubes are fully pliable and in sections of varying length up to Flanged welded sheet-steel tubes: 30 m. Each end features a semi-rigid ring allowing the sections to These are made of welded sheet-steel and incorporate assembly Fan

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Blowing direction


flanges at their ends, which can be screwed together against a rubber seal. This type of ventilation tubing is used more for dust extraction ducting. Clasped rolled sheet-steel tubes: They are made from thin, often galvanized, helically wound sheet-steel, with a single seam for ordinary ducting or with multiple seams for tear-resistant ducting. Junctions feature flexible sleeves with clamping collars or riveted metal sleeves. b) Characteristic values These are essentially characterized by the allowable positive and negative pressures, which depend on steel grade, sheet-steel gage and duct diameter. Weak points are localised at the connections.

comprise a soundproof tubular casing of similar diameter to the fan and are mounted in series with it. Their efficiency depends on the soundproofing material used and their length. Polyurethane foams should not be used as soundproofing material (production of hydrocyanic acid in the event of fire) and, moreover, they are acoustically inefficient. b) Baffle mufflers When a very major reduction in noise is required, baffle devices incorporating soundproof parallel sound deflector panels must be resorted to. Their efficiency is much higher than that of axial mufflers, but both their cost and their size are also much greater.

4.1.3 - Ancillary ventilation equipment

4.1.3.4 - Electrical equipment In general, it is advisable to vary the power of fans used during work progress. To do this, the electric motor is acted on by considering speed variation of asynchronous motors. Motor speed depends on the frequency of rotation (N = frequency of rotation in rpm, F = frequency in Hz) and the number of polar pairs P. To vary the speed of an asynchronous motor, we can: • either alter the number of polar pairs: a mechanical solution exclusive to 2-speed motors, • or alter the motor supply frequency: an electronic solution, which is simpler and offers a wider speed variation range. a) Mechanical solution Polar connection cage motors: these motors incorporate 6 terminals and only allow speed ratios of 1 to 2. Low speed: delta connection. High speed: star connection. Separate stator winding cage motors: these motors incorporate two independent stator windings allowing two speeds of any ratio to be obtained. Slip ring motors: motor speed is adjusted by altering the sliding contact. Slip ring rotor terminal resistances are simply varied. The higher the resistance value, the greater the speed reduction. Resistance variation is ensured by coupling as for rotor start-up. b) Electronic solution From a fixed frequency, single or 3-phase alternating current network, the frequency converter supplies variable frequency rootmean-square alternating voltage.

4.1.3.1 - Distribution devices a) Branches and bifurcations These are usually metal components, but are sometimes made of flexible ducting. They allow air supplied by the main ventilation duct to be distributed to secondary ducts supplying air to the various site tunnels. Their implementation should take into account the major head losses they can cause. b) Dampers Dampers are devices that enable duct flow to be regulated or flow distribution to be changed at branches or bifurcations. They can be manually or automatically controlled. At fan start-up, they also permit controlled inflation of very long flexible ventubes. c) Inlets, outlets, couplings The geometry of air inlets, outlets and ventube connection devices to fans represents an improvement factor for optimizing the performance characteristics of the whole ventilation installation. Special care should therefore be given to designing these components if the head losses they cause are to be reduced to a minimum. 4.1.3.2 - Protection devices Air inlet orifices are generally fitted with a protective grill either to prevent any foreign bodies colliding with the fan blades or to prevent any object being ejected from the duct outlet. When the fan is installed near the face and the tunnel is excavated by blasting, a steel protective shield is installed to protect the fan from blast matter. This shield should be controlled from the rear of the construction area to start the fan without having to return to the face before blast fumes are discharged. 4.1.3.3 - Soundproofing devices Fan-generated noise pollution is significant and requires installing soundproofing devices, which can be mounted in front of and behind fans. a) Annular mufflers These are the most commonly used soundproofing devices. They

4.1.4 - Dust collection and treatment devices The basic principle retained is that one must try to control dust production, whatever the ventilation method used. • Limit dust production by resorting to "wet process" techniques. • Prevent dust propagation through the tunnel by collecting it as near as possible to its production source. 4.1.4.1 - Limiting dust production Methods should be favoured that prevent or limit dust production, such as drilling using water, foam or any fluid suited to the ground, resorting to wet process shotcreting, systematic spraying


19


of concrete inverts during haulage and of muck spoil during the mucking operation. Preferably, automatic irrigation lines should be used for the latter spraying operations to prevent operator exposure to pollution. As regards roadheaders, fogging techniques can enable dust production to be effectively cut down (0.5 micron dust is collected by a 0.5 micron water droplet). 4.1.4.2 - Containment systems Enclosing as much as possible polluting operations using walls, curtains, etc. is recommended, to simultaneously maximise pollutant containment, reduce air transit cross-sections and mitigate the harmful effects of draughts. This principle allows discharge system efficiency to be increased and extraction flow rates to be reduced. 4.1.4.3 - Dust extractors A dust extractor enables solid particles in suspension to be separated from a gas flow. Four major classes of dust extractor can be distinguished. Mechanical dust extractors (cyclones), which can operate dry or liquid injection under the action of centrifugal, inertial or gravitational force. Electrical dust extractors: the gas flow is subjected to an electrical charge (ionisation) and the dust particles thereby charged are then attracted to surfaces of opposing polarity, on which they are deposited. Hydraulic dust extractors (scrubbers): forces applied by this system make the dust particles heavier by forming clusters in contact with fine water droplets and cause clusters so formed to be halted when they collide with wet surfaces. Porous layer dust extractors: the gas flow crosses a porous layer, which retains particles by adhesion. The porous layer is usually made up of separate elements packed together to form fibrous or granular layers. It should be remembered, however, that resorting to a dust collector does not guarantee that the quality of air discharged is at least equal to fresh air and thus it cannot be recirculated in the eyes of the legislator. Ventilation ducting should therefore be connected to dust collectors before discharging the air directly to the exterior. 4.1.5 - Exhaust fume treatment 4.1.5.1 - Petrol engines Whatever their power, petrol engines should be PROHIBITED because their CO (10% of exhaust fumes) and nitrous fume emissions are very high and odourless. 4.1.5.2 - Diesel engines Under similar operating conditions, CO emissions are much lower for diesel than for petrol engines. Diesel engines also produce less unburnt hydrocarbons but, on the other hand, they produce sulphur dioxide (SO2). Other diesel engine pollutants are nitrous fumes (Nox), inorganic acids, soot and smoke.

