1. #1
    Forum Member
    SCOOBY14B's Avatar
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    Sep 2001

    Default Need some information please - have searched

    Was involved in a rescue from a below grade pit used for dead chickens. We utilized structural gear and SCBA's. We had two victims, one lived, the child didn't. After the event our gas meter arrived and found the following. O2 was at 11.6%, CO 58%, LEL 3. That's the only information I have.

    My questions are:
    Can anyone point me to the resource that shows/ ot tell me at what levels of oxygen defficiency does the body react?

    Also, any ideas what was in the pit causing the LEL of 3. We were guessing Methane and Ammonia at least from the dead and decaying chickens and maggots in there.

    Any help would be appreciated.


  2. #2
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    Lewiston2FF's Avatar
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    Mar 2000
    Niagara Falls, NY, USA


    I got this info from the Chemical Hazard Investigation Board web site. ( http://www.csb.gov/news_releases/doc...#548,4,Effects of Oxygen Deficiency on the Human Body )

    % O2 Concentration Results
    20.9 Normal
    19.0 Some unnoticable adverse physiological effects
    16.0 Increased Pulse and Breathing rate, impared
    thinking and attention, reduced coordination

    14.0 Abnormal Fatigue upon exertion, emotional upset
    Faulty coordination, poor judgement

    12.5 Very poor judgement and coordination, impared
    respiration that may cause permanant heart
    damage, nausea, and vomiting.

    < 10 Inability to move, loss of consciousness,
    convulsions, death.
    Shawn M. Cecula
    IACOJ Division of Fire and EMS

  3. #3
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    SafetyPro's Avatar
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    Dec 2003
    Santa Cruz, CA


    This is the table from the confined space entry training I used to do at my last job. Don't remember where the numbers came from...think they were in the training materials I got from my predecessor.

    19.5 % - Minimum acceptable oxygen level.
    15 to 19% - Decreased ability to work strenuously. Impaired coordination. Early symptoms.
    10 to 15% - Respiration increases. Poor judgment, loss of coordination, fatigue. Lips blue.
    8 to 10% - Mental failure, fainting, nausea, vomiting.
    6 to 8% - 8 minutes - fatal, 6 minutes - 50% fatal, 4-5 minutes - possible recovery.
    4 to 6% - Coma in 40 seconds. Death in minutes.

    Interesting side note, CPR using mouth-to-mouth supplies around 15% O2, so you can see why its not a great choice (aside from the health risks).

    One thing to keep in mind is that most flammable gas meters will NOT give an accurate reading in low oxygen atmospheres. The LEL sensor requires a certain amount of O2 to function, so if the O2 level is low, your LEL reading may be off significantly.

    Would also have been interesting to see what the hydrogen sulfide (H2S) level was. Most people only consider H2S a hazard with petroleum products, but its actually a common byproduct of decomposition too, and it could contribute to the LEL reading (though would take a relatively high concentration to do so).
    Chris Gaylord
    Emergency Planner / Fire Captain, UC Santa Cruz FD

  4. #4
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    Farmun's Avatar
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    Jun 2005


    First off, GOOD JOB! You handled the situation the right way...with an SCBA. Many firefighters have died in confined spaces over the years due to a lack of SCBA's.

    When it comes to your LEL reading there are a few other things to consider.

    First of all our monitors (and most others I have used in Pennsylvania) are calibrated to read a percentage of the maximum allowable atmosphere per OSHA which is 10% of the LEL. Therefore if you monitor is reading 99% then you are dangerously close be at 10% of the LEL. You must be at 100% (or more) of the LEL for ignition to occur. It is true that some types of monitors will read poorly in oxygen deficient environments. However, some new types will still ready accurately.

    Your CO reading should have been in parts per million instead of a %. CO is produced by incomplete combustion so I am unsure why you would have any CO present in this space. Vehicle exhaust maybe? However, 3ppm is a very low reading and some older monitors will bounce around between 0 and 5 all the time.

    It was the low oxygen atmosphere that would have been the killer in your scenario. Coincidentally, that is the culprit in most confined space FF and civilian deaths.

  5. #5
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    Jun 2005


    As SafetyPro points out interesting about the H2S. CO sensors are cross sensitized by H2S and vice versa. Your 58ppm CO may infact be H2S, ie CO 0ppm =~100ppmv H2S in the same way 3ppm on a H2S sensor can be up to 125ppm CO. If time permits and it rarely does gas tubes may help to answer this as their prelayering and colour change help to reduce or highlight this interference. Good work with the use of BA.

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