The Anaerobic Digestion process can potentially be dangerous due to a buildup of gases over time that can make the atmosphere become explosive. This being said it is important to be able to recognise the gases and know the damage they can cause if humans come into contact with them.
4 Common Gases
Methane – CH4
Methane is the desired output from the system so will be present in every biogas application. This doesn’t mean that it is not harmful.
- Odourless
- Lighter than air
- Highly flammable (Explosion limits 5-15% CH4 in the air)
- Displaces air (O2)
Carbon Dioxide – CO2
- Smells sour
- Heavier than air
- 6-10% CO2 means increased respiration, high blood pressure, heart palpitations and headaches
- 10%+ CO2 means paralysis of breathing, narcosis and death
Hydrogen Sulphide – H2S
- Smells like rotten eggs
- Humans can smell up to 250-300ppm and then after this our receptors become numb, and you cannot smell the gas
- Heavier than air
- Highly inflammable (explosive at 4.3-4.5% vol in the air)
- Effects of exposure
- <100ppm – life-threatening over several hours
- >100ppm – life-threatening <1 hour
- 500ppm – life-threatening in 30 min
- 1000pm – life-threatening in a few minutes
- 5000ppm – deadly within seconds
Ammonia – NH3
- Commonly causes eyes to water and visual problems
- Smell threshold 5-30ppm
- Lighter than air
- Highly inflammable
- Caustic on moist skin and mucus membranes
- Deadly at a volume of 0.5% (5000ppm) after 30-60 minutes
Reference – Roots Organics Ltd
