"no fly" time

[Gene_Hobbs]

If it does, for whatever reason, and if you have an N2 load in your blood and tissues, then you will be SOL, if it happens.

I think "SOL" is a little strong given the gas loading and time component involved in the depressurization, bubble growth, and subsequent decrease in altitude by the aviator, but that's just me. "Bent" - likely but SOL, not hardly.

That opinion is based partially on my experience with our "Military Free Fall After Diving" study since it included a flight to 25,000 feet after diving (subjects on Oxygen at altitude w/ 30 minute prebreathe - which is normal procedure for 25k flight). (1)

High altitude exposure has it's own risk without a dive prior but that probability of DCS given the estimated altitude and short exposure just does not seem that high based on one evidence based review by NASA. (2) The US Navy has reported 11 Cases of DCS in one case review of 205 cases of "loss of cabin pressure" covering the years 1969 to 1990 (3). The Canadian Military reviewed "loss of cabin pressure" in transport aircraft and reported no cases of DCS in 47 incidents (4).

Dr. Deco is in a MUCH better position to discuss this but I just can't see an exposure on the order of minutes creating an "SOL" level of DCS given the amount of risk most of us "might" be willing to take flying after a recreational dive. (Though, Doc, I really want to hear your thoughts on this)

1. Pollock et. al. Risk of decompression sickness during exposure to high cabin altitude after diving. Aviat Space Environ Med. 2003 Nov;74(11):1163-8. PMID: 14620473
2. Robinson, Dervay, and Conkin*. 1999. An Evidenced-Based Approach for Estimating Decompression Sickness Risk in Aircraft Operations. NASA/TM—1999–209374
3. Bason and Yacavone. Loss of cabin pressurization in U.S. Naval aircraft: 1969-90. Aviat Space Environ Med. 1992 May;63(5):341-5. PubMed ID: 1599378
4. Brooks. Loss of cabin pressure in Canadian Forces transport aircraft, 1963-1984. Aviat Space Environ Med. 1987 Mar;58(3):268-75. PubMed ID: 3579812

*This is the second time today I have referred to Johnny's work... interesting...
**I have to second the opinion that this has been a fun thread.

 

[Thalassamania]

... I have a (very) vague recollection of a US NTSB/FAA statistic of 1 in 100,000 flights having a severe pressurisation problem. Don't know if that's rapid decompression, or just any significant problem including failure to pressurise on takeoff. ...

Any idea where we might track that number down? So far I've failed.

Luckily, I haven't been on any planes that lost pressure, but I have been on a plane that was purposefully depressurized to just slightly over 10,000' altitude to make it more likely that a cargo door that was ajar would stay in place.

As the Maui to SFO flight was diverting over to Honolulu, the pilot explained to passengers that they might feel a bit faint because he had reduced the pressure to just below the automatic trigger point of the emergency O2 system at 11,000'.

I had done a night dive about 14 hours before the flight.

That's one of those moments that you feel like a Christian Scientist with appendicitis. Glad it worked out.

 

[Bismark]

Any idea where we might track that number down? So far I've failed.

That's one of those moments that you feel like a Christian Scientist with appendicitis. Glad it worked out.

ROTFLMAO................ (and I have a rough floor here.........)

That is too funny, I am absolutely going to have to save that one.

 

[Thalassamania]

ROTFLMAO................ (and I have a rough floor here.........)

That is too funny, I am absolutely going to have to save that one.

That's not original, credit goes to Tom Leherer.

 

[bleeb]

... I have a (very) vague recollection of a US NTSB/FAA statistic of 1 in 100,000 flights having a severe pressurisation problem. Don't know if that's rapid decompression, or just any significant problem including failure to pressurise on takeoff. ...

Any idea where we might track that number down? So far I've failed.

I think it was in AvLeak (Aviation Week and Space Technology) a few years back, where they were talking about some annual or every-four-years NTSB or FAA (or both) summary of accident statistics, maybe talking mainly about commercial passenger flights. It might have have been mentioned as a footnote rather than as one of the main reportable categories because of the relatively low frequency and therefore bad statistics.

 

[Charlie99]

Dr. Deco is in a MUCH better position to discuss this but I just can't see an exposure on the order of minutes creating an "SOL" level of DCS given the amount of risk most of us "might" be willing to take flying after a recreational dive. (Though, Doc, I really want to hear your thoughts on this)

I can't find it right now, but I do remember Dr Deco addressing the catastrophic loss of cabin pressure scenario and the gist of his post was that because of the short (less than 5 or 10 minutes) exposure to low pressure was not likely to cause DCS because there just wasn't enough time for enough bubble growth to cause problems.

 

[bleeb]

I can't find it right now, but I do remember Dr Deco addressing the catastrophic loss of cabin pressure scenario and the gist of his post was that because of the short (less than 5 or 10 minutes) exposure to low pressure was not likely to cause DCS because there just wasn't enough time for enough bubble growth to cause problems.

This brings up something that's been lurking in the back of my mind through a good part of this thread. I've seen a lot of comments (here on SB and elsewhere), especially in the last year or so, that rate of ascent is a significant factor in DCS showing itself. Without getting out the calculator, I assume the window blow-out case could drop the pressure to say 41,000' pretty fast (if you're in something long-haul), after which I think the procedure for commercial passenger flights is to dive the aircraft back down to below 10,000'-ish within 2 minutes. Anyone knowledgeable care to comment whether this is really a factor, or if anyone has managed to look at it scientifically in detail?

 

[Gene_Hobbs]

I can't find it right now, but I do remember Dr Deco addressing the catastrophic loss of cabin pressure scenario and the gist of his post was that because of the short (less than 5 or 10 minutes) exposure to low pressure was not likely to cause DCS because there just wasn't enough time for enough bubble growth to cause problems.

Now that you mention it, I do remember this coming up before... and here it is. Thanks again Charlie99!

Bleeb - download the file linked as reference 2 and I think you will happy with that as a starting point.

 

[Charlie99]

Also http://www.scubaboard.com/forums/1301132-post8.html

Hello readers:

DCS at Altitude

This is a question that has been examined by the FAA. Fortunately for passengers (and divers) DCS does not occur immediately with decompression. Every diver is aware that there is actually a time lag. For altitudes up to 40,000 feet, this time lag is sufficient that a controlled descent by the pilots would be easily possible and DCS should not occur within at least 20 minutes. By this time, a plane could descend from 40,000 feet to at least 15,000 feet.

For altitudes between 40,000 and 50,000, there still is enough time to descend before DCS becomes a problem.

Recall, also, that seated individuals [most of the passengers are in this category] are more resistant to DCS [they have fewer tissue micronuclei] than those walking around.

Dr Deco

A couple of posts after that BigJetDriver (R.I.P.) says that the descent rate will be on the order of 2,000 to 3,000 feet per minute.

 

[nereas]

This brings up something that's been lurking in the back of my mind through a good part of this thread. I've seen a lot of comments (here on SB and elsewhere), especially in the last year or so, that rate of ascent is a significant factor in DCS showing itself. Without getting out the calculator, I assume the window blow-out case could drop the pressure to say 41,000' pretty fast (if you're in something long-haul), after which I think the procedure for commercial passenger flights is to dive the aircraft back down to below 10,000'-ish within 2 minutes. Anyone knowledgeable care to comment whether this is really a factor, or if anyone has managed to look at it scientifically in detail?

If an aircraft rapidly depressurizes, there are indeed going to be bigger problems in addition to DCS. Being sucked through the blown out window would certainly ruin your body sculpting.

Still, ascending to altitude with an N2 load is a violation of NDLs, and it would be one of your many problems. Maybe Dr Deco is right, that the risk is small, for the issue of cabin depressurization on the plane.

I prefer to avoid the risk completely by simply waiting 24 hours before flying (or 48 hours after deco diving).

The incidence of DCS from too short a surface interval before flying happens more often than does cabin depressurizations, sure. That still does not justify the risk taken by flying too soon.