A History of Research and a Review of Recent Developments

3
Propellant, dust, gas and vapour
3.1 LIQUID PROPELLANT EXPLOSIONS
We now turn to the nature of explosions other than those caused by TNT or
nuclear-type detonation, and the first of these is the accidental explosion of
the liquid propellant used in missiles and space rockets. Fully fuelled missiles
have been known to fall back onto the launching pad and explode, forming a
fireball and causing major structural damage, and it is important to know the
factors involved in order to assess structural response. The characteristics of
liquid propellant explosions were discussed by Fletcher [3.1], who was a member
of the US Manned Spacecraft Center at Houston in the mid-1960s, and much
of what follows is taken from his contribution to the New York Academy of
Sciences conference on the prevention of the accidental explosion of hazardous
mixtures, held in 1968. He pointed out that liquid propellant explosions occur
in two phases, detonation followed by deflagration. The detonation process
is limited, soon becomes extinguished, and is rather unsteady. This is in contrast
to the detonation of TNT, which as we have seen proceeds through the mass
of explosive in an orderly way. The detonation of liquid propellant continues
for a longer period and at a lower pressure than that of an equivalent quantity
of conventional explosive.
Detonation only occurs in a relatively small proportion of the total mass of
the propellant, and most of the mass is consumed by deflagration, during
which a large amount of chemical energy is transformed into thermal energy.
The fireball is spherical and grows to a diameter of several hundreds of feet in
a few seconds. The diameter in feet is about 10 times the cube root of the
propellant weight in lbs, and the duration about 0.2 times the cube root of
weight. The fireball growth from the contents of an Atlas missile reaches a
maximum of about 400 feet diameter in approximately 1.5 seconds.
The shock wave from the detonation gives pressures that decrease linearly
from the instantaneous peak, in contrast to TNT shocks, which decay
exponentially. Close to the centre of the explosion peak propellant pressures
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