Home LMS THMG156 – Chemical Agent Monitors, Part I

THMG156 – Chemical Agent Monitors, Part I


In this episode we review a few of the technologies that are out there. Some are out of service, some in and some coming into vogue. We discuss the good, bad and ugly of each one. 2 part series!

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(2)  Chemical agent monitors (CAMs)

    1. There are a few meters that land in this category. Well, there is more than a few basic technologies behind them.
    2. While technology is always changing and by the time you hear this there maybe be something new or better out there, we going to highlight the basic once and give a quick overview of them. We are giving brands as examples not to push their product.


  • Tims for flame spectroscopy
  • What are they?
  • How do they work?


        1. What are there capabilities?
          1. Does a pretty good job of picking up phosphorus and sulfur bonds
          2. Instant results and clears fast
        2. What are there limiting factors?
          1. What makes them great can also limit them. It can only pick up a select few bonds
          2. It’s not telling you a specific chemical is in the air, just something containing the bonds. Which depending on how you look at it can be good or bad i guess.


  • APD2000/cam/chempro/chemRae/Raid-m and Raid-m 100 for ion mobility spectroscopy
  • What are they?
  • How do they work?


        1. What are there capabilities?
        2. What are there limiting factors?
          1. Lots of false alarms.
            1. When it ions things that are coming in it does it in a way that is non-discriminatory. So basically if it gets into the drift tube and happens to have the same mobility time as a chemical agent the detector is going to see that as a chemical adjacent
            2. As these get smaller their ability to have shorter drift tubes decreases there sensitivity and causes more detection interference
          2. They are affected by things in the air like temperature and moisture
            1. The humidity can actually affect the formation of the ion and produce totally different time runs.
          3. They can over saturate and take some time to clear out.


  • Haz cad plus, Surface acoustic wave
  • What are they?
  • How do they work?


        1. I am going to be totally honest with you. I don’t really know how this works. I study physics and chemistry and I can’t grasp how this works.
        2. We have two plates that are coated with a polymer. This polymer is chemically selective.  So here are the words right out a manual. The SAW operates when an alternating voltage is applied to the input transducer generating an alternating mechanical strain (tension or compression) that initiates a SAW that travels along the surface of the substrate before being converted back into an electrical signal by the output transducers. Hence the two major processes which contribute to the detection of CAs with a SAW device are the generation and change of surface waves on a piezoelectric crystal plate and the sorption/desorption of chemicals on the surface. For these SAW devices to selectively detect targeted chemicals, the propagation path of the acoustic wave is coated with a selected polymer substance. This is because the piezoelectric crystal itself does not have the ability to attract and sorb target chemicals. A thin layer of the polymer substrate is normally chosen as polymers have many free, active sorption sites that can effectively sorb the incoming chemical molecules. Sorption is thus defined as the simultaneous adsorption and absorption of a molecule by the substrate. When a sample vapour enters the SAW detector, molecules in the vapour come in contact with the polymer surface at a certain rate, depending upon the vapour flow. When a CA molecule hits the surface, it will be either bonded to the active sorption sites on the surface of the polymer or deflected by the surface. An important requirement for the polymer coating is that the sorption of targeted chemicals must be totally reversible after an analysis
      1. What are there capabilities?
        1. good detection sensitivity
        2. respond rapidly
        3. Good at low levels of CWA, especially blister and nerve
        4. Very few false alarms
      2. What are there limiting factors?
        1. Product specific
        2. temperature and humidity
        3. The polymer coating can be damaged by highly reactive vapours
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