Hold a bottle of unopened seltzer water to the light.
The contents look exactly like water. If it is shaken the bubbles quickly
go to the surface. There are no lingering bubbles. There is no effervescence.
Now, open the bottle and after the blast of gas there are bubbles galore.
Amazingly the bubbles continue for some time.
You are assigned to open the bottle of seltzer in such
a way no bubbles will form. Is it possible? Let's say there is a special
cap on the bottle that has a valve. When the valve is turned ever so slightly
a minute amount of gas escapes. The valve is immediately shut to keep more
gas from escaping. If this were done numerous times over a period of time
it would be possible to fulfill your assignment. The seltzer would go flat
and no bubbles would have formed.
We should analyze what is happening when seltzer is
decompressed. When the bottle is opened rapidly the carbon dioxide gas, which
has a pressure of approximately 50 psi, on top of the water leaves rapidly
to the atmosphere. This is the old story: High pressure flows to low pressure.
Meanwhile, the CO2 in the water is still under high pressure. The molecules
near the surface of the water start jumping from the water to the air. The
molecules below them start moving toward the lower pressure CO2 created when
those jumped out of the water, and so on. However, some of the molecules
find a better escape route. If there is a nucleus nearby, such as a piece
of dust, a scratch on the inside of the container, etc., the molecules may
latch onto that. More and more join those and soon a bubble appears. The
bubble grows big enough and takes billions of molecules to the surface all
at once. That is more efficient than taking the time to have each molecule
migrate to the surface.
Now, if the container is designed to be opened in small
spurts, the minute loss of pressure above the water does not create the tension
caused when the seltzer is opened suddenly. Simply, some of the CO2 escapes,
a few molecules migrate through the surface to where the pressure was lowered,
those below migrate upward to cause equal pressure throughout the inside
of the seltzer bottle. There is not enough reduction in pressure to create
a bubble on a nucleus. If the process is repeated over and over the seltzer
can be made to go flat without forming bubbles.
What does this have to do with you as a scuba diver?
You are a bottle of seltzer complete with a myriad of nuclei. platelets,
blood cells, clots, are in you blood to mention a few. Go under pressure
and then coming up rapidly is similar to opening the seltzer bottle rapidly.
Poof! You have decompression sickness caused by the formation of bubbles
in the blood and elsewhere. Once a bubble forms it is attacked by the body's
defenses and a clot forms.that may interfere wilth life-sustaining processes.
After a deep dive, coming up slowly will allow the high-pressure gas to leave
the body without forming bubbles.
The question is: "How deep do you have to dive in order
to be subjected to bubbles causing decompression sickness?" J.S. Haldane
in the early 1900's discovered if a person halved their pressure they could
have bubble formation. This is a 2:1 ratio. Haldane invented the first dive
tables for the British Navy. If a diver descends to 33' of seawater, where
the pressure is 2 atmospheres, and then ascends to the surface too rapidly
they could have bubble formation. That is a 2:1 ratio. (The U.S. Navy ammended
this to a 1.7 to 1 ratio.) If they confined their diving to 23', where the
pressure is 1.7 atmospheres and then went to the surface they would not be
cutting the pressure by half. To carry this a bit further, if a diver went
to 66' (3 atm.) and ascended to 33' (2 atm.) the chance of DCS is slim because
that is a 3:2 ratio. If they went to 99' (4 atm.) and then ascended too rapidly
to 33' (2 atm.) it would be a ratio of 4:2 which is 2:1 and DCS becomes a
possibility.
When one analyzes decompression sickness bubbles they
are found to contain almost 100% nitrogen at the onset.. This was discovered
in 1880 by Paul Bert, a French scientist working on cases of the "Bends."
Since oxygen is metabolized in the body and carbon dioxide is in limited
quantities and dissolves readily in water, it is only logical to find nitrogen
as the main culprit in DCS. However, afetr a short period of time the bubbles
with equilibrate with other gases around them (high pressure to low pressure)
so oxygen, water and carbon dioxide may enter and mix with the nitrogen.
Nitrogen dissolves in fat 5.3 times better than in water. Not only do nitrogen
bubbles form in a watery environment such as the blood, they will readily
form in areas where fat is located. Nitrogen targets the fat under the skin,
in the spinal column, and in the joints. Obese divers must really be careful
because they are at an increased risk for decompression sickness!