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Precombustion chamber and direct injection, electronic control diesel engines represent a solution which provides the best results today. These engines reduce considerably not only operating cycle problems, but also pollution due to noise and vibration. 4.1.5.3 - Different fuels We consider here very low sulphur content fuels. Their systematic use allows the SO2 in engine exhaust fumes to be practically eliminated. The use of desulphurised fuels is therefore recommended. 4.1.5.4 - Exhaust fume treatment devices The main devices currently in existence for treating exhaust fumes at engine outlets are described below. On the one hand, it should be noted that this list is not exhaustive and, on the other hand, that technology in this field is constantly evolving such that new methods appear regularly on the market. a) Bubble tank Originally, the bubble tank was intended for machines working in a firedamp atmosphere and was designed to eliminate the risk of sparks. It therefore has no effect on exhaust fumes and retains only 30% of particles in suspension. Its only advantage is that it cools fumes and therefore enables paper filters to be used to retain soot particles. Its disadvantage is that it affects engine performance and causes significant humidification of the ambient air. b) Fume dilution devices These are mechanical devices that are mounted on the exhaust and are designed to accelerate the fumes to encourage their ejection far away from the operator to a better ventilated area. They act by centrifugal effect. c) Paper filters These are very efficient to trapping soot particles (80% eliminated). But they can only be used after cooling the exhaust fumes (T < 120 °C) and have to be frequently changed (8 to 20 h usage, depending on engine pollution level). d) Ceramic filters with catalysers Soot accumulation in a ceramic filter causes a temperature increase, which induces the catalysing reaction that destroys the soot. The minimum temperature required by catalysis is 300 °C. This system reduces soot by 50 - 70%, but also has an effect on the fumes (approximately 50% reduction in pollutants). The temperature required for catalysis can be decreased by adding a catalyser to diesel fuel. e) Oxy-catalytic exhaust pipes These exhaust pipes have to be custom-designed for each engine and require very careful servicing. They act by oxidation, reduce soot emission by approximately 50%, but are also very effective in relation to fumes and destroy in particular aromatic nuclei. On the other hand, when sulphur is present, the emitted SO2 is


converted into SO4, which in a humid environment (bubble tank) produces H2 SO4. Presence of sulphur in fuels also has the disadvantage of promoting the appearance of hard particles, which lead to combustion chamber damage. This is the reason for the recommendation drawn up in the USA aimed at reducing the presence of sulphur in fuels (sulphur content < 0.05% by weight). f ) Catalytic exhaust pipes with burners Connecting a catalytic exhaust pipe to a burner raises the fume temperature to 600 °C, which improves catalysis results. Research is currently being conducted in Germany for both cars and tractor units. 4.1.6 - Treatment of heat 4.1.6.1 - Treatment of heat sources Machines used for construction represent heat sources, whose significance can lead to a temperature rise that can be, at least locally, detrimental to working conditions. This is especially the case for tunnel boring machines. A comprehensive cooling system should therefore be implemented to discharge calories to the exterior. 4.1.6.2 - Air cooling Cooling of fresh air introduced into construction areas by industrial cooling/air-conditioning methods may prove necessary, especially when confronted with a temperature gradient associated with increasing depth of construction or an active volcanic-type geological environment. 4.1.6.3 - Air heating Conversely, when fresh air is taken from the exterior at too low a temperature, it may prove necessary to direct it through a heating unit prior to introduction into construction areas.

4.2 - Implementation and installation 4.2.1 - Fans Fan installation should be carried out according to guidelines provided by the supplier. In particular, it should be stressed that fans must: • remain permanently accessible to allow them to be serviced and repaired, • be fitted with mufflers to limit their noise when installed near working areas or in a manned environment, • be fitted with protective grills mounted on their exhaust cones, • be connected to the first ventube section by means of a conical connecting unit with an apex angle of at least 20°. 4.2.1.1 - At the tunnel portal All fans installed at the tunnel portal should imperatively take account of meteorological conditions specific to the site and ground topography.

Fan positioning and installation can lead to foul air recirculation or mixing with the fresh air supply. In urban areas, consideration of these factors, combined with that of dust, odor and noise emissions, will be decisive when selecting fan location and orientation. All open air duct sections should be protected against risks associated with construction traffic, rock falls, icing, etc. 4.2.1.2 - In the tunnel driving area Fan installation in the tunnel driving area occurs especially when extraction ventilation is required near the face. It can also apply if sweeping of the face with fresh air taken from the rear in the tunnel is desired. In general, placing the fan itself near the face is difficult. Most of the time, it is therefore installed to the rear of the face, for example on a portal frame allowing machines to pass, and extended forward by a rigid or flexible duct section, which can be retractable or not, depending on the type of ventilation. However, fan installation in the tunnel driving area often remains problematic either because of machine size or because of the noise pollution it generates. 4.2.2 - Ventilation ducting The overall efficiency of the installation and the quality of air distributed very often depend on the quality of ventilation duct installation. Special care should therefore be given to duct suspension systems. 4.2.2.1 - Flexible duct erection and suspension Flexible synthetic ducting should be suspended from tension cables. Especially when there is no fan start-up control unit, it is advisable to always keep part of the ventube cross-section open to reduce the surge effect when the fan is started. Either twin cable suspension or single cable suspension, but with supporting hangers, can be adopted to achieve this. Duct sections should be assembled using screw- or cam-closed flanged couplings. Flexible duct elongation should be rectified by retensioning during erection and special care should be given to cable fixing points as well as to the fire resistance and proofing of the products used. 4.2.2.2 - Rigid duct erection and suspension Longitudinally or helically welded rigid duct sections should be suspended from several points to prevent airtightness defects during assembly resulting from deformation under their own weight. Joints should be minimally stressed by moments or shear forces. 4.2.2.3 - Duct replacement Duct suspension should be designed to allow rapid replacement of damaged sections to limit major leaks, which can occur especially in additional work areas.


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4.2.2.4 - Passing through equipment Tunnel construction management can lead to several successive work areas, which must be crossed by ventilation ducting (waterproofing, invert concreting, vault concreting areas, etc.). These passages should be carefully studied so that they do not cause additional head losses or damage to the duct itself. 4.2.2.5 - Tunnel driving area It is in this area that ducting is most exposed either because of machine movement, which is particularly intense in this area, or and above all, because of blasting, when explosives are used. The last duct section is the most exposed and should always be kept as the end section, as long as it can be reused. Implementation of telescopic sections, which can be folded away during blasting, can also be adopted.

4.3 - Ventilation procedures and instructions for use Even if site ventilation is suitably designed, dimensioning of sections correct and implementation carried out according to the rules, ventilation can be insufficient during certain construction phases simply because its operation is misunderstood or its day-to-day use is incorrect. It is therefore essential that the Organisation manager drafts a document detailing procedures and instructions for use of the site ventilation system, indicating in particular: • the fan start-up sequence for different construction phases,

• the ventilation ducting advance process and distances to be respected in relation to the face, • the frequency of different inspection operations, • regular servicing operations and their frequency, • in general, all measures to be taken to ensure satisfactory operation of installed ventilation.

4.4 - Personnel protective equipment In view of the prevention principles stated above, resorting to the equipment referred to below can only be exceptional or represent back-up to more general measures aimed at ensuring air quality during construction. 4.4.1 - Collective protection This involves mainly pressurized and/or air-conditioned cabs fitted to production machinery, especially roadheaders, shotcreting robots or muck loading machines. We should also classify under this heading the "Respir" cabin, a collective pressurised room supplied with fresh air from the exterior, designed to safeguard the tunneling crew during the blast kickback phase and to prevent it having to leave the tunnel. 4.4.2 - Personal protection For the record, we include under this heading specific protective breathing equipment resorted to only in the event of danger or absolute need to penetrate into a polluted atmosphere area.

