hydrogen behaves differently from gasoline. But generally it is about as safe as the gasoline we now put in most vehicles' fuel tanks. In fact, the average gasoline tank holds three to four times the energy — and thus three to four times the explosive power — of the hydrogen tanks that the first fuel-cell electric vehicles will be using.
Hydrogen is the lightest of the elements, approximately 14 times lighter than air. So even though it is highly flammable, escaped hydrogen (burning or not) dissipates quickly and typically in a narrow column shooting straight up into the atmosphere.
Its vapors don't pool on the ground, as do gasoline's heavier-than-air vapors. So in most cases, hydrogen doesn't present as great a fire or explosive danger. To further minimize the potential for explosion, almost all hydrogen fuel stations store the gas above the ground in well-vented areas.
The University of California at Irvine has operated a public hydrogen station for a dozen years without incident, says Carl Baust, alternative energy projects specialist for the Orange County Fire Authority. Several other hydrogen stations opened in Southern California and the Sacramento area to fuel test the vehicles that have been plying the state's highways since 2002. So far, they also have been incident-free.
The vehicles themselves have arrays of hydrogen sensors that sound alarms and seal valves and fuel lines in case of a hydrogen leak. Additionally, the pressurized tanks that hold the hydrogen have been tested repeatedly and found to be safe in collisions.
One test involves firing live ammunition into the tanks to pierce them. Pierced tanks typically vent their hydrogen so quickly that even if the gas catches fire it is out of the tank before explosive pressure could build up.
In 2001, researchers at the University Of Miami's College of Engineering set fire to the hydrogen in a tank mounted in an SUV and later punctured the fuel line on a conventional gasoline-powered vehicle and set the leaking gas on fire. The
burning hydrogen versus gasoline test showed that flames caused "severe" damage to the gasoline vehicle, whereas the hydrogen vehicle was undamaged because the burning hydrogen gas vented up and away from the vehicle.
