STEM
THE SCIENCE OF THE
HYPERBARIC CHAMBER
Brief history of the Hyperbaric Chamber in
the Cayman Islands
After fundraising and generous donations by
Cayman businesses, a reconditioned
hyperbaric chamber was bought in the U.S.
and placed in a hut behind Cayman Clinic in
1972. It was run by the British Sub-aqua Club.
It is now in a room at the Hospital near the
Forensic Science lab and the Morgue.
THE HYPERBARIC CHAMBER
A few years ago
THE HYPERBARIC CHAMBER
From Right
THE HYPERBARIC CHAMBER
From Left
THE HYPERBARIC CHAMBER
THE HYPERBARIC CHAMBER
Looking Inside
THE HYPERBARIC CHAMBER
Inside looking Out
Dive Physics
THE GAS LAWS
Most Important to the Hyperbaric Chamber
Boyle’s Law
Dalton’s Law of Partial Pressure
Henry’s Law
THE GAS LAWS - Pressure
Pressure = force per unit area
The Gas Laws refer to absolute pressure (Pabs).
We are subject to a pressure at the surface because of the
weight of 10 miles of air above us.
The pressure at the surface is l atmosphere (l atm).
A pressure gauge is made to read zero at the surface despite
the weight of the atmosphere, and therefore reads pressure
extra to the already existing atmospheric pressure. Each 33ft,
or 10 meters of water, exert the same pressure as atmospheric
air at sea level.
(Continued on next slide)
10
THE GAS LAWS - Pressure
continued
Absolute pressure refers to Gauge pressure +1 atm. ie the total
pressure including atmospheric
Example
the gauge pressure 99 ft below the surface of the sea is 3 atm
due to the weight of the water. However the absolute pressure
is 4 atm, due to the combined effect of the water plus the
weight of the atmosphere pressing down on the surface of the
water. Pabs = Pg+ 1 atm
11
THE GAS LAWS – Pressure
Compressor Room and Pressure Tanks
THE GAS LAWS – Pressure Gauge on
Chamber
Pressure Units
1 atmosphere (atm) at sea level is (approximately)
= 1 kg per square cm (1 kg/cm2) (1 bar)
= 14.7 pounds per square inch (p.s.i.)
= 760mm of mercury (torr)
= 29.92in Hg
= 101,300 (Newtons per square meter) (pascals) (Pa)
= 33ft of sea water
Boyles Law: -The volume of a fixed mass of gas at a constant
temperature varies inversely as the (absolute) pressure.
P x V = Constant
(As the pressure goes up the volume
goes down & vice-versa.)
P1 x Vl = P2 x V2
If a diver fills his lungs and then holds his breath while
he ascends, the volume of his lungs will expand until either
he decides to breathe out or the lungs rupture (embolism).
15
Depth
Pressure
Gas Volume
0’
1 atm
Full
33’
2 atm
½ full
66’
3 atm
1/
3
full
99’
4 atm ¼ full
132’
5 atm
1/
5
full
16
QUESTION
A diver ascends from 132 ft to 99ft while holding his breath.
If his lungs contained 4 litres of air at 132ft, what is the
volume at 99ft?
P2xV2 = P1xV1 (Boyles Law)
V2= P1xV1 / P2 = 5atm ab x 4/ 4atm abs= 5 litres
A trainee diver at 33ft shoots to the surface while holding his
breath. If his lungs held 4 litres at 33 ft what is the volume at
the surface.
P2xV2=P1xV1
V2=P1xV1 / P2 = 2atm x 4 / 1atm = 8 litres.
Both divers ascended 33ft, which one is most likely to suffer
an embolism?
DALTONS LAW. Dalton’s Law is a concept that states that
the total pressure exerted by a mixture of gases is the sum of
the partial pressures that each gas would exert if it alone filled
the container.
Air at the surface contains 21% oxygen and 79% nitrogen
(Including the 1% of other gases with the nitrogen).
air at the surface(1atm) = ppO2 0.21 atm +ppN2 0.79 atm
air at 33 fsw(2atm) = ppO2 0.42 atm + ppN2 l.58 atm
The importance of Daltons Law to divers and the Chamber is
that the beneficial/toxic effect of gases is dependent on their
partial pressures, not the total pressure of the gas mixture that
contains them.
18
HENRY’S LAW
Henry’s Law of solubility states that the amount of gas
absorbed by a particular liquid is proportional to the
partial pressure of the gas .
E.g. If you triple the absolute pressure then the amount of
gas absorbed by the liquid will be tripled. ppN in air at a
pressure of 66ft of seawater = 3 x .79=2.37 atm
Therefore the divers blood would eventually contain three
times the amount of nitrogen at sixty six feet than it does
at the surface.
