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Chamber Recompression Therapy
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.
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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.
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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 hourn
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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