Hydrogen is the lightest of all gases and disperses very quickly, it is also non-polluting and hazardous to the surrounding environment (unlike gasoline a spillage / leak will not cause an environmental disaster). Hydrogen, like natural gas and petrol, is a fuel and will burn when ignited. Hydrogen is only explosive when it is able to build up in a enclosed space, which is very difficult as it has a habit of escaping (hydrogen is the smallest of all elements). As long as appropriate safety procedures are followed, as they should with any fuel, hydrogen is a safe fuel.