T K See Tho
26th May 2009
I did a bit of research on the net and found some interesting facts regarding the question of flying after a long (4 hours) pool session at a maximum depth of 2 msw.
The first thing is to determine how much pressure change in involved when getting on to a commercial flight. Under normal circumstances airplanes are pressurized gradually to about 6,000 - 8,000 ft of cabin pressure during flight. Upon approach to the destination the cabin pressure is again slowly adjusted to match that of the ground level of the airport. Assuming a maximum of 8,000 ft the pressure is about 0.75 atm. This is a change of about 0.25 atm from sea level. Adding the 0.2 atm change from the bottom of the 2m pool we get a total change of 0.45 atm. This is roughly equivalent to surfacing from 4.5 msw. So now the question becomes: Is there a risk of DCS upon surfacing from very long dives (say 240 minutes) at 4.5 msw?
There was one experiment (Decompression Sickness Resulting From Long Shallow Air Dives - Shalke, Weathersby, Wray and Parker) conducted by the Naval Submarine Medical Research Laboratory (http://www.med.navy.mil) in 1996 to answer this question. In the experiment 57 navy divers were pressurized to between 8.5 to 12.2 msw for 6 hours breathing air. During the 6 hour dives the divers did mild exercise to simulate normal diving workloads. After six hours the diver were brought to the surface at an average rate 17 m/min. Out of the 57 divers 3 had DCS symptoms within 1 to 2 hours of surfacing and another 2 had marginal cases of DCS. All recovered well after treatment. All the 5 DCS cases were from dives to 11.6 m or more. None of the divers from shallower dives showed any symptoms.
The research concluded that very long dives at very shallow depths will not likely put the diver at risk of DCS. However the paper also noted that the number of subjects in the experiment is low (due to cost reasons) and so may not be sufficient to form accurate statistics.
Based on the above experiment, we can safely assume that flying after 4 hours in a 2m pool will most likely not bring forth any DCS in a normal person. However susceptibility to DCS is variable from one person to another and it is always prudent to practice safe diving procedures. Even though I know that I will not likely get DCS after such shallow dives I will still try to avoid flying - just like I always do a minimum of a 3 minute safety stop at 5 msw from dives to any depth regardless. Make safety procedures a habit and you will reduce your risk of injury.
Dive safe.