5 - MAINTENANCE AND INSPECTIONS 5.1 - General Statutory measures require the Organisation manager and selfemployed worker to adopt, in particular, organisational measures specific to detecting in time any damage likely to cause danger, in order to ensure safety and protect the health of workers in his Organisation. Amongst these measures, the French employment code requires periodic checks and inspections to ensure the proper state of conformity not only of premises, installations and work equipment, but also of protection equipment and means. Moreover, these periodic checks and inspections are limited to the obligations under the French employment code and do not include those imposed by other French ministries (industry town planning and housing – transport, etc.). The nature and content of each check and inspection are laid down in specific statutory orders, which should be referred to for further detail. Checking frequency should correspond to a minimum requirement and both examinations and checks should be compulsory after any failure that may or may not have caused an accident or

22


after any abnormal force or incident that may have caused a disorder in the installation (clause 22 of French decree of 08/01/1965). Furthermore, the work inspector can require additional checks at any time. Checking represents an inspection of the installation with a view to ensuring its proper operation and must be included in a maintenance action. Definitions An inspection is an assessment of equipment or situation conformity. In most cases, it is performed by a certified technical inspection body or by the administration. The term "leakage inspection" sometimes refers to the notion of examination. In most cases, it is used in regulations when in the presence of tanks, pipes and ducts, storage tanks, hollow containers or equipment incorporating a cavity. The notion of servicing refers to routine equipment cleaning or repair operations. The term "pressure test" is especially used in the pressurised equipment field. A pressure test involves subjecting the equipment to a suitable hydraulic pressure greater than its maximum


working pressure. This pressure is maintained throughout the time required for the equipment and, in particular, its walls to be fully examined. The equipment will be considered to have successfully passed the pressure test if it has resisted the test pressure without leaking or permanently deforming.

5.2 - Maintenance and checking Working equipment not covered by a specific statutory measure is subject to obligations laid down by French employment code clause L 233.5-1, which details equipment that must be kept in good condition, whence the need to undertake maintenance. Performance tests should be determined with respect to the equipment and the site on which it is installed. These tests are detailed in the maintenance manual. Equipment maintenance should be ensured to preserve the health and safety of workers. The Contractor is responsible for seeking all installation anomalies and damage likely to adversely affect working conditions and influence worker health and safety. To achieve this, the Contractor should appoint one or more persons in charge of equipment maintenance, who should then be specifically designated and specially trained to respect the requirements and performance conditions of their respective tasks (French employment code clauses R 233-9 and R 233-10). Moreover, the French employment code requires both initial and periodic tests and checks on many different equipment items and it fixes their frequency and content (see tables below). Clause R 233-11 stipulates that these "checks are performed by qualified persons, employed or not by the organisation, whose list is kept at the disposal of the work inspector or controller. These persons shall be skilled in the prevention field for risks presented by the work equipment". The result of periodic general checking should be recorded in the Organisation safety logbook. Reports drawn up following periodic checks should be attached to the safety logbook, when they are performed by persons not employed by the Organisation. The safety logbook should be kept at the disposal of the work inspectorate, the CRAM [French regional health insurance fund] and the OPPBTP [French building and civil engineering industry professional prevention body]. 5.2.1 - Training and information of maintenance personnel French employment code clause R 233-2 stipulates that the Organisation manager shall, by appropriate means, inform workers in charge of working equipment maintenance implementation of: • operating or maintenance conditions for this working equipment, • instructions and procedures concerning it, • action to be taken in foreseeable abnormal situations, • experience-based conclusions allowing certain risks to be eliminated.

This information should be drawn up based on the instruction manual normally supplied when acquiring any working equipment in accordance with marketing conventions. "By appropriate means" involves safety training, in relation to which French employment code clause R 233-3 states, "must be renewed and complemented as often as required to take account of equipment changes for which these workers are responsible". 5.2.2 - The maintenance logbook This logbook should show the equipment to be checked, the checking frequency and content. Inspections, their dates and the equipment concerned should feature in this logbook. Monitoring of observations and findings should be clearly shown and initialed by the person charged with restoring conformity and fault elimination. This logbook can be computerised subject to the approval of the work inspectorate.

5.3 - Inspections 5.3.1 - General Inspections and servicing work should be regularly performed: first, to check that dimensioning assumptions made are indeed validated and that ventilation characteristics obtained do effectively conform with the design calculation and, second, to ensure proper operation of the installation throughout the construction period. The Contractor is responsible for servicing and inspection of the site ventilation installation and should take all necessary measures to fulfill satisfactorily this assignment. 5.3.2 - Contractor inspections The different inspections to be performed can be broken down as follows: • ventilation and electrical inspections enabling the quantities of fresh air supplied to different site locations to be checked, • dust and polluting gas content inspections enabling validation of effective compliance of the atmosphere with regulations, • technical inspections of the installation itself, especially involving duct leakage inspection or fan operation. All inspections performed should be recorded in a logbook specially provided for this purpose, which should be kept at the disposal of the Engineer, inspection and prevention bodies. 5.3.2.1 - Ventilation and electrical inspections The Contractor should measure the ventilation system characteristics and, in particular, take measurements of: • flow and pressure in representative ducts (upstream and downstream of fans, changes of cross-section, non airtight ducts, etc.), • fan electrical power. These inspection measurements may indicate flow inadequacies and the Contractor should therefore undertake the repairs and


23


modifications required to maintain the installation in perfect condition. Flow rates and pressures should preferably be measured in measuring sections installed for this purpose. Measuring points should be located at a distance of more than 30 x diameter of the considered duct from fans or irregular points. Suitable flow rate and pressure measuring instruments should be permanently available on site and measurements themselves should form the subject of a special procedure. 5.3.2.2 - Atmospheric inspection The Contractor should regularly undertake atmospheric inspections designed to check concentrations of gas, dust and polluting elements. Concentrations should not exceed values stipulated by statutory texts at the different work stations. These inspections should be separately performed on each pollutant considered in the site ventilation design. Inspection frequency should be determined in agreement with prevention bodies according to progress of the different construction phases. Inspections should be performed at the face and at work stations spread along the different ventilated sections of the structure. They concern, in particular: • gas and fume contents – carbon dioxide, carbon monoxide, nitrous fumes, sulphur dioxide, • dust contents, • silica contents. Pollutant content should in all cases, at all places and at all times remain below each threshold defined in current statutory texts, such as French decree n° 97-331 of 10th April 1997 concerning silica dust concentration in workplaces. Results of the Contractor inspection should be forwarded each week to the Engineer and each document should include at least: • the type of pollution measuring apparatus and the data processing measures, • the alarm system used to undertake evacuation of all underground personnel in the event that an authorized threshold is exceeded, • the detailed report addressed to the Engineer and the Health and Safety Coordinator indicating in particular: - the measured pollution level, - the immediate measures taken on site, - the origin and causes of exceeding the threshold along with the measures taken to remedy this in the future. When possible, the Contractor should propose complementing these measurements with permanent recording devices for certain pollutants; in this case, the Contractor ventilation project should detail the characteristics and prices of equipment used. 5.3.2.3 - Technical inspections Contractor inspections concern all mechanical components included in the ventilation design, not only fans and ducting, but also special systems such as dust extraction installations and gas treatment devices.

