hmm, just don't light a match?
This is pretty scary - Hydrogen gas is highly flammable and will burn at concentrations as low as 4% H2 in air. Pure hydrogen-oxygen flames burn in the ultraviolet color range and are nearly invisible to the naked eye (definately not good). The good news, it burns quickly and upwards so if you want to get rid of the house....
Open the windows and get a fan running!