Introduction to Scuba Diving Unit 4- Diving Science

Unit 4: Diving Science

Unit 4 - Diving Science

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Characteristics of Air and Water.

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Buoyancy.

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What is Pressure?

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Your Body.

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The Anatomy of Your Lungs.

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Indirect Effects of Pressure.

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Thermal Effects of Diving.

Instructor Materials: Teaching notes, various training aids use to demonstrate topics of diving sciences. INTRODUCTION Attention step: The underwater world presents a new totally different environment from the air world in which you live. Importance of Value: This unit addresses physical properties of air and water and ways specific parts of your body are affected while diving. The better you understand these differences, the easier it will be for you to function as a diver. Main Points: See presentation slides. Student Materials and Conduct: note taking material, student book kit, and your undivided attention Body: See presentation slides.

Unit 4 - Diving Science - Inst Notes

1

Student Performance:

By the end of the lesson students will be able to:


• State some of the characteristics of air. • Describe the concept of buoyancy and how it affects us under water. • Describe the concept of pressure and how it affects volume and density in a closed container. • Describe how pressure affects air spaces in our body and how prevent problems from pressure changes. • State the different types of lung overpressure injuries and how to prevent them. • Describe the indirect effects of pressure on our body. • Describe the thermal effects of air and water temperature on our body.

Performance Statement: Describe to the students what, by the end of this lesson, will be expected of them, and to what degree.

Unit 4 - Diving Science- Inst Notes

2

Direct Effects of Pressure

You will learn how pressure increases under water and how it affects your body. n

When we descend in water, the force from the combined weight of air and water will increase.

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Density and it’s Effects.


When we descend in water, the force from the combined weight of air and water will increase. This force is called pressure. Density and it’s Effects. Density is the mass of an element per unit volume. The Density of a gas depends on it’s pressure and temperature. The density of water is constant over a wide range of temperature and pressure. Air weights 1.29 grams per liter or 0.08 pounds per cubic foot Freshwater weights 1.0 kilogram per liter or 62.4 pounds per cubic foot Saltwater weights 1.025 kilogram per liter or 64 pounds per cubic foot


3

The Air You Breathe

Most of the time, we do not think about air, because breathing is an automatic activity. n

Air is a mixture of gases.

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Air can be easily compressed.


Air is a mixture of gases. The gases in air are colorless, odorless and tasteless. Air is composed of approximately 20.9% oxygen, 78% nitrogen and 1.1% miscellaneous gases. The most important component of air is oxygen. Nitrogen is metabolically inert. Air can be easily compressed. When pressure is applied to a volume of air, it can be forced to occupy a smaller area. The air surrounding the earth at sea level is compressed by the weight of the air above it. The air at sea level is denser than the air at higher altitudes.


4

In the Water

Water affects our vision, hearing, ability to retain heat and how we move through it.


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The density of water at any depth is the same as the density at the surface.

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Vision:

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Colors:

The density of water at any depth is the same as the density at the surface. Water is about 800 times denser than air. Vision: The human eye is designed to focus light rays in air. Objects underwater appear blurry. The mask allows you to put an air space in front of your eyes to see without the blur. Objects appear 1/3 closer and larger under water. Colors: Colors look much different under water. As light passes through the water, the water absorbs the colors of the spectrum of the sunlight. The first to be absorbed is the color red followed by orange. You need artificial light to see the true colors underwater.


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Hearing, Heat Loss, Drag Noises sound different under water than they do in air.


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Because of the greater density of water compared to air, sound waves travel about 4 times faster in the water than they do in air.

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Heat Loss:

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Drag:

Because of the greater density of water compared to air, sound waves travel about 4 times faster in the water than they do in air. You can hear sound getting louder or softer, but you can not tell it’s direction. Heat Loss: Heat can be conducted out of your body by direct contact with water at a rate nearly 25 times faster than by air. When you start to shiver on a dive, you must end your dive and get out of the water to rewarm. Drag: The water resists your movement. This resistance is called drag. The more you can streamline yourself and your equipment, the easier it will be for you to move through the water.


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Review on Effects of Density What have you learned so far?

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List the two main components of air. Describe the difference in the density of air in the mountains and at sea level. Describe the difference in the density of water at 30 meters (99 feet) and 3 meters (10 feet). Describe one way of reducing drag under water. Describe how objects appear under water compared to air. State how many times faster sound travels under water.

Summarize this section Review the main points of each slide:

Emphasis key points of each main point. State the objective statements as questions .


7

Buoyancy

By understanding buoyancy, you can control it to your advantage for diving. n

Archimedes Principle:

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States of buoyancy:


Archimedes Principle: An object in a fluid is buoyed up (lifted) by a force equal to the weight of the fluid it displaces. States of buoyancy: As a diver you control your buoyancy primarily by the amount of weight you wear and the amount of air in your BC. Positive: If an object floats, it means the object displaces an amount of water that weighs more than the object does. Neutral: If an object hovers, it means the object displaces an amount of water that weighs same as the object does. Negative: If an object sinks, it means the object displaces an amount of water that weighs less than the object does.


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Factors Affecting Buoyancy Your weight and your volume affect your buoyancy.


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Your Weight includes the weight of your body and gear you wear.

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Your volume depends on your body size, thickness of your suit, and your gear.

Your Weight includes the weight of your body and gear you wear. Your volume depends on your body size, thickness of your suit, and your gear. As the bubbles compress in a wetsuit, it displaces less water and therefore, loses some of it’s buoyancy. To compensate for the loss of buoyancy, you must add air to your BC, which increases your volume to regain the lost buoyancy. To compensate for additional buoyancy, you must vent air from yo ur BC to control your ascent. Uncontrolled ascents are extremely dangerous.


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Factors Affecting Buoyancy The density of the water in which you dive also affects your buoyancy.


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If you are weighted to be neutral in salt water and you dive in fresh water with the same amount of weight, you will sink.

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Neutral buoyancy beneath the surface is:

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Diving without buoyancy control is:

If you are weighted to be neutral in salt water and you dive in fresh water with the same amount of weight, you will sink. Neutral buoyancy beneath the surface: Is your constant goal, and it is important to help protect marine life. Diving without buoyancy control: Is tiring, hazardous, and a sign of an unskilled, unthinking, and uncaring diver.


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Review on Buoyancy Affects What have you learned so far?


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Name three factors that affect your buoyancy.

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List three ways you can change your buoyancy.

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Describe what an ocean diver must do to their weight in order to dive in fresh water.

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Describe what happens to a wetsuited diver’s buoyancy during descent.




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What is Pressure?

When you descend in water, the force from the weight of the air and the water above you affects you.


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This force is called pressure.

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If you weighed a column of air.

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This constant pressure is called 1 atmosphere of pressure.

This force is called pressure and is measured in bar or pounds per square inch (psi) If you weighed a column of air that extended all the way to the edge of the atmosphere: 1 inch by inch = 14.7 psi 1 centimeter by 1 centimeter = 1 kilogram This constant pressure is called 1 atmosphere of pressure. As long as the pressure in a body’s air spaces matches the surrounding atmospheric pressure, the pressure is equalized and you do not feel any effects from your surrounding atmospheric pressure.


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What is Pressure?

When you descend in water, the force from the weight of the air and the water above affects you. n

Fresh Water:

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Salt Water:

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Units of Pressure:


Fresh Water: If you took a column of fresh water that was 10.3 meters (34 feet) tall and weighed it. It would exert 1 bar (14.7psi) = 1 atmosphere Salt Water: If you took a column of fresh water that was 10 meters (33 feet) tall and weighed it. It would exert 1 bar (14.7psi) = 1 atmosphere Units of Pressure: At sea level, you are already under 1 atmosphere of pressure absolute (ata). At a depth of 10 meters (33 feet saltwater) you are under 2 atmospheres of pressure absolute. Top diagram shows weight in pounds per cubic foot. Bottom diagram shows weight in kilograms.

Unit 4 - Diving Science - Inst Notes 13

What is Pressure?

When you descend in water, the force from the weight of the air and the water above you affects you. n

Gauge pressure:


Gauge pressure: Because atmospheric pressure is nearly constant at sea level, most diving depth gauges (pressure gauges) are adjusted or calibrated to read zero at sea level. Gauge pressure ignores the 1 atmosphere from the air above the water.


