Rapid Decompression

[ArcticDiver]

A question for Doc Deco and anyone else who has any knowldge/ideas.

What is the likelyhood of DCS from a rapid decompression in an airplane? To establish the parameters: Airplane is at FL35, or higher. Airplane is normally pressurized, i.e. at about 8,000 feet or lower. For whatever reason there is a rapid decompression that is explosive or takes place over a very few minutes.

Crew takes correct action per the checklist. Fuel reserves allow continued flight at lower levels. But runway availability does not allow immediate landing.

DCS probability for crew? Passengers?

 

[gangrel441]

A question for Doc Deco and anyone else who has any knowldge/ideas.

What is the likelyhood of DCS from a rapid decompression in an airplane? To establish the parameters: Airplane is at FL35, or higher. Airplane is normally pressurized, i.e. at about 8,000 feet or lower. For whatever reason there is a rapid decompression that is explosive or takes place over a very few minutes.

Crew takes correct action per the checklist. Fuel reserves allow continued flight at lower levels. But runway availability does not allow immediate landing.

DCS probability?

From what I have heard about rapid decompression on an airplane at altitude, you would have bigger things to worry about than DCS. I think back to the plane that was carrying Payne Stewart in 1999. Turned into a Flying Dutchman, a little more literally than the term was originally intended...

 

[Kaiser442]

I found a cool applet that will show you the atmospheric pressure at various altitudes... might help with your question a little:

APPLET

Looks like pressure is halved evey 18000 feet or so.

 

[Goose75]

First thing that happens is that you put on the oxygen mask or black out such as the payne stewart incident (theirs was a slow leak so the masks didn't drop). The next thing is that the pilot puts the aircraft at a safe altitude where the paasnegers no longer need oxygen. This all happens very quickly. If it doesn't happen DCS is probably not a worry any longer. So, I would take a look at what is the likelyhood of getting DCS with these factors included.

 

[NSDiver]

It seems to me that there would probably be larger things to worry about - as I've heard, a plane is pressurized to about 10,000 feet, and even if it is flying at 35,000 when rapid decompression occurs, the change in pressure is still less than one atmosphere (kinda like diving for a few hours at 20 feet I suppose - probably won't get bent).

 

[ArcticDiver]

Yep, that is a cool applet.

There may, or may not be any other problem of significance. But that just dodges the question.

Is there a likelyhood of DCS, or not?

 

[Charlie99]

There may, or may not be any other problem of significance. But that just dodges the question.

Is there a likelyhood of DCS, or not?

There would be if the plane stayed at altitude, but the protocol for this sort of incident is to descend rapidly to a lower altitude. There are some pilots on the board ( calling BigJetDriver!!) that can fill in the details, but I believe the descent is down to below 10,000 or 8,000 foot in a 5 to 10 minute period. Staying at 35,000 feet, even breathing O2, DCS would be likely, but the short 5 t0 10 minute exposure helps keep down DCS probability. Kind of like the old "surface decompression" technique where hard hat divers were rushed from the 30' deco stop up to the surface and popped into a chamber to complete the rest of their decompression.

As for NSDiver's comments that it's like a 20' dive for a few hours --- that's way off. There were many cases of DCS during WWII on the unpressurized bombers flying in the 25,000' range, and DCS has been sometimes observed in ascents to as low as 18,000. What counts is the pressure RATIO. Surface to 18,000' just happens to be the 2 to 1 ratio set as the limit in JS Haldane's original goat bending tests.

 

[Dr Deco]

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 :doctor:

 

[ArcticDiver]

I believe that nominally half the earth's atmosphere is below 18000' and the atmospheric pressure is essentially zero by 100,000'. Usually airplanes are pressurized to a cabin altitude of around 8000'. Therefore, the pressure change during rapid decompression for an airplane at FL30 - FL40 will be less than 1 atmosphere, isn't very significant, especially for essentially unmoving people during the expected time frame. Therefore, it was my impression that DCS should not be a problem as a result of pressure change.

But, I've not done any personal biological study and there are some hyperbaric physicians who believe that DCS is a possibility following rapid decompression at altitude. Hence the question.

Thanks everyone for your inputs.

 

[BigJetDriver]

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: