Remember the 21 days a Jag would sit on Q then someone realised in that period a good layer of fuel vapour would settle close to the ground in the HAS and the Static inverters in the HAS's were not sealed or fireproof, so the possibility existed of the open electric motor setting the lot off... The typical RAF cure to fix the issue was to stick it on top of a 4 inch deep lump of timber to lift it out of the danger zone, as they had worked out the vapour layer wouldn't get that high, even though no one seemed to have thought that doing the morning checks would stir the vapour up...