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Review on What is Pressure? What have you learned so far?

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State the depths that are equal to one atmosphere in salt and fresh water. State how many times greater the pressure is at 40 meters (132 feet) of sea water, than at the surface. State the absolute pressure at 20.7 meters (68 feet) in fresh water.

Summarize this section Review the main points of each slide: Emphasis key points of each main point. State the objective statements as questions .


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How Pressure Affects Volume To understand the direct effects of pressure, consider the effects of pressure on an open and closed system. n

Open system:


Open system: If you invert a bucket, force it below the surface of the ocean, and take it to depth, the pressure surrounding the bucket increases and compresses the air in the bucket. When you take the bucket back to the surface, the pressure decreases, and the air expands to its original volume. This inverse relationship between pressure and volume is known as Boyle’s Law, which is named for the scientist who first recognized the relationship


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How Pressure Affects Volume The effects of pressure on a closed system can be much more dramatic.


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Closed System:

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You must NEVER hold your breath when breathing compressed air under water.

Closed System: You must NEVER hold your breath when breathing compressed air under water. If you take a sealed plastic bag filled with air down to depth, the bag becomes smaller and smaller as the air compresses and the volume decreases. When you return the bag to the surface, the air expands and the volume increases back to its original size. Take the same bag down to depth, open it, fill it with air back to its original volume, and close it again. When you bring the bag back to the surface, the air expands, but it cannot escape because the bag is sealed The bag will expand slightly, but will finally burst to release the expanding air. The only way to prevent the bag from bursting is to vent the excess air from the bag during its ascent.


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How Pressure Affects Density You use your air faster when you dive deeper.

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Increasing pressure:


Increasing pressure: The increasing pressure under water not only affects the volume of air, it also affects the density of the air. As the pressure increases, the air compresses to a smaller volume. As the air compresses, it becomes denser. When you scuba dive, you breathe air that is compressed to the ambient pressure at your depth, which is much denser than the air you breathe on the surface.


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Review on Volume and Density What have you learned so far?

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Describe what happens to pressure, volume, and density at 2ata, 3ata, and 4ata.


Pressure

Volume

Density

2ata

2x

1/2

2x

33 fsw

3ata

3x

1/3

3x

66 fsw

4ata

4x

1/4

4x

99 fsw


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Pressure and Air Consumption The rate at which you consume the air in your cylinder is directly proportional to the depth you dive. n

Air consumption factors:

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Physical activity has the greatest effect.


Air consumption factors: Your activity level during your dive Your mental state. Your body size. The warmth of your diving suit. Your level of physical fitness. Physical activity has the greatest effect. You can use up 4 times as much as air exerting yourself than whe n resting. Develop a slow and relaxed breathing pattern as well as a slow rate of breathing. Larger people have larger lungs and use more air than smaller people with smaller lungs and overall metabolic needs.


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Monitoring Air Consumption As you gain experience you can keep a record in a logbook of how long your air lasted at different depths and conditions.


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Monitor your SPG, dive timer, and computer to determine when to begin your ascent.

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Even if you calculate your air consumption mathematically, which is possible, many factors can change your predicted air consumption.

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In certain specialty areas of diving, it is essential that you predict your air consumption to avoid running out of air.

Monitor your SPG, dive timer, and computer to determine when to begin your ascent. Even if you calculate your air consumption mathematically, which is possible, many factors can change your predicted air consumption. In certain specialty areas of diving, it is essential that you predict your air consumption to avoid running out of air.


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Review on Air Consumption What have you learned so far?


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List two factors that affect your air consumption under water.

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Name the device you check to monitor your air supply under water.




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Your Body

When you dive, the pressure of the water effects your air spaces as well as your breathing.


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How pressure affects your air spaces.

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Squeezes:

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Blocks:

How pressure affects your air spaces. The air spaces in your body include your lungs, sinuses, and middle ears. Squeezes: Whenever the pressure outside an air space is greater than the pressure inside an air space, the situation is called a squeeze and it can cause damage to your body. This type of injury is called barotrauma (pressure injury). Blocks: A reverse block is the opposite of a squeeze. Air is trapped inside an air space and the air tries to expand as the surrounding pressure decreases.


