Alternative Fuel Sources - Hydrogen and Fuel Cells: Advances in Transportation and Power - page 102

to the ground by a steel cable, which acts as an antenna for electrical dis-
charges.
Prior to the fire, the Hindenburg had completed 10 round trips be-
tween the U.S. and Europe. A sister ship, the Graf Zeppelin, made regu-
lar scheduled transatlantic crossings from 1928 to 1939 with no incidents.
There were 161 rigid airships that flew between 1897 and 1940, almost all
of these used hydrogen and 20 were destroyed by fires. Of these 20, sev-
enteen were lost in military action where in many cases the fires resulted
from enemy fire during World War I.
Hydrogen explosions can be powerful when they occur, but they are
rare. Hydrogen must be in a confined space for an explosion to occur. In
the open it is difficult to cause a hydrogen explosion without using heavy
blasting caps.
In 1974, NASA examined 96 accidents or incidents involving hydro-
gen. At this time, NASA tanker trailers had moved more than 16 million
gallons of liquid hydrogen for the Apollo-Saturn program. There were five
highway accidents that involved extensive damage to the liquid hydrogen
transport vehicles. If gasoline or aviation fuel had been used, a spectacular
fire would have resulted, but none of these accidents caused a hydrogen
explosion or fire.
A well publicized event where explosive mixtures of hydrogen
and oxygen were present in a confined space occurred during the events
in 1979 at the Three Mile Island (TMI) nuclear facility in Pennsylvania.
Nuclear reactors operate at very high temperatures. To prevent their six to
eight inch thick steel reactor vessels from melting, large amounts of cool-
ing water are continuously circulated in and around the reactor vessel. An
average commercial-sized reactor requires about 350,000 gallons of water
per minute. During the process of nuclear fission, the center of the urani-
um fuel pellets in the fuel rods can reach 5,000°F. The cooling water keeps
the surface temperature of the pellets down to about 600°. If the circulat-
ing water is not present, in 30 seconds the temperatures in the reactor ves-
sel can be over 5,000°. This temperature is high enough to melt steel and
thermochemically split any water present into an explosive mixture of hy-
drogen and oxygen. This is what happened at TMI. If a spark had ignited
the hydrogen gas bubble that drifted to the top of the containment build-
ing, the resulting explosion could have fractured the walls. This would
have resulted in the release of large amounts of radiation at ground level.
The hydrogen gas bubble was vented, since as long as it remained in the
confined space of the containment building, the potential for detonation