The risk of fire due to carrying out hot works is a matter of serious concern - while firesafe roofing products can be promoted as fire retardant they can still pose a significant fire risk during application.
For instance, many bitumen roofing products still require the use of naked flame. Halogen can assist with fire retardancy, but it carries a carcinogenic risk and will be reclassified and ultimately banned under the new EU directive EC793/93. Once removed, bituminous compounds will become flammable again. Another method is to use a fire resistant carrier fleece sandwiched between coats of bitumen, but the two outer coats still remain inflammable.
Using hot air instead of naked flame does not reduce the risk either, as the three elements of fire ignition remain, namely fuel (eg bitumen/ PVC membrane), oxygen (air) and an ignition source (a hot air gun). Hot air guns are based on the theory that, by forcing hot gas at high pressure onto a roofing membrane, the area will be heated while being starved of oxygen. This works while the gun is pointed at the roof, but as soon as it is removed, oxygen (air) rushes in to fill the void left by the pressurised hot gas.
Liquid Plastics Limited (LPL) has much interest in their state-of-the-art liquid roofing membrane, Decothane. This can be cold applied using zero flame, zero heat technology. Decothane has been successfully tested to stringent BS and DD ENV standards.