Oleg, if you need any more info on the oxygen mask (RAF) then I am happy to help.
BTW, during the Battle of Britain, the RAF were using the type d-oxygen mask. This was made a wool, similiar to barethea, and the mask itself had no real self-sealing capability on the wearer's face (unlike the later rubber masks).
Now, if you are to model oxygen effects, then the next part becomes very important

Because the mask had no real sealing capablilities, a lot of the oxygen espcaped at the sides of the mask. In the event of a fire, if the pilot never turned off his oxygen then the mask would become a human-blow-torch, and the effects of this really speak for themselves; this was the fate of many BoB RAF pilots.
My question to you is, could SoW model this feature? It wouldn't be pretty, but it would be extremely realistic.