When the experimental Airlander airship – the world’s largest aircraft – took a nosedive at Cardington on a test flight the other week, there’s a reason why it didn’t do so in a fiery ball.
It’s filled with helium, an inert, lighter-than-air gas whose most sinister effect is making your voice squeaky, as opposed to hydrogen, the lightest element whose sometimes troublesome characteristic is its explosiveness when exposed to a naked flame. Or perhaps some sunshine. Or sometimes just for the fun of it.
The excellent thing about hydrogen, mind, is that when it’s combusted it gives off water, which is not, unlike conventional fuels, a greenhouse gas. Otherwise, hydrogen – a hugely tempting source of automotive power though it is, because of its tremendous potential – can be a right pain.
It has to be handled safely. That’s no big deal, but doing so isn’t cheap. Hydrogen can make some metals brittle, limiting what you can store it in, but you can put a pressurised carbonfibre tank in a car and it won’t let go even in an extreme crash. Neither do they leak, like those in some early hydrogen-powered cars, which couldn’t be parked inside; a slow seep could fill the upper part of your garage with highly explosive gas. Then you could stroll in and switch on the lights…