A Fire Prevention Sub-Committee of the Aeronautical Research Council published its findings in 1922. At that time the major risk was from crash fires in which the fuel was ignited by the engine either directly or indirectly through the medium of oil, wood, fabric or dry grass. Preventive measures recommended included crash-proof tanks, with a suggestion that these should be carried on the wings; fire-proof bulkheads; fire-proofing of inflammable materials; cooling of exhaust pipes; and fire-proofing of magnetos. Fires in flight were usually in the carburettor and a successful carbon tetrachloride extinguisher was designed at the Royal Aircraft Establishment and tested in flight by the late Squadron Leader Norman. However, the weight of the system, about 35 lb. per engine, was considered excessive and the action recommended was to turn off the fuel and dive the aeroplane.