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After letter bombers struck for a third day in a row, the Science Media Centre asked an engineering expert to comment on the police announcement that the letters contained a pyrotechnic charge.
Dr Clifford Jones, Reader in the Department of Engineering at the University of Aberdeen, said:
“The major difference between a pyrotechnic and a conventional explosive is in the size of the blast. With a conventional explosive the major cause of damage is the pressure which results from escaping gases moving at around the speed of sound. In a pyrotechnic, the whole reaction is much slower and the slower moving gases cause less explosive damage although they still have the ability to cause significant burns. A pyrotechnic is unlikely to cause a major blast.”