Decompression risks in aviation

[bluebanded goby]

Dr. Powell, I know you have a lot of experience looking at decompression issues with people who go up instead of down, so I thought I might try this out on you:

I've heard that commercial jet planes typically compress their cabins at a pressure about 1/3 of an atmosphere less than Earth surface pressure (or, viewed another way, it's the equivalent air pressure you would experience if you had a window open at an altitude of 8,000 feet).

I would think that coming up 1/3 of an atmosphere in five minutes (or however long it takes to ascend) would be pretty benign, although untoward effects might not be impossible. Apart from DCS per se, could someone with really bad lung congestion suffer lung problems of one sort or another (up to and including an embolism)? If not, what is the minimum pressure change under which embolism or DCS problems have ever been seen in aviation?

I once had a frightful flight (flying to JSC, as a matter of fact) when I traveled from California to Texas and made not one but two stops in Arizona and New Mexico. I had a cold and, unbeknownst to me, a plugged eustachian tube, and ended up with a bloody eardrum when I got to Houston.

Thanks for any input.

 

[Dr Deco]

Dear bluebanded goby:

Cabin Altitude

You are correct in the assumption that commercial airliners fly with a pressurized cabin and this is equivalent to 8,000 feet. It actually requires about one-half hour to reach cruising altitude, but max cabin pressure is probably less time.

Lung problems

The FAA does generally not mention these in the list of passenger medical problems. The major problem would be reduced oxygen partial pressure for some individuals. An embolism would not be a problem as far as I have ever heard.

Minimum altitude for DCS

This is generally given as about 20,000 feet elevation. As is true with anything concerning DCS, the pressure is variable from individual to individual. Unless there is breach of the cabin wall (or other reason for a loss of pressure) you could not really get DCS in a plane. In addition, it requires time for the gas phase to grow and the plane will descend during this interval.

Air Trapping

Barotrauma is the worst that most encounter, but you will not die. Those who have experienced a ruptured eardrum might have wished they died; I am told it is very uncomfortable.

In addition, the paranasal sinuses are problem spots and can be very painful. I know of one fellow taken to the hospital and given an injection of morphine. He, surprisingly, was not given nasal decongestant in a spray form.

Dr Deco :doctor:

 

[c555]

the only problem i have ever had with flying is not being able to equalize. i have been unable to clear my earrs some and get some pressure problems but have never had any problem with DCS, nor have I heard of it. Just wait 18 or 24 hours after diving and you should be fine.

 

[NJMike]

As a former professional pilot with lots of flight experience in jet aircraft, the question that I always come back to is how soon after diving should you fly.

It seems that the current information suggests that you wait 24 hours. And since the cabin pressure is only 8000' (approx., although it takes a lot less than 30 min. to get there), it's easy to buy into...

But here's my question...

You dive today twice today, first dive you hit 100', second dive you hit 70'. You get out of the water from the second dive at 2pm, and then depart tomorrow on any standard commercial jet aircraft at 4pm. That's 26 hrs. The aircraft ascends to an altitude of 36,000 feet which would normally take about 30-45 mins. (assuming no traffic delays, which is pretty standard today with all the high tech computers).

Fifteen minutes later (one hour into the flight) at an altitude of 36,000', there is a sudden decompression (blowout). A window blows out, A 25' FOOT SECTION OF THE FUSELAGE BLOWS OUT, a cargo door blows out...now the cabin pressure drops to the outside ambient pressure in a matter of seconds...

In this scenario, relative to the diver on board, what are the possible consequences to him because of the sudden, drastic, immediate reduction of pressure?

 

[victor]

Fifteen minutes later (one hour into the flight) at an altitude of 36,000', there is a sudden decompression (blowout). A window blows out, A 25' FOOT SECTION OF THE FUSELAGE BLOWS OUT, a cargo door blows out...now the cabin pressure drops to the outside ambient pressure in a matter of seconds...

In this scenario, relative to the diver on board, what are the possible consequences to him because of the sudden, drastic, immediate reduction of pressure?

In my case an immediate requirement to change my underpants

 

[NJMike]

victor, put you O2 mask on first!

 

[Gene_Hobbs]

It seems that the current information suggests that you wait 24 hours. And since the cabin pressure is only 8000' (approx., although it takes a lot less than 30 min. to get there), it's easy to buy into...

Here are my comments in a previous thread about current guidelines for Flying After Diving (FAD).
http://www.scubaboard.com/showpost.php?p=2312379&postcount=7

Fifteen minutes later (one hour into the flight) at an altitude of 36,000', there is a sudden decompression (blowout). A window blows out, A 25' FOOT SECTION OF THE FUSELAGE BLOWS OUT, a cargo door blows out...now the cabin pressure drops to the outside ambient pressure in a matter of seconds...

The only testing we did was looking at flights to 25,000' following a 60'/ 60 min chamber dive for the US Navy.

