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Thread: Low O2 Levels

  1. #1
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    Question Low O2 Levels

    Looking for some help with a recent call we had. Here is the scenario:

    Called to a single family dwelling for an odor of gas. Told by occupant that Gas company at residence earlier in day, unable to locate a leak. Crew began monitoring residence with 4 gas meter, at top of steps to basement 02 reading dropped to 19%. Crew donned SCBA and re-entered house and went to basement where O2 reading was 11%. All other readings (LEL, CO, H2SO) reading zero. Crew unable to locate anything unusual in basement. Readings confirmed with 2nd 4 gas meter.

    Other details: Brand new house (2 years old), sump pump in basement, weather at time heavy rain/wind.

    Crew ventilated basement with electric fan and after 20 minutes O2 level up to 20.9 %. Re checked residence after 90 minutes, O2 still at 20.9 %.

    In the absence of any other readings (CO, LEL, H2SO) anyone have any thoughts on what would have displaced the oxygen in this situation ?


  2. #2
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    Was the LEL reading 0 at the top of the stairs as well?

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    Forum Member GTRider245's Avatar
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    No idea what it could have been, but I do believe if you had a meter with a PID installed you more than likely would have picked up something on the VOC reading. SOMETHING was there displacing the O2, and it seems that you guys removed it.
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    Is the home heated with propane? I would think that even in a low O2 situation the LEL would have read something. Propane obviously could settle in the basement and displace the O2. A bad back up battery for a sump pump can give strange results on a 4 gas (usually high CO) but the smell would give it away.
    If it were a business like a fast food place I would looktowards a CO2 system, but in a home again that is unlikely. Since ventilation returned the air to normal I agree something was there.
    What was the weather like outside? could something been forced into the home from outside?

    Keep us posted, very interesting.

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    Quote Originally Posted by ADSNWFLD View Post
    Is the home heated with propane? I would think that even in a low O2 situation the LEL would have read something. Propane obviously could settle in the basement and displace the O2. A bad back up battery for a sump pump can give strange results on a 4 gas (usually high CO) but the smell would give it away.
    If it were a business like a fast food place I would looktowards a CO2 system, but in a home again that is unlikely. Since ventilation returned the air to normal I agree something was there.
    What was the weather like outside? could something been forced into the home from outside?

    Keep us posted, very interesting.
    Our department has ran into the CO2 issue twice in the last few years with a local resturaunt. But like you said, not likely in a residence. My first thought was VOC because of the lack of an LEL, confirmed with two meters.
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    Was there an A/C or air to air heat pump? Its possible the refrigerant may have leaked.out, displacing the oxygen.
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    Forum Member GTRider245's Avatar
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    Ok, called a fellow hazmatter and we discussed this. He reminded me of the formula to figure out just how much of this mystery gas you had in the area.

    Your inital O2 reading was 19%, roughly 2 % below normal. 2% of O2 is equal to 20,000PPM displaced.

    Being as O2 is 20% (rounded down for math's sake) of the total atmosphere, you multiply the 20,000PPM of displaced O2 by 5 to find out how much mystery gas you hand in the atmosphere. This gives you 100,000PPM of something else there.

    What it was is the question. Any old appliances in the basement? Drains that may have been leaking something? Sewer gas would be a go to, but you say you had nothing on the H2S sensor.
    Last edited by GTRider245; 11-07-2012 at 06:03 PM. Reason: Typo
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    This is absolutely fascinating. The bad part is that I bet nobody ever figures out what it was.
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    Was the house equiped with a radon sensor? Displaces O2, No LEL, Odorless and would not show up on a 4 gas CGI.
    Last edited by Trkco1; 11-09-2012 at 10:06 AM.
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    Quote Originally Posted by Trkco1 View Post
    Was the house equiped with a radon sensor? Displaces O2, No LEL, Odorless and would not show up on a 4 gas CGI.
    You know, I wondered about radon, but I couldn't imagine a house having a level so high that it would significantly displace oxygen. Per GTRider's calculations, 100,000ppm of radon?? Holy crap.

    But to find out, I did a bunch of research and discovered, first, that radon isn't measured in ppm. I tried to convert but didn't get answers that made sense. Suffice it to say, I think it would have to be an inSANE amount of radon to displace that much O2.
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    how about the idea of going back on a perodic bases, say over a month and a half or so, and seeing what readings you get???

    also, see if they have smelled any more odors???

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    This incident reminds of one I confronted some years ago...... in my office! While working as assistant emergency manager and hazmat coordinator, I had an instrument salesman stop by to demo his product (4 gas meter). While chatting about the wonderful things his instrument could do for me, he allowed the instrument to go through the warm up checks. When the instrument completed the operational check, the instrument went into alarm, indicating an O2 level of 18.5%. IN MY OFFICE!

    We took the instrument outside, shut it down, and powered it back up. The outside O2 level was 20.9%. On the trip into the building and to my office, the O2 levels lowered, stopping again at 18.5%. My office was in the basement of an old hospital; the basement housed the entire emergency services department. Everyone was booted from the basement and the FD was called to ventilate and help us find the problem. Prior to ventilating and during the two other times the instrument was in the building, no problems were indicated with the other 3 instrument sensors (LEL, H2S, and CO). A second instrument was used and confirmed the low oxygen level. Ventilating the building for nearly one hour(lots of square footage) brought the oxygen levels back to normal. We never discovered what the problem was.

    The basement housed the facility emergency generator; the generator was powered by diesel and hadn't been operated in the several days prior to the identified problem. Also, several diesel powered ambulances would idle near a basement doorway. The basement was the lowest area of the building. That problem still comes to mind when I'm conducting atmospheric monitoring classes.

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