Science of Diving: How Science Helps Navy Divers Stay Safe

Science Topic: Physiology and Physics

Feel the Pressure!

• What happens when you shake a can of soda and then open it?

• What is happening to the gases in the can of soda?

Breathe Deep

• Are gases in soda the same that you breathe?• What gases do scuba divers breathe when

they go underwater?• Like gases in soda, gases breathed by divers

are under pressure.

Navy Divers in Action

I’d Like to be Under the Sea

• How would you breathe underwater?

SCUBA

• Self-Contained Underwater Breathing Apparatus

Is Diving Safe?

• SCUBA is safe, like motorcycling or sky-diving• If you understand the physics and physiology

diving is safe

Gas Laws and Diving

• Essential Question: “What conditions lead to perils facing divers including the bends and embolism?”

Review!

• How much does air weigh at sea level?• What is the weight of water at 33 feet (10

meters)?• What is the pressure on a divers body at 33

feet underwater?

Around the Bends

• What are the bends?• How is decompression sickness treated?

Bends and embolism

• The bends result when dissolved gases (mostly nitrogen) absorbed as air is breathed under pressure are released as gas back into the bloodstream.

• Embolism results when gases in the lung expand during ascent and rupture lung tissue, causing air bubbles to enter the bloodstream.

• These conditions can happen if a diver ascends too quickly.

Law Makers

• Boyle: volume and pressure• Charles: temperature and volume

Cartesian Diver Activity

1. Fill medicine dropper for neutral buoyancy2. Fill soda bottle to just below top3. Place dropper in soda bottle4. Tighten bottle cap5. Squeeze bottle6. Note observationsBoyle’s Law – When a gas is at constant temperature, there is an inverse relationship between the volume and pressure of the gas. As the volume decreases, pressure increases and as the volume increases, pressure decreases.

Pressure Can Activity

1. Add small amount of water to soda can2. Place can on hot plate3. When water in can boils remove can4. Quickly invert can and place in bowl of water5. Note your observations

Charles’ Law – When a gas is at constant pressure, there is a positive relationship between the volume of a given mass of the gas increases and its temperature. As the temperature increases its volume increases and vice versa.

The Gas Laws

• Essential Questions: – What are the principles of Boyle’s Law and

Charles’ Law?– How is the ideal gas law used to calculate changes

in volume, pressure and temperature when one or the other variables is held constant?

The Equations

• Boyle’s Law: PV = k

• Charles’ Law: V1/T1 = V2/T2

• Ideal Gas Law: PV = nRT– n = number of moles of gas– R = gas constant (0.0821 L·atm/mol·K)– T = temperature in Kelvin

Boyle’s Law: What does it look like?

Volume

Pres

sure

Volume

Pres

sure

Charles’ Law: What does it look like?

TemperatureTemperature

Volu

me

Should divers care about the gas laws?

• Essential question: How do the gas laws relate to safe diving practices?

Why should divers care about Boyle’s Law?

• Divers who know Boyle’s Law know if pressure decreases, volume increases.

• A diver breathes gases under pressure.• If a diver ascends too quickly pressure goes

down so gases dissolved in the bloodstream increase in volume.

• Remember what happens when you shake a soda can? Yup. Gases start to fizz in the diver’s bloodstream. Not good.

Why should divers care about Charles’ Law?

• Air in a scuba tank is pressurized to about 3000 psi.

• What happens if the tank is heated, for example in a car on a summer’s day? Yup. The tank could explode. Not good.

• If a diver is close to a bends or embolism situation and is hypothermic, what could happen if the diver is quickly warmed up?

Safe Diving!

• What can divers do to avoid the bends and embolism?

• What is a safety stop?• What is a decompression stop?

Dive Tables

• What are dive tables?

Items for your concept map

pressure

temperature

volume

diving

depth

atmospheres

scuba

dissolved gases

nitrogen

the bends

embolism

ascentBoyle’s Law

Charles’ Law

hyperbaric chamber

Why are gas laws important to divers?

Graph of Dive Table DataBottom time at 70 feet (21.3 m)

Misinterpreting Dive Computers

• Dive computers help divers avoid risky situations

• Algorithms use depth and time data to estimate the likelihood of decompression sickness

• What happens if a diver cannot use the dive computer properly?

How Does Volume Decrease With Depth?

• Assume a pressure increase of 1.0 atm for every 10 m of depth below the surface

• Use Boyle’s Law to calculate the volume of a gas at pressure every 10 m of depth to 100 m

• Chart your data on graph paper

Volume Decreases With Depth

Depth vs. Volume vs. Pressure

Example Problem

• If a diver runs out of air at 15 meters underwater, and immediately ascends to the surface, what are the risks of an embolism?

• Assumptions:– Constant temperature– Lung capacity = 6 liters– Pressure increases 1.0 atmosphere for every 10.0

m of depth below the surface.

Solution• Let P1, V1 and T1 = pressure, volume, and temperature respectively of the

air in the diver’s lungs when the last underwater breath is taken.• Let P2, V2 and T2 = pressure, volume, and temperature respectively of the

air in the diver’s lungs at the surface. • Since temperature is constant, use Boyle’s Law to calculate the increase in

volume of the air in the diver’s lungs: P1 x V1=P2 x V2• Rearranging, V2 = (P1 x V1)/P2

– P1 (pressure at depth) = 2.5 atmospheres, since = 15/10 x 1 = 1.5 + 1 = 2.5 (Note that 1 is added for the 1 atmosphere of pressure at the surface.)

– V1 (initial breath underwater) = 6 L– P2 (pressure at surface) = 1 atm

• Therefore, V2 = (2.5 x 6)/1 = 15 L• The volume of air is 15 liters at the surface. Since lung capacity is 6 liters,

embolism is inevitable.

Enriched Air (Nitrox)

• How might divers overcome the problem of absorbing nitrogen which then turns to bubbles if the ascent is too fast?

• Breathing pure oxygen under pressure carries a significant risk of oxygen toxicity.

• Divers use enriched air (nitrox) which has a higher percentage of oxygen than air, but with a lower risk of oxygen toxicity.

Enriched Air (Nitrox)

Essential Questions

• What conditions lead to perils facing divers including the bends, embolism and oxygen toxicity?

• How do the gas laws relate to safe diving practices?• What are the principles of Boyle’s Law and Charles’

Law?• How is the ideal gas law used to calculate changes in

volume, pressure and temperature when one or the other variables is held constant?