Medical gas distribution system: Lifeline of a modern hospital Prabir Kumar Nag
The exacting nature of medical science focuses demand on improved medical facilities with more reliable and effective medical support services. It is primary objective of suppliers of medical gas distribution systems to provide the creative technical service and quality products that keep pace with changing needs. Since central piping systems supply medical gases in life support situations, it is essential that the reliability and integrity of the system be the responsibility of all professions- manufacturing, design, installation, testing and operation. There are four medical gas systems normally installed and piped into medical care facilities. Oxygen is used primarily for respiratory therapy and anaesthesia. Constant supply and immediate availability throughout the hospital is essential. The system is designed to provide 60 psig at the outlets. Nitrous oxide is used primarily used in OT area. Pressure required at each outlet is 60 psig. Medical air (compressed air) is primarily used for respiratory therapy in areas like nurseries, emergency rooms, intensive intensive care areas, etc. It is also widely used in OT a rea. The air used for medical purpose must be free from oil, moisture and contaminants. The system is designed to provide an outlet pressure of 60 psig. Although vacuum is not a medical gas, it is an essential part of medical gas system. Vacuum is widely used throughout hospital facilities in patient treatment and in laboratory. In surgical recovery and intensive care areas, it is used to remove fluids from incisions and assists vital post- operative drainage. Vacuum systems are normally designed to provide 15-20” of Hg at the furthest point from the central vacuum system. For ensuring this, the entire system need to be designed, installed and commissioned with high degree of technical expertise skill and experience. The design and planning of a medical gas distribution system may be divided under the following: 1. Location where it is required and the number of outlets 2. System pipeline routing and determination of size of pipes 3. Medical gas supply source. 4. Intermediate pipeline controls 5. Gas service outlets 6. Critical care area equipment 7. Alarm monitoring equipment 8. System specification International design and safety standards followed worldwide include NFPA 99 (USA), HTM 2022 (UK), DIN (Germany), CSA (Canada), EN (Europe) etc. Following standards ensures safety, low infection rate, low post-operative care, and assurance of the functionality of the system. It gives confidence to the medical fraternity and works out to be more economical. It also helps in obtaining the acceptance of the accreditation authority, health insurance sector and avoids medico legal complications. Basic principles during routing of medical gas system Piping shall be protected against physical damage, corrosion etc. Buried piping subject to surface load shall be installed at sufficient depth to prevent the piping from excessive stress. The minimum backfilled cover should be 36”. Trenches shall be excavated so that the pipe has a firm and substantial continuous bearing on the bottom of the trench.
Piping shall not be installed in kitchens or electrical switchgear rooms. Avoid areas/corridors where movement of equipment may cause physical damage. If unavoidable protective shields to be used. Correct size piping is one of the most important aspects to be considered in designing system for central for medical gas delivery system. Undersized pipes may not give adequate pressure and flow under peak load. O versized pipes would make the system more expensive. In general diameter of pipes tend to reduce from source to end of distribution system. Good system design requires that risers be larger than laterals and laterals be larger than drops. Piping system are sized to confine the pressure drop over the total system within 5 psig for positive pressure gases and 3” of Hg for vacuum system. Separate rooms are recommended for housing the Gas Control Panels and other equipment. The room where Gas Control Panels are kept is known as Manifold Room. It is preferable that this room is located on the ground floor and should have easy access to delivery vehicles. It should be well ventilated and lit. For ease of handling of cylinders the floor level should be at a height of one meter from the ground level. A separate room called Plant Room should be used compressors and vacuum pumps. This room should be in close proximity of the Manifold Room. Oil or oil mist and other hazardous material should not contaminate the surrounding atmosphere. No grease, oil or naked flame should be used in the near vicinity and the area should be a ‘No Smoking’ zone. Oxygen is normally supplied as compressed gas in cylinders at a pressure of app. 2000 psig. The color code for oxygen cylinder is black body with white neck. In hospitals where the consumption is high and space is available liquid oxygen vessel is preferred. For installing liquid vessels guidelines laid down by Chief Controller of explosives need to be followed. For ensuring uninterrupted supply two separate banks are used. Gas from one bank is utilised at any point of time. The other bank is kept as stand by or reserve. A control panel installed between the two banks ensures that both banks are not depleted simultaneously and the control of the manifold automatically shift the flow of gas from the primary side to secondary side when the primary bank pressure falls below the set level. The control panel used should be built in accordance to the international standards. There should be a regulator for each cylinder bank to initially reduce the cylinder pressure to the two line regulators that control the final pressure. Both line pressure regulators should be in service at all times. The change over from the depleted bank to secondary bank should be immediate with out fluctuation of line pressure. Isolation of banks for ensuring on-line servicing is necessary. The manifold should have intermediate and line pressure relief valve. Separate gauges indicating the pressure of each bank and also the line pressure should be an integral part. Alarms indicating fall or rise of pressure in any bank or in the supply line is essential. Separate power supply to be furnished with the manifold to convert 240V AC to 24 V AC output power. Nitrous Oxide consumption varies with the type of surgical schedules, type of surgery performed and as well as administering techniques. While the requirement of manifold and control panel is in line with that of oxygen, it is recommended to use an on line heater at the inlet of the control panel to prevent freezing of regulators. Medical compressed air system consists of two compressor units duplexed, with
