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To 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 2

by cess11 1y ago

To 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 ago
Diving on normal air, oxygen toxicity occurs around 60m. Are you sure you aren't talking about Nitrogen narcosis ('raptures of the deep')?
- bonzini 1y ago
  Yes, 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 ago
  Got the symptoms wrong, but oxygen toxicity is also present from 25 meters down.
  - hermitcrab 1y ago
    Have you got a reference for that?
    - cess11 1y ago
      E.g. https://dan.org/health-medicine/health-resources/diseases-conditions/oxygen-toxicity/ https://dan.org/health-medicine/health-resources/diseases-co....
      - hermitcrab 1y ago
        I don't see any thing that supports "when diving with compressed air most people get woozy and otherwise intoxicated from oxygen around 30 meters from the surface".
        hermitcrab 1y ago
        It does say: "Be aware that oxygen toxicity is unpredictable. Divers have experienced convulsions at shallow depths under conditions where most experts would not have expected them to occur." But that doesn't say what depth, what oxygen % and how often it happens.
        bonzini 1y ago
        It also says that oxygen toxicity is a possibility only above 21% oxygen. In fact, with regular air there are way too many things that have already gone wrong if you are at 65 m depth (or even 50 m). It's clear from reading the document that convulsions at "shallow depths" refers to the case of breathing 100% oxygen, where 1.5 m difference is the difference between <1.6 bar (safe) and >1.7 bar (absolutely not safe).
  - bonzini 1y ago
    Not with 21% oxygen. 25 meters is 3.5*0.21=0.73 bar of O2 partial pressure, which is within even the strictest limits that apply to rebreathers (1.3 bar). If you're breathing 100% oxygen for decompression, that's a completely different story and not something a recreational divers will do.

by cess11 1y ago

hermitcrab 1y ago

Diving on normal air, oxygen toxicity occurs around 60m. Are you sure you aren't talking about Nitrogen narcosis ('raptures of the deep')?

bonzini 1y ago
Yes, 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 ago
Got the symptoms wrong, but oxygen toxicity is also present from 25 meters down.
- hermitcrab 1y ago
  Have you got a reference for that?
  - cess11 1y ago
    E.g. https://dan.org/health-medicine/health-resources/diseases-conditions/oxygen-toxicity/ https://dan.org/health-medicine/health-resources/diseases-co....
    - hermitcrab 1y ago
      I don't see any thing that supports "when diving with compressed air most people get woozy and otherwise intoxicated from oxygen around 30 meters from the surface".
      - hermitcrab 1y ago
        It does say: "Be aware that oxygen toxicity is unpredictable. Divers have experienced convulsions at shallow depths under conditions where most experts would not have expected them to occur." But that doesn't say what depth, what oxygen % and how often it happens.
        bonzini 1y ago
        It also says that oxygen toxicity is a possibility only above 21% oxygen. In fact, with regular air there are way too many things that have already gone wrong if you are at 65 m depth (or even 50 m). It's clear from reading the document that convulsions at "shallow depths" refers to the case of breathing 100% oxygen, where 1.5 m difference is the difference between <1.6 bar (safe) and >1.7 bar (absolutely not safe).
- bonzini 1y ago
  Not with 21% oxygen. 25 meters is 3.5*0.21=0.73 bar of O2 partial pressure, which is within even the strictest limits that apply to rebreathers (1.3 bar). If you're breathing 100% oxygen for decompression, that's a completely different story and not something a recreational divers will do.