[Mark Scott-Simons]

In hospital they have different methods of delivering oxygen mask, nasal tube, tent etc each give different FO2 eg a nasel tube gives, IIRC, FO2 of 40% ish.

As to exposure times diving increases your susceptability to CNS toxicity for reasons not completely understood but one of which, very relevant here, is exercise level. A seriously ill patient obviously is not doing any where near the exercise level of even a relaxed diver decoing on a blob.

Divers have had tox events at 1.2 Bar (Comex diver working) yet bent divers are regularly treated at 2.8 bar with an almost zero incidence rate in pots. Though some do report "fried" lungs as an after effect from the pulmonary effect.

As for pulmonary exposure, ppO2 of 0.9 bar for 24 hours gives a UPTD count of 1100 which is well within limits even if continued for a few days [OTU of 4000 produces in 50% of people a reduction in vital capacity of 50%, plus pain. IIRC]. Again the relaxed state of the patient would increase their tolerance. The patient once taken off a mask would probably be suffering some effects from the exposure including pain and decreased breathing efficiency but as they are stuck in bed and probably on pain medication these side effects are very acceptable especially given the alternatives - seriously ill or dead.

Its possible your friends didnot realise the effect that being at pressure and underwater has on the sport and commercial diving fraternities. Toxing is often fatal underwater and is not uncommon whereas its very possible your friends wont have seen an OxTox event. Plus finishing a dive with lungs fried from pulmonary effects hurts. And for people doing this for fun or work is unacceptable.

So bottom line we have different degrees of acceptable exposure cos we are after different experiences.

Scotty

Edit: missing 0 in "OTU of 4000 produces in 50% of people a reduction in vital capacity of 5%, plus pain. IIRC" 5% -> 50%