51¶¯Âþ

51¶¯Âþs at the Porton Down chemical and biological defence centre in
Wiltshire are worried about nerve gas attacks affecting aircraft (WO 01/07118).
If the gas is released into the atmosphere ahead of a plane, the engine’s air
intakes sucks in the poison and the air-conditioning system distributes it
around the cabin. No system currently available gives protection, admits Porton
Down. Conventional carbon filters are destroyed by the engine heat. To counter
the gas, Porton Down uses a filter made of zeolite crystals impregnated with
copper or chromium. This can handle the engine heat, and filters sarin, mustard
gas and the irritant gas lewisite before they can get into the cabin.