Home Podcasts THMG141 – Laser Methane Detectors

THMG141 – Laser Methane Detectors

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In this episode, Mike and Bob discuss a new tool for laser methane detection, which has been in the hazmat industry for a long time.

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Complete Show Notes

3:45 What are Laser Methane Detectors?

  • Like so many of our meters, laser methane detectors have their roots in industry
  • Originally a piece of large, non-portable equipment consisting of a laser source and a detector
  • Laser source and detector were placed in such a way that if a container (pipeline, cylinder, rail car, etc.) started to leak, the rising gas would go between the source and the detector and trigger an alarm
  • As with most technology, this basic technology became smaller and smaller until we reached today’s topic – the portable laser methane detector

7:25 How Do Laser Methane Detectors Work?

  • Each unit is equipped with 2-3 lasers
  • Visible light laser
    • Difference between 2 and 3 laser units depends on whether it has a visible light laser
    • This type of laser acts as a visual cue to see the end point and is also a distance calculator
    • Some detectors also use a screen similar to that of a thermal imaging camera – look through the screen and place a dot on the end target
  • IR laser
    • Methane has a very specific frequency and absorbs IR radiation, so one of these lasers will be set to frequency (most popular is around 3.3um)
  • Reference laser
    • Isn’t picked up by methane, so it passes through it unchanged
  • Note that some units split one laser and use it as a reference, but the idea is the same – one for spotting/distance taking, one for reference, and one to hit/be absorbed by methane
  • Keep in mind that the laser must always have something to bounce off of – if it doesn’t have anything to reflect off of, it can’t get the IR light back to the sensor

11:35 Example Scenario

  • We shoot the laser across the room – it encounters a cloud of methane and adsorbs some of the light photons
  • The rest of the laser moves through the cloud, hits a surface, and scatters
  • Some of the light makes its way back to the meter, and the differences between the two are analyzed
  • Detector gives us a reading of 500 ppm m.
  • Keep in mind that these aren’t point source detectors – they’re only seeing the total distance the laser travels and the amount of light absorbed by the methane during travel
  • We’re not measuring ppm in a specific spot like we would with a point source detector – instead, our reading represents the concentration through all the points in space the laser traveled (both high and low methane areas)
  • This means that instead of just saying “ppm,” we have to clarify that it’s an averaged ppm based on distance traveled

19:10 Operational Uses of Laser Methane Detectors

  • We are NOT using these meters to determine whether we’re in a flammable range
  • We use laser methane detectors in three different ways:
    • To determine if there’s methane present in a quick and safe way
    • To determine if our actions produced a difference
    • To triangulate where a gas leak is coming from (especially useful for underground leaks or leaks along pipelines)
  • As you can see, there are many uses for these meters, but we’re never using them to determine if we’re in an LEL

26:25 Pros and Cons of Laser Methane Detectors

  • Pros:
    • Can cover large open areas, reducing the time spent on searching for leaks, as well as manpower
    • Measurements can be made remotely, keeping team members out of harm’s way
    • Calibration is minimal, and drift is non-existent
    • Units respond almost instantaneously
    • No cross-sensitivity – methane lasers only pick up methane
  • Cons:
    • Only picks up methane
    • Corners really screw with readings, so make sure you’re not shining off of a corner
    • Can’t use in open fields since there’s no spot for the laser to reflect back to you
    • Unless there’s some kind of ceiling, you won’t get a reading outside above ground
    • Can’t be used for gauging flammability

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