Prevention of Decompression Accidents
Compiled and maintained
by Ernest S Campbell,
Some Causes of
The best way to categorize
the various ways a diver
prevent the occurrence of DCS is by looking for the causes of the
Some predisposing causes
for DCS are as follows:
the no-decompression limits. By surfacing too rapidly and not
safety stops a diver allows bubbles to form and to get larger as the
differential decreases. Nitrogen loads in all the tissues at different
pressures and times and violation of the NDL (no-decompression limits)
is a major cause of DCS.
to decrease accumulated nitrogen). Surface times are outlined for
diving profiles and failure to adhere to the prescribed length of time
does not allow "off-gassing" of onboard nitrogen. The accumulated
is then added to by the next dive, increasing the risk of DCS.
or going to higher altitude soon after diving (12-24
which increases the pressure gradient. This in reality is a
of an ascent from a dive. This allows any nitrogen that is in the
to come out of solution and form bubbles, leading to DCS.
physiological differences that have
thought of as increasing the risk of DCS are as follows:
is probably the most important of the predisposing factors. Taking
in adequate quantities of water (8-10 glasses/day).This is needed to
the drying effect of compressed air and the obligatory diuresis that
divers get from immersion. Dehydration, due to any cause (coffee, oral
diuretics, alcohol, vomiting and diarrhea states, failure to drink
or circulatory efficiency: The lung acts as a filter for the
that occur in all divers. Chronic lung disease, heart failure both tend
to increase the risk of DCS. Decreased perfusion from any source can
the possibility of DCS. Intracardiac septal defect (PFO) bypasses the
effect of the lungs and increases risk of bubbles. Undeserved DCS (DCS
that has no other causative factors) should have investigation for this
(scar tissue decreases diffusion). Areas of decreased and increased
flow have been incriminated in leading to DCS. Whether this is
in the growth plates of teenagers is unknown. Nitrogen off-gassing is
by factors that alter perfusion.
women have been shown to have a slightly higher rate of DCS,
during the menses.
is lipid soluble).
Several studies have incriminated obesity as a factor in increasing the
risk of DCS. Fat is poorly supplied with blood vessels and decreased
(ability to off-gas) can lead to DCS.
making process, often leading to mistakes and DCS. Fatigue is also a
symptom of decompression sickness. Exertion during the deep part of the
dive is a risk factor.
The older diver has long been thought to be have increased tendencies
have DCS. Studies done by the Navy show a definite increase in DCS in
divers (all under 50 years of age). Other studies have not borne this
Older divers have a higher percentage of body fat. Age and obesity:
possibly increases in proportion to increase in age. Greater age and
fat content are traditionally associated with increased incidence
of DCS but the evidence is not consistent, recent reports showing no
physical fitness increases perfusion and ensures good gas exchange.
the incidence of DCS from 22% to 46%. Exercise at depth is detrimental,
increasing nitrogen uptake. (Requiring three times the decompression).
Immersion in cold water with exercise causes increased incidence of
Exercise while decompressing is beneficial.
Environmental factors that
are important include the
- Cold water (vasoconstriction
nitrogen off-loading). Warm water immersion (vasodilation)
the head down position increases nitrogen elimination.
- Heavy work (vacuum
which tendon use causes gas pockets). Exercise at depth increases
uptake and is detrimental.
- Rough sea conditions
- Heated diving suits (leads
- Divers who have been chilled on decompression
near the no-decompression limit) and take very hot baths or showers may
stimulate bubble formation.
Sport divers mainly need
to avoid dehydration, dive
ascend slower and spend more time between dives eliminating nitrogen.
Here are some of the factors
to increase the risk of
- Exceeded No-decompression limits
- Running out of air, rapid ascent
- Diving on the edge of No-decompression
- Deep or repetitive dives using computer
of the tables or no-decompression limits
- Flying after
- Diving at altitude
There are other factors
that are thought to increase
the chances of getting DCS but have little data in support; some of
Gorman, Pearce and Webb, Dysbaric illness
at the Royal Adelaide Hospital, 1987: A factorial analysis. SPUMS
Wilmshurst PT, Byrne JC, Webb-Peploe MM: Relation
inter-atrial shunts and decompression sickness in divers. Lancet,
Moon RE, Camporesi EM,
Kisslo JA: Patent foramen
and decompression sickness in divers. Lancet 1: 513-514, 1989.