How are toxic gases, for instance Phosgene or Hydrogen cyanide monitored?
Compur Monitors history as manufacturer of gas detection began, when chemical industries started requesting monitors for toxic gases. Gas detection in general goes back to mining industries. In mines fire damp atmosphere monitoring was very important. Fire damp means life threatening atmosphere carrying explosive Methane or toxic Carbon monoxide.
In chemical industries the requirements in terms of sensitivity and accuracy are even higher. Many substances handled in chemical plants do have very low alarm thresholds (TLV).
Mainly Phosgene - COCl2, Chlorine - Cl2, Hydrogen cyanide – HCN are omnipresent and do have very low TLVs. The European Union for instance is planning to lower the TLV of HCN to 0,9 ppm, the TLV of Phosgene is already at 0,1 ppm.
For the detection of very toxic gases mainly electrochemical sensors are used. They are very sensitive and specific at the same time. In principle they operate like a half battery, where gas brings the other half to the party making it produce an electrical current. As every molecule delivers an exact number of molecules with a certain charge, one could say a gas detector is a “molecule counter”. The current produced is measured by an accurate amplifier.
Not only are electrochemical sensors very sensitive and specific, they also do not need any outside energy. Therefore gas detectors with electrochemical sensors can be designed very small and light weight. A big advantage when designing portable instruments.