Hi Sir George,
Obviously, not all crashes are survivable precisely because of impact injuries, but many are. However you don't have to have a crash for fire to be a hazard. An instructor acquaintance of mine had a cockpit fire in the air and had to land the aircraft PDQ. He survived the flight but was severely burned and spent some time in hospital. He, of course, was wearing one of those silly, poncy, cheapo, flammable, navy-blue, poly-cotton uniforms, which many instructors are required to wear, which didn't help. Cockpit fires generally start in the electrics, but in most small aircraft you have fuel lines going through the cockpit uncomfortably close to the instrument panel.
BP.