I understand that the common advice given is to avoid flying for at least 12 hours after diving (24 hours for deep and/or consecutive days of diving). I further understand that the purpose of this is to give more time for our tissues to off-gas and equalize at around 1ATA prior to being subject to the relatively high aircraft cabin altitude/lower atmospheric pressure of around 8,000ft and thereby subjecting the body to further expedited off-gassing thereby increasing the risk of DCS.
When you think about it, controlling the risk of DCS is all about controlling the relative change is pressure. One atmosphere at sea level is defined as 14.78 pounds per square inch. But at 8,000 feet above sea level (approx cabin pressure) the atmospheric pressure is roughly 0.74 or 74 percent of sea level pressure. Thus, we would be at .75ATA. So for argument's sake, there's really not THAT much of a relative change in pressure. As opposed to ascending from 33 FSW to sea level where there is a 2:1 change in atmospheres.
The "founding fathers" of deco theory initially came up with a 2:1 "safe" relative change in ATA's which was later narrowed down to approx. 1.5:1. These are the bases behind some of the most popular Buehlman/Navy model deco tables we use today. Accordingly, the relative pressure change that one would experience in flying after diving would still fall within these ratios.
My question is: If one limits diving to two repetitive sub-2 ATA (i.e., 33 or less FSW) dives and then flies within a relatively short period of time (say around 6-10 hours after surfacing after the second dive), why is there a risk given the relatively minor change in ATA's? For that matter, why can't one just jump right on a plane after diving shallow? Can any risk be mitigated by using EAN36 or higher? What am I missing?
I'm sure that most of the answers will be "we don't know that much about it so why risk it" - which in the absence of concrete science - I agree with. I'm also not trying to promote or condone any unsafe practice. I'm just curious about the science/rationale behind this often repeated advice in the context of shallow dives.
Cheers
When you think about it, controlling the risk of DCS is all about controlling the relative change is pressure. One atmosphere at sea level is defined as 14.78 pounds per square inch. But at 8,000 feet above sea level (approx cabin pressure) the atmospheric pressure is roughly 0.74 or 74 percent of sea level pressure. Thus, we would be at .75ATA. So for argument's sake, there's really not THAT much of a relative change in pressure. As opposed to ascending from 33 FSW to sea level where there is a 2:1 change in atmospheres.
The "founding fathers" of deco theory initially came up with a 2:1 "safe" relative change in ATA's which was later narrowed down to approx. 1.5:1. These are the bases behind some of the most popular Buehlman/Navy model deco tables we use today. Accordingly, the relative pressure change that one would experience in flying after diving would still fall within these ratios.
My question is: If one limits diving to two repetitive sub-2 ATA (i.e., 33 or less FSW) dives and then flies within a relatively short period of time (say around 6-10 hours after surfacing after the second dive), why is there a risk given the relatively minor change in ATA's? For that matter, why can't one just jump right on a plane after diving shallow? Can any risk be mitigated by using EAN36 or higher? What am I missing?
I'm sure that most of the answers will be "we don't know that much about it so why risk it" - which in the absence of concrete science - I agree with. I'm also not trying to promote or condone any unsafe practice. I'm just curious about the science/rationale behind this often repeated advice in the context of shallow dives.
Cheers