On Tue, 28 May 1996, Peter N.R. Heseltine wrote:

> No self respecting techhead will accept a limitation of a pPO2 of 1.4 ATA.

Either I have no self respect, or I'm not a "techhead" (the latter, to be 
sure), because I accept a PO2 limit of 1.4 atm - for bottom *AND* 
decompression.

Good points, good post.

> 4.  The EAD is calculated by assuming the FiO2 the at the MOD is
> calculated by subtracting *maximal* O2 consumption (2L O2/min)
> from the operational FiO2 (i.e., not including the contribution of any
> override) at the MOD, with all remaining gas considered nitrogen.

This *might* be overly conservative..especially for a dive whereon 
exertion never gets very high.  If you folled this rule strictly, I think 
you'd almost always find that OC nitrox is better than an active-addition 
SCR (which may well be the case, but I still think this might be too 
conservative).  Incidently,some of this stuff applies more to 
active-addition SCR systems than to passive-addition systems.

> So, now the real truth is out. Your EAD will actually be a lot deeper than
> you would have predicted from the equation for your nitrox used on open
> scuba. You're not just breathing from that nice little yellow bottle,
> your breathing your own nitrogen too from the bag. So your NDLs will be
> *shorter*.

If you want to be that conservative.  I probably would be, but I wouldn't 
necessarily try to impose that level of conservatism as a community 
standard. Perhaps a better community standard would be to require all  SCR
students to become familiar with their own O2 consumption characteristics 
at different workloads during the training course, using a special 
version of the rebreather they're being trained on that is equipped with 
O2 sensors.  The idea is that they would wear this modified SCR and do a 
series of drills at a series of depths and watch how the PO2 changes. 
That way, the students could all become familiar with these 
characteristics for their own bodies.



> 5.  The SCR must deliver a volume of gas at the MOD that exceeds the
> minute volume of the user by at least 10%.
> 
> Others may disagree, but I think this is *minimal* to blow off CO2.
> 

But isn't the CO2 being pulled out of the loop by the absorbent canister?

Aloha,
Rich

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