19
HYPERBARIC OXYGEN TREATMENTS
Dive related
Arterial Gas Embolism
Decompression Sickness
Other Treatments
Wound Healing
Restoration of Circulation (Advanced
Diabetes)
Skin Grafts
Carbon Monoxide Poisoning
HYPERBARIC OXYGEN TREATMENTS
1. Arterial Gas Embolism
Caused by over-expansion of alveolar tissue
resulting from gas trapped in the lung
expanding on ascent and subsequent entry of
gas bubbles into the bloodstream.
HYPERBARIC OXYGEN TREATMENTS
2. Decompression Sickness
Caused by rapid reduction of environmental
pressure resulting in Nitrogen (previously
dissolved in the body tissues) being released
as bubbles in the blood stream.
TYPES OF DECOMPRESSION
SICKNESS
Type I DCS
Joint pain and skin bends only. Caused by
the physical effects of he bubbles and
immune reaction on the tissues.
TYPES OF DECOMPRESSION
SICKNESS
Type II DCS
Typically due to bubbles in the nerve tissue
of the spinal cord or brain, causing a wide
range of neurological problems.
TYPES OF DECOMPRESSION
SICKNESS
The Chokes
Nitrogen bubble froth in the blood in right
side of heart and/or in the lungs. The heart
compresses the bubbles rather than
pumping the blood. Bubbles in the alveoli
capillaries prevent gas exchange and result
in extreme shortness of breath.
BENEFITS OF HIGH ppO2
Normally people at sea level breathe
oxygen at a partial pressure of 0.21atm
In the hyperbaric chamber at 60ft the patient is
breathing pure oxygen at a pressure of almost 3 atm
Next 2 slides – places where higher
than normal ppO2 is available
To Combat Pressure reduction in Aircraft at Altitude
Passengers breathe pure oxygen in order to remain conscious
27
To Reduce Chance of Decompression Sickness
Divers can breathe nitrox,
a mixture of 32% Oxygen and 68% Nitrogen
28
HYPERBARIC OXYGEN
Pure Oxygen is used as well as pressure in
hyperbaric treatments.
1. It reduces the amount of nitrogen taken
into the lungs during breathing to zero,
thus speeding up the release of dissolved
nitrogen from the blood into the lungs.
HYPERBARIC OXYGEN
2. The high partial pressure of oxygen in the
lungs means there is far more oxygen
dissolved in the blood plasma than usual.
Despite the patient’s reduced circulation
this allows more oxygen to reach the tissues
and so promotes healing and reduces
swelling.
OXYGEN CYLINDERS
OXYGEN MASKS
PROBLEMS WITH HIGH ppO2
1. Breathing a high ppO2 for an extended
period can lead to Oxygen Toxicity – this affects the
brain and causes a convulsion similar to an epilectic fit.
In the chamber the patient is on pure oxygen for 20 minute
periods followed by a 5 minute air break.
Next slide – Table 6 – Decompression Sickness showing air
breaks
CLOCKS – INNER LOCK
CLOCKS – OUTER LOCK
OTHER
CYLINDERS
PROBLEMS WITH HIGH ppO2
2. The high ppO2 in the chamber is a serious fire hazard.
Oxygen sometimes leaks from patients mask, increasing
% O2 in Inner Lock
Flammable materials, including paper, avoided.
No equipment or material that could cause a spark is
allowed inside. The air supplied to chamber is very dry
so increases the risk of sparks from static electricity.
Chamber has “fire wands” and a high pressure sprinkler
system.
There is an oxygen analyzer on the exhaust air, set to
alarm when the oxygen level reaches 24%.
Next slides – fire wands. Oxygen analyzer
FIRE WAND
OXYGEN ANALYZER
BANNED ITEMS
LIGHTS ARE EXTERNAL
2
QUESTIONS?
THE END
INTERESTED IN BEING
ON
THE CHAMBER TEAM?
Call John Elliot
9161198
Or Ann Elliott
9161957
To find out when the next
training course will be
offered
Diving physics questions
1) A gauge reads a pressure of 3 atmospheres. What is the
actual pressure? ……………………
2) Why must you never hold your breath as you ascend in
the chamber? ______________________
3) A balloon is blown up in the chamber. What will
happen to the size of this balloon when you ascend?
_________________________________________
4) What will happen to the volume of the liquid in a
drinking water bottle during ascent?
47
The General Gas Law
A combination of Boyles Law and Charles Law leads
to the General Gas Law:
P1 xVl = P2xV2 = a constant
T1
T2
If you heat a fixed volume of gas the pressure will go
up. If you leave a dive tank already filled to a high
pressure out in the sun, then the pressure will rise
until...
If you reduce the volume, and try to keep the
temperature constant, the pressure will go up.
WHENEVER YOU USE THE GAS,LAWS YOU
MUST USE ABSOLUTE PRESSURE AND
KELVIN DEGREES (otherwise it won’t work!)