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For ducting, these inspections should be specifically based on the following points: • leaks, • connection airtightness defects, • suspensions and fixings, • accumulation of water or dust at irregular points. With regard to fans, inspections should be based on fan effective operating points and on servicing operations foreseen by the manufacturer. With regard to all other devices, whose function is to eliminate partly or fully a given pollutant produced by construction machinery or site activity itself, inspections should endeavor to check that the efficiency of these devices conforms effectively with what has been taken into account in the pollution treatment design. In the special case of dust extractors, these inspections shall be based, in particular, on: • filters • sedimentation in supply ducts, • dust control as far as the point of discharge, • water supply and condition of nozzles for wet process dust extractors. 5.3.3 - External inspection External inspection, performed by a specialist body commissioned by the Engineer, features the following assignments. For ventilation installations: • checking the terms of the Contractor's technical memorandum during contract finalisation, • reviewing dimensioning-related performance procedures, calculations and phasing, • clearing check points during the different installation modifications. For atmospheric quality: • defining, right from the Contractor’s design stage, inspection means and measuring methods (measuring apparatus, maximum level not to be exceeded, etc.) for all identified pollution phenomena (gases, fumes, dust, hygrometry, temperature) to be monitored during construction not only underground, but also in the open air, • ensuring on-site compliance with procedures decided and planned for critical or check points, • monitoring poorly ventilated volumes underground (side drifts, garages, recesses, etc.) that may be penetrated by toxic gases, • keeping a logbook in which the different results are recorded. 5.3.4 - Measuring apparatus 5.3.4.1 - Flow rate measurement Flow rate is usually calculated from measured air velocity and the duct cross-section. Different types of apparatus can be used to measure air velocity.

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www.aftes.asso.fr - 2008

Safety logbook

- Every 12 months

- stocks of gas protection General checking filter cartridges for protective breathing apparatus

Safety logbook Safety logbook

- Every 12 months

- Before issuing to a new person

Certified body's report

- Every 12 months

General checking

Checking and cleaning

Checking by certified body

- After maintenance operation

Safety logbook

Fr. Empl. Code Cl. 233.42.2 Order of 19.03.1993



Cl. 16 (D.08.01.65) R 233.11

Fr. Empl. Code Cl. 233-5-2 (all equipt.) Cl 233-80 (used equipt.)

Fr. Empl. Code Cl. R 233-4

Clauses 22 and 23 (D.08.01.65) R 233-11

Safety logbook

- Before commissioning - After failure, incident, after disassembly followed by assembly, modification

Statutory references

Record of frequency

Minimum frequency

General checking

- equipment for personal protection against falls

- inflatable life jackets

- all equipment

Personal protective equipment

- At Work Inspector's demand

Testing Checking

Examination

All working equipment

- At Organisation Manager's request

Type of intervention

Equipment Installation

Qualified person

Organisation Manager

Certified body

Qualified person (skilled)

Persons in charge of checking

Person in charge of intervention

TABLE OF MAIN STATUTORY EQUIPMENT AND INSTALLATION CHECKS

List kept at disposal of Work Inspectorate

Notes

26

Leakage inspections

Dust coverage inspection

Measurement

Measurement

Drums, basins and storage tanks containing corrosive products

Silica

Noise

Noisy premises

- Periodic general checking

Checking

- Every 6 months


Electrical installations

- Every 6 months


. Permanently installed equipment and accessories . Permanently uninstalled elevators subjected to frequent displacement . Work station elevators

Initial - Periodic On formal demand of Work Inspectorate

After exceeding limiting values

Initial

- Every 12 months

- After commissioning and after structural modification - Every 12 months

- Every 3 months - Every 6 months

- Every 12 months

Commissioning check Recommissioning check

Lifting equipment and accessories . All lifting equipment and accessorie

- Periodic general checking - Periodic general checking

- Every 12 months (by installation supplier)

Checking

. Hand-moved work station elevators . High-level personnel transporters

- Every 3 months

Checking and testing

Fire fighting . Organisation of more than 50 persons and premises on which Group 1 inflammable materials are stored and handled (e.g. petrol, fuel-oil, various solvents, wood dust) . Extinguishers

Minimum frequency

Type of intervention

Equipment Installation

Decree of 14.11.1988 (Cl. 53, 54, 55) Order of 20.12.1988 amended

Inspection logbook + check report

Fr. Empl. Code R 232.8-1 to 4 R 232.8-7

Inspection logbook

R 235.11 Order 30.08.90

Decree 10.4.97 Order 10.04.99 Fr. Empl. Code Cl. 23154.6 Order 10.04.97

Inspection logbook Inspection logbook

Fr. Empl. Code Cl. R 233.43






Industrial Order of 20.05.1963 C.N.M.I.H. principles

Fr. Empl. Code – Cl. R 233-40

Statutory references

Safety logbook Safety logbook

Safety logbook

Safety logbook

Safety logbook

Safety logbook

Safety logbook

Record of frequency

Certified body

Employer

Employer

Certified bodies

See safety notice C9 F 01 Air compressors Compressed air receivers

See safety notice G1 F 01 Typical site electrical installation layout

Periodic checking report at control station

See circular 93 / 22 of 22.09.1993. If external checker, report to be attached to safety logbook

C.N.M.I.H. (Fr. nat. committee for certified fire equipment)

See safety notice A6 F 01 "Lutte contre le feu" (fire fighting)

Observations

Medical supervision Worker training

Medical supervision

See Appendix B

See Appendix A

Notes


• Pitot tube (measures dynamic pressure) • Hot wire anemometer • Plate anemometer • Ultrasound anemometer The flow rate can also be measured by tracing. In this case, it is calculated by measuring the concentration of a tracer gas emitted by a constant amount upstream of the measuring point. 5.3.4.2 - Pressure measurement Pressure measurements can be taken using hydrostatic, mechanical or electronic manometers. 5.3.4.3 - Gas content measurement Gas concentration measurements can be taken using instantaneous response portable or fixed apparatus. A type of measuring apparatus suited to the nature of the gas or gases should be used. a) Calorimeter tubes This apparatus is both inexpensive and easy to use. However, it offers only mediocre accuracy and sensitivity. b) Electrochemical cell-bed apparatus This apparatus is easy to use. However, the measurement result can be distorted by interference linked to simultaneous presence of several pollutants. Furthermore, it must be regularly calibrated to compensate for aging of the measuring cells. c) Infrared absorption analysers This type of apparatus allows accurate measurement of many pollutants. Furthermore, it permits the concentration of several gases to be simultaneously measured. Infrared absorption analysers require frequent calibration, which can only be performed by spe-

