House-Sized "Fireball" from London Bomb?

The car bomb found near London's Picadilly Circus may have been the work of "keen amateurs," explosives experts tell the British press. But it would have likely created a "fireball the size of a house."

Patio gas cylinders found by police in the light green Mercedes would have been an unlikely weapon for experienced terrorists unless they wanted to create a fireball for the cameras, Sidney Alford, founder of explosives company Alford Technologies, told Guardian
Unlimited.

As a readily available combustible material, the propane gas held in such cylinders might be considered by someone unable to source high explosives.

"If you are making a bomb and you are limited in the amount of explosives you can acquire you could easily get some gas cylinders of propane to add to them. They would give a more impressive fireball on TV," he said.

"They are probably keen amateurs who could not get their hands on the real thing and do not realise the limits of what they are doing..."

[However,] "As the IRA knew, you do not need a real bomb to cause real havoc," he said.

Especially not when that fireball is "the size of a small house" with a shock wave several hundred yards big. Earlier today, DANGER ROOM's David Hambling compared the car bomb to a D.I.Y. fuel-air explosive.

The propane cylinders and petrol used in the device would have triggered a huge conflagration, as well as causing shrapnel and blast injuries from the exploding car chassis and the nails packed around the bomb, according to
Hans Michels, Professor of Safety Engineering at Imperial College, London.
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Just one 13kg propane canister — the type sold by Calor under the brand name
“Patio Gas” — would release a highly flammable cloud of vapour that would spread over an area of 50 to 60 cubic metres before igniting into a still larger fireball, he said.
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“The vapour cloud from one cylinder would fill the order of a big room, and when it ignited the effect would be even bigger,” Professor Michels said.
“In addition to the power of the explosion and the shrapnel, you would get a fireball the size of a small house...”
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Andy Oppenheimer, editor of Nuclear, Biological and Chemical International, said... “With that amount of petrol and an unknown quantity of pressurised gas, the blast would have been about 200 yards. If high explosive was involved, the blast could have reached half a mile...

“This would have been an explosion on the scale of those seen in the Middle
East, although not as big as some that have been seen in Baghdad recently.”*

Rendering the bomb safe might have involved "a water disruptor often delivered through a 'pig stick' - similar to a gun barrel - to try and separate the components of the charge without triggering an explosion," according to the Guardian. "Water could be fired at near-supersonic speeds down the stick and its force would be enough to pierce metal and destroy the bomb, but without causing a spark."