Dear Tom and Ray:

I have been wondering about the safety of hydrogen fuel cells and the cars that plan to use them. While I'm sure that the volume of the stored fuel would be less than, say, the space shuttle Challenger, I know that hydrogen is extremely flammable in the presence of oxygen. I am wondering if a traffic accident with one of these vehicles poses the potential for a conflagration? Have any tests been conducted? -- Walt

TOM: Tests? Well, there's the Hindenburg.

RAY: Actually, the hydrogen in the Hindenburg was contained in a huge cloth bag -- not exactly the height of safety engineering. So that's not really a fair analogy to today's composite hydrogen holding tanks.

TOM: Hydrogen has some advantages over gasoline, too. In the event of a leak, it disappears very quickly -- and straight up, into the atmosphere, since it's lighter than air. It doesn't spill and hang around, and it's not toxic to humans and animals, like gasoline or diesel fuel is. But given a spark, it certainly can create the world's most exciting Roman candle!

RAY: And yes, there have been real tests of the tanks that hold both liquid and gaseous hydrogen. Engineers obviously believe they are safe enough to be used in vehicles. Do we know, for a fact, that they're right? No.

TOM: Like most new technologies, on-board hydrogen has been tested in all of the situations in which engineers can predict it might fail. But inevitably, they can't predict everything. And there will be surprises once it comes into widespread use. That's just the way things happen: A product comes out, engineers do the best they can to make it safe, and then a few accidents and some unfortunate deaths later, we learn a little more and make adjustments. It's a pattern you can see throughout history.

RAY: Right. Using gasoline in cars was thought to be safe, but Pintos still blew up when hit from behind. So that design isn't used anymore.

TOM: Hydraulic brakes were thought to be safe, until some of them ruptured and failed. Now all cars have two, separate braking systems in case one gives out.

RAY: So I think, in general, hydrogen fuel cells will be safe, if and when they debut in cars. But I won't be surprised if we discover, with some unfortunate accidents, some ways they can be made safer. And personally, what worries me more than the cars are the refueling stations.

TOM: Right -- where the guy making $5.15 an hour with the cigarette dangling off his lip is pumping pressurized hydrogen out of a giant storage tank! That's why I'm planning to always have my brother handle the fill-ups on my first hydrogen car.