[Drmike]

Quote: (Originally Posted by UKSteve)

Must play havoc with the p-valve catheters!!!

S.

yeh its a bugger trying to get them off afterwards

[AM]

Oh dear! Only just back and already I've lowered the tone!

So, out of interest, do the courses nowadays teach anything about O2 flushing on decompression?

Regards
AnneMarie

[RichClark]

Quote: (Originally Posted by am)

Oh dear! Only just back and already I've lowered the tone!

So, out of interest, do the courses nowadays teach anything about O2 flushing on decompression?

Regards
AnneMarie

Yep, but I guess it many depend on your instructor.

[AM]

Yes, fine point, fine point.

Which reinforces the need for quality control on the courses, so every student should sign a "checklist" of items that were covered so if your instructor is a wrong 'un you can spit in his pint ROFL

[PCDiver]

Quote: (Originally Posted by am)

Yes, fine point, fine point.

Which reinforces the need for quality control on the courses, so every student should sign a "checklist" of items that were covered so if your instructor is a wrong 'un you can spit in his pint ROFL

Interesting point AM, but I see some problems. Who is going to create and validate the checklist?

Many items on that list will fall into the catergory of "best practices". The problem with that is that they might be "best practices" for some but certainly not for all.
A couple of examples:

• heliox vs trimix
• diluent switches on CCR
• air breaks
• alpinist, semi alpinist, full bailout
• PP2 levels (1.0, 1.3, 1.6)
• hot diluent vs 1.0 PPO2 diluent

[AM]

A basic checklist would be a great start - things that were covered:

Current limiting
Bailout
CCR maintenance

Etc etc etc. OR cover the general subjects of flushing etc and both schools of thought, because there is no hard and fast right answer to a lot of this stuff.

But yes, as you say, a percentage of it is "best practice" so we're back at the standardisation approach.

OR we need another course which covers Rebreather Fundamentals!!!!

[Joe]

The real problem is that O2 is a lung irritant and on long exposures it compromises their gas exchange capabilities. Anecdotal evidence seems to indicate that inert gasses in the decompression gas (loop in this case) has no ill effect. Many, including myself, would routinely put He in their OC deco gas and not account for it in the tables resulting in what felt like a cleaner deco. Real or imagined I can't say.

On a series of long, deep exposures (300' for 60-70 min BT's) we had far better results lowering PO2's to 1.0 or less on the bottom and avoiding high PO2's on deco. Experience has shown (me personally - no science here) that He is far easier to decompress from and that it actually requires less time than N2 even though the models penalize you for it. I have done things on high He mixes (by circumstance, not by design) that would have undoubtedly resulted in a chamber ride were I on air. Maybe I was just lucky but there were others with me so I doubt it.

(Please note I am not advocating a cavelier attitude towards deco because you are on He. Only saying that when things go south it seems to be more versatile.)

Air breaks are good for several reasons. First, you give your lungs a rest from the O2 irritation, and second they minimize the risk of CNS toxicity.

Even if you balk at the CNS clock theory, the effects of Pulmonary toxicity when doing long decompressions are lessened which would enhance the "Oxygen Window" effect and result in a better decompression.

Disclaimer - I'm not a scientist by any stretch of the imagination. I'm just a diver. There are many who forgot more about the science of this stuff than I will ever know. I just know what works for me.

[PCDiver]

Quote: (Originally Posted by am)

OR cover the general subjects of flushing etc and both schools of thought, because there is no hard and fast right answer to a lot of this stuff.

That would be my preferred approach. The student is made aware of alternatives and has to pick what he thinks is best for him.