Optimized Protection against Explosion Hazards and Toxic Gases using photo ionisation detectors - Dr. Horst Bleichert

A lot of combustible gases and vapours are toxic long before they reach their lower explosion warning limit. An additional measurement of volatile organic compounds (VOC) in the ppm range with a photo ionisation detector (PID) provides the optimal protection for exposed workers. Thus, a combination of LEL and ppm measurement is the ideal solution.

The Benefits of LEL and VOC Detection Simultaneously

One of the most commonly used techniques to measure explosion hazards is the catalytic bead technology. On the hot surface of an active pellistor, flammable gases or vapours are oxidized by the oxygen in the air. This process forms a heat of reaction and the temperature of the active pellistor rises. The resulting signal is a measurement of the gas concentration. With these catalytic bead combustible sensors, all flammable gases can be detected down to the percent LEL range.

However, for most VOCs, long before they reach a concentration high enough to activate the alarm of a common LEL detector, they could have easily exceeded the toxic exposure limits. To detect VOCs, PID technology is the best solution. An ultraviolet lamp is used to break down the gases and vapours for measurement. The molecules are ionized through radiation and produce a current. This electrical current is proportional to the gas concentration and is displayed on the meter. Most common PID detectors operate with a 10.6 eV lamp, so that any gas or vapour with an ionisation energy lower than 10.6 eV can be detected in the ppm range.