provision for operation alternately or simultaneously depending on demand. Each unit should be capable of meeting the peak demand of compressed air. Medical compressed air should not have any contaminants in the form of particulate matter, odour, oil vapour or other gases. The air intake of medical air compressors should be located outdoors and at a distance of at least 10 feet from an opening in the building such as doors/ windows. Particles including water and oil aerosol present in breathing air should be , or = 0.1 micron and the oil content, if any must be, 0.01 mg/ cu m. The dew point of the air given to patients should be, - 40 deg centigrade. Air compressors suitable for producing medical air must be designed to prevent the introduction of oil, moisture or contaminants into the pipeline. Several types of compressors are available for the purpose - liquid ring, oil-less, scroll etc. By-pass valves are necessary to isolate the compressors during maintenance. Dual air dryers, dual air filters and dual line pressure regulators are required on all systems. Use of CO monitors and Dew Point monitors is also recommended. The said monitors should be connected to the master alarm. The Vacuum source should consist of two or more vacuum pumps duplexed with provision for operation alternately or simultaneously depending on demand. Each pump should be capable of maintaining the required vacuum at 100 per cent of the total calculated system demand. Each pump should have by-pass valves to isolate it from the central piped system and other pump for maintenance. Alarm should indicate failure of any vacuum pump. Exhaust from vacuum pumps must be discharged outdoors and located in such a fashion that noise and contamination to the surroundings shall be minimised. It is recommended to use bacterial filter between drain trap and reservoir having a maximum penetration up to 0.005 per cent. Several types of vacuum pumps suitable for producing medical-surgical vacuum are available: Liquid ring, Rotary vane, Dynamic among others. Installation of Carbon Dioxide and anaesthetic waste gas disposal system are also recommended as a part of medical gas delivery system. Nonflammable waste anaesthetic gases may be disposed of by medical-surgical vacuum systems long as it does not affect the performance of the system. However, dedicated WAGD system offer advantages in terms of safety and operating economy. Copper pipes used should chemically tested as per BS 6017, 1981 and manufactured as per BS 2871, 1971, Part 1, Table X. A reputed inspection firm having necessary facilities should carry out these tests. All pipes should be delivered to site cleaned labelled and plugged/capped. Welding of pipes is critical in installation of medical gas delivery system. Improper welding and cleaning of pipes can lead to accumulation of particles leading to failure of medical equipment like ventilators, anaesthesia machines etc. Pipes should be joined by flux less silver brazing with continuous purging with oil free dry nitrogen to avoid formation of copper oxide on the inside surface. Outlets should be gas specific and prevent use of other probes. It should be double locking type to prevent loss of gas due to leakage and also for facilitating on line servicing. These
should be quick connect/ disconnect type. Outlets are available for surface or concealed mounting. A growing trend is the requirement for patient care units, intensive care columns and head wall systems. These units include medical gas outlets, electrical outlets, examination lights, nurse call systems, patient monitoring receptacles, etc. Essential to the operation and routine function of the medical gas systems within a hospital are the monitoring alarms. Properly designed alarm systems provide audiovisual indication of system pressure levels and reorder conditions necessary to provide continuous supply of gases. Alarm systems are comprised of master alarm panels, area alarm panels and remote sensing devices. Master Alarm Panel provide audible and non-cancelable visual signals indicating when pressure or vacuum exceeds or falls beyond 20 per cent of normal limit. Area alarms monitor pressures in the branches of the piping system serving critical areas of the hospital. Some healthcare facilities require the medical gas alarm system to be connected to the overall building management system providing permanent records of any malfunctioning of the system. Before the system is finally handed over the following tests should be carried out: 1. Pressure drop test to ensure that there is no leakage in the system. 2. Valve tightness and correct valve zoning. 3. Satisfactory mechanical operation and non-interchangeability of each terminal outlet y means of probes. 4. Anti-confusion test for checking cross connection. 5. Flow rate and pressure at each terminal outlet. 6. Change over mechanism of Gas Control panels. 7. Satisfactory performance of compressors, vacuum pumps and WAGD. 8. Performance of alarm system The complete system should be purged with nitrogen followed by oxygen. Finally the complete system should be purged with working gas. Safety measures for medical gas delivery system a. Safety valves provided to be set at 1.5 times the working pressure b. Locknut provision on regulators for preventing inadvertent high-pressure settings c. Two stage regulators for avoiding fluctuation in flow d. Line pressure alarms for continuous monitoring pipeline pressure e. Gas specific color-coding in each pipeline f. Gas specific color-coding on cylinders. g. Specific color-coding on each outlet h. Non-interchangeable adaptor for each outlet.
