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Oxygen weathering is a primary constraint on life on Earth, and every carbon-hydrogen based organism in the past 2.5 billion years has had to develop biochemica
by mapt 1y ago
Oxygen weathering is a primary constraint on life on Earth, and every carbon-hydrogen based organism in the past 2.5 billion years has had to develop biochemical coping mechanisms for this toxic gas that wants to react with carbon and with hydrogen; It is harnessing this reaction ("respiration") with biologically mediated processes and modulating it to specific rates that permits us life.
For humans, acute breathing gas toxicity only happens in a high pressure environment.
Air approximates an 80/20 nitrogen-oxygen mix. Atmospheric pressure is 14.7psi.
The 120psi air compressor in your auto body shop is equivalent to a dive only 81 meters deep. SCUBA divers and later saturation divers have probed the various limits of the human cardiopulmonary system using very specialized gas blends all the way down to 700 meters. Too much oxygen partial pressure causes all the symptoms you see listed, and higher partial pressures cause symptoms to appear faster.
> The curves show typical decrement in lung vital capacity when breathing oxygen. Lambertsen concluded in 1987 that 0.5 bar (50 kPa) could be tolerated indefinitely.
This means you could breath 80/20 nitrox at 2.5 bar, or 37 psi, or 25 meters depth, "indefinitely" in the sense of hours or days.
PS: Chronic use of 100% oxygen at atmospheric pressure causes other types of toxicity. Some of the oxidative damage therein, accumulated over the years at a normal 20%, probably directly analogizes parts of the human aging process. Other types of oxidative damage probably work faster than proportional exposure. We only start to notice damage like this in people with impaired lung function who rely on an artificial supply of oxygen boosted to beyond an 80/20 ratio, to breath.
- thrown-0825 1y agoFound the SCUBA diver
- SOLAR_FIELDS 1y agoIndeed, the grandparent post is a pretty good summary of the takeaways you get from taking PADI’s enriched air nitrox course (which is a requirement if you ever want to dive with enriched air). In the olden days this was tracked manually (the ratio of your depth to percentage of air and time under water) via so called “dive tables”. The purpose and output of the dive table is to determine the safe amount of time you could dive at a certain depth without risking narcosis. As this is a sliding window based on multiple variables - and you are very rarely maintaining a constant depth as you dive - it’s of course annoying and less accurate to hand calculate this. Modern dive computers just seamlessly calculate it all for you nowadays.
- thrown-0825 1y agoFun fact: those dive tables were created by the US Navy conducting experiments on its own divers, there was a real human cost to acquire that information.
- nradov 1y agoNumerous other training agencies also teach how to use nitrox safely. PADI training isn't specifically required (or even particularly good).
- acjohnson55 1y agoI don't see where the person you replied to claimed there was anything special about PADI.
- mapt 1y agoNever done it, never gonna. Thank _Neoshade_'s legendary story in a Reddit comment for that - https://www.reddit.com/r/todayilearned/comments/dv99nf/til_the_blue_hole_is_a_120metredeep_sinkhole_five/f7bzg5a/ https://www.reddit.com/r/todayilearned/comments/dv99nf/til_t... With a side helping of Neal Stephenson's Cryptonomicon, and the submarine / treasure hunting arc which describes decompression sickness.
- thrown-0825 1y agoI have over 5000 logged dives and have only suffered DCS once, with the right training SCUBA can be very safe.
- agos 1y agothat comment is a classic and certainly entertaining, but there are multiple levels of safety to prevent something like this from happening, the first of which is the wall of tombstones that greets you when you arrive at that specific dive site. To end up in that situation means to have already made a number of big, big errors. I remember the Blue Hole as one the best dives I made, and not even the scariest: that prize goes to the time I was in calm waters at 20 meters, and the pressure regulator just failed, leaving me without air from both mouthpieces. And that's why you have a buddy...
- thrown-0825 1y agosame, blue hole is notorious because inexperienced divers get pressured into deep dives they haven't trained for by local guides looking to make a quick buck. my scariest dive was when a 14 year old got separated from the group and thought it would be a good idea to continue his dive for 30 minutes.
