When the subject of hydrogen cars is brought up, the immediate response from some people is to bring up the Hindenburg disaster.
The Hindenburg was a German zeppelin that burst into flames at the Lakehurst Naval Air Station in New Jersey on May 6, 1937. Since the Hindenburg was filled with hydrogen, the concern is that this event shows that hydrogen is not safe.
However, Addison Bain is a retired NASA engineer that showed the disaster was due to the coating on the fabric skin of the Hindenburg. The coating used on the airship contained iron oxide and aluminum-impregnated cellulose acetate butyrate which are used in solid rocket fuel. A spark caused by static electricity ignited the outer skin which led to the destruction of the Hindenburg.
Furthermore, here is an excerpt from the Rocky Mountain Institute (which was co-founded by Amory Lovins) website about safety concerns with hydrogen due to the Hindenburg:
The Hindenburg Myth
Most hydrogen concerns stem from the Hindenburg disaster of 1937. The hydrogen gas that once filled the Hindenburg zeppelin did burn, but it did so quickly, upwardly, and away from the people below. When the airship was docking, an unexpected electrical discharge ignited the airship’s canvas (which was unknowingly treated with two major components of rocket fuel!). The clean hydrogen flames swirled above the occupants of the passenger compartment, and all those who rode the airship down to the ground survived. Thirty-five of the thirty-seven casualties perished from jumping to the ground, and most other injuries resulted from diesel burns.
While the pictures of the Hindenburg disaster like the one above are sometimes shown by hydrogen critics, the following link (you will need to scroll down a little) has pictures of a gasoline car and a hydrogen car on fire. You can decide for yourself which one is safer.
Furthermore, the following blog post titled Hydrogen cars are safe has information from several car companies about the safety of hydrogen fuel cell vehicles.
[Photo credit: ubberdave]