cialists, moreover they are relatively fragile and more expensive. d) Dust measurement Clause 3 of the French decree of 10th April 1997, concerning health monitoring of workers exposed to crystalline silica dust, stipulates that determination of the average crystalline silica concentration of alveolar dust particles shall be performed in accordance with the following standardised methods (or according to any other equivalent standardised method). • AFNOR standard NF X 43 - 295 - Détermination par rayons X de la concentration de dépôt alvéolaire de silice cristalline et échantillonnage par dispositif à coupelle rotative (type CIP 10) [X-ray determination of the concentration of crystalline silica alveolar deposit and sampling using a rotary cup device (CIP 10 type)]. • AFNOR standard NF X 43 - 296 - Détermination par rayons X de la fraction conventionnelle alvéolaire de silice cristalline et échantillonnage sur membrane filtrante (cyclone 10 mm) [X-ray determination of the statutory alveolar fraction of crystalline silica and filter membrane sampling (10 mm cyclone)]. 5.3.5 - Inspection frequency Inspection implementation and the frequency of different types of inspection should form the subject of an agreement based on the advancement of the different work areas, phasing of operations and different modifications to which the site is subjected as construction progresses. Note: external inspection will require certified bodies, the list of which can be obtained from CRAMs [French regional health insurance funds] or the OPPBTP [French building and civil engineering industry professional prevention body].

6 - ORGANISATION - ADMINISTRATIVE FRAMEWORK 6.1 - General approach Site ventilation represents one of the key issues in the construction of an underground structure. Its design and implementation are therefore intimately linked to the development of the project, as a whole, from its initiation to its completion. The following parties intervene in a project. • The Owner • The Health / Safety – Design / Construction Coordinator • The Engineer • Contractors • Public Authorities • Inspection and Prevention Bodies All these entities have a part to play - through their opinions and decisions - in designing and executing the project including the design, installation and operation of site ventilation, the subject of this recommendation.

6.1.1 - Level of intervention of the different players During project execution, intervention of the following three main players will determine the final design of the works. • The Owner and his Health / Safety Coordinator • The Engineer • The Contractor Each has a part to play in the following different project stages. • Preliminary Design • Detailed design • Construction 6.1.1.1 - Preliminary and detailed design Owner: - defines the Operation general programme, - performs all the administrative procedures required for Operation execution,


27


- appoints the Health / Safety Coordinator at the design stage and grants him the necessary authority and resources to fulfill his assignment, - has the Health / Safety Coordinator draw up the Operation General Coordination Plan for Health and Safety (G.C.P.H.S), - informs the main players of the Health / Safety Coordinator’s observations. Engineer: - on behalf of the Owner, undertakes Operation Preliminary Design and Detailed Design studies, checking the engineering feasibility of the proposed works in accordance with current regulations, - invites the Health / Safety Coordinator to meetings, - informs the Health / Safety Coordinator of planned measures and delivers to him all the required documents, - takes into account the Health / Safety Coordinator’s observations. 6.1.1.2 - Construction a) Owner - performs all the administrative procedures required for Operation execution, - appoints the Health / Safety Coordinator at construction stage and grants him the necessary authority and resources to fulfill his assignment, - supervises application of the Operation GCPHS, - takes into account the Health / Safety Coordinator’s observations, - demands Special Safety and Health Protection Plans S.S.H.P.P. from contractors, - forms the Intercompany College for Health, Safety and Working Conditions (I.C.H.S.W.C) if conditions are met. b) Engineer - ensures that ventilation construction studies meet the programme requirements, invites the Health / Safety Coordinator to meetings - informs the Health / Safety Coordinator of planned measures and delivers to him all the required documents, - takes into account the Health / Safety Coordinator’s observations. - takes part in I.C.H.S.W.C. activities, - supervises application of the S.S.H.P.P. and implementation of planned safety-related measures. c) Contractor - determines risks associated with his activity in executing the Operation - studies site measures in relation to the construction methods and means proposed during the call for tenders or that are implemented during construction, - draws up the S.S.H.P.P., - performs all the inspections and operations required for proper installation operation in compliance with regulations. 6.1.2 - Parties intervening in ventilation design The combined ventilation and site atmospheric quality control systems should be considered a structure in their own right and should therefore be designed as such, according to conventional design logic for the overall structure.

28


• Collection of basic data, specifically including: - geometrical characteristics of the works, - construction phases, - methods used, - different pollution source characteristics, - determination of fresh air requirements. • Adopted ventilation principle and general characteristics, • Special measures for controlling pollution sources and protecting against risks, • Dimensioning of different units, • Construction measures, drawings and diagrams, • Implementation and inspections, • In this process, the most delicate stage is the design of the ventilation system and the choice of methods allowing the site’s fresh air requirements to be met.

6.2 - Contractor consultation The choice of ventilation system and determination of air flow rates depend generally on the excavation method and implementation means. The tender file should therefore contain a number of specific items concerning site ventilation and environment physical conditions. The latter point should include: • ground properties, • presence of silica, asbestos, • radioactivity, • gases - methane, etc., • temperature conditions. Site ventilation is a work item in its own right and it is therefore recommended that payment for ventilation systems be clearly characterised in tender documents by one of the following methods: • preferably, by a set of unit prices accompanied by a bill of quantities showing the different parts of the installation, special units and power cost to ensure ventilation payment reflects accurately its implementation, • possibly, by a lump sum price paid in several installments; in this case, the Contractor must provide a break-down of his proposed lump sums, i.e.: - xx% on completion of general ventilation installations, - xx% xx months after initial payment, - xx% after installation disassembly and equipment removal. It is also recommended that external air quality control be subject to separate payment.

6.3 - Contractor's ventilation project 6.3.1 - Technical offer The Contractor should submit with his overall tender a site ventilation project to justify the ventilation system’s adequacy for the proposed construction methods. The Contractor should endeavour to seek solutions that limit


pollution emission to a minimum and that, in particular, favour resorting to electrical equipment. • Priority should be given to extracting gases, fumes and dust as near as possible to the pollution emission areas to collect pollutants at source (face excavation, center core excavation, support erection area, lining area, etc.). • If these conditions cannot be set up (temporary work areas, etc.), auxiliary blowing ventilation should be installed to prevent persistence of dead areas. The tender should include: • all necessary information concerning ventilation dimensioning, • all implementation restrictions concerning tunnel construction equipment. The following points should be particularly detailed: - assumptions concerning fresh air or extraction requirements with respect to work to be performed, - ventilation principle and diagrams (blowing-extraction, etc.), - ventilation and electrical calculations, - fan characteristics (flow rates, pressures, positions), - duct characteristics, - special devices and characteristics of implemented equipment such as dust extractors, mufflers, etc. 6.3.2 - Cost Whether it be clearly identified in the contract by a set of unit prices and/or by a lump sum price under "Ventilation equipment installation", or whether it be considered included under "General site installations", the cost of ventilation equipment should include: • availability of all ventilation equipment required for executing the underground works, • commissioning and performance tests, • routine ventilation servicing and maintenance, • equipment reorganisation, adjustment, strengthening and movement throughout the construction period and in relation to construction phases,

