1. #1
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    Question Natural Gas Monitoring

    I would like to know what everyone's procedures / preferences are regarding air monitoring at natural gas leaks. Specifically, a leak outside, what criteria is used when determining evacuation areas. Is it a sepcific % LEL, Proximity from leak, something else???, Thank you for your information.

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    Default

    As a rule of thumb here in the Houston area is : 20% LEL outside and 10% LEL inside a structure or space.

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    Default Re: Natural Gas Monitoring

    This is a difficult question to answer with the limited information provided. I would want to know is this a residential, commercial, or industrial setting? What is the source of the leak, where is the source in reference to other buildings or outside processes? What are the weather conditions? What is the lay of the land? Without ,at least, this baseline information one can not make a informed decision regarding evacuation distances as it really is a dynamic decision vs. a static one.

    In regards to %LEL, all monitoring devices alarm at 10% of the LEL by default. Regardless of location if you find yourself in an atmosphere that has reached 10% of the LEL you should back-out and find some way of bringing the atmosphere below this level, i.e. removal of source, engineering controls, etc. Reason? Due to the nature of gases it is extremely easy for you to be in an atmosphere that is say 10% LEL, walk several feet in any direction and then you find yourself in 100% LEL.

    Chris DePaola, CHMM

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    I am mainly thinking about gas lines hit underground in residential or light commercial type areas, I also understand that the situation is dynamic and needs to be evaluated on a case by case basis. Do you use %LEL readings to determine your evacuation area? If so, say you did not have %LEL monitoring capability then what else could you use to create a safe evacuation area while not going way overboard. I also have understood that 20%LEL is the standard for an outside gas leak, and 10%LEL for an enclosed area. My issue here is my department recently took away all of our LEL monitors. We have no good monitoring equipment and it seems sometimes the decision makers base their evacuations off of smell, which to me is a huge mistake. My veiw point is that natural gas outside is not really that dangerous and we sometimes over evacuate with no basis, but natural gas in a structure is a big concern and evacuation area around +10%LEL building should be significant as there is a concern for explosion. Just some rambling thoughts, tell me what you think.

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