A comparison of DCS and AGE bubbles is in order:
-
DCS bubbles form when a diver comes up too fast, AGE bubbles form when a
diver holds his or her breath as they ascend causing lung over-expansion
and bubble injection into the blood stream.
-
DCS bubbles tend to form in the low-pressure veins and then get trapped in
the lungs, AGE bubbles are forced into the arteries and many get trapped
in the brain.
-
DCS bubbles form over a period of time, AGE bubbles are pushed into the blood
stream all at once.
-
DCS bubbles intially are mainly nitrogen, AGE bubbles are air (78% Nitrogen
and 21% oxygen).
-
DCS bubbles may form in fat as well as blood, AGE bubbles are found mainly
in the blood stream.
Decompression tables for the US Navy were first developed
in 1915 using the information Haldane discovered. They were revised in 1937,
1957, and finally in 1985. At this point it is important
to learn how to use a decompression table such as the NAUI Table, the PADI
Recreational Dive Planner, and/or the United States Navy Decompression Table.
The complete table should be understood before you read further.
After learning to use the United States Navy Decompression
Table, please do the following 2 problems:
-
A diver goes to 40' for a bottom time of 135 minutes. After leaving the water
the diver stays on the surface for 1 hour and 30 minutes. The diver reenters
the water and dives to 100' for a bottom time of 20 minutes. What is the
final stage decompression (if any), and what repetitive group is the diver
in after leaving the water?
-
A diver goes to 100' for a bottom time of 20 minutes. After leaving the water
the diver stays on the surface for 1 hour and 30 minutes. The diver reenters
the water and dives to 40' for a bottom time of 135 minutes. What is the
final stage decompression (if any), and what repetitive group is the diver
in after leaving the water?
After doing the above problems it should be noticed the
outcome is vastly different but the dive depths, times, and surface interval
are exactly the same. In the first case the diver could get decompression
sickness. In the 2nd it is highly unlikely. That points out a very important
rule in scuba diving: Do the deeper dive first!
That is known as a "normal dive profile."
Divers using computers are doing reverse profiles commonly.
That is, they are not always doing the deep dive first. Properly using the
computer, and staying away from stage decompression, has not shown that reverse
profiles are in any way more conducive to getting DCS! This cannot be said
for table use.
There are provisions in most log books to chart your
dive. Noting the profile of your dives is important for many reasons. If,
for example, you were found unconscious 4 hours after a dive, the logged
profile could be a determining factor in deciding what life-saving treatment
would be applied. If you had a record of diving to 100' for 30 minutes with
little or no stage decompression then a call to DAN would be in order. Learning
how to record your dives in a log book is an important part of any scuba
course.
Decompression computers are now very popular among divers.
They are neat electronic instruments that simulate the diver's nitrogen
levels in various "tissue compartments" in the body. They allow more freedom
underwater and have been proven to be safe and reliable. Without a computer
the diver is at the mercy of the decompression table and that is oftentimes
very limited for the way sport divers dive. For example, if you were to go
to 100' for 15 minutes bottom time, and then ascend to 90' there would be
no way to determine how long you could stay at 90'. The USN tables tell you
there is a maximum bottom time at 100' of 25 minutes. At that point you must
ascend at 1'/second. There is no provision for stopping at 90' on the way
up. You are supposed to exit the water 100 seconds (1'/second) after leaving
the bottom. But we do not usually dive that way. A typical dive in the warm
ocean is to go down to 100' and stay there for 5-10 minutes and then begin
heading toward shallow water. There may be some exploring at 60' for a short
time, and then there might be a descent to 70' for a minute or so, and then
the diver may go up to water that is less than 20' and stay there until the
tank is low on air. With a dive computer the in and out-gassing of
nitrogen is continuously monitored. The diver is kept well-informed as to
how much time they have left at any depth before a danger of decompression
sickness becomes a real threat. Dive computers also keep track of compartment
nitrogen levels while the diver is out of the water. Repetitive dives take
into consideration the amount of nitrogen left in the body from previous
dives and surface intervals!
In the US, slightly less than 1,000 divers are treated
for DCS each year. Over 1/2 of those are divers that did not exceed their
NDL limits on the table or computer! There were no evident violations of
the rules of diving! There are about 100 divers that die from DCS each year.
