Functionaing with only 92% O2

Hey everyone,

I am taking off in April to hit the Truk Odyssey for a week for my 40th and they said they only have 92% O2. I am trying to figure out whether I should take my CCR or not. This trip is really why I originally bought and trained on the unit.

Does anyone have any data on how to adjust to the lower percentage safely? Can you calibrate under pressure or modify the Hammerhead settings somehow?

Thanks,

Bill

PO2 is PO2. With 92% ean you will not be able to get a 1.3 set point until about 46 fsw. So you may want to fly the unit at a set point of 1.1 or 1.2. I suspect you will be using Air as the diluent there so the nitrogen that is in the "oxygen" is insignificant.

Many PSA - Pressure Swing Adsorption oxygen generators can only produce up to 95% oxygen (balance inert) some as low as 88%.

If you ran a profile using EAN 92 and Air as a dill and 100% and Air as dill you will see there is virtually no difference in the decompression schedule.

Cheers

According to the June 2007 version of the owner's manual, the Optima HH (not sure about the other HH versions, but I assume they work the same?) will reject any cell during cal. with a mV less than 40. My three cells right now are about 6 months old and still return about 50ish mV in 100% O2; so nothing would stop me from calibrating with a low 90's% mixture; but of course this would play havoc with all subsequent calculations - solenoid firing, setpoint maintenance, PO2s, deco, etc.

For those not familiar with the Optima, the standard cal. procedure is to purge and fill the loop with pure O2 four times and on the last verify the mV readings, select 'calibrate O2' on the handsets (each separately as they are independent) and then that mV value represents 100% O2. There isn't any provision with the electronics to tell them what % the mixture really is. The new manual does describe the alternate option of putting the assembled sensor plate in a plastic baggie and flushing with pure O2, but again you're back to the supply issue.

FWIW the last paragraph of the 'CALIBRATION' section of said new manual does state "Although not endorsed by the manufacturer, alternate procedures for calibration can be found in an article published on REBREATHERWORLDdotCOM entitled Accurate PO2 Calibration. This article discusses hardware, procedures and warnings necessary to calibrate various types of Rebreather electronics using alternate oxygen concentrations and at altitude when not specifically ... by the electronics". Interestingly I just went and searched high and low for the article to link to it, but I can't find it. Mind you I am still on my first cup of coffee - does anyone else know where this article might be??

Sorry Joel I should have read the posts before my reply above, your "P02 is P02" is not fully correct IMHO in this particular situation also I would like to expand the general held belief of that "balance inert" comment.

IMHO in the rush to re "calibrate" we seem to have lost sight of the question. A 92% mixture from a PSA plant is also producing 4.5 to 5% ARGON it is only the balance 3% Nitrogen that is arguably "inert" to divers.

Further comments on an O2 Tox may be the product of an Argon tox hence why some diver feel tired or bendy on PSA produced gas when diving.

Some big aguments over here on PSA and membranes used in sports diving (mostly from me I'm afraid) but I hold that while 5% argon may have no effect in the medical enviroment, (At atomosheric pressure) there is little evidence on the effect 5% Argon has on divers other than damaging.
Iain Middlebrook

Ian fortunately, the deeper you go the lower the Argon percentage will be in the loop.. On each injection argon is being added, but as you go deeper, more of the loop "volume" is made up of the diluent gas.. As long as the diver flushes the loop periodically (more often when shallow) the argon% in the loop can be kept quite low..

The San Fran Maru is in 75m

Yeah right, think your depth gauge needs calibrating. it is 50m to the deck and about 40m to the top of the bridge. I went through the first two levels below deck and did not exceed 55m. It is a single tank air dive, if you can handle the waah waah effect

Andy

Randy, the narc'd thing is something to look at. If you are running your PO2 high you may be experiencing minor effects of ox tox (many of the signs and symptoms are similar to nitrogen narcosis). You mention task loading. Not really sure why you think CCR is more task loaded than OC diving. You may also be getting some breakthrough and getting some minor CO2 issues.

Try to get a better handle on that one the next time you go out.

Cheers

JDS

Hi Joel,

I would say that CCR is more task loading that OC for a number of reasons. Maintaining PO2 is one of the issues that comes to mind.

I don't really think that OxTox plays into the equation. I don't really tend to go for high PO2s at depth. I guess the CO2 is a posibiiity, but I have never really experienced break through that I am aware of. When diving CCR, I tend to keep my WOB under control.

I have spoken with several CCR divers that tend to agree with me on the narcosis issue. On OC, I can go at least a good 30-40 feet deeper on air with less noticeable narcosis. I'm not saying that there is actually less narcosis going on, but it definately feels different to me. For me, the task loading issue seems a logical issue.