Dangerous gases from Septic Tanks

A number of people have emailed me concerning fumes from septic tanks.  The problem with all stored organic wastewaters that go anaerobic is that large quantities of hydrogen sulphide and methane will be produced.  These gases are much heavier than air and displace the air within the tank, so once opened, the gas will rise from the tank and form a dense layer around the manhole at ground level. Hydrogen sulphide is very dangerous and as I said earlier odourless at high (lethal) concentrations so there is always a potential problem.  The key thing here is to ensure that all septic tanks are cross vented.   Cesspools or sealed septic tanks are highly dangerous in this regard.  The most dangerous scenario is where the tank is in a hollow or the entrance is contained in a riser or in a building so that the gas can build up. Never climb into a tank which has only been partially emptied unless you are sure it has been vented with air.  Most complete treatment systems such as the Biocycle are continuously vented via the aeration system, so that such gases should not build up.  However, if you are working in this area, and some of you who emailed me are, you should always have a gas detector.  It is worth the investment.  For more information see Link and more safety information see Link.