hgroberts (ironically, hg is chemical for Mercury, often used for pressure):

I have a story somewhere in my library of a USAF T-39 Sabreliner, cruising at 390 or 410, as I recall. It was in the early 1960s.

Aircraft commander doesn't have his mask on. Copilot has his dangling around his neck.

The main cabin door opens, which hinges down. Whoosh.

Copilot gets his mask on within 5 seconds and assumes control of the aircraft; starts the emergency descent. Aircraft Commander is incapacitated and fighting him on the controls.

Amazing part: a spare pilot back in the cabin dons a portable bottle, and walks past the open door (!!!) to get to the cockpit.

He gets to the cockpit and they put oxygen on the AC. He revives, but has nitrogen bubbles in his brain, so he is acting like a blithering idiot. The spare pilot finally has to drag him out of the cockpit.

On the ground, the AC is fighting with medical crews and tries to slug them as they try to put him in an ambulance. They took him to a compression chamber, and he eventually fully recovered.

Cheyenne: We all have dissolved nitrogen in our blood. Uncork the Coke bottle too fast (ie, remove pressurization from your body too quickly, whether that is from an airplane or scuba diving), and you get bubbles.

Those bubbles can manifest themselves as:

1. The Bends. Bubbles that form at joints of limbs or in the abdomen.

2. The Creeps: bubbles that form just under the skin, giving a "creepy-crawly" sensation of insects under the skin. (Rarely occurs).

3. The Chokes: bubbles in the pneumothorax (lungs) that make it seem like you can't get a full breath of air, no matter how hard you try.

4. Central Nervous System: Minor cases involve tingling, numbness, or partial paralysis, the F-4 guys I mention below saw flashing lights and vision loss; worst case is unconciousness or loss of autonomous motor functions (like heartbeat and respiration). Correct me if I'm wrong but I think N2 Narcosis deals with bubbles in the brain or spinal column.

When I was going through F-4 school, two F-4 pilots (on two different occasions) got central-nervous system problems after leaving Edwards AFB's chamber on their way back to George AFB (they were driving their cars). One of them never flew again.

As far as DAN, yes, that is true for normal pressurization in an airliner. I'm talking about rapid-decompression--the whole point of wearing the mask above FL350.

Boredw:

Atmospheric pressure at FL290 is about 310 mb. At FL390 it is about 150 mb. The partial pressure of O2 (Boyle's Law) at FL390 means O2 (no mask) has 30mb of pressure. Normal partial pressure of O2 in your blood is (I believe) 220 mb, so any O2 in your bloodstream has to leach out to equalize.

Not freaking out--just a statement of physical fact. FL390 is way worse than 290.

FAR Part 135 Federal Aviation Regulations

(3) Whenever a pressurized aircraft is operated at altitudes above
35,000 feet MSL, at least one pilot at the controls shall wear, secured
and sealed, an oxygen mask required by paragraph (b)(2)(i) of this
section.

this is paragraph (b)(2)(i):
(i) At least one pilot at the controls shall wear, secured and
sealed, an oxygen mask that either supplies oxygen at all times or
automatically supplies oxygen whenever the cabin pressure altitude
exceeds 12,000 feet MSL; and

So the way I read it, you only have to use the O2 mask if you are above
35,000 feet MSL AND your cabin altitude exceeds 12,000 feet. Am I missing something?

i think the way you read the second paragraph is that the MASK will automatically supply O2 if the cabin exceeds 12,000'

Read higher above,

(i) At least one pilot at the controls shall wear, secured and
sealed, an oxygen mask that either supplies oxygen at all times or
automatically supplies oxygen whenever the cabin pressure altitude
exceeds 12,000 feet MSL; and

So based on this reg it either needs to supply oxygen always when its on, OR it automatically supplies in the event the cabin pressure reaches or exceeds 12,000.

You still have to have it on. It just might not be necessary to be sucking the oxygen.

ahhh... I see. Seems like a silly reg in my opinion.

N2 narcosis is different from the bubble issues you mention - although the mechanism of it is not fully understood, the narcotic effect is caused by prolonged breathing of high-pressure nitrogen (i.e. scuba air, at depth), not the sudden removal of pressure from an uncontrolled ascent from depth, or a rapid decompression at high altitude. Regarding the F4 guys, decompression injuries can manifest some time after the actual decompression - bubbles can travel around the body and lodge just like clots, causing the symptoms you described. Bubbles in your blood are one of the worst things there is.

Damon:

Thanks for the clarification--I learned something today.