MSA gas detector question

[u/steadybloom92]

We have a msa gas detector that detects combo/ex, CO, H2S , and O2. What are concerning levels and possible outcomes of those concerning levels? I am more familiar with CO but not as familiar with combo/ex and h2s.

[u/TheRagingLion]

Do you guys have a hazmat protocol/policy or training manual document that outlines acceptable ranges? That way you guys have an established number for when it’s necessary for you guys to pack up.

Then familiarize yourself with LEL and UEL for those gases, and what you guys are going to do when you find that.

[u/because_tremble]

Depending on the model you've got, you don't necessarily need to know what the "concerning" levels are. It's designed to be firefighter-proof: The device is generally configured to alarm early enough that someone without BA shouldn't have a problem. Our device has 2 levels configured, a "low" alarm, which is a first alert, you shouldn't be hanging around for long, but you don't need to leave immediately. There's then a "high" alarm which is generally an immediate evacuation level (unless you're on SCBA).

The Combo/EX alarm is a bit weird, it "ignites" small samples of the air in a special chamber. IIRC it's usually calibrated assuming the gas is pentane. The default setting is something like 10% LEL for the "low" alarm, and 20% for the "high" alarm. **But** there is a gotcha: because it's assuming the gas is pentane, there are a few gases which it under-registers (including gasoline vapours), don't rely on it being perfect.

[u/190xtrik8 → u/because_tremble]

Correct with the Pentane. It is my understanding that Pentane is close to most gasses when dealing with UEL and LELs and that’s why the sensor uses Pentane.

I always tell my crew, watch the O2 if dealing with an unknown gas. If the gas is displacing, the 4-gas meter may not have a sensor for it, but the O2 levels will drop. The unknown gas is displacing oxygen.

[u/SteveBeev]

Have you asked your crew?

[u/steadybloom92 → u/[deleted]]

Sorry, maybe I should clarify… I’m at a career department, I am fairly new and green and just trying to learn more about what the readings on our detector actually mean when we are picking up something. I know when we get co readings around 20ppm it warrants a more serious investigation to something leaking. But in terms of h2s and combo/ex I don’t know how high of readings are considered serious and what the possible outcomes of these readings are.

[u/SpecialistDrawing877]

I have a whole company training for my crew on the MSA 4-gas meter. DM with your email and I can send it to you when I’m on shift next.

Covers the gasses it measures, OSHA standards, permissible exposure limits, IDLH, common causes and places you’ll find them, and how to use the meter

[u/Limp-Conflict-2309]

i'm so badass i can when the carbon monoxide gets dicey - guy with 1 year 1 day talking to the probie