• routine servicing and maintenance of meter cabinet allowing power consumption to be measured, • equipment installation design to be submitted to the Engineer for approval and which features: - ventilation design for all site configurations, - installation dimensioning, - provision of equipment drawings. • operation monitoring procedures and, in particular, ventilation performance measurements to be regularly taken (we recommend every month) as the driving face advances and as the ventilation ducting becomes longer, along with pollution level monitoring measurements, in accordance with the G.C.P.H.S., • power consumptions, • installation removal. 6.3.3 - Construction When executing the project, the Contractor should specify detailed measures embodied in the technical solution chosen at the time of tendering and the means he will adopt for its implementation. During the construction phase, the ventilation project should specifically feature: • drawings showing the general ventilation installation (fans, ducting, portal frames, etc.), electrical installations (transformers, cabinets, etc.) and special installations (dust extractors, mufflers, etc.), • the programme of phases and diagrams required for performing the work (advancing of face and polluting work areas, etc.), • supporting calculations for ventilation installations and their characteristics for each construction phase. Assumptions made concerning gas, fume and dust emissions should be checked in the construction design for each face advance phase and each type of work area composition concerned. The construction study should also consider possible leaks in the duct network and interference between different underground localised construction areas.

7 - STATUTORY TEXTS 7.1 - Regulation

7.2 - Standards

• French decree n° 84-1093 of 7th December 1984 "Aération et assainissement" [aeration and purification] • French decree n° 97-331 of 10th April 1997 concerning protection of certain workers exposed to inhalation of silica dust particles in their workplaces. • French decree n° 2001-97 of 1st February 2001 concerning special rules for preventing carcinogenic, mutagenic or toxic risks for reproduction. • French decree n° 2001-1016 of 5th November 2001 prompting creation of a document concerning the assessment of worker health and safety risks foreseen by clause L 230-2 (amendment) of the French Employment Code. • French Employment Code - Orders of 15/3/1953 and 9/6/1993.

• AFNOR standard NF X 43 - 295 - Détermination par rayons X de la concentration de dépôt alvéolaire de silice cristalline et échantillonnage par dispositif à coupelle rotative (type CIP 10) [X-ray determination of the concentration of crystalline silica alveolar deposit and sampling using a rotary cup device (CIP 10 type)]. • AFNOR standard NF X 43 - 296 - Détermination par rayons X de la fraction conventionnelle alvéolaire de silice cristalline et échantillonnage sur membrane filtrante (cyclone 10 mm) [X-ray determination of the statutory alveolar fraction of crystalline silica and filter membrane sampling (10 mm cyclone)]. • AFNOR standard NF X 44-052 – Détermination des débits des ventilateurs sur le site [Determination of fan flow rates on site].


29


APPENDICES

CONTENTS Pages

1 - APPENDIX 1 – DIMENSIONING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.1 - Dimensioning of ventilation components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

100 100

1.1.1 - Design assumptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.1.2 - Design principles – Basic equations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.1.2.1 - Head losses in ventilation ducting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.1.2.2 - Fan design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.1.2.3 - Special design case of tunnel network ventilation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.1.2.4 - Atmospheric data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

100 100 100 101 101 102

1.2 - Calculation outcome – Interpretation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.3 - Final design - Implementation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

102 102

2 - APPENDIX II - GLOSSARY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

103

APPENDIX 1 - DIMENSIONING

1.1 - Dimensioning of ventilation components Site ventilation system design should be undertaken so as to demonstrate that fresh air flow rates and adopted measures allow the stipulated limiting values to be respected at all points and during each construction phase. Ventilation calculations are based on basic laws of fluid mechanics. They should enable the following characteristics to be determined: • the number, position and characteristics of the fans installed, • the optimum diameter and characteristics of ducting, • the power consumptions of the ventilation system. 1.1.1 - Design assumptions To be able to perform simply the calculations, a number of assumptions concerning air behaviour should be taken into account: • air is considered incompressible for the pressure level commonly encountered in site ventilation, • steady flow conditions prevail, •"pipe"-type turbulent flow head losses are considered. 1.1.2 - Design principles - Basic equations Air circulation in a network comprises fans, ventilation ducting and tunnels, in which the air is distributed, and causes head losses that have to be evaluated: this is the purpose of ventilation design.

30


The basic Bernoulli equation complemented by a term characterising the head losses between two points of a duct allows us to state:

where: H p ρ g z V

flow head (Pa) static pressure in section (Pa) air density (kg/m3) acceleration due to gravity (m/s2) elevation of considered cross-section (m) discharge velocity of air in section (m 3/s) = flow rate/cross-section Generally, the total head loss ΔH equals the sum of the head losses per unit length (friction head losses) ΔH F caused by fluid friction along the duct walls and the irregular head losses ΔH S associated with streamline separation or turbulence generation when passing obstacles or irregular points.

Note: given the low density of air (1.2 kg/m3 at 20 °C), the term ρ gz is usually neglected. 1.1.2.1 - Head losses in ventilation ducting The pressure delivered by the fan should take into account head losses generated by the unit itself, accessories (soundproofing,


outlets, etc.), ventilation ducting, duct and connection leakage and all construction phases, which are often characterised by increasing duct length. In some cases, head losses due to tunnel air flow should be considered. The total pressure delivered by the fan is therefore obtained by evaluating all head losses. a) Symboles L (m) duct length dx (m) length of duct section concerned (i) hydraulic diameter of duct or section (= 4.S./PH) DH (m) cross-section of duct or section S (m2) wetted perimeter of duct or section PH (m) 3 ρ (kg/m ) air density (usual value = 1.2 kg/m3 at 20 °C) v (m/s) air flow velocity in duct (no leaks) dv (m/s) velocity variation in section (i) vx (m/s) air flow velocity in section (i) at abscissa x px (Pa) static pressure in section (i) at abscissa x dp (Pa) pressure variation in section (i) ζ irregularity coefficient (inlet, outlet, elbows, narrowing, vents, leaks, etc.) λ average friction coefficient for duct section 2 2 ƒ'(mm /m ) ratio of leakage area to peripheral area (i) duct section identification number (x) abscissa within duct starting from origin x = 0 b) Head loss calculation • Friction head losses in duct - For a section without leaks (constant air velocity)

ρ 2 Pfriction = λ . L . v 2 DH

- For a section with leaks (velocity variation)

velocity variation:

Note: a network has always points featuring airtightness defects, small tears or imperfect joints between duct sections. For calculation purposes, we accept that these inevitable defects are uniformly distributed throughout the length of the considered section and that leakage losses are proportional to leakage area and leak air flow velocity. This design method does not take into account major isolated leaks because these can be easily detected and eliminated. • Head loss at irregular points pirregular Example: local narrowing of duct cross-section

Value ζ can be obtained from specialised catalogues, for example that of I.C. Idel-Cik. • Flexible duct classes The following 3 major classes of flexible ducting used in ventilation networks and defined in the Swiss Sia Recommendation are retained. • Quality class S ducting: new ducts erected very carefully and well, regularly maintained and made up of long sections (≥ 100 m) with few couplings (very small leaks and low friction losses). • Quality class A ducting: new, properly maintained ducts erected to ensure a low risk of damage (minimal airtightness defects and friction losses), characteristics allowable only for execution by "successive phases". • Quality class B ducting: regularly maintained ducts in service for some time or reused (moderately large airtightness defects and friction losses). • Friction and irregular loss coefficients