- acjohnson55 1y agoI don't think I've ever had anything fail on me diving, but I've been with people who have run out of air (my buddy was constantly using all his up), so having to breathe off someone else's tank isn't uncommon. As I mentioned in my sibling comment, I did have a scary time on the Blue Hole. I think my other most nervous dives were: - Pacific dive in Costa Rica in rough seas and surge. We suddenly had visibility drop to near zero when we hit the outflow current of a river. Definitely a lesson in how quick conditions can change. - Cavern diving in a cenote in Mexico. Nothing weird happened, but we went kinda far in, and I get nervous in overhead environments.
- actinium226 1y ago> all the way down to 700 meters. 700m! That's wild, I mean nuclear submarine crush depths are at like 400-500m? I get that it's not like you can compare a hard steel tube with a human body but regardless, it's wild.
- jandrewrogers 1y agoThe published data for military submarines is the nominal test depth, not the actual design limit. The operational depth may be much deeper but that will be classified. Recent US submarines all have test depths described by as being in excess of the same few hundred meters. In all likelihood that is a throwaway value. It seems unlikely that they produced generations of submarines that were less capable than their older ones.
- bluGill 1y ago>It seems unlikely that they produced generations of submarines that were less capable than their older ones. i wouldn't be sure. There seems to be no military advantage to deeper so why spend the money. A sub needs to hide, but it can't do any other job when too deep. sinking ships can only be done when near the surface. If the sub can get under a couple thermo layers that is good enough, any deeper is more a party trick than useful. i'm not in the navy but that is how I read the unclassified information I have access to.
- yownie 1y ago> sinking ships can only be done when near the surface. Isn't this itself a huge assumption? Sinking ships via upward facing torpedoes would be a huge tactical advantage at first glance. Less time to detection and deploy countermeasures or evasive maneuvers. Perhaps, I am wrong in assuming they cannot be fired below a certain depth?
- yownie 1y agojust watched: https://www.youtube.com/watch?v=V-mzZXwCn68&t=2s https://www.youtube.com/watch?v=V-mzZXwCn68&t=2s while these torpedoes are going in the other direction seems like the technology for surviving, functioning and navigating depths definitely exist.
- cess11 1y agoTo add to this, when diving with compressed air most people get woozy and otherwise intoxicated from oxygen around 30 meters from the surface. For some people 25 meters is enough for such symptoms to occur.
- hermitcrab 1y agoDiving on normal air, oxygen toxicity occurs around 60m. Are you sure you aren't talking about Nitrogen narcosis ('raptures of the deep')?
- bonzini 1y agoYes, he is. Oxygen toxicity causes seizures, not narcosis, and kicks in at around 1.6 bar of partial pressure (just below 65 m when breathing 21% oxygen as in regular air). PADI uses 1.4 bar to add an extra safety margin. Oxygen toxicity is really the one thing in recreational diving that will kill you if you do it wrong, though for recreational divers the risk only exists when using enriched air(*). Fortunately it's trivial to avoid it by only using enriched air where the sea floor is at a safe depth, but you should know the math nevertheless. For example if the sea floor is at 35 m (4.5 bar) you won't enrich air above 1.4/4.5=31% oxygen, probably more like 28%. Oxygen toxicity is also the (or the main) reason why enriched air must never be stored in white or yellow bottles. If you see yellow you can assume it's 21%, while for any other color you must use an oxymeter before using it. Not doing so can be literally the difference between life and death. Scuba diving is safe but a lot of the safety is about procedures, as you can see. (*) Enriching air above 21% oxygen is done to avoid the other issue with nitrogen, which is decompression sickness. It lets you stay longer on the bottom. In other words, enriched air improves the trade-off between bottom time (limited by nitrogen) and maximum depth (limited by oxygen toxicity).
- cess11 1y agoGot the symptoms wrong, but oxygen toxicity is also present from 25 meters down.
- hermitcrab 1y ago