DAN Flying and Diving Study published

[AlexL]

Unfortunately, I do not know if there is a way to safely and accurately evaluate the actual effects on the bubbles in the event of a cabin pressurization failure where the cabin pressure can go from 4500-8000 ft to actual aircraft altitude in a matter of minutes or seconds.

according to the FAA, unpressurized cabins above 18k feet have a non trivial risk of DCS even without additional prior nitrogen loading and a gradual ascent rate. if you have an rapid decompression event in an airplane cabin from 8k ft pressure to 30k ft ambient pressure, being assuredly bent like a pretzel is going to be the least of your many adrenaline fueled concerns of the moment.

 

[AlexL]

We know they were ALL bubble free at 24 hours. We do not know, at least as far as I can tell from this story, when they became bubble free. It could have been after 12 hours or 18 hours or 20 hours.

bubble free at 1 ATM does not imply that you are not at risk from DCS when going to altitude.

the hypothesis they were verifying was 'is the current recommended 24 hour time between dive and flight adequate?', thats all. even then, some of the outliers of the 'bubble prone' group were recommended to extend their dive to fly time to 36 hours, of which they then did not show bubbles during flight. the only people who showed bubbles in flight were already in the 'bubble prone' group. a good number of the group never showed bubbles post dive at all, and that entire group did not produce bubbles during flight. so, i'd take away that some people, who are 'bubble resistant' could 'get away' with shorter dive to flight times, but, as phrased from the summary "Even though a 24-hour PFSI is recommended on the basis of clinical trials showing a low risk of decompression sickness (DCS), the presence of venous gas bubbles in-flight in eight of 56 divers leads us to suspect that in real-life situations DCS risk after such a PFSI is not zero." already tickling the dragon with 24 hour SI.

decompression is a crap shoot, profiles matter, and peoples bodies react differently to decompression stress. some people are nearly unbendable, while others.. well.. Some Come Up Bubbling Alot.

 

[Altamira]

according to the FAA, unpressurized cabins above 18k feet have a non trivial risk of DCS even without additional prior nitrogen loading and a gradual ascent rate. if you have an rapid decompression event in an airplane cabin from 8k ft pressure to 30k ft ambient pressure, being assuredly bent like a pretzel is going to be the least of your many adrenaline fueled concerns of the moment.

I am not sure whether all of your comments were based on FAA data, or you interjected opinion into the issue, but I don't recall seeing anything from FAA that says "...If you have an rapid decompression event in an airplane cabin from 8k ft pressure to 30k ft ambient pressure, being assuredly bent like a pretzel is going to be the least of your many adrenaline fueled concerns of the moment." Although it is considered an emergency procedure, a loss, even a rapid loss, of cabin pressure is not normally a serious threat to passengers lives because the first thing that happens in the cabin is automatic dropping of masks supplying 100% O2, and all aircrews are trained to deal with a loss of cabin pressure. Pilots that fly pressurized aircraft routinely train for, and are evaluated on, this emergency procedure.

As a retired pilot, I feel confident in saying that in the grand scheme of possible aircraft emergencies, a loss of cabin pressure is pretty far down the list of problems that increase a pilot's "pucker factor." However, if I am a diver that has had the minimum, or less than minimum, recommended dive/fly surface interval, and I am on an aircraft with a loss of cabin pressurization, I am going to be very concerned, and getting bent is going to be my only concern.

This link has a very good FAA brochure on potential DCS at altitude, and specific guidelines for divers:
https://www.faa.gov/pilots/safety/pilotsafetybrochures/media/DCS.pdf

 

[AlexL]

I am not sure whether all of your comments were based on FAA data, or you interjected opinion into the issue

the first sentence was from the FAA article linked, which is the same one you posted. the key term from the second statement is 'explosive decompression event', which i meant to imply some sort of structural failure in the pressure vessel and a very rapid decompression to 30k ambient. goes to reason that if a pilot, with a slow ascent to 18k ft ambient pressure and no nitrogen loading above surface ambient is at risk of DCS, rapidly going from 8k ambient to 30k ambient pressure, especially near the start of the flight, is going to have a non negligible amount of DCS risk, even without a prior nitrogen loading.

we're in agreement that the statement does not apply for minor / slow losses of pressure in the cabin, as the decent would put you below the non loaded DCS ceiling before cabin pressure drops that low, and everyone is going to be on 100% o2 well before it becomes an issue.

you're a trained pilot, you're expected to be calm, cool, and collected when things go sideways. as a passenger, if the masks drop, there's going to be a very high pucker factor involved, even if your logical brain knows that everything will most likely be completely fine. getting bent is just going to be icing on the cake.