I was just reading a news report of a collision between a light rail train and a city bus in Los Angeles this morning. One sentence in the story mentioned that even an hour later, the smell of natural gas still lingered in the air.

That got me to thinking--more and more cities are switching their bus fleets to greener, compressed natural gas (CNG). How dangerous are they when they leak after some accident? We all know the danger of sparking an explosion in some gas leak at home. I'm just wondering if the physics of a vehicle crash change the danger any? For example, unless the gas is leaking into the interior of the bus, I don't think you'll be building up any appreciable quantity of natural gas, like you might inside your home.

I'll be taking a first aid refresher course in a couple weeks and so I was just thinking about one of the first things to do--surveying the scene. If I came upon an accident scene like I mentioned above and could smell the natural gas leaking, is that scene too dangerous to approach?

We've discussed the issue of electric hybrid vehicles after a crash before. I don't think we've ever covered CNG-powered vehicles after a crash, though.