Mention hydrogen energy and the reaction can be wild. Talk of fleets of buses powered by fuel cells produces jibes about "rolling hydrogen bombs". This is unfair: properly handled, hydrogen is as safe as other fuels, such as natural gas and propane. The scepticism hardly mattered while hydrogen energy remained largely theoretical, but that is changing. A combination of factors is propelling it towards commercialisation. Even staid car and oil firms are placing bets on a role for hydrogen, based on the fuel cell.