Health and safety officials have been checking gas appliances inside the flat to trace a leak, and the apartment block has been evacuated while tests continue.

BBC: Neil McFerran (l) and Aaron Davidson (r)

This, he believes, will make it possible to work out which country, even which factory, supplied the original chemicals for the mustard gas - it will not be possible to trace the source of the nerve agents.

BBC: Magazine

But with emerging technologies, raw biogas can be stripped of carbon dioxide and other trace gases, bringing it up to the quality level of natural gas.

FORBES: Biogas and the Shale Gas Bonanza