If you get DCS what happens? Generally the symptoms/signs
include:
-
Unusual fatigue. It is not a common symptom. This is not like you feel
like you could take a nap after a strenuous dive. It is overwhelming. One
diver in Lake George ran out of air at 90' and rapidly ascended. Upon entering
the rowboat the diver got under the seats and fell asleep. When the buddies
arrived in the boat they had trouble waking him up.
-
An itch and/or rash. This is caused by nitrogen bubbles appearing in the
fat under the skin. The bubble raises the skin causing it to stretch and
pull on the nerves causing an itch. When the blood arrives to "fight" the
bubble it causes a reddening. It is similar to a mosquito bite. This rash
is usually associated with cold water diving. It has been associated with
a dry suit squeeze. The condition may disappear in a short period of time.
-
Dizziness. Sometimes nitrogen bubbles will appear in the fluids of the inner
ear. This will cause the diver to experience dizziness and a feeling of
light-headedness. It can last for several hours until the bubbles are reabsorbed.
-
Severe pain, especially in the joints. Type I DCS involves pain in the muscles
and/or the bones and joints. This is the most common complaint, and the upper
body (arms and shoulders) is more affected than the lower. When nitrogen
bubbles appear in the joints pain will be created when the joint is moved.
DCS pain usually gets worse up to a point with time, unlike if you banged
your shoulder on a tank valve after which the pain usually subsides over
a period of time.
-
The "Chokes". If a large amount of nitrogen bubbles appear in the veins they
will progress through the heart to the lungs. There many will get caught
as the vessels narrow to capillaries. If enough bubbles get stuck in the
lungs breathing will be interfered with. Some bubbles may accumulate in the
right ventricle of the heart. The diver will gasp for air but will still
feel like they are suffocating. It is similar to emphysema. The "Chokes"
represents a severe case of DCS. The chance of survival is greatly diminished.
-
Neurological problems. If the nitrogen bubbles grow in the fat found in the
spinal column the nerves may be pinched and electrical transmission interrupted.
This is known as "Type II" DCS. If sensory nerves are affected there may
be tingling, numbness, or a loss of feeling throughout the body. If the motor
nerves are pinched there may be signs of paralysis. Type I DCS responds
better to treatment than Type II.
The Diving Accident Network (DAN) did a study in 1990
of the most frequent symptoms reported by divers affected by DCS. The results
are:
-
Pain 41.0% (DAN: 37% in 2004 Report) However, most bubbles DO NOT cause pain.
-
Numbness and tingling 17.9% (DAN: 26% in 2004 Report)
-
Dizziness 7.8%
-
Weakness 5.7%
-
Headache 5.7%
-
Nausea 3.9%
-
Extreme fatigue 3.9%
Another set of data on the most frequent symptoms of
DCS appeared in the magazine, Immersed. The article, in the Winter 1998 edition,
showed the following results:
Another interesting set of statistics concerns the time
of onset of DCS symptoms. According to DAN in 1990, 60% of divers that got
DCS had recognizable symptoms within 30 minutes. That leaves 40% that will
not get "a hit" until after they have been out of the water for 30 minutes
or more. Of those 40%, 1/4 will feel the effects before 2 hours, another
quarter may go as long as 6 hours, and the remainder might go as long as
a day or more. Continuing, DAN found that 95% of divers experiencing DCS
got symptoms prior to 24 hours after surfacing. It is possible for some divers
to have a dive in the morning and have their head fall into their soup at
dinner!
Many divers experiencing DCS deny they have "that" problem.
In fact, denial is the number one problem with decompression sickness. Not
wanting to admit to failure, not wanting to go through the expensive chamber
route, and the similarity of DCS symptoms to ordinary problems are some of
the reasons for denial. Unfortunately, with DCS the condition will usually
worsen if it is not treated promptly! The earlier the treatment, the better
the chances for complete recovery. According to DAN, half of the divers treated
for DCS were seen by medical personnel after 24 hours had elapsed. Incidentally,
after 2 weeks, treating a case of DCS will do little good. The damage will
most likely be permanent.
