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Tuesday, 13 November, 2001, 15:52 GMT
Your questions on the war
Maria Gongora in Santiago, Chile:

I have read that the Americans are using a special kind of bombs in Afghanistan known as "daisy cutters" which have the power to incinerate everything within a distance of 500 metres. Could you tell me more?

BBC News Online writes:

"Daisy Cutter" is an extraordinary name for a huge bomb that can cause massive destruction.

It is similar in effect to fuel-air bombs which have been likened to tactical nuclear weapons, albeit without the radiation.

The effect is so horrific that one of the main reasons merely for threatening its use against an enemy is psychological

Fuel-air weapons exploit the devastating potential of almost any dust to explode in air - the cause of many accidents in coal mines, chemical plants and even grain stores.

They vaporise a fuel in the air then ignite it. This produces a fireball, and a rapidly-expanding blast wave many times greater than that from conventional explosives.

The BLU-82 is too big for that to work reliably, so it contains an oxidiser rather than using oxygen from the surrounding air.

Sowing fear

The massive blast is so horrific that one of the main reasons merely for threatening its use against an enemy is psychological.

In the Gulf War, US aircraft dropped leaflets on Iraqi troops depicting a huge bomb, with the slogan "Flee and Live, or Stay and Die!"

The type depicted in the leaflets, and now used in Afghanistan, is the BLU-82B Commando Vault or Big Blue 82, also known as the Daisy Cutter - so named for the blast pattern it leaves when viewed from above.

According to the US Air Force, 11 of these were dropped on Iraq.

They were used in the Vietnam War for creating instant helicopter landing sites in dense jungle.

Parachute descent

The bomb's warhead contains 12,600 lb (5,700 kg) of GSX, a slurry of ammonium nitrate - the basis of nitrogen fertiliser - highly flammable aluminium powder, and polystyrene-based soap as a thickener.

A Daisy Cutter is so big that it can be "launched" only by pushing it out of the open back door of a transport plane - typically the MC-130 special forces version of the Hercules is used.

The bomb descends under a stabilising parachute and is detonated just above the ground by a 38-in (97 cm) fuse, which sticks out of its nose.

When it explodes, it generates a massive pressure wave. Ordinarily, atmospheric pressure is just over 1 kg/sq cm (14.2 psi). In a Daisy Cutter explosion the pressure reaches about 70 kg/sq cm (1,000 psi) at the centre.

The effects are felt over an area typically reported to be the size of several football pitches.

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