Although it might sound quite harmless, Black Dust is causing big problems for gas consumers throughout the UK and Ireland. Black Dust is caused when hydrogen sulphide attacks metal. Hydrogen sulphide is present in natural gas, which is commonly used in the home in central heating systems. Hydrogen sulphide has a distinctive smell – that of rotten eggs – and is a toxic gas. It is highly corrosive and reacts with metals by creating a layer of metal sulphide, which covers the surface of the metal. In boilers this metal sulphide occurs as copper sulphide - a black film present on copper piping.
Natural gas used by consumers in their homes normally contains very low levels of hydrogen sulphide (commonly less than 1 part per million). At this level a film develops inside of copper pipes but it is relatively harmless as it remains intact. If the amount of hydrogen sulphide rises the copper sulphide layer can fracture and break off into metallic-like pieces. These pieces break down further to form Black Dust which can block valves and injectors in appliances. The blockage normally causes a reduction in heat output from the boiler. In rare cases Black Dust can block gas pipes.
Unfortunately there seems to be no way to eradicate Black Dust other than reducing hydrogen sulphide levels in natural gas. There are methods that can be used to help control it which include:
- cleaning affected appliances (however, copper sulphide and Black Dust will remain in the pipework);
- fitting filters (however, filters need fairly regular removal and cleaning);
- sealing internal pipe surfaces to help stabilise film and prevent Black Dust (however, the long term efficiency of this method has not yet been proved).