Gilldiver
Contributor
If you are at say 90 feet and have to do an emergency assent - you are just out of air and no one is around - go for it. Any gas is better then water and hurt on the surface I can do something about - dead on the bottom is only a body recovery.
Do not try to breath into a BC - you just don't have to.
If you had say 8 pounds of lift at 90 feet when you start heading up in your BC, you have a bit over 1 gallon or just about 4 liters of gas volume. As you ascend that volume will expand - you should do the math P1 x V1 = P2 x V2
But for ease of this example, lets say it will expand 3 time by the time you reach the surface. So, you will need to vent at least 2 gallons or 7 liters of gas from your BC. All you are doing is venting some of this amount through your mouth and out your nose. As for O2% - remember, you are not breathing into the BC as you are venting from the BC and the O2% will always be the same as what you had in your tank.
Last, remember in an emergency assent you are not doing 30 or 60 feet per minute - you will be doing 120 to 200+ feet a minute.
Someone will also probably bring up the possibility of a lung infection from any critters in the BC's bag - So what - infected on the surface is still much better then dead on the bottom.
Do not try to breath into a BC - you just don't have to.
If you had say 8 pounds of lift at 90 feet when you start heading up in your BC, you have a bit over 1 gallon or just about 4 liters of gas volume. As you ascend that volume will expand - you should do the math P1 x V1 = P2 x V2
But for ease of this example, lets say it will expand 3 time by the time you reach the surface. So, you will need to vent at least 2 gallons or 7 liters of gas from your BC. All you are doing is venting some of this amount through your mouth and out your nose. As for O2% - remember, you are not breathing into the BC as you are venting from the BC and the O2% will always be the same as what you had in your tank.
Last, remember in an emergency assent you are not doing 30 or 60 feet per minute - you will be doing 120 to 200+ feet a minute.
Someone will also probably bring up the possibility of a lung infection from any critters in the BC's bag - So what - infected on the surface is still much better then dead on the bottom.