>> Monday, August 31, 2009
I ran out of questions again, despite Jeff King's best efforts. So, here's atrivia break.
I owe my daughter an apology. She mentioned oxygen toxicity to me and, despite my years working EVA, I pooh-poohed the notion because I knew that the EVA crew breathed 100% oxygen. Yeah, well I was wrong.
Oh, not that crewmembers don’t breathe 100% oxygen – they do – but, because they are using lower than atmospheric levels of oxygen, it’s not an issue.
Oxygen toxicity is something that happens when oxygen levels exceed the normal partial pressure of oxygen in ambient air. In other words, if the total air pressure is high (but percentage of oxygen remains the same) you can get it OR if you breathe air that has a higher than normal percentage of oxygen. This is a big deal for divers (which is where my daughter got her correct information) and hyperbaric chambers (like those used to treat the bends after a diving accident, but hyperbaric treatments can also be used for certain types of wounds and burns, embolisms and carbon monoxide poisoning), where any of the three main types of poisoning can occur, including effects on the central nervous system (high pressure only), pulmonary and ocular oxygen poisoning.
Here are some things to note. Regular people, breathing ambient air (or air at higher elevations) don’t have to worry about these conditions because oxygen in air (0.21 bar) has a “partial pressure” below the toxic level (0.3 bar) - so you can’t get oxygen poisoning from hyperventilating.
At ambient pressures (regular pressure, not in a tank or underwater), you can’t get central nervous system oxygen toxicity because you actually have to have a partial pressure greater than an atmospheric (so, even at 100% oxygen, there wouldn’t be enough), but you can do damage to lungs and eyes and this has happened for people on chronic oxygen levels (greater than 50%) and neonatal units with premature newborns.
It seems to be counterintuitive that breathing too much (or two high a partial pressure) of oxygen can ruin your lungs, but there you go.
Just goes to show, you can get too much of a good thing.
(For those of you whose eyes rolled back into your head during this, there’s a much better description in the link I provided – gotta love Wikipedia. Or you can just leave whistling and hope for something less technical next time.)