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The Middle Ear

You must be able to equalize the pressure inside your ears to comfortably and safely dive. n

Anatomy of the ear:


Anatomy of the ear: Your ears are divided into three sections: Outer ear The outer ear is the ear canal The ear drum separates the out and middle ear Middle ear Contains a series of three small bones that transmit sound waves from the ear drum to the inner ear. Contains the airway link called the eustachian tube. Inner ear Contains the balance mechanism. Sudden changes in pressure or temperature in one ear and not the other will cause dizziness or vertigo.


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Middle Ear Squeezes

Occurs when the air or water pressure in your outer ear is greater than the air pressure in your middle ear.


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Equalizing your middle ear:

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Before you feel the slightest pressure in your ears, you need to equalize.

Equalizing your middle ear: Move air from your throat through the eustachian tube into your middle ear. For most people this is not an automatic process. If you cannot equalize your ears during a dive, you must end the dive and return to the surface. Before you feel the slightest pressure in your ears, you need to equalize. Most common method Close your mouth tightly or block it with your tongue (on scuba), close your nostrils by pinching them shut, and exhale lightly.


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Middle Ear Squeezes

Never force equalizing your ears. You could cause serious damage to your ears.


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The key to successful ear equalization:

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If problems occur:

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If you have a head cold, you must not attempt to equalize by any method.

The key to successful ear equalization: Keep the pressure differences between the water and the middle ear to a minimum. This means that you must equalize early and often, starting at just beneath the surface. If problems occur: Ascend a few feet to reduce the pressure, and attempt to equalize again. Descending feet first makes equalizing much easier for most people. Never try to equalize the pressure by performing forceful blowing. If you have a head cold, you must not attempt to equalize by any method.


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Middle Ear Blocks

If you begin to ascend and your ear hurts and feels “full”, stop your ascent and descend until the feeling goes away. n

If the block does not equalize:


If the block does not equalize: If you must surface, close your nose and mouth and breathe in. If nothing works ascend as slowly as possible. If the block releases quickly and there is a sudden change in yo ur middle ear pressure, you might experience dizziness. It will pass quickly. Hold on to something if you experience vertigo.


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Sinuses

Your sinuses are air cavities lined with mucous membranes and surrounded by the bones of your head.


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Sinus squeeze and blockage:

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Never dive when you have a cold or sinus congestion.

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Decongestant drugs:

Sinus squeeze and blockage: If air is trapped inside a clogged sinus, and you attempt to dive, you will feel pressure on your sinuses. This is painful and can cause blood to flow into the sinus to fill it. During ascent the air in the sinus will try to expand to it’s original volume but it can not because of the fluid. Blood can be forced into your nose, mouth, or mask. Never dive when you have a cold or sinus congestion. Decongestant drugs: Avoid taking any medication that you know produces side effects when use it.


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Other Air Spaces

Any air space trapped in or around your body will be affected.


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Stomach and intestines:

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Teeth:

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Mask space:

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Dry suit:

Stomach and intestines Any gas that forms in your stomach or intestines during your dive will expand during ascent. Teeth There is nothing you can do to equalize air pressure in a tooth. Mask space Simply exhale a small amount of air through your nose into the mask every time you feel pulling on your face and eyes. Dry suit To keep the suit from squeezing simply add air to the suit using the power inflator valve.


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Review on Your Body What have you learned so far?

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Name the air spaces in your body that are affected by pressure. Describe why you should not dive with a cold. Describe what you should do when pressure is felt on your face. Name the condition when pressure outside an air space is greater than the pressure in an air space. Name the most likely cause of sinus squeeze. Name the type of squeeze that is the easiest to prevent. Name the condition when the pressure inside an air space is greater than the outside pressure.




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The Anatomy of Your Lungs Your lungs consist of millions of tiny air sacs, called alveoli.

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Lung over-expansion injuries:


Lung over-expansion injuries: With your airway closed, the air expanding in your lungs will cause the alveoli to rupture soon after they reach their full volume. There is no sensation of discomfort that warns you when this rup ture is about to occur. This type of accident most commonly occurs when divers panic und er water and make a rapid ascent holding their breath. The best technique is maintain normal lung volume during your ascent by breathing normally. As long as you breathe normally during ascent there is little danger of suffering a lung over-expansion injury.