Incidentally, the outdated term "Bends" is was coined
bgecause of the way many of the Cassion workers walked when afflicted. They
had a stance that resembled the 1800 womens' fashion called the "Grecian
Bend". Check out the following photograph:
The initial treatment for suspected cases of DCS is the
administration of pure oxygen. There should be no dilution with air. This
will cause the level of oxygen in the body to soar. Even in areas where there
might be a bubble of nitrogen from DCS that impedes blood flow, the oxygen
will migrate (high pressure to low pressure) into the surrounding tissue.
That will save cells. As more and more pure oxygen is breathed, the levels
of nitrogen will drop as the nitrogen moves into the oxygen-rich environment,
to the blood stream, and then out of the body through the lungs. At the same
time, the nitrogen in the bubbles will be at high pressure compared to the
extremely low level of nitrogen in the tissue surrounding the bubble. That
will cause the nitrogen in the bubble to leave and become dissolved in the
tissue fluid. Breathing pure oxygen shrinks nitrogen bubbles! The same can
be said for AGE bubbles. The part of those bubbles that are of concern is
the nitrogen gas. The oxygen will be used by cells to sustain life. But,
do not stop the flow of oxygen! Returning a diver to breathing air will reverse
the process and the nitrogen will return to the bubbles and the tissue.
Recompression must start before a change in gas mixture happens. It is noteworthy
to mention that oxygen is used less than 1/3 of the time, and when it is
administered the concentration is less than required in 90% of the cases!
Recompression in the water is risky. But, according to the Navy Diving Manual,
if there is no chance of reaching a hyperbaric facility within 12 hours water
recompression should be a considered option.
According to John Paul Longphre,
M.D. in DAN's Alert Diver 7-8/2005, the pressure gradients (high pressure
to low) are:
-
Breathing air: pN2 pressure gradient from the bubble to body tissue is 142
mm Hg
-
Breathing O2: pN2 pressure gradient from the bubble to body tissue is 713
mm Hg
-
Breathing 2.82 atm O2 in a chamber: pN2 pressure gradient from the bubble
to body tissue is 2096 mm Hg
In the meantime, DAN should be consulted and evacuation
must be arranged. The diver with suspected DCS should be taken to the nearest
hospital emergency room. The doctor(s) on duty should be instructed to contact
DAN. Then the DAN and EMR doctors can decide on the best treatment. If conditions
warrant, a trip to the nearest operational
recompression chamber needs to be made. DAN will be
able to assist if that is the case. Oxygen must be continued until the diver
is under the care of the recompression chamber personnel.
Depth is on the vertical (Y) axis. This is the US Navy
Table 6 used for treating DCI. Green is oxygen breathing, blue is air breathing.
Notice there is a 2.4 minute descent to 60' breathing oxygen. That is followed
by a 20 minute session breathing 100% oxygen at 60', followed by a 5 minute
session on air. The rest is obvious. The entire treatment time is 4 hours,
and 47.4 minutes. For difficult cases the oxygen breathing may be extended
at the 60' and/or the 30' depths. For brain bubble cases (AGE), pressure
may be increased to a depth equivalent of 165'. At that depth bubbles are
reduced to 1/5 of their original volume. The switch from air to oxygen is
usually accomplished by breathing air from the chamber and then putting a
mask to the face for pure oxygen. In single-person chambers that is not practical
so they usually treat cases of DCI with oxygen at a depth of 30'. This avoids
oxygen poisoning!
A few words about DAN are in order: The Divers Alert
Network (DAN) was established in 1980 and is a non-profit organization dedicated
to helping divers with medical emergencies. DAN operates a 24-hour emergency
medical hotline (919) 684-8111.
When a diver or physician calls DAN a medical doctor specializing in underwater
medical problems is available for consultation. They also have at their
fingertips an updated list of hyperbaric chambers that might be used for
treating suspected cases of AGE and/or DCS. This list is made
available to medical personnel only!
For years this author dove with the mistaken notion that
if we surfaced properly (then 25'/minute, now 60'/minute), and did not exceed
the time allowed on the USN Decompression Table at various depths in order
to avoid a ceiling, we would avoid having those horrible nitrogen bubbles
form creating decompression sickness. Then came the Doppler studies. Doppler
detectors were invented that could monitor from the outside of the chest
bubbles that were passing through the right side of the heart. Ultrasound
pulses are reflected by the bubbles. Someone decided to check divers'
blood after a series of "safe" dives. What they found was amazing.
