HAD Guy Fawkes succeeded in blowing up the Palace of Westminster 398 years ago today, large parts of Central London would have been flattened, new calculations show.

Westminster Hall, the Abbey and surrounding streets would have been destroyed, with damage spreading into Whitehall, according to experts at the Centre for Explosion Studies at the University of Wales in Aberystwyth.

There would have been complete destruction of all buildings within 135ft, and partial collapses of walls and roofs of houses out to 354ft. Ceilings would have fallen in and glass been damaged up to 1,600ft away.

Fawkes and his co-conspirators were detected on the eve of Parliament reassembling after a six-month recess. They had stuffed the cellar beneath the House of Lords with enough gunpowder to demolish it 25 times over.

To mark the annual celebration of the Gunpowder Plot, the Institute of Physics asked the Aberystwyth scientists to work out just how much damage it would have done. Contemporary accounts say that Fawkes placed as many as 36 barrels of gunpowder in the cellar. The most reliable source is Robert Cecil, Secretary of State to James I, who described the amount as “two hogshead and 32 small barrels, all of which he had cunningly covered with great store of billets and faggots”.

From this description, an explosives expert, Dr Sidney Alford, worked out almost 20 years ago that Fawkes had in place 2,500kg (5,500lb) of explosive. Modern research by the Royal Armouries in Leeds has shown that oldfashioned gunpowder was a very effective explosive.

The Aberystwyth scientists used equations that measure the destructive power of TNT. “Gunpowder is generally not as strong as TNT,” Dr Geraint Thomas, head of the Centre for Explosive Studies, said. “But Guy Fawkes was an expert in explosives and so knew what we was doing. If he had the gunpowder confined in barrels and well packed in, it could have been almost as powerful as the equivalent TNT explosion.”

The equations used in explosion physics are generally employed after the event, using the damage done to assess the size of the explosive charge. In this case they were applied in reverse to work out the damage from the charge. “We can use the weight of explosive to work out how it will affect its surroundings,” Dr Thomas said. “We know that the more explosive we have the more energy will be released when the charge is set off. From the pressure pulse generated by the explosion we can tell if windows are going to be smashed or if whole buildings will be demolished. From the amount of explosive that Guy Fawkes had we can work out that if you are a third of a mile away you should be OK.”

There is no doubt that Fawkes had provided more than enough gunpowder to blow up Parliament. In a report for New Civil Engineer in 1987, Dr Alford concluded that the blast would have lifted the wooden floor above the cellar, carrying timber up to the second floor where Parliament sat.

The upper floor would have fallen back into the building, so that anybody not killed by blast, flame or flying debris would have fallen back into burning rubble and an atmosphere full of smoke and carbon monoxide sufficient to kill a healthy man within minutes.

But on the November 4, the plot was uncovered and Fawkes was arrested. The conspirators were executed.

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