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Hydrogen Fuel Cells Hit the Road
caffeined writes "Well, it looks like Honda is doing a real test of their fuel-cell car. A family in California is renting the car for $500/mo. Honda is charging them so that they take it seriously - an executive explained that if it were free they might not get the kind of feedback they want. If someone is paying for something and they're not happy - then you're going to hear about it. This is apparently the first fuel-cell car on the road anywhere in the world, according to Honda."
Nothing will explode a la Hindenburg unless it's painted with rocket fuel a la Hindenburg. Pure hydrogen doesn't explode very well (just like gasoline) because you have to get enough oxygen to it fast enough. Hindenburg had the benefit of being painted with a nice solid rocket oxidizer that releases oxygen when it gets hot.
Er,
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For hydrogen to explode, it needs oxygen.
If the tank ruptures, the gas as light as it is would expand throughout the air very very quickly.
This isn't like lighting a balloon filled with hydrogen with a candle and watching the brief poof of flame.
This is like having a candle five feet away from a balloon filled with hydrogen and popping the balloon. That is, if there is a fire involved in the collission.
How often do collisions result in fire? I did a little bit of research into this, but the best I could find was that "crashes with fires are relatively rare" (http://www.nhtsa.dot.gov/cars/rules/regrev/evalu
To explore this a little further:
What causes a fire in an automotive accident? Faulty gas tanks and fuel lines. This results in leakage. The vapors (which are MUCH heavier than hydrogen) then get sparked by something. This ignites the vapors, leading back to the fuel tank which then catches fire. I've witnessed car fires before (a few months ago, a car in the parking lot of my apartment complex caught fire). The fire burned for 10 minutes before fire response arrived. In that time, the fire spread from one car to the two cars on either side. It took fire response about five minutes to put the fires out. During this 15 minute time period, the materials that were burning included the interior of the car, under the hood, and the tires. The only violent explosions that occurred were the tires exploding.
I'm theorizing the reason the gas tanks didn't ignite is that gasoline requires a very oxygen rich environment. Gasoline requires a 1.4% - 7.6% concentration in air for it to be explosive. Any less than this and it will merely ignite; any more than this and there isn't enough oxygen for it to explode. It will simply ignite. The pre-existing fire probably used up most of the oxygen near the fuel lines. There was probably a phenomenon similar to what you see with an oil well - a jet of flame from the fuel line. Hollywood car explosions just don't happen.
Now, on to hydrogen.
Hydrogen, being much lighter than air (as opposed to natural gas or gasoline vapors), dissipates very quickly in air. At concentrations of less than 10%, it would require the same ammount of energy to ignite as would natural gas. The main point here, is that hydrogen dissipates so quickly that the concentration would very quickly reach less than 4% (the lower limit of explosivity). The likelyhood of explosions is much less likely than with even gasoline because of this.
Hydrogen Fuel Cells do not use any sparking or arcing componants. Similarly, the engine is a simple electronic engine. If something shorted, it could spark - but there is no combustion inherent in a fuel cell car. This limits the chances of even igniting the hydrogen in the case of a leak.
Fuel cells are also equipped with automatic shutoffs in case a leak is detected. This can't help if the storage tank itself is ruptured, but that would be difficult (Normal air tanks for scuba divers are very difficult to rupture, and tanks used to transport flamable liquid are even more difficult to rupture).
The myth of the exploding hydrogen car can be linked to two things: the hindenberg and the hydrogen bomb.
The hindenberg burned, rather than exploded. The color of the flame was wrong for hydrogen to be the propellant. It's very likely that it was the flamable fabric covering the zeppelin that ignited, not a leaking hydrogen tank.
A hydrogen bomb requires special isotopes of H2, and very high temperatures. Neither of which would be found in a car fire or a hydrogen fuel cell car.
For more on hydrogen fuel cell safety: http://sanewsletters.com/FCIR/fcirfctpart1.pdf
In the meantime, stop propogating myth and FUD.
You are correct however about the death toll on the passengers. From the Wiki: