Wastewater and potable water treatment facilities produce and use various toxic and explosive gases such as methane, hydrogen sulfide, ammonia, carbon dioxide, carbon monoxide, chlorine, ozone, etc.

In addition, in confined spaces, the increased formation of toxic gases and the decreased concentration of oxygen make these areas particularly dangerous for workers.

The risk can be evaluated by measuring worker exposure to various pollutants present in the air in work areas.

The measured concentrations are then compared to the 8-hour time weighted averages for exposure (TWA) and to recommended exposure limits for shorter time periods (less than 15 minutes).

Several technologies can be employed to detect gases present in water treatment facilities.

Electrochemical sensors are used to monitor oxygen rates in the air, or the presence of toxic gases such as CO, H2S, and Cl2.

Semi-conductor sensors are used where there are high concentrations of H2S or where the ambient temperature is high. Catalytic sensors are used for the detection of explosive gases.

Infrared sensors are used for the detection of explosive gases such as CH4 or carbon dioxide (CO2), also recommended for corrosive atmospheres or where high levels of H2S are present.

Continued high concentration of H2S (above 3 ppm) will create a risk of saturation and poisoning for standard catalytic cells.