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Will, this 2 percent problem is not too bad when you are partial pressure mixing for middle readings, like 35%, for example.You have the double check of the partial pressure and the reading, and the use of the gas is not a problem from either a toxicity or a decompression standpoint. Where this gets tougher is maxing the real deep mixes, but then the partial pressure still applies and the totals are still valid. You can start to see where the rebreather becomes a problem, however. The big trick is to be sure you actually added the gases in mixing ,and did not have a valve off while you THOUGHT you added 35 psi of oxygen, or some such number, when in fact you did not, and then the miniox reading seems "acceptable". A real good anal way of doing this proceedure is what is necessary to get it right. Bill Mee and I do it together, and we have a whole checklist to go through before disconnecting the tanks, and in the whole process. Adding oxygen to a high helium mix can feel like yoiu are adding it when youi are not. Just presurizing a big fill line fr9omt hat pressure to a small increment higher, even with a very accurate digital guage is a fooler since you can hear the gas moving even when the tank is not in fact open to accept it - a real dangerous situation. You have to depressurise the line afterwards and note the tank change on the same guage that the system was on to begin with , and you must do it quickly. There is no way the pressure has risen without the addition, even if the number is thrown off by the cooling - it can not decrease. Little double checks like that , and then immediately throwing the analyzer on the result will give you some comfort. The go and throw it ont he pure helium to be sure it is not offset. A lot of work, but you are always betting your life with this stuff. William M. Smithers wrote: > > On Thu, 13 Nov 1997, Jim Cobb wrote: > > > Julian- > > If you are worried about it, throw in a 5% safety factor instead of a 2% > > saftey factor, which is what we do when mixing in adverse conditions. > > You know, how many of you guys have actually read your MiniOx I manual? > +-2% is what the sensor is good for. That's 4% total, which > is either pretty scary, or pretty indicative of the default conservatism > that's built into modern tables and deco algorithms. > > The fact that it also quotes such potential "skew" factors > as 0.000X% for a Helium component is *such* a joke, in light > of the overall precision. > > -Will > > -- > Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. > Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'. -- Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'.
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