Risk of Decompression Sickness during exposure to High Cabin Altitude After Diving.
Aviat Space Environ Med. 2003 Nov;74(11):1163-8.
PMID: 14620473
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Retrieve&dopt=AbstractPlus&list_uids=14620473&query_hl=1&itool=pubmed_docsum

The Aerospace Medical Association allows older content to be available to the public. If you find this useful, let them know.
http://www.ingentaconnect.com/content/asma/asem
This article: http://www.ingentaconnect.com/content/asma/asem/2003/00000074/00000011;jsessionid=tvh7vjso4v5p.victoria

We are still in need of subjects for our FAD trials as well as other protocols.
http://hyperbaric.mc.duke.edu/research/fad.htm
http://hyperbaric.mc.duke.edu/research/index.htm

Hope this helps!
Take care,
G

 

[Rick Murchison]

As a former professional pilot with lots of flight experience in jet aircraft, the question that I always come back to is how soon after diving should you fly.

It seems that the current information suggests that you wait 24 hours. And since the cabin pressure is only 8000' (approx., although it takes a lot less than 30 min. to get there), it's easy to buy into...

But here's my question...

You dive today twice today, first dive you hit 100', second dive you hit 70'. You get out of the water from the second dive at 2pm, and then depart tomorrow on any standard commercial jet aircraft at 4pm. That's 26 hrs. The aircraft ascends to an altitude of 36,000 feet which would normally take about 30-45 mins. (assuming no traffic delays, which is pretty standard today with all the high tech computers).

Fifteen minutes later (one hour into the flight) at an altitude of 36,000', there is a sudden decompression (blowout). A window blows out, A 25' FOOT SECTION OF THE FUSELAGE BLOWS OUT, a cargo door blows out...now the cabin pressure drops to the outside ambient pressure in a matter of seconds...

In this scenario, relative to the diver on board, what are the possible consequences to him because of the sudden, drastic, immediate reduction of pressure?

In that scenario, unless the aircraft was dropped to a survivable altitude right quick, you'd either freeze to death or die from lack of oxygen long before DCS became a problem.
If the descent were quick enough to save you from freezing or asphyxia, you wouldn't have to worry about DCS anyway.
So... no problemo!
Rick

 

[NJMike]

Hmm...let's think about that for a minute.

When a decompression occurs in an aircraft, the pilots' job is to get the aircraft down to an altitude where people can breathe ambient oxygen on their own - without the masks. The masks only serve to allow them to have oxygen during the time it takes to descend.

So the oxygen masks give the passengers oxygen, and second, the time it takes to descend is short enough that freezing to death is not a concern.

But, and again, my question is...since the decrease in pressure causes the bubbles to come out of solution, and in this scenario, the decrease in pressure is sudden and rapid...

I'm trying to remember the info...I believe that 18,000' is equivalent to 1 ATA (could be wrong on this). If the cabin pressure was set to 8000' and decompressed to 36,000 in ... I don't know, 15 seconds...the altitude change would be 28,000', or approx. 1.5 ATA's.

But again, if all the nitrogen has been released from the body within 24 hours, then the whole conversation is moot. If the flying after diving rule is based on it being safe for cabin pressures up to 8000', then that's where my question comes in.


Gene, I will check out the links you sent, thanks.

 

[Rick Murchison]

Hmm...let's think about that for a minute.

When a decompression occurs in an aircraft, the pilots' job is to get the aircraft down to an altitude where people can breathe ambient oxygen on their own - without the masks. The masks only serve to allow them to have oxygen during the time it takes to descend.

So the oxygen masks give the passengers oxygen, and second, the time it takes to descend is short enough that freezing to death is not a concern.

But, and again, my question is...since the decrease in pressure causes the bubbles to come out of solution, and in this scenario, the decrease in pressure is sudden and rapid...

I'm trying to remember the info...I believe that 18,000' is equivalent to 1 ATA (could be wrong on this). If the cabin pressure was set to 8000' and decompressed to 36,000 in ... I don't know, 15 seconds...the altitude change would be 28,000', or approx. 1.5 ATA's.

But again, if all the nitrogen has been released from the body within 24 hours, then the whole conversation is moot. If the flying after diving rule is based on it being safe for cabin pressures up to 8000', then that's where my question comes in.


Gene, I will check out the links you sent, thanks.

18K is 0.5 ATA. And the change in pressure is not linear, because you're dealing with a gas (which is compressible) and not a liquid (which is - essentially - not).
To reduce the pressure the other 0.5 ATA you have to ascend beyond the atmosphere. As another data point in your contemplations, blood boils at about 55K ambient...
And another... bubbles don't just pop out of solution and immediately grow - it takes time for the seed bubbles to gather gas from the neighborhood to gain any appreciable size. That's why you can bring divers up quickly and stick 'em in a dry chamber (the nominal limit is generally five minutes) and recompress 'em quickly for a long, slow, safe decompression in some commercial and military diving operations.
Bottom line - DCS is the least of your worries should you be in an airliner that has an "explosive decompression" event.
Rick