Rapid Decompression

[kraken]

Would the 24 wait eliminate this risk? Or should someone wait a longer period of time?

 

[BigJetDriver]

Would the 24 wait eliminate this risk? Or should someone wait a longer period of time?

No procedure will "eliminate" the risk speaking statistically. A 24 hour period would certainly bring it as low as possible.

DAN studies have recently recommended 18 hours, and if you look up the Flying After Diving Table (FAD) in the NOAA Diving Manual, you will see a sliding scale.

All one can do is pick a procedure, and follow it. No one can promise zero risk.

 

[ArcticDiver]

I, just like most current jet pilots, have done the "Altitude Course" at least once, and in my case many times via the military, DAN, and various hyperbaric facilities (most will work in reverse ).

In the chamber scenarios that I have done, no one has had DCS even though we remained at altitude for as long as 10 minutes before starting the chamber down.

Time of Useful Consciousness (TUC) at high altitudes is very short if you do not have pressure oxygen available. It can be as low as 30 seconds, depending upon your altitude. In the cockpit we have full face masks not connected to the passenger system which supply O2 under pressure.

Our routine is this: Oxygen--On, Crew Communication--Establish, Begin Emergency Descent Procedures.

With throttles at idle, speedbrakes deployed, and the nose down, we attain between 2000 to 3000 ft/min rate of descent. As you can see that gives us about 10 minutes required to get from as high as 40,000 ft to 10,000 ft.

In short, for the average passenger who started at sea level, while DCS is "possible", it is extremely unlikely. Now for someone who already has a high nitrogen load, such as a diver who has not waited a safe amount of time to equilibrate, that person will be writhing in pain, and we will not be able to spend time to help.

Unbelievably, there are some instructors who advocate going straight from decompression diving to flying (one MHK comes to mind), sort of "flying with your hair wet"! As our very own Doc Deco has pointed out, given the vagaries of decompression physics one might get away with that for a while but the failure, when it occurs, will be SPECTACULAR! :11:

Do you folks still require one crew member to have a mask on when at altitude?

Fly After Dive: As you know I'm in the Wait A Long Time crowd. The rule for fliers has been, and still is in most places, 24 hours between diving and flying. We frequently see posts and articles pointing out that even then all the hyperbaric effects are not washed out of the diver's body. The DAN papers merely point out that with there limited data, and based on some folks opinions the chances of DCS at the reduced wait times are minimal. So, given that diving is a hobby for most all of us it absolutely blows my mind why anyone would push the envelope when the potential consquences are so severe.

 

[Dr Deco]

Hello readers:



The whole “trick” with altitude DCS [as with any form of DCS] is that a given time interval is required for the diffusion of dissolved nitrogen to enter the tissue nuclei. Because this interval is, by experiment, several minutes, there is a “safe interval.” A graph appears below to illustrate the time before first appearance of DCS.

This of course is assuming saturation at sea level nitrogen pressure. If one had been diving and boarded with wet hair, the situation could be considerably direr.

For the higher elevations, the “time of useful consciousness” would be short. It is necessary that one done the oxygen mask. As is always instructed, you should don your drop-down oxygen mask first. You can put a mask on an unconsciousness seatmate [e.g., a child] if you are conscious yourself. Attempting to place the mask on a child first is liable to result in two individuals that are unconscious.

Excessive Movement

Excessive movement will result in more rapid generation of decompression bubbles. Most likely, passengers will remain seated or be unconscious and not moving as a consequence.

While this has not been tested in an aircraft cabin scenario, it is “standard stuff” where attitude chamber work is concerned. Thus, it is not theoretical but rather demonstrable by experiment.

Dr Deco :doctor:

 

[Dr Deco]

For reasons that are not clear, the graph is not appearing - and I can not deleat it.
The time limits for DCS are:

40,000 feet 5 minutes
35,000 feet 12 minutes
30,000 feet 20 minutes
20,000 feet 120 minutes

 

[ArcticDiver]

Too bad we don't have similiar scrubbed data from the other end of the hyperbaric spectrum. It would make discussions about delay time between diving and flying outmoded. Of course I guess there will always be those divers who are trying to fit in just one more set of dives, no matter what the risk. And there will be those operators who are after the last bit of income, no matter what the risk to someone else.

Back to the original topic:

So, there is a bit of change from the earlier posts? DCS from Rapid Decompression is probable unless the airplane can descend quickly? i.e. If I'm on a plane over the South Pacific where a landing may not be possible for hours and altitude must be maintained DCS is a possibility? Where if I'm on a plane where there can be immediate descent DCS is not likely? In either case I'd better sit still and let the cabin crew move around?

 

[miketsp]

For reasons that are not clear, the graph is not appearing - and I can not deleat it.
..snip..

If you save the attachment and then open it locally with Powerpoint it looks fine.

 

[miketsp]

..snip..
So, there is a bit of change from the earlier posts? DCS from Rapid Decompression is probable unless the airplane can descend quickly? i.e. If I'm on a plane over the South Pacific where a landing may not be possible for hours and altitude must be maintained DCS is a possibility? Where if I'm on a plane where there can be immediate descent DCS is not likely? In either case I'd better sit still and let the cabin crew move around?

So what are the comparative odds of DVT against DCS?
Better to keep moving.

 

[DiveGolfSki]

So, there is a bit of change from the earlier posts? DCS from Rapid Decompression is probable unless the airplane can descend quickly? i.e. If I'm on a plane over the South Pacific where a landing may not be possible for hours and altitude must be maintained DCS is a possibility? Where if I'm on a plane where there can be immediate descent DCS is not likely? In either case I'd better sit still and let the cabin crew move around?

Under your scenario, why would the pilots NOT descend to a lower level EVEN if no landing area is possible? If a rapid decompression occurs, you're assuming that the Pilots would insist to fly at altitude and all passengers keep their O2 masks on? Kinda risky.

Perhaps, bigjet would comment on whether or not pilots do or don't descend after a rapid decompression.

 

[2Tours N Iraq`]

My suggestion is to have a plan and stick to it. Plan an alternate activity you can do in lieu of diving the last day or two of your trip in order to reduce the possibility of DCS while flying. It also helps in keeping relations with non-diving significant others. For me, that activity is either fly fishing or sight seeing.