Pfriction

Friction losses in ducting (blowing and/or extraction ducts) Ducting class

Friction coefficient λ

Metal

0,010 à 0,015

Concrete Flexible

pressure variation: Pfriction

0,015 à 0,02 Duct class S

0,015

Duct class A

0,018

Duct class B

0,024

Spiraducts (spiral ducting)

> 0,025 depending on design


31


Facing class

Friction losses in tunnels (air circulation) Friction coefficient λ

Concrete or masonry walls

0,02

TBM excavation

0,02 à 0,05

Excavation by blasting without support

0,04 à 0,10

Excavation by blasting with support

0,06 à 0,15

Leakage losses in flexible ducting Leakage area f' Leakage coefficient ζ m2/m2 (airtightness defects) Duct class S 5 . 10-5 Flexible Duct class A 10 . 10-5 De 0,10 à 20 Duct class B 20 . 10-5 Spiragaines 5 à 20. 10-5 De 0,10 à 20 Ducting class

Irregular losses Irregularities Free air intake Air intake with grill Discharge Extraction louver

Coefficient ζ 2à4 0,2 à 40 1 0,1 à 0,5

Contraction

0,05 à 0,2

Diffuser

0,05 à 0,35

Sudden narrowing

0,05 à 0,60

Sudden widening

0,05 à 1

Isolating damper

0,15 à 0,3

45° elbow

0,1 à 0,25

90° elbow

0,15 à 0,8

Branch

0,1 à 1,3

1.1.2.2 - Fan design a) Pressure Fan pressure (total fan P) is the sum of all friction and irregular losses and allows the fan power to be determined. A fixed static pressure reserve (Pfixed) is added for possible circuit modification (phasing) and a static pressure reserve to take into account wind action at the tunnel portal and snow cover. b) Fan selection For each air flow rate, fan characteristic curves show the total pressure difference between cross-sections determined, on the one hand, on the fan extraction side and, on the other hand, on the fan delivery side. If these two cross-sections are equal, the dynamic pressure is also equal on both sides of the fan and an increase in total pressure corresponds to an increase in static pressure. c) Electrical power Electrical power depends on the total pressure P, on the flow Q calculated at the fan, and on fan efficiency and motor performance.

N (kW) fan electrical power Q (m3/s) fan flow rate P (Pa) fan total head loss ventilation efficiency coefficient ηv (from fan performance chart) motor performance coefficient ηM (according to manufacturer's data) Generally, overall efficiency is in the order of 0,6 à 0,7. If frequency-based variable speed controls are used, their efficiency coefficients should be considered in addition to that of the motor. d) Use of booster fans For phasing modifications, the required pressure may exceed the design pressure. In this case, the use of booster fans can provide an economical solution. The combined fan power (tunnel portal fans + booster fans) may be less than the pressure required for fans installed in series at the tunnel portal (see diagram on following page). Several simple rules may use the booster circuit defined in the Swiss recommendation: • a steel tube of length L ≥ 5 Dn should be erected at the end of flexible duct section n, which can be reduced by the extraction flow caused by the negative pressure generated by the fan in the next duct section n+1, • compared with duct section n+1, the air flow in duct section n should be sufficient to prevent the fan in duct section n+1 from extracting tunnel air instead of fresh air supplied by duct section n, • the internal diameter Dn+1 of the duct section n+1 cone should be £ 0.8 Dn and the distance d between the end of duct section n and the duct section n+1 cone should satisfy the following condition: 0.5Dn ≤ d ≤ 1.0 Dn • air quantity Qn should exceed quantity 10-20 % à la quantité Qn+1 1.1.2.3 - Special design case of tunnel network ventilation Leakage losses are virtually inexistent in a tunnel or shaft. The usual pipe flow equations - total losses made up of friction and irregular head losses - therefore apply to an air circulation-based ventilation system.

P totale du ventilateur ≥ P forfaitaire

32



1.1.2.4. Atmospheric data a) Variation in air density The table below gives the characteristics of the international standard atmosphere for a 0 - 2000 m altitude range. In an air circulation-based system, dynamic pressure losses are low (same velocity between tunnel and extraction outlet). However, if the rock thermal gradient is high, the pressure differences resulting from air specific mass variations due to average temperature variations should be considered. Altitude (m)

Temperature (°C)

Pressure (hPa)

Air density ρ(kg/m3)

0 200 400 600 800 1000 1200 1400 1600 1800 2000

15 13,7 12,4 11,1 9,8 8,5 7,2 5,9 4,6 3,3 2

1013 989 966 943 921 899 877 856 835 815 794

1,23 1,2 1,18 1,16 1,13 1,11 1,09 1,07 1,05 1,03 1,01

b) Atmospheric influences Pressure differences that are significant for total pressure calculation can occur in air circulation-based systems featuring long shafts or inclines. The additional pressure required from the fan should therefore be taken into account. The following expression provides an initial approximation of the pressure difference.

Δρ Δh ρe ρp

pressure difference (Pa) shaft depth [m] external air density (kg/m3) air density in shaft (kg/m3)

Moreover, for meteorological reasons, pressure differences of up to 100 Pa can occur between tunnel or horizontal gallery entrances (sometimes called portals). c) Fog formation Under certain conditions, fog formation may be observed, which can be extremely disruptive to work. For example, this can occur when laying a road asphalt in a particularly humid atmosphere. This also occurs in tunnel networks and especially in mines. During excavation of the ventilation shaft for the Fréjus Tunnel, fog formed at the Alimak heading breakthrough into the full bore shaft due to expansion of warm air coming from the tunnel. The ventilation system should be adapted such that the dew point can be controlled. In the case of extraction ventilation in winter, fresh air can freeze water inflows near the tunnel entrance. This problem should therefore be taken into account when designing the ventilation system.

1.2 - Calculation outcome - Interpretation In general, ventilation calculation results should not lead to the operating limits for the equipment selected and the installation. Validity of the design solution can only be retained if it is associated with a sensitivity study, in which construction conditions should be considered as leeway: increase in number of polluting machines, lengthening of site to be ventilated (case of driving from both ends of a tunnel), etc.

1.3 - Final design - Implementation Dimensioning having been performed on the worst case involving the most constraints (assumptions and sensitivity study), the suitability of the solution retained to the different cases that will arise during construction should then be studied. Ventilation system design should consider constraints involving equipment installation, extension and movement of different units (fans, ventubes), passing through successive work areas, construction of ancillary structures as well as performance of all finishing work, concrete lining, painting, asphalt. Production of diagrams for each site configuration will lead to a proper understanding of measures adopted.


