London Bomb Plot: Fuel-Air Attack? (Updated)

Sometimes, it sucks being right. Our own David Hambling has been predicting for years that terrorists might try to jury-rig their own, devastating fuel-air attack -- an explosion with many times the strength of a normal bomb. The news from London today, about a thwarted car-bomb strike, just might confirm Hambling's dark forecast, unfortunately.

The BBC reports that the car was "packed with 60 litres of petrol, gas cylinders and nails," and noted the similarity to a plot by Dhiren Barot, who "was jailed for life last November for conspiring to park limousines packed with gas canisters underneath high-profile buildings before detonating them."

Back in November, Hambling took note of the so-called "Gas Limos" scheme, and observed that those cylinders might be an attempt to trigger a devastating fuel-air explosion.

This type of blast is much more effective at destroying buildings from the inside than normal ("condensed") explosives. One factor is the greater energy release from explosive mix that takes oxygen from the air, but the other is the sustained impulse that a fuel-air blast produces. Many structures rely on gravity for their structural strength - arches are a good example - or have very limited ability to withstand a horizontal load. A fuel-air blast has long enough duration to cause such structures to lose their integrity, and basically they just fall apart.

Luckily, that didn't happen today. And, as Hambling writes in, "the fact that the car was also said to have contained a quantity of nails - presumably intended as shrapnel - suggests that whoever assembled the device did not have much idea about fuel-air blasts. An exploding cloud would not project anything deep inside it outwards at any great speed."

UPDATE: A warning for the future though: traditional defenses against car bombs may not work against this kind of attack. "In particular," Hambling notes, "barriers set up to give a safe stand-off distance from truck or car bombs packed with conventional explosives may be not enough to prevent a fuel-air blast which can create dangerous overpressure at a much greater range."

"One other thing," he adds: We're Not Afraid