Bubbles were created during what was thought to be a "safe" dive. Evidently
these "few" bubbles did not do any damage. They are usually captured in the
lungs and are dissipated into the atmosphere. There are no obvious symptoms,
hence they were nicknamed, "silent bubbles."
Even silent bubbles are unwanted. Further Doppler studies
were done. Referring to the 3 graphs above, it was found the bubbles could
be reduced significantly if an ascending diver stopped at a depth of 10 feet
and stayed there for 2 minutes. It was found the bubbles could be reduced
even more if the safety stop started at 20' for 1 minute and then 4 minutes
at 10'. Since the latter is a bit long, a comprise was made: If you are planning
to dive to 33' or more, it is always a good idea to make a safety stop at
15' for 3 minutes. It is NOT a required part of decompression. It is only
precautionary. If it is not done it should not send the diver into mental
anguish!
Many dive boats have a hang bar they throw over the side.
It may simply be a piece of pvc pipe suspended to a depth of 15' by lines
at the ends. The bar makes it convenient for a diver (or group) to hang for
3 minutes following a dive. Some of the boats have a scuba attached to the
bar, or a long-hose alternate air regulator, so that a diver running low
on air could switch to that source. Coming up the anchor line or float line
and stopping at 15' is an alternate method. However, too many divers on an
anchor line may dislodge the anchor from the bottom so a hang bar is preferred.
In most fresh water lakes the diver can simply stand or kneel on the bottom.
Incidentally, when depths are measured they should be done at
chest level according to the US Navy.
To keep commercial airplanes from expanding and contracting
too much as they change altitude, the interior pressure is reduced to about
3/4 atm., equivalent to what is found at 8000'. That means, it would be possible
to get decompression sickness if one were to fly right after diving. Although
there is no hard and fast rule here, different suggestions have been made
over the years. One recommendation is to not fly until the diver has moved
into Group D on the Surface Interval Credit Table. Another is to wait 12
hours following a no-decompression dive, and 24 hours following a decompression
dive where a ceiling was created. Some recommend waiting 24 hours following
any dive. The latter is the safest but may not be the most practical. Diving
computers usually have a "Wait-to-Fly" indicator on them which makes it important
to not turn the computer off after the last dive until the OK is indicated.
The latest research from DAN indicates that it would
be wise to wait no less than 18 hours before flying. If the diver
has done very deep dives, lots of multi-day diving it would be wise to wait
even longer. One last point: If a diver has had hyperbaric treatment they
should wait 72 hours prior to flying!
Diving at high altitude presents further problems for
DCS possibilities. Although this would not be true, let's suppose a diver
makes a decision to dive in a lake at 18,000'. The atmospheric pressure would
be 0.5 atm. If the diver descended to 34' (fresh water) the absolute pressure
would be 1.5 atm. (1 from the water and 0.5 from the air). Going to the surface
would be a change from 1.5 to 0.5 and that is 3:1. Remember, Haldane said
DCS could occur if the pressure was reduced 2:1. So, the likelihood of DCS
is increased at high altitude. How deep would that diver have to go to have
a pressure change of 2:1? Only 17'! At 17' there would be a pressure of 1.0
atm. (0.5 from the air and 0.5 from the water). Going to the surface from
only 17' down would be a change of 1.0 to 0.5 atm. and that is 2:1. Decompression
sickness could occur in a rapid ascent from 17'! Lake Tahoe in Nevada is
at the high altitude of 6,229'. If you stop at a dive shop in the area you
will find for sale special decompression tables for diving there. Most dive
computers take the altitude into consideration if they are turned on
at the dive site prior
to entering the water.
Whew! There are other altitude considerations. Let's
say you are diving in Saba. After the dive you drive to your hotel. Being
a volcanic island the are steep climbs to villages and living quarters. As
you progress to your hotel, which is at an altitide of 1000' you must pass
through 2 small villages which are about 1500' high. This trek is similar
to flying after diving. There is a distinct possibility you could get a
decompression hit. So, what should you do? The best course of action would
be to stay at sea level (the dive site) for a period of time in order to
de-gas somewhat. Have a leisurely lunch perhaps. The following table willl
give you the wait times following a dive before proceeding to altitude.
