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Thread: Fire and Gas Mapping study

  1. Smile Fire and Gas Mapping study

    Dear Friends,
    Can any body put light on "Fire and Gas Mapping Study "
    I am looking for its methodology, Report or specific guidline on it.

    Thanking you in advance,

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  3. vp,
    CFD is used for mapping studies wherein the numbers or safetty, are high enough to warrant it.

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    • Agreed that CFD is used for F&G mapping using 3D model of plant. The basic which i understand is that , using CFD or PHAST prepare the flash fire extent, Gas cloud extent on the plot plan and then study where to place your detector.
      Now my worries are
      1. what kind of scenario's should be considered (leak-various hole sizes, ruptures etc)?
      2. What Cocentration is to be looked for in dispersion ( LFL, 25% LFL, 50% LFL etc for TOXIC 10ppm etc)

      This is where i am confused , and need some guidance on it.


    • CFD is one methodology that can be used, there is another methodolgy that determines a generic cloud or a specific cloud based on process conditions. For Plant installations, alarm levels typically depend on the Site requriements, typically a site may have a preset global alarm level setting of 40% for gas as having different alarm levels in different zones may produce confusion.

      Alarm levels are at the sites discression although levels will apply company wide (with exceptions), toxic values can also vary - although the current trend to detect 10ppm everywhere is nonsensicle, there are point detectors that can detect 10ppm, but typically point detectors require direct impingement in order to register, given the probability of release direction and impingment, point detection (although all we have atm) is not very good at detecting leaks. Toxic LOS detection is becoming a little more widespread and may provide great assistance in detectability, yet cost is the concern. But even these are being subjected to very low levels of detection, which is very hard to achieve in TDLS devices without controlled cooling and a price tag.

      back to the OP....
      typically detection is based upon the process conditions, generation of cloud sizes can be determined with software applications for this sort of thing, with the PFDs for a given zone/area in mind
      typically detection is based on a precentage visible of a predetermined fire size, the percentage visible is based on the manufacturers detection settings

      3D models can be used for gas and for proper detectability - flame (2D flame mapping is worthless imho) although gas is typically an accumulation model which removes the need for complex and lengthy calculations in CFD software


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      • Vinod,
        For this kind of study you should use 20% LFL, 50% LFL
        since for fire/gas detectors the first alarm is usually at 20% of LFL.


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        • #6

          I worked for developing such study,basically we used QRA report for it.
          It depends upon size of leak small bore or full bore with it disperssion cloud as determined in QRA based upon Weather conture


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