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Lung over-expansion injuries There are three general types of injuries.


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Air embolism:

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Pneumothorax:

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Tissue Emphysema:

Air embolism: The most serious injury The word embolism means plug and an air embolism refers to a plug of air in the blood stream. Can cause unconsciousness, paralysis, permanent brain damage, and even death. Pneumothorax: When the air escaping a lung rupture the air gets into the plural lining surrounding the lung, which collapses the lung. Tissue Emphysema: Mediastinal emphysema Air escapes into the chest cavity Subcutaneous emphysema air collects under the skin, usually in the neck area


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Hyperbaric Treatment

If you suffer an air embolism, you will need to treated in a recompression or hyperbaric chamber. n

You should never go back under water to try to relieve symptoms.


You should never go back under water to try to relieve symptoms.


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Breathing and Circulation

Transporting oxygen through your body is a vital function of the circulatory system.


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Carbon dioxide controls your breathing.

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How to breathe under water.

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Shallow breathing:

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Hyperventilation:

Carbon dioxide controls your breathing. Your breathing rate is controlled by the amount of carbon dioxide in your bloodstream. How to breathe under water. For maximum efficiency, your breathing should be slightly slower than normal and deeper than you usually breathe. Shallow breathing. If you breathe too shallowly, you do not exchange enough air with each breath. Be especially sure to exhale fully with each breathing cycle Hyperventilation: Deliberately breathing deeply and rapidly. Deliberate hyperventilation can be hazardous when you follow it with a breath-hold dive.


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Breathing and Circulation

Transporting oxygen through your body is a vital function of the circulatory system. n

Skip breathing:

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Air Starvation:


Skip breathing: When a diver slip breathes, they hold each breath for an extended period of time rather than breathing normally. Two dangers, lung over-expansion injury and build up of carbon dioxide in the body. Air Starvation: Regulators have a limit as to how much air they can give you. If you feel starved for air, and you feel that your regulator is not supplying you with the amount of air you need: Stop what you are doing, rest, and breathe slowly and deeply until you recover, being sure to exhale fully with each breath.


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Review on Lungs and Breathing What have you learned so far?


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Describe the cause of lung over-expansion injuries.

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Describe what your lung volume should be during ascent.

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Name the component that stimulates breathing.

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Describe the proper way of breathing on scuba.




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Indirect Effects of Pressure These indirect effects of pressure impact divers by means of the gases in the air we breathe while diving. n

Ingassing and offgassing:


Ingassing and offgassing: 78% of the air we breathe is nitrogen. Nitrogen is an inert gas, but is absorbed and dissolved in the bloodstream and tissues. Normally, the pressure of nitrogen is balanced between the air and your body. This state is called equilibrium. Under increased pressure, the air you breathe is denser and than the partial pressure of nitrogen you inhale with each breath is increased. With changes in the ambient pressure your body ingasses or offgasses until the nitrogen is balanced between air and your body.


37

Decompression Sickness

Can occur if you absorb a great deal of nitrogen and then ascend to quickly.


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It takes time for nitrogen to enter and to leave the body.

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When bubbles form in your blood:

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Prevention:

It takes time for nitrogen to enter and to leave the body. When you ascend your body begins to eliminate nitrogen. If too much is still present after you surface, the excess nitrogen forms bubbles in your body. When bubbles form in your blood, they can create microscopic clots that impair your circulation. Symptoms of DCS can range from skin rash, extreme fatigue, coughing and painful joints to paralysis and unconsciousness. Prevention: Dive tables Ascent Rate


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Decompression Sickness If you do suffer DCS you will need to be treated in a recompression chamber. n

The chamber is pressurized to cause the nitrogen bubbles to go back into solution. Then slowly released.


The chamber is pressurized to cause the nitrogen bubbles to go back into solution. Then slowly released.


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Nitrogen Narcosis

When nitrogen is under pressure it can produce an effect on your body also called “rapture of the deep”.


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At depths approaching 24 meters (80 feet).

