using "hand-held" type O2 analyzers for deco mixes

[tursiops]

All of us have a breathable air tank

.....I dare say MOST of the traveling divers who show up at a boat or a resort do NOT have their own breathable air tank with them. And it is not a best practice to assume the tank of "air" you see sitting there is actually air, and use it to calibrate.

 

[fsardone]

.....I dare say MOST of the traveling divers who show up at a boat or a resort do NOT have their own breathable air tank with them. And it is not a best practice to assume the tank of "air" you see sitting there is actually air, and use it to calibrate.

Right!
Most have thermometers (wet bulb and dry bulb with tables to calculate RH or a dry bulb thermometer and an hygrometer) ...

Easier to calibrate in ambient and accept the error or use a bottle of air. Also you can use to check the ambient calibration.

cheers

 

[tursiops]

use a bottle of air

You can't trust it has air in it. Some places use the same bottle for air and nitrox.....a bit of residual nitrox is in the tank.
Seriously? Your own wet-bulb/dry-bulb? You're just being silly now. The temperature on your phone is plenty good enough...the calibration varies 0.1% for 6C temperature change.... Humidity? Guess. 10% change in relative humidity only affects the calibration by 0.2% at the most.
Even if you guess the temp and RH you'll be closer than simply ignoring it....

I've lost the bubble; are you going to ONLY analyze the tank if you can get to lab accuracies?

 

[fsardone]

Seriously? Your own wet-bulb/dry-bulb? You're just being silly now. The temperature on your phone is ple
I've lost the bubble; are you going to ONLY analyze the tank if you can get to lab accuracies?

I am Air Force physics of atmosphere is important so I do have (for fun) a psycromether What is a Psychrometer? but you are reading me wrong.

I am saying that you do not need to have such precision in analyzing a deco gas. Ambient air even w/o correction or a bottle of air would do and would not affect significantly deco or MOD. The question the OP asked about not using handheld to analyse deco gas due to lack of temp and humidity and pressure compensation is groundless. If you have table, approxx temp and humidity, be my guest and calibrate with the corrected content of oxygen, Ambient air pressure is no factor if analyzing and calibrating at same place/time.

Cheers

 

[EireDiver606]

As rjack and others said, as you go deeper, the compound effect of having a greater difference of O2 than what you think you have, gets more critically dangerous. If it’s critical at extreme depths, how do they measure it so accurately to not cause fatalities with a false O2 content than what you want?

At extreme depths like 300m, what is the method to measuring O2 content?

Also, at extremely insane depths like the NED use for tests like 1000m, how do they accurately measure O2 content there?

Very interesting subject.

 

[fsardone]

Well there are high precision analyzers like the following:
Portable Oxygen Analyzers from 0.1 ppm up to 100% oxygen GPR-1000, GPR-1100, GPR-2000 & GPR-3500 MO | AII Inc
You can reliably measure from .1 ppm to 100% oxygen.

Now forget about scuba diver shop prices.
People doing very deep dives need to think about the precision of the analysis in order to avoid the mistakes Dr Deep made in planning his gases.

If diving in a normal range (like up to 100 meters 330 feet) were most of the rec reb stay within wob for certification using heliox, you are pretty safe with galvanic cells analysis.

 

[RainPilot]

Also, at extremely insane depths like the NED use for tests like 1000m, how do they accurately measure O2 content there?

You can order gases from laboratory supply places. The higher the precision, the greater the cost, generally. IIRC they blend those gases by adding according to molecular weight rather than by pressure. Requires a pretty precise scale system. They are also made by adding together O2, N2 and He in their pure forms rather than air plus oxygen and helium.

 

[mderrick]

Some of that DGX tektip could use deeper explanation but it was starting to be an article and not a brief tip... always the danger in generalizing and simplifying a complex topic.

The major issue is NOT the accuracy of equipment for the handheld vs technical models, they all basically use the same galvanic sensor technology. The issues are that in our extensive experience watching and dealing with people analyzing cylinders is their poor technique setting up and doing the analysis. The technical analyzers offer multi-point automatic calibration that's better at detecting and rejecting sensor issues, and have flow limiters. The low cost handhelds in general are more sensitive to calibration errors, very sensitive to sampling technique (some are much better than others). In years of watching divers in shops analyze gas I've seen some incredible errors in performing analysis. Offering many different types of analyzers to divers for their selection and use in the shop has demonstrated to me that divers will consistently get better answers using a technical over an inexpensive hand-held.

Can I get an very accurate analysis with a low-end handheld? Yes, I have and I can, so can many others. But as a general rule, it's also more likely that the typical diver will get a more accurate result using a better analyzer.

 

[rjack321]

As rjack and others said, as you go deeper, the compound effect of having a greater difference of O2 than what you think you have, gets more critically dangerous. If it’s critical at extreme depths, how do they measure it so accurately to not cause fatalities with a false O2 content than what you want?

At extreme depths like 300m, what is the method to measuring O2 content?

Also, at extremely insane depths like the NED use for tests like 1000m, how do they accurately measure O2 content there?

Very interesting subject.

You would never use a galvanic sensor when tiny fractions of a percent are the difference between life and death. A mass spectrometer is a much more precise tool used for analyses like that. That would be after mixing the gases by weight in the first place so you already have very high confidence in the expected mix.

 

[Manatee Diver]

So at what point should one get an expedition grade analyzer? Trimix? Advanced Trimix? When one starts to push even deeper?