Re: [PSUBS-MAILIST] Question about pressure compensation

[MerlinSub@t-online.de (Carsten Standfuss)]

Hi Thijs - imagine that in your (in this sample) very small battery box
are just 100 O2 atoms at 1 atms and 21 % PPO2 equal to 0,21. Imagine a
spark inside.. Nothing will happens. 

Now you dive and pressure compansate the box to a pressure equal to the
deep with air as compensation gas. Say 10 atmosphers with a P02 of 2,1
atmos. How many atoms 02 you have now close to the spark ? Right = 1000
atoms. 

The o2 Partial pressure in the Apollo-capsul which catch fire was below
1,0 atm. 

Thats is also the reason that in manned decompression chambers the
equipment is nonflammbale and everything which can create sparks is
strickly forbitten. 

Use argon or Co2 to compress the battery-compartment an it will be fine.
On the other side normaly you have no sparks in your battery
compartment...

On a manned dry ambient boat this can create a real risk. 
At a deep of about 47 meters you have a PO2 equal to the same boat on
the surface filed with pure oxygen ! (The same amount of o2 atoms in the
cabin..)

Another problem. A Po2 of 1,6 or more in the loop is a great risk for
rebreather divers ! To much oxygen (to much o2 atoms per square inch)
damage your lungs and body. This pressure is equal to 1,6/0,21 or 7,6
times 1 bar equal to a dive deep of 66 meter or 216 feet. 

If you want to ge deeper with the ambient boat you have to lower the
oxygen percent in the gas mix.. But thi gas mix has a to low PO2 on the
surface.. 

For that reason we will go in our diver lock out chamber with heliox gas
mixes with reduce PO2 mix if we go for greater deeps. And we chang the
po2 if we go higher or deeper. 

regards Carsten

> Thijs Struijs schrieb:
> 
> Bill and the rest,
> 
> Pressure compensation of battery pods and trusters with air seems the
> most simple and clean way to do it i think. It also has the advantage
> that you don't have to put a square battery in a bulky round box. But
> in a discussion on this subject a view years ago Michael Wludarczyk
> wrote that at higher pressure (300 psi / 200 mtr.)  the partial
> pressure of the oxygen (PPO2) becomes so high that there is a
> substantial fire risk. This is of course a lethal depth for an ambient
> sub but i want to go to 100 mtr. in an 1 atm. sub. Eigther i missed
> something during my schooldays or i simply forgot but PPO2 doesn't
> mean anything to me.  Is there someone on the list who can say
> something sensible about this?
> 
> Thanks,
> 
> Thijs Struijs
> The Netherlands




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