Biogas is as a technical unpurified gas-mixture of methane and carbon dioxide with componentes of other trace-gases. The relation between methane and carbon dioxide depends on the composition of the organic initial material, such as the gas yield, the methane content and the heat value.  The table compares the composition in percentage of the technical biogas with other (bio-)gases.

 

              

Basically, biogas is a non-toxic gas and it is odourless as soon as it is desulphurised. However, toxic characteristics have to be seriously considered when handling with biogas. There is a danger particularly in rooms with insufficient aeration. Carbon dioxide leads to suffocation; a volume share of more than 9 % of carbon dioxide in the air is lethal within 5-10 minutes. Hydrogen sulphide is very toxic, a volume share of 800 ppm can be lethal after 5-10 minutes. Misjudgements of these issues very often led to fatalities on simple silo plants. In the following scale the physical features are assorted.