Biogas Safety first!

General requirements
3. Properties of biogas
Biogas essentially consists of methane (50 to 75 % by
volume), carbon dioxide (20 to 50 % v / v), hydrogen
sulphide (0.01 to 0.4 % v / v) and traces of ammonia,
hydrogen, nitrogen and carbon monoxide. In addition,
it may contain volatile substances. An example of the
composition of biogas from an average biogas plant
using manure: methane 60 % v / v, carbon dioxide
38 % v / v, residual gases 2 % v / v (see Table 1).
According to the Globally Harmonized System of
Classification and Labelling of Chemicals (GHS)
(United, 2015), biogas is described as an extremely
flammable gas (H220) and it should be kept away
from heat, hot surfaces, sparks, open flames and
other ignition sources, such as smoking (P210); it
should be stored in a tightly closed container (P233)
and in a well-ventilated place (P403 + P235). Hazard
and precautionary statements (H and P statements
or phrases) are brief safety instructions concerning
the use of chemicals. H statements describe
physical hazards, health hazards and environmental
hazards. P statements are safety instructions that
describe general precautions, preventive measures,
responses (measures to be taken following an accident),
storage instructions and disposal instructions.
1.3.1. Density
Further information is available
on the website of the Globally
Harmonized System of Classification
and Labelling of Chemicals (GHS).
The density of biogas may vary, depending on its
composition, moisture content and temperature. Biogas
may be heavier or lighter than air, and does not
separate under the influence of gravity. This property
must be borne in mind when determining protective
measures (e.g. the positioning of fixed gas warning
systems).
Table 1: Properties of various gases (SVLFG, 2016).
Biogas (60 % CH 4
) Natural gas Propane Methane Hydrogen
Heating value (kWh / m 3 ) 6 10 26 10 3
Density (kg / m 3 ) 1.2 0.7 2.01 0.72 0.09
Density relative to air 0.9 0.54 1.51 0.55 0.07
Ignition temperature (°C) 700 650 470 595 585
Max. flame propagation speed in air (m / s) 0.25 0.39 0.42 0.47 0.43
Explosive range (% v / v) 6 – 22 4.4 – 15 1.7– 10.9 4.4 – 16.5 4 – 77
Theoretical air consumption (m 3 / m 3 ) 5.7 9.5 23.9 9.5 2.4
9