Home LMS THMG156 – Chemical Agent Monitors, Part I

THMG156 – Chemical Agent Monitors, Part I

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In this episode, Bob and Mike review a few of the chemical agent monitor options out there. Some are out of service, some are in service, and others are just coming into vogue. We discuss the good, the bad, and the ugly in this first installment of a two part series.

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Complete Show Notes

5:15 Chemical Agent Monitors (CAMs) Overview

  • While the technology is always changing, we’ll highlight basic products and provide a quick overview
  • Specialize in detecting chemical warfare agents
  • Keep in mind that we’re using certain brands as examples, not to push their product

10:15 Flame Spectroscopy Monitors

  • Chemical warfare agent that picks up nerve, blister, VX, and Lewisite agents
  • Meter burns the sample – color of the flame tells you which chemical you’re dealing with
  • The more intense the wavelength, the larger the concentration of chemicals
  • Capabilities:
    • Does a pretty good job at picking up phosphorus and sulfur bonds
    • Offers instant results and clears quickly
  • Limiting factors:
    • Can only pick up a few select bonds
    • Not telling you which specific chemical is in the air – tells you something containing the bonds is present

17:30 Ion Mobility Spectroscopy Monitors

  • Example: RAID-M 100 from Bruker
  • The most sensitive meters that are commercially available – works in the parts per billion range
  • When the sample comes into the tube, the beta radiation source inside the tube hits the sample and ionizes it
  • The ionized sample is put into a separate tube and floated down the tube through magnetic fields
  • Meter times how long it takes the sample to get from the beginning of the tube to the end of the tube
  • Time determines whether the chemical warfare agent the meter is looking for is present
  • Capabilities:
    • Non-discriminatory when detecting ions
    • If something gets into the drift tube and happens to have the same mobility time as a chemical agent, the detector will see it as a chemical adjacent
    • As these meters get smaller, their shorter drift tubes decrease their sensitivity and cause more detection interference
    • Affected by things like air temperature and moisture – humidity can affect the formation of the ion and produce totally different time runs
    • Can oversaturate and take some time to clear out

27:00 Surface Acoustic Wave (SAW) Monitors

  • Example: HAZMATCAD from MSA
  • We can’t really grasp how these work, but here’s our best guess:
    • Two plates coated with a polymer that’s chemically selective
    • Surface acoustic wave (SAW) operates when an alternating voltage is applied to the input transducer
    • This generates an alternating mechanical strain (tension or compression) that initiates a SAW
    • SAW travels the surface of the substrate before being converted back into an electrical signal by the output transducers
    • The two major processes that 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
    • Polymer substance is necessary because the piezoelectric crystal itself doesn’t have the ability to attract and sorb target chemicals – on the other hand, polymers have many free, active sorption sites
    • Sorption is defined as the simultaneous adsorption and absorption of a molecule by the substrate
    • When a sample vapor enters the SAW detector, molecules in the vapor come in contact with the polymer surface at a certain rate depending upon the vapor flow
    • When a CA molecule hits the surface, it will either be 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
  • Capabilities:
    • Good detection sensitivity
    • Responds rapidly
    • Works well at low levels of CWA (especially blister and nerve)
    • Very few false alarms
  • Limiting factors:
    • Product specific
    • Affected by temperature and humidity
    • Polymer coating can be damaged by highly-reactive vapors

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