The following items will increase the chances of a diver
getting DCS:
-
Cold water causing a cold diver. Gases dissolve in cold liquids better than
warm. That is why soda "explodes" if opened warm. If the diver is cold, nitrogen
will uptake to a greater degree.
-
A working dive will take in more nitrogen and oxygen than a diver at rest.
So, the more work that is done the greater the chance of getting DCS.
-
An obese diver is at a higher risk for DCS. Again, nitrogen dissolves in
fat 5.3 times better that in a watery environment. Obesity is defined as
having a Body Mass Index (BMI) at 30 or above. The BMI is your weight in
kg divided by your height in meters squared.
-
Poor buoyancy control contributes to over 40% of the DCS cases!
-
Being dehydrated increases the chance. Drink plenty of fluids during scuba
diving periods (and other times as well).
-
Taking a hot shower or tub following a dive may cause DCS. Warming up the
body could cause gases to come out of solution because they dissolve better
in cold liquids.
-
A deficiency in the vitamin B6 has been shown to increase the likelihood
of DCS.
-
Going to the limits of the decompression tables, and multi-day diving to
excess increases the risk.
-
The accumulation of CO2 causes vasodilation and that increases nitrogen uptake.
Skip breathing (breathing and holding your breath for a short period of time)
should be avoided.
-
One DAN study found older divers had more silent bubbles than younger divers
after diving. There was a 30% increase in bubbles in divers near 60 years
old when compared to divers in their early 30s.
So, if you are diving in cold water and/or working
hard use the next depth and the next time on the decompression table, or
be conservative with the dive computer. If you are fat do the same, as well
as get some exercise. Drink plenty of fluids, and wait several hours after
diving before heating the body. Take 50 mg/day of vitamin B6 everyday. Stay
away from the maximum times allowed at depth on the tables or the computer,
and if you are diving everyday for a week or more, take a day off in the
middle to allow some of the "slow" tissues to return to normal atmospheric
pressure. Lastly, breathe normally while diving. Do not "skip breathe" to
make your air last longer. Remember, it could cost you about $40,000 to treat
a case of decompression illness!
Dan Leigh, in the DAN magazine,
Alert Diver (January/February 2006): "The Utila Chamber
is the only one on the island....(Jim) Engel said the chamber used to handle
more than 20 divers a year, but that number is now reduced from previous
years. 'The chamber enabled us to gather research and interview divers about
their diving,' he said. 'We found that as many as 90 percent of divers were
dehydrated. We met with the shops and instructors and they all have
been pushing a lot of water down their divers and have cut our cases to almost
none.'"
David Buch, in the DAN magazine,
Alert Diver (7/8 2004): "...heavy smokers who
manifested DCI were almost twice as likely to have more severe symptoms than
mild symptoms. Approximately 37 percent of injured heavy smokers showed
severe symptoms, whereas only about 24 percent of nonsmokers manifested severe
symptoms."
According to Dr. Alfred A.
Boyd, about 30% of people have an incomplete closure of the foramen
ovale. This opening between the 2 upper chambers of the heart is supposed
to close at birth so blood is forced through the lungs and the 4 chambers
of the heart. In 30% of us the opening remains. It is called a patent foramen
ovale, or PFO. Since some blood leaks directly from the right atrium to the
left atrium of the heart if a PFO is present, DCS bubbles could also follow
that route. The bubbles would not be filtered out of the bloodstream by the
lung capillaries. This could result in an arterial gas embolism by decompression
bubbles! Should one dive with a PFO? The risk for neurological bends may
be greater unless the diver becomes more conservative with bottom times,
depths, and ascent rates!
According to DAN, the diver suffering from DCI (both
DCS and AGE) is most likely to be male (69%), between 30 and 49 years old
(64.6%), diving with a computer (60%), and have a total number of lifetime
dives of 101 or more (44.2%). Also, if a diver does get DCI, the best
advice from DAN is to wait 4 weeks after all symptoms disappear before diving
again. Consultation with a physician that has experience with DCI would be
advisable. As far as divers using computers having a higher incidence of
DCS, it is my feeling it is because they are now able to risk extreme exposures
underwater. For example, before computers a dive to 300' would be difficult
to accomplish because table diving would warrant lengthy decompression stops.
