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Flying After Diving
Recreational divers frequently return home after diving holidays by
air.
Divers using compressed air for breathing under water will have an
excess of nitrogen dissolved within their body tissues after each
dive for a considerable amount of time (known as the supersaturation
period). Flying shortly after diving puts a diver under increased
risk of Decompression Sickness (DCS) since flying is known to
decreases the pressure to which the body is exposed. (the same
effect as ascending to an altitude shortly after diving).
According to international aviation guidelines, all passengers
flying commercial aircrafts (with a few exceptions) are not exposed
to pressure less than three-quarters of an atmosphere (¾ ATA) which
is equal to an altitude of 8000 feet (2438 meters). So, most
commercial airplanes adjust their cabin pressure to 8000 feet, no
matter how high they actually fly.
To reduce the risk of DCS divers are repeatedly encouraged of
delaying decreasing ambient pressure (flying or ascending to an
altitude) for some time after diving.
The answer to the question of how soon after diving can a person fly
safely is still not definitively known.
Many years ago dive instructors frequently taught divers to work out
their dive tables and make sure they would wait at the surface till
their residual nitrogen dropped to a maximum of group D (C, B or A)
before flying, & now a common feature in most dive computers is to
display No flying sign based on calculating the desaturation
requirements and residual nitrogen remaining in the diver’s body.
Many agencies have achieved a lot of research based on experimental
work in the last few years and they all came up with this
recommendation:
# A minimum surface interval of 12 hours is required before ascent
in a commercial aircraft (or the equivalent altitude) after a single
dive or single-dive days, while the interval should be extended
beyond 12 hours after daily multiple dives, diving for several days
or individual dives that require decompression stops.
For multi-dives, the Divers Alert Network (DAN) recommended that
divers should wait a minimum of 16 hours before flying while the
Undersea & Hyperbaric Medical Society (UHMS) recommended waiting 24
hours.
The National Oceanographic & Atmospheric Administration (NOAA)
guidelines stipulated that a diver should wait until reverting back
to group B (residual nitrogen) before flying in a commercial
aircraft.
Most researchers agree that experimental work done on FAD is not 100
% reliable as it is always performed by exposing volunteers to
increased pressure normally in a hyperbaric chamber (to simulate
diving) and then exposing them to a Hypobaric condition in another
chamber (to simulate flying) where the subjects are non- exercising,
non-stressed, well hydrated & not exposed to cold, the circumstances
which are way different to those encountered during real diving
practice.
Reports of more than 1000 DCS cases during recreational diving were
analyzed for the effect of flying after diving and the results
showed that almost no incidents were recorded in divers who waited
more than 24 hours at the surface before flying except for those who
suffered from mild symptoms prior to flying.
Based upon the above recommendations & analysis, it is postulated
that the recommended time between a last dive and his or her flight-
for someone who has made multiple dives-is 24 hours.(better to be
safe than sorry)
The above recommendations do not apply to commercial or mixed gas
divers.
Altitude considerations
Note:
8000 feet (2438 meters) equals ¾ ATA
18000 feet (5486 meters) equals ½ ATA
23000 feet (7010 meters) DCS can happen even without any hyperbaric
exposure (diving).
30000 feet (9144 meters) equals ¼ ATA
When diving at altitudes, surface intervals before flying are
definitely shorter than those required when flying after diving at
sea level & it is readily understandable that persons diving at
altitudes higher than 8000 feet do not require any intervals before
flying in a commercial aircraft.
Divers who visit Galapagos Island normally transit in the airport of
Ecuador, which is 9200 feet high above sea level, so they are always
instructed to pay more attention to planning their intervals before
flying back home.
In Egypt, divers who visit the monastery of Saint Catherine during
or after their Sinai diving vacations should consider waiting a
proper interval as the elevation there is as high as 6000 feet.
A victim suffering from DCS should be evacuated by helicopter or
aircraft flying at very low altitude or in a pressurized aircraft
with a cabin pressure not less than 800 feet while breathing 100 %
Oxygen until arrival to the nearest recompression facility.
Driving DCS victims through elevations should be avoided as this
almost always aggravates the picture. A good example is the Dahab
–Sharm El-Sheikh road where victims though breathing 100 % oxygen
all the way to Sharm, they usually undergo deterioration in their
physical findings as the road slopes up to more than 1000 feet.
Flying after chamber treatment has always been a point of
controversy, as a matter of fact bubbles may still persist without
evidence (symptoms) after chamber treatment, as well, lack of oxygen
(hypoxia resulting from altitude effect) might cause recurrence of
symptoms when flying patients treated for neurological DCS.
So, it is recommended to wait at least 4 days after the treated DCS
patient appears cured or 7 days after he/she reaches a plateau in
responding to daily treatment before flying in a normal commercial
aircraft.
If the patient has to be flown earlier, this should be done in:
1- an air craft pressurized at sea level, or
2- A commercial aircraft while breathing 100% oxygen all the
duration of the flight preceded by 2-4 hours of oxygen breathing at
sea level, or
3- An 800 feet pressurized craft while breathing oxygen all the
flight.
Chamber inside tenders (people who accompany & attend victims inside
chambers during treatment) on short treatment tables should wait at
least 12 hours before flying while tenders on long tables should
wait at least 48 hours.
Patients receiving Chamber treatment for non-diving related maladies
(HBO) therapy can fly shortly after any chamber session provided
that the tables used did not employ longer air breaks.
Conclusion
# Flying shortly after diving (during the super-saturation period)
is a recognized hazard that should be avoided.
# Remember that the one unshakable truth is that the longer the
surface interval after diving, the less the risk of DCS when flying
afterwards.
# Consider that the greater the diving (regarding depths, bottom
times and intervals between dives), the longer the duration
recommended before flying.
Recommendations for surface intervals are:
# Wait 12 hours before flying after single or single-day diving.
# Wait 24 hours after multiple dives.
# If you develop symptoms that you can not explain consult a diving
physician before flying.
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