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Oxygen toxicity:

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Carbon Monoxide Toxicity:

At depths approaching 24 meters (80 feet). Nitrogen can be intoxicating, impairing judgment. Recovery is as simple as ascending to a shallower depth. Oxygen toxicity: Pure oxygen at depths below 7.5 meters (25 feet). The percentage of oxygen in regular air is not toxic until well below the sport diving limit of 40 meters (130 feet). Carbon Monoxide Toxicity: Is formed by incomplete combustion of a petroleum products such as gasoline or oil. Symptoms include nausea, blue lips and nail beds, confusion, headache, and unconsciousness. Pure oxygen and medical attention are the proper treatment.


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Review on Indirect Effects What have you learned so far?


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Describe how to avoid oxygen toxicity.

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Describe how to avoid DCS.

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Describe how to avoid nitrogen narcosis.

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Describe what must be done if your buddy has symptoms of nitrogen narcosis.




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Thermal Effects of Diving You loss heat under water in several ways.


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Water conducts heat away from you body rapidly.

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Breathing cold compressed air from a cylinder.

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Humidity and temperature:

Water conducts heat away from you body rapidly. Breathing cold compressed air from a cylinder. Humidity and temperature: Humidity is the amount of water vapor in the air. If the air containing the water vapor is cooled, the water vapor condenses. When water condenses on the lens of a mask, it forms beads of water. (fogging) Defogging solution reduces the surface tension of the water. Having to humidify the air we breathe causes dehydration. Dehydration decreases your ability to exercise at full capacity and makes you more susceptible to DCS. You must drink plenty of fluids before, between, and after dives.


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Cylinders and Temperature Cylinders should be kept from extreme heat after they are filled.

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The pressure will increase or decrease:


The pressure will increase or decrease by approximately 0.6 bar for each change of 1 degree centigrade (5 psi per degree Fahrenheit)


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Review on Thermal Effects What have you learned so far?


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Name two primary ways of losing heat while on scuba.

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Describe how water vapor condenses to a liquid.

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State what must be lowered in order to prevent a mask from fogging.

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Name what drinking plenty of fluids helps to prevent.

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Describe what happens to the pressure in a scuba cylinder if the temperature is increased.




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Diving Science:


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Characteristics of Air and Water.

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Buoyancy.

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What is Pressure?

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Your Body.

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The Anatomy of Your Lungs.

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Indirect Effects of Pressure.

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Thermal Effects of Diving.

End of Unit 4

Transition Statement: We have completed unit 4 these topics show us how the underwater world presents a new and totally different environment from the air world in which we live. We have addressed the physical properties of air and water and ways in which specific parts of your body are affected while diving. The better you understand these differences, the easier it will be for you to function as a diver.

Review of Main Points: See this presentation slide. Emphasize Key Points: Characteristics of Air and Water •Water is 800 times denser an air •Air is composed of approximately 20.9% oxygen, 78% nitrogen and 1.1% miscellaneous gases. •Objects appear 1/3 closer and larger under water. Buoyancy •You want to be neutrally buoyant during your dive. What is Pressure? •One atmosphere of pressure is about 1 bar (14.7 psi) •Every 10 meters (33fsw) or 10.3 meters (34ffw) is equal to one atmosphere Your Body •Whenever the pressure outside an air space is greater than the pressure inside an air space, the situation is called a squeeze and it can cause damage to your body. You must equalize early and often. Anatomy of Your Lungs •As long as you breathe normally during ascent there is little danger of suffering a lung over-expansion injury. • Never hold your breathe when using scuba Indirect Affects of Pressure •Your body ingasses of offgasses until the nitrogen is balanced between air and your body. Thermal Affects of Diving •Water conducts heat away from you body rapidly.

Ask Students for Questions:


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Student Performance:

By the end of the lesson students will be able to:


• State some of the characteristics of air. • Describe the concept of buoyancy and how it affects us under water. • Describe the concept of pressure and how it affects volume and density in a closed container. • Describe how pressure affects air spaces in our body and how prevent problems from these pressure changes. • State the different types of lung overpressure injuries and how to prevent them. • Describe the indirect effects of pressure on our body. • Describe the thermal effects of air and water temperature on our body.

Restate the students performance statements as questions: Assignment: Instruct the students read chapter 5 in preparation for the next lesson.


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Introduction to Scuba Diving Unit 4- Diving Science

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