Sir: I am afraid that the title of Christopher Bellamy's article on improvised explosives based upon ammonium nitrate ("Bomb built for damage, not slaughter," 22 April) may give the mistaken impression that they make less lethal bombs than those containing other explosives.
The higher the initial pressure, the more rapidly it decreases with distance from the explosion. The exceedingly high pressure generated by a bomb containing plastic explosive has so decreased within a foot or two that a target a few feet away really does not know the difference. The effect produced by a vehicle stuffed full of explosives on a nearby building depends little upon the nature of the explosives: it is the quantity that counts. Therefore the attractiveness of ammonium nitrate to the terrorist remains its very ready availability in the form of unlimited amounts of fertiliser. Plastic explosive, if he has any, is better conserved for those very short-range, small-scale effects for which it is markedly superior.
To take an example nearer to home, the possibly spectacular result of Eurotunnel's recent quietly announced decision to permit the carriage of containers full of ammonium nitrate through its tunnel would not depend upon its being a particularly powerful or sensitive explosive or its enhancement by the addition of other ingredients: these would just serve to make it more easily initiated. What makes the mind boggle is the effect of the high and sustained pressure produced by, say, 50 times as much explosive as that which caused the damage in Oklahoma or the City, within the confines of a large tube.
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