33


APPENDIX II - GLOSSARY Ventilation systems Blowing

Air forced through ducting extended to work locations

Extraction

Air extracted by ducting at work locations

Circulation

System circulating air by creating a pressure difference between two distant points in a circuit

Reversible ventilation

System operating either in blowing or in extraction mode

Additional ventilation

Additional ventilation system complementing main system to deal with a specific aspect (e.g. fume dilution)

Fans Axial or helical fan

Propeller fan with blades driving air along impeller axis

Radial or centrifugal fan

Paddle wheel fan driving air by centrifugal action

Fans in series

Fans mounted one after the other in the same circuit creating increased pressure for a given flow

Fans in parallel

Fans mounted side by side, connected to the same circuit, creating increased flow for a given pressure

Accelerator

Fan creating dynamic pressure (this type of fan is never associated with ducting) causing air displacement directly in the tunnel (or circuit open section)

Ventilation circuit

Entire air flow route from fresh air intake to foul air discharge including, in particular, fans, ducting and all devices to be considered in relation to circuit resistance

Muffler

Static device intended to reduce the noise level of a fan

Characteristic curve density

Curve expressing relationship between fan pressure and flow rate for given rotational speed, blade orientation and air

Pressure difference

Total pressure rise (static and dynamic) between fan inlet and outlet cross-sections

Head

Resistance of all or part of a circuit downstream of a fan or accelerator

Volume flow rate

Quantity of air supplied by a fan per unit time

Ducting Ventilation duct

Flexible or rigid tube for conveying air between two points in an air circuit, excluding fans and associated devices (soundproofing device, damper, distributor)

Duct sections

Flexible or rigid components forming a duct when assembled

Air pipe

A ventilation duct (by common understanding)

Ventube

Flexible ventilation duct (by common understanding)

Ventube magazine (ventube cassette)

Device allowing several ventube sections to be stored and unfolded as excavation advances

Ducting suspension

Fixing components allowing ducting to be suspended from tunnel walls

Leak

Air lost through a duct airtightness defect

Damper

Unit installed in air circuit allowing air flow circulating through circuit to be controlled or circuit to be shut off

Distributor

Unit installed in air circuit allowing air to be distributed at a meeting point of two separate ducts

Dust extraction Dry process

Device separating dust particles by dry-fixing to sleeve, bag or plate filters

Wet process

Device separating dust particles by vaporisation or water curtain wet-fixing

34



Ventilation flow rates Q

Duct flow rate (m3/s)

QS

Blowing fan flow rate (m3/s)

QA

Extraction fan flow rate (m3/s)

QDdf

Air flow rate for diluting diesel engine exhaust fumes at face (m3/s)

QDda

Air flow rate for diluting diesel engine exhaust fumes in work areas (m3/s)

QDdr

Air flow rate for diluting diesel engine exhaust fumes from haulage (m3/s)

QDdt

Total air flow rate for diluting diesel engine exhaust fumes (m3/s)

QEpr

Air flow rate for discharging haulage dust (m3/s)

QCpt

Air flow rate for collecting blast dust (m3/s)

QCpp

Air flow rate for collecting roadheader dust (m3/s)

QCprb

Air flow rate for collecting shotcreting robot dust (m3/s)

QCpbr

Air flow rate for collecting rockbreaker dust (m3/s)

QCpa

Total air flow rate for collecting work area dust (m3/s)

QACC

Accelerator flow rate Ventilation power

N

Fan power (kW) – Nominal / Thermal output / At impeller

NS

Blowing fan power (kW)

NA

Extraction fan power (kW)

NACC

Accelerator power Characteristic values, Units and Symbols

H

Flow head (static p + dynamic p) (Pa)

p

Static pressure in section (Pa)

g

Acceleration due to gravity (m/s2)

z

Elevation of considered cross-section (m)

A

Characteristic cross-section of duct or tunnel section (m2)

D

Characteristic diameter of duct or tunnel section (m)

HF = P friction

Head losses due to friction on duct walls - Friction losses (Pa)

HS = P irregular

Irregular head losses (change of direction, widening, junction, etc.) (Pa)

H

Total head loss in circuit (Pa)

p

Pressure difference (Pa)

h

Depth of shaft or between two circuit ends (m)

dx

Length of duct or tunnel section (m)

dp

Pressure variation in duct or tunnel section (Pa)

dp /dx

Pressure gradient along duct or tunnel section (Pa/m)

dv

Flow velocity variation in duct or tunnel section (m/s)

dv/dx

Flow velocity variation along duct section (m/s)

L

Length of circuit, duct or tunnel (m)

Pdyn

Dynamic pressure = ρ v2 (Pa) 2

Pfixed

Fixed static pressure (Pa)

Ptot

Total pressure (Pa)

T

Air temperature (°C)


35


Characteristic values, Units and Symbols

V vx Px x ρ - ρe - ρp λ ζ ƒ' ηM ηV

Air flow velocity in duct = flow rate / cross-section (m/s) Air flow velocity in duct section at abscissa x (m/s) Static pressure in section at abscissa x (Pa) Abscissa along duct axis (m) Air density (kg/m3) (e = exterior / p = shaft) Friction head loss coefficient of duct or tunnel (dimensionless) Irregular head loss coefficient (dimensionless) Ratio of leakage area to peripheral area (mm2/m2) Motor performance coefficient (dimensionless) = shaft power / thermal output Fan efficiency coefficient (dimensionless) = ventilation power / shaft power Limiting values

A.E.V.

Average exposure limiting value of a polluting product

E.L.V.

Short term exposure limiting value of a polluting product Official bodies

C.N.A.M.

Caisse Nationale d'Assurance Maladie (French national health insurance fund)

C.R.A.M.

Caisse Régionale d'Assurance Maladie (French regional health insurance fund)

C.G.S.S.

Caisse Générale de Sécurité Sociale (French social security general fund)

O.P.P.B.T.P.

Organisme Professionnel de Prévention du Bâtiment et des Travaux Publics (French professional prevention body for the building and civil engineering industry)

D.D.T.E.

Direction Départementale du Travail et de l'Emploi (French departmental employment office

D.R.T.E.

Direction Régionale du Travail et de l'Emploi (French regional employment office

D.R.I.R.E.

Direction Régionale de l'Industrie, de la Recherche et de l'Environnement (French regional department for industry, research and the environment)

C.C.A.G.

Cahier des Clauses Administratives Générales (French general administrative conditions of contract for public works)

C.C.T.G.

Cahier des Clauses Techniques Générales (French general technical conditions of contract for public works)

P.S.

Preliminary Studies

P.D.

Preliminary Design

D.D.

Detailed Design

S.D.

Structural Design

C.C.F.

Contractor Consultation File

Design / Contract documents

Coordination C.I.S.S.C.T.

Collège Inter-entreprise pour la Sécurité, la Santé et les Conditions de Travail (Intercompany Committee for Health, Safety and Working Conditions / ICHS-WC)

S.P.S.

Sécurité et Protection de la Santé (Safety and health protection)

P.P.S.P.S.

Plan Particulier de Sécurité et de Protection de la Santé (Special Safety and Health Protection Plan / S.S.H.P.P.)

D.I.U.O.

Dossier d'Interventions Ultérieures sur l'Ouvrage (Structural Retrofitting File / S.R.F.)

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GT27R1A1 Ventilation of Underground Works During Construction

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