Major 2 categories are available:
Detectors for gases which create an immediate health hazard (eg. H2S, CO, HF, HCl, Cl2)
Detectors for gases that create a health hazard on long term exposure (eg. Vinyl Chloride, Benzene, Toluene etc.)
The two types of H2S detectors available are:
This type is based on an electro-chemical cell, developed to react exclusively to H2S. As a result of chemical reaction of the cell organic electrolyte with H2S, an electric current is generated, which is proportional to the H2S concentration in the sample gas.
Working principle: The semi-conductor type is based on the adsorption of H2S molecules on the surface of a solid-state semi-conductor crystal which causes a change in electrical resistance of the electrical circuit of which the semi-conductor forms the part.
Set Point: H2S detectors have a typical recommended minimum alarm setting of 5 ppm. If second stage alarm is used, 10 ppm shall be used.