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20 November 2009
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A number of myths have evolved round hydrogen and its safety. This
page describes some of them, some of them "proving" it is safe to use
hydrogen, some of them exactly the opposite. It should not be forgotten
that there are tens of industrial hydrogen explosions of varying degrees
of gravity, throughout the world each year. Inevitably, some of them
result in "cover-ups" and it is often difficult to find the truth. It is
unfortunate that many of them are where hydrogen is used as a coolant,
such as in nuclear and non-nuclear power stations; almost inevitably,
the media report those in nuclear stations and ignore those in
non-nuclear ones, even though they most frequently are identical!
Probably the most famous myth surrounds the Hindenburg disaster. This was
the swansong of lighter-than-air mass dirigible airship transport.
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“Hindenburg”
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Some persons have claimed that the disaster was due to a hydrogen
explosion. Others have claimed that it was due to the envelope having caught
fire. The truth is that both protagonists are both right and wrong.
The airship was a 245 metre long aluminium frame, over which was fixed a
doped cotton envelope. Inside this was a number of ballonets, holding the
hydrogen. The passenger compartment and engine nacelles were attached to the
underside of the frame. It had made 10 successful round trips between
Germany and the USA, carrying over 1,000 passengers between its inauguration
in 1936 and the disaster in 1937. On 6 May of that year, it arrived at
Lakehurst in New Jersey and was approaching the mooring mast when there was
a deflagration, as can be seen in the photograph above. This resulted in the
deaths of 36 of the 97 persons on board.
There has been some speculation as to the actual sequence of events, but
the most likely cause was that, as the airship descended, the atmospheric
pressure and temperature increased sufficiently that a certain amount of
hydrogen escaped from the ballonets, through a vent in the outer envelope at
the bottom rear of the envelope, foreseen for this purpose. As it approached
the steel mooring mast, tail first, there was a static electricity discharge
from the airship to the mast, which was, of course, at earth potential, and
this ignited the escaping hydrogen, producing a very minor explosion. The
energy of this was sufficient to rip the envelope, igniting the hydrogen in
the ballonets and setting fire to the outer envelope itself. The photograph
shows clearly two deflagrations from ballonets and a separate fire in the
region of the vent, as well as the burning outer envelope.
The burning outer envelope wrapped itself around the passenger nacelle
and this was the direct cause of the unfortunate death of some of the
passengers (some died jumping from the nacelle), not a massive hydrogen
explosion as some have suggested. However, it does seem very likely that a
small hydrogen explosion was the initial cause.
It has been reported that a Japanese brewery has been producing beer
gasified with hydrogen instead of carbon dioxide. A
report
described a consumer who deflagrated in his stomach. This would appear to be
a myth.
The Chalk River, Canada, nuclear reactor meltdown was not caused by a
hydrogen explosion on 12 December 1952. However, it did cause a series of
hydrogen explosions which displaced the hydrogen tank.
The Challenger disaster on 28 January 1986 was not caused by a liquid
hydrogen leak, causing an explosion. The direct cause was an O-ring in the
seal between sections of one of the two solid fuel rocket boosters, which
was too rigid because of low temperatures at lift-off, causing hot gases
from the combustion of the fuel to burn it up. Even if there were a hydrogen
leak at that altitude (about 15,000 m), it could not cause an explosion as
there is little oxygen in the atmosphere. However, the leak from the booster
did impinge on the hydrogen tank, which failed, and subsequently the liquid
oxygen tank, and this did eventually contribute greatly to the severity of
the accident. See
here for a full explanation.
It is true that a lead-acid battery produces hydrogen and oxygen on
charge, and particularly when overcharged. It is equally true that these are
produced at a potentially dangerous H2:O2 ratio (volumetrically 2:1). It
would seem, therefore, that the conditions are right to produce an
explosion, in the event of an ignition source being placed close to a vented
battery. In reality, this is an extremely rare occurrence; so rare, that it
almost never happens with the millions of cars on the world's roads, each
with a lead-acid battery and the means of igniting it within the same
compartment. From the point of view of hydrogen explosions, lead-acid
batteries are safe under normal conditions. It is true, however that
catastrophic explosions have occurred, such as at
Fort Detrick, but, as in this case, it is usually because of senseless
human actions.
On 17 February 2000, the Thor Emilie cargo vessel was lost in the
Mediterranean as the result of a "vehement" hydrogen explosion, with the
loss of six members of the crew of seven. According to the manifest, the
ship was carrying zinc ore, essentially zinc oxide. The myth, in this case,
was that the cargo was not zinc oxide but zinc skimmings (finely divided
scrapings removed from galvanised goods). In the presence of moisture, these
can produce hydrogen. The explosion was violent enough to cause the vessel
to sink almost instantaneously.
It is often stated that hydrogen explosions cannot occur in the open air.
On 3 March 1983 there was a hydrogen explosion in an open street,
called Brahegatan, in Stockholm, Sweden. The event occurred when gas
cylinders were unloaded from a lorry and hydrogen suddenly started to leak
out. The hydrogen was in 18 cylinders containing about 10 kg of hydrogen.
The blast wave from the explosion broke windows in a range of about 90
meters, causing 16 persons to be injured. Note that the quantity of hydrogen
here is about 1/3 the quantity that would be needed to give a car an
autonomy of 500 km.
The biggest myth, in the public mind, is caused by the ignorance
confusing a hydrogen explosion with that of a so-called "hydrogen bomb or
H-bomb". The latter is a thermonuclear device with the fusion of hydrogen
into heavier elements, such as helium. The former is purely chemical and
involves no danger from radiation of nucleides.
End Notes
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