Darwin award winner?

[markmantei]

But their question was not entirely unreasonable.

I agree it's not a bad question for your OW class, just seems to me like something you should know before you get handed a c-card.

 

[String]

Don't think thats a darwin award contender at all. If it all went wrong he's uninsured though. Cabin altitude of about 5500ft wont affect him - his only real risk would be a loss of cabin pressure and thats rare.
Probably a calculated risk and its his choice. I dont see it as a massive risk. It could go wrong but ultimately probably wont.

Ive gone under 12 hours a few times previously, again my choice. My assumption of risk.

 

[nauga]

If there was a sudden loss of cabin pressure at high cruising altitude (and the pilot did not immediately decrease altitude), wouldn't everyone on board get DCS? I thought I'd read that WW-2 bomber pilots in unpressurized cabins were getting DCS during long, high altitude missions over Europe, and sypmtoms that were originally thought to be symptoms of hypoxia, were later determined to be DCS?

Finally something I can answer!
Somewhere in my reference library (read: piles of paper) I have a hardcopy of an article in the Navy's aviation safety magazine ("Approach") about a Naval Flight Officer who experienced DCS after losing cabin pressure at high altitude in an EA-6B Prowler. He ended up with a chamber ride. I tried to find it online but no joy. On the other hand I and a lot of other people have lost cabin pressure at altitude with no ill effects other than the smell.

Nauga,
fragrantly.

 

[Charlie99]

And I met an Air Force pilot that got DCS from some sort of annual training/checkout on rapid decompression procedures. For safety purposes they breathe O2 for something like 30 minutes before their simulator ride. I forget the exact details of the actual rapid decompression, but he spent a few minutes of this 30 minutes O2 time breathing air for some reason. He suspects that this is why he got DCS.

He had minor symptoms a few hours later and went to the base clinic. They checked him out and sent him on his way. A couple hours later the duty medical officer heard about it and a massive manhunt ensued since he had headed into town with his girlfriend.

I visited a few months after the incident and his buddies were still giving him a hard time about the massive manhunt and all-points-bulletin used to track him down.

 

[seaducer]

That should tell you everything you need to know.

I was on a trip to Bonaire one time. There was a fellow in our group from NYC. Dude and his buddy had the room next to ours ... they had to borrow a dolly from housekeeping to get all the booze they bought up to their room. When they weren't diving, they were drinking.

Well, having grown up in a NYC resort destination (think Jersey Shore) I can't help but laugh. However I do have an issue...here in the NE it is well known that alcohol is lighter than water, which means it will thin the blood, meaning that blood will run through the vessels faster, in turn off gassing faster. Therefor drinking copious amounts of booze on a dive vacation means safer diving

To keep it fair though, I spent part of one Bonaire trip making sure I was up before the Washington State couple woke, as they would literally eat all of the sausage and bacon at the buffet every morning:shocked2:.

No, they're based on not getting DCS in a pressurised cabin

Just thinking about it, I would think a bigger issue (aside from the obvious fact that the plane is not working properly at the moment), if it were explosive depressurization I think trauma to ears and other spaces we equalize may be affected, but the amount of bubbling, if any, would be minimal as the pilot is probably making a quick decent to a level that the cabin was pressurized to in the first place...

 

[Charlie99]

Cabin altitude of about 5500ft wont affect him - his only real risk would be a loss of cabin pressure and thats rare.

The FAA limit on cabin altitude for US airlines is 8,000 feet and they often are above 7000' as the ventilation system is cranked back to reduce fuel consumption.

With my luck, the time I cut things close by flying out the morning following a night dive the plane was partially depressurized to 10,000' in response to a cargo-door-open alarm.

The pressure difference of about 1/4 atmosphere or 7fsw really only makes a difference to the very slow tissues/compartments.

Some computers do the calculations and show a time-to-fly. There is nothing magic or unusual about those calculations. They are done the same way as a deco stop calculation.
Just as algorithms such as Buehlmann's ZHL16 are used to calculate deco stops on the way up from a dive, you can plug in the reduced pressure of about 0.75atm and see how long of a stop (surface interval) at 1atm is needed before that additional ascent to about 0.75atm.

 

[DaMaDo]

And I met an Air Force pilot that got DCS from some sort of annual training/checkout on rapid decompression procedures. For safety purposes they breathe O2 for something like 30 minutes before their simulator ride. I forget the exact details of the actual rapid decompression, but he spent a few minutes of this 30 minutes O2 time breathing air for some reason. He suspects that this is why he got DCS.

He had minor symptoms a few hours later and went to the base clinic. They checked him out and sent him on his way. A couple hours later the duty medical officer heard about it and a massive manhunt ensued since he had headed into town with his girlfriend.

I visited a few months after the incident and his buddies were still giving him a hard time about the massive manhunt and all-points-bulletin used to track him down.

Was he a U-2 pilot? Those guys pre-breath O2 and wear what basically amounts to a space-suit. I'm sure they must have some intense depressurization training.

Here's a pic of a buddy that went on to fly it. You can see the atmosphere in the reflection of his helmet:

 

[Tortuga68]

... that's going from 1 bar to .5 bar, which is the same as rapidly going up from 33 feet to 16.5 feet in the water.... if you go on a normal flight after a dive, you're going up ~0.3 bar max (0.743 ata) which like going from 10 feet to the surface

I'm not sure if my cross-reference with water depths is accurate, but pressure is pressure no?

In relative terms you're correct, but in absolute terms you're not. Going from 33' (2ATA) to 16.5' (1.5ATA) is a pressure change of 25%, compared to 1ATA to 0.5ATA which is 50%. As someone else metioned it's the gradient which can hurt you

 

[Mr Carcharodon]

Stop me if I am mistaken but isn't gradient is a difference and not a percent. Specifically the difference between ambient pressure and tissue inert gas pressure.

The M value does decrease with as altitude. For nitrogen in the 635 minute compartment M is 42 fswa at sea level, 34 fswa at 8000 feet, and 18 fswa at 30,000. Tissue pressure, assuming you have been at sea level for a couple days is 24.4 fswa. So since the idea is to keep tissue pressure less than the allowable M that says you can go to 8000 feet elevation immediately without risk of getting bent, but 30,000 feet would be a problem. Of course if your plane depressurized several hours into your flight you might be OK because of the offgassing that had already occurred.

 

[Tortuga68]

Perhaps I should have started a new paragraph with the second sentance...

Anyway, gradient has at least two factors, typically rate & magnitude - eg the difference in pressure and the difference in time