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.
2.
3.
4.
5.
6.
Fill medicine dropper for neutral buoyancy
Fill soda bottle to just below top
Place dropper in soda bottle
Tighten bottle cap
Squeeze bottle
Note observations
Boyle’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.
2.
3.
4.
5.
Add small amount of water to soda can
Place can on hot plate
When water in can boils remove can
Quickly invert can and place in bowl of water
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
Pressure
Boyle’s Law: What does it look like?
Volume
Volume
Charles’ Law: What does it look like?
Temperature
Temperature
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
Charles’ Law
pressure
the bends
scuba
diving
atmospheres
depth
hyperbaric chamber
embolism
Boyle’s Law
nitrogen
ascent
volume
dissolved gases
temperature
Why are gas laws important to divers?
Graph of Dive Table Data
Bottom 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?