November 5, 2003

Gunpowder Plot no flash in the pan

A new analysis by physicists shows that if the 1605 Gunpowder Plot to destroy the English parliament and kill the King had succeeded, it would have taken a large part of central London with it.

Experts from the Centre for Explosion Studies, at the University of Wales, Aberystwyth, used modern methods to estimate that severe structural damage would have been sustained by buildings up to half a kilometre away. The explosion would have destroyed Westminster Abbey and undermined buildings as far away as Whitehall, the site of Downing Street today.

I'm not sure about the soundness of the methodology, however, at least from this magazine article summary:
First, the amount of material is determined to calculate the energy of the explosion. In the Gunpowder Plot, an estimated 2500 kilograms of gunpowder had been amassed. As a working assumption, Thomas's team supposed this would have the same power as an equivalent amount of the standard explosive TNT.
What is "equivalent amount" here? If the same weight, the calculations will be way off -- black powder is much less powerful than TNT, and since it burns rather than detonates, it wouldn't have anything like the shattering effect of a high explosive.
Next, they worked out how the blast wave from such an explosion would attenuate as it sped away from the detonation site at supersonic speeds. Comparing the pressure of the blast wave at different radii with damage data tables enabled them to predict the damage that would have been caused.

The tables are largely drawn up from assessments of the damage caused to London buildings by bombing during World War Two, as well as by subsequent IRA bombs.

All high explosives, however.
They found that within a radius of about 40 metres, everything would have been razed to the ground. Within 110 metres, buildings would have been at least partially destroyed. And some windows would have been blown out even as far as 900 metres away.

Thomas cautions that there are a number of factors that could affect the calculations. Gunpowder is generally less powerful than TNT, but Fawkes was an expert, having used explosives while serving in the Spanish army during their occupation of the Netherlands. Packing it properly into the barrels and arranging them carefully would increase the power of the blast.

Also, the standard data tables assume a blast occurs in the open air, not in a cellar. However, the buildings of 17th Century London would have been less robust than those of 1940s London. Overall, he told New Scientist, "it would have probably balanced out".

This all sounds pretty loosey-goosey -- certainly nothing I'd dare turn in as a dissertation. From New Scientist.

Posted by David on November 5, 2003 10:14 PM




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