February 5, 2007

engineering expert comments on the explosion of a letter bomb in central London

The letter bomb exploded in an office on Victoria street.

Dr Clifford Jones, Reader in the Department of Engineering at the University of Aberdeen, said:

“A letter bomb is an explosive device disguised as a postal package. On disturbance it detonates, that is, undergoes reaction with a significant overpressure. ‘Disturbance’, by means of impact or friction, might well be due to opening. Small amounts of solid explosives can cause sufficient overpressure for personal injury and damage to the surroundings. The effectiveness of a letter bomb depends on the reliability of its detonating device, also on the direction of the detonation propagation and therefore on the spatial relationship of the bomb and the victim. The good news that the victim of this morning’s letter bomb has fairly minor injuries might fortuitously have been due to the spatial factor.

“The mixing of two materials to give an explosive effect is very straightforward: gunpowder was being used in Europe in the 14th Century and in China long before that. In planning the construction of an explosive device from readily available materials ammonium nitrate is a choice of ingredient that comes readily to mind.”