Comment by hinkley
7 years ago
Not necessarily.
Nobody could adequately explain to those of us in the CS dept why we had to take 3 semesters of Chemistry. Bits of it hung on and from other sources such as space exploration articles I recall this much:
Fires and lungs both operate on partial pressure of oxygen. As long as nothing else in the air is toxic, your body cares that it gets X oxygen molecules per cubic centimeter of air in your lungs, not Y parts per million. Those deep sea submariners are breathing mostly helium with a small fraction of oxygen in it. If you just compressed surface air there would be so much oxygen that your hair would explode when you ran your hand through it. Assuming the electronics didn't burst into flames first. And if you didn't set yourself on fire, that much nitrogen would kill you pretty quick.
So the question is, does helium displace air or mix in with it? I believe the answer is 'some of both'. If that's the case (and I think we can infer that from "the alarms didn't go off") then a good amount of helium might reduce the oxygen partial pressure less than going to 3000 feet above sea level. So what's the Venn diagram of COPD sufferers, in a hospital wing near the MRI machine, that aren't currently on supplemental oxygen?
Moreover, helium floats to the top and escapes through any opening (staircases, HVAC ducts, gaps in ceiling tiles) because it is lighter than air. This makes it much less dangerous than a heavier gas such as CO2 even if there's enough of it to displace a significant amount of air.
Not just any opening: just about any microscopic crack would let it out and most non-metal materials are effectively porous when trying to contain helium under pressure. It's even used to detect leaks in high vacuum chambers.
You don’t even need cracks. Helium (and hydrogen) can diffuse through metal, especially at high temperatures. Hydrogen embrittlement is a problem for processes that use high temp hiydrogen like the Haber process.
2 replies →
That is not true by any stretch of the imagination. If gases behaved like that then we'd all be choking on a layer of argon with all of the oxygen out of reach above us. No, gases diffuse and mix easily.
Gases diffuse and mix given enough time. There's not enough time when you have a massive indoor gas leak.
Even outdoors, large amounts of CO2 tend to sink to the ground and suffocate people in low-lying areas. Look up Lake Nyos for a particularly grizzly example of that.
Helium breathing mixes are for deep sea divers, not submariners. Most submarines run an interior gas mix nearly identical to regular air.
I didn’t mean navy boys, I meant research submarines at extreme depth.
Research submarines at extreme depths also use regular air. There's really no benefit to helium mixes for submarines. The breathing gas isn't compressed, it's at about 1 bar.
7 replies →
I assume the first two semesters were first-year (freshman) chemistry. What was the third year? Organic?