With a computer it is possible to dart down to that depth and come back up
to shallower depths within minutes. Although it is dangerous to do a dive
such as this because of narcosis, blackouts, etc. the computer may very well
indicate it would be safe to surface in a short time interval.
Do not dive if you are pregnant. The fetus will absorb
nitrogen from the mother's circulatory system through the umbilical cord.
Getting rid of the excess nitrogen from the fetus does not happen as quickly
as from the mother because of the extra distance due to the cord. It has
been shown that decompressed sheep fetuses get DCS when the mother sheep
do not. Also, if bubbles do form in the fetus they may travel through the
foramen ovale, by-passing the lungs, directly to the brain creating an embolism.
Also, if a pregnant diver is treated for DCI, the high pressure oxygen in
the chamber may cause blindness in the fetus!
The Double-Lock Hyperbaric Chamber, Single-Place Chamber at the
Regional Hyperbaric Center, Westchester Medical Center, Valhalla, NY, USA
A Single-Place Hyperbaric Chamber at the
Regional Hyperbaric Center, Westchester Medical Center, Valhalla, NY, USA
The DSUS Shop Decompression Table:
Download PDF of The
Deep-Six Shop Decompression Table, Side 1
Download PDF of The
Deep-Six Shop Decompression Table, Side 2
The NOAA Decompression Table:
EXCERPTS FROM Skin Diver Magazine EDITORIAL BY BILL GLEASON 1987 SKIN DIVER
VOL 36 #4:
THE $30,000 SPEEDING
TICKET
"I got caught speeding, "Strangely enough, these four
words usually provoke a sympathetic and friendly response such as, "Oh, that's
too bad. You have to watch out for those cops on I-55." And, for those able
to think ahead about their own speeding, there follows the almost universal,
"Where did you get caught?" and "How fast were you going?"
"I always wondered if our national tolerance of highway
speeding extended to diving. So, sharing beautiful and dramatic 60-80 foot
deep dive in clear water, with 16 other divers, I decided, slate in hand
to time the ascent rates of the different sets of buddies. With about five
minutes to spare on a 40 minute dive, the divemaster signaled for an ascent
from 62 feet. No anchorline was present since it was a drift dive. There
were just 62 feet of blue water to rise through and then we'd be back on
the surface. Since diving's "speed limit" is 60 feet per minute, it should
have taken the divers a minimum of 62 seconds to reach the surface.
"Twenty-eight seconds later, the first buddy team broke
the surface. The next five buddy teams all came up in 35-45 seconds. Only
two buddy teams took longer than 60 seconds, and both of them stopped for
a ten foot safety decompression stop.
"Of course, there are no "smokeys' underwater. But, there
are expensive "speeding tickets." Decompression sickness, air evacuation,
recompression treatment, etc. can cost as much as $30,000. Lifetime paralysis
is thrown in at no extra charge. That's a big speeding ticket.
I'd like to report that this was an isolated incident,
but I repeated my ascent rate survey with four different groups with similar
results. I didn't catch anyone going more than "100" again (nearly doubling
the safe ascent rate) but more than 50 percent of the divers exceeded the
60 foot per minute rate. The finding, therefore, is that most divers do not
make safe ascents - particularly when not using an anchorline or ascent line!
"The biggest cause of speeding ascents is lack of buoyancy
control. Divers who are religious about maintaining their buoyancy on the
bottom seem to get disoriented when they're ascending without a line or other
reference point. Many divers are also overweighted, causing too much air
to be pumped into their BC's. All this air has to be let out as it expands
on the ascent and most of it has to come out between 30 feet and the surface.
And, that's the "danger zone", where you should go the slowest!
"Follow these guidelines for making safe ascents:
"1. Give yourself enough time to make a safe ascent.
Start up at least five minutes before the no-decompression limit.
"2. When you're a new diver, use the anchorline and slowly
pull yourself up to the surface (gloves help). As you become comfortable,
time yourself next to the line until you become proficient in all aspects
of buoyancy control. That means you can stop and maintain your depth (within
a couple of feet) at any point during your ascent. (This is much harder than
it sounds!)
"3. Make a 15' safety stop if you have been diving below
30'."
