April 10, 2019
Biogas is a mixture of CH4, CO2, H2S and NH3.
CH4 is a colorless, odorless gas. It is explosive at concentration range of 4.4 –16.5% in air.
CO2 is also colorless and odorless gas, but it is heavier than air. This poses an asphyxiation risk when the CO2 concentration is above 8% in air.
H2S is a highly toxic, colorless gas. At low concentration, it smells of rotten eggs. Above a concentration of 200 ppm the sense of smell becomes deadened and the gas is no longer perceived. Above 700 ppm, inhaling H2S can lead to respiratory arrest. The EU workplace concentration limit is 5ppm.
NH3 is present when nitrogen rich substrate is used to produce biogas. It is colorless and pungent-smelling. At above 30 –40 ppm mucous membranes, respiratory tract and eyes become irritated. At above 1000 ppm breathing difficulties, potentially inducing loss of consciousness.