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