At what % oxygen would smoking start to become...problematic?

Factual Questions
21

I don’t know about subs but we can WAG up some numbers from aviation. What matters is the partial pressure of oxygen.

15,000 feet is not far from the highest altitude an unacclimated person can remain conscious indefinitely. Certainly by 20,000 your time is getting real limited. At 15,000ft the standard atmospheric pressure is about 8.3 inHg which is 8.3/14.7 = 56% of sea level pressure. The normal Earth atmosphere is 21% oxygen.

56% of 21% = 11.8%. Once the oxygen level gets below about 12% at sea level, you’re going to have a hard time staying conscious just sitting there. Much less exercising or working. This assumes that whatever is substituting for the missing oxygen is mostly biologically inert, such as nitrogen. If instead the missing ~9% that had been oxygen was replaced with, e.g. CO2 or worse yet, CO, that would be much worse for you. Probably promptly fatally so.

Moving back towards safer numbers, we’re required to have and use supplemental oxygen above 10,000ft = 10.1 InHg or 10.1/14.7 = 68% of sea level pressure. That’s equivalent to a 68% * 21% = 14% oxygen atmosphere at sea level.

That’s kinda scary. Assuming sea level pressure, at 14% oxygen you can be fine for hours. At 12% it’s getting iffy. By 10% you’re unconscious quickly.


This OSHA standard is interesting. The consider anything outside 19.5% to 22% to be dangerous enough to need warning signs, precautions, breathing apparatus, etc.

So 1.5% to the low side but just 1% to the high side. Recognizing that 19.5/21 ~= 92% of normal or an 8% reduction in absolute oxygen levels, whereas 22/21 ~= 105% of normal or a 5% increase in absolute oxygen levels.

Oxygen be very, very powerful stuff. And real important to the proper functioning of human bodies.

22

There was a guy at Purdue in the '90s who was famous for doing that. Dave Barry even wrote a column about it. The guy was a chem professor or something, so he had the knowledge to approach it sort of safely. He said it was important to have a lit cigarette on top of the pile of charcoal before adding the LOX, to assure ignition before the LOX soaked into the briquettes. Why? He said it was because a briquette soaked in LOX had the explosive potential of a stick of dynamite.

Back when I was in grad school we had a wintertime party during which it was so cold outside that we could not keep a charcoal grill lit. So for the next wintertime party, we got a tank of (gaseous) O2 and set it to trickle O2 into the charcoal heap, allowing it to burn hotter. It sure did. A single match easily lit a briquette without starter fluid, and then every single spark that landed on another briquette lit that briquette. We had to really dial back the O2 flow rate to keep it from burning meat on the outside (while leaving the inside hot). O2 is weird, weird stuff.