Testing your air before you dive

[IrishPaul]

When I used to change toxic gas bottles wearing SCBA, we used to put on our gear one at a time, and breathe for 30 seconds while a buddy watched. This way, if someone collapsed (if the air line was connected to a pure N2 source, or if the air was otherwise bad), there was someone to help.

There was an an incident many years ago when someone had been breathing pure N2. He passed out and died.



Before I dive, I usually breathe thru the regulator for 30 seconds or so, and ensure that I am not dizzy etc.
I do this since I do not know what is in my tank as I don't fill them myself.

Is this overkill? I see many divers just take a quick breath or 2 then dive straight under.

 

[Mopar]

I would say you can not be to careful. I am guilty of the 2 or 3 quick breaths. I assume that if I had bad air I could taste it. I could be wrong I am curious what the true answer is.

 

[DivemasterDennis]

I think it's a very prudent practice and intend to extend my current 2 breath habit to 5 breaths. Thanks for the suggestion! While a breath or two will detect odor or taste of some contaminants, there are many that are odorless and tasteless. I learn something new on the board all the time. This is today's lesson!
DivemasterDennis

 

[emoreira]

It depends on the installation. If the LDS fills the tanks with a compressor powered with a gas engine, you have to look to where the intake is, the integrity of the hose, the relative possition regarding to wind (if possible). If the compressor is powered with an electric motor, it's simpler. You cannot asses the status of the filters, but in any case, if the air has traces of oil or CO, 30 seconds seems not enough time.
In the majority of the LDSs, it near impossible to have a scuba tank with 100 % N2, as it's not available.

 

[JahJahwarrior]

As others pointed out, there are only a few gases you'll find at most dive shops:
oxygen
78% nitrogen
helium
argon
carbon monoxide (small amounts, not 100%)

Because most dive shops don't blend air by mixing oxygen and nitrogen, but by compressing air, you are unlikely to end up with more than 78% nitrogen.

Helium and argon are dealt with at 100% concentrations but typically at lower pressures than 3000 psi, so it's unlikely you'd end up with a tank that read 3000 and was 100% helium or argon. Helium is pretty noticiable...take a breath and ask your buddy if he is ready. If he giggles, then you've probably got helium in your mix Argon, not so much that I know of, but it's also less used than helium even.

Carbon monoxide is a risk because it's formed by gas engine compressors and can easily be introduced if the air plumbing isn't done right. It's odorless and lethal. Fortunately, it's also not a very common risk.


Breathing at the surface is a good tactic. Because many of these gasses aren't going to be present in high enough concentrations to cause you to pass out immediately, if at all, you might not catch them in 30 seconds on the surface. If at any point underwater you start to feel odd, it's prudent to share air with a buddy. If you start feeling better, it might be your gas. If you keep feeling bad and you both got fills at the same place, it might be your gas. Either way, no point to continue a dive if you feel bad or odd.

Always always always always always always ALWAYS without exception ask to see the latest compressor results at a dive shop that fills your tanks. If it's more than 3-4 months old, think about going to a different shop.

Ask if the shop has a carbon monoxide monitor, either inline with their fill station, or as a hand held unit for you to check your tank. Ask if they'll show you their fill setup. Count the number of filters, more is better. Ask how often they change the filters. Look where the intake is, see how much care they take when filling.

Even if you get air, ask if you can use their o2 analyzer to check the mix.

 

[spectrum]

Knowing that some dive shops will have oxygen, helium and argon in addition to air it's hard to call this a bad idea. This potential combined with the range of fill station skills makes for a nearly compelling case.

While many errors will show up in 30 seconds of breathing it's good to note that a less obvious concentration of contaminants may only become apparent when breathed at multiple atmospheres.

Pete

 

[Searcaigh]

Where I pick up my Nitrox we always do a check and sign off in a log. I also got into the habit of using my own O2 analyser on my air tanks.

Generally I initially breath off my reg to check that my gas is turned on, so an additional extra few breaths to taste the gas is not a bad idea

 

[Darnold9999]

The only caveat to all of this is that in cold conditions breathing that much from a reg out of the water is not a good idea.

 

[SandyRobinson]

I test all of my tanks for O2 and CO. For OW dives, I take a couple of breaths off my reg at the surface. For overhead diving, I take about 4-5 breathes on each reg/tank at 1 foot or so.

 

[faster7581]

I only dive nitrox, and I test them when I pick them up after a fill.. I take 2-3 breathes to verify my air is on.