Lightening - Powerful source of energy and fire creation. Mechanical - due to friction when objects are rubbed together. Ancients lit fires that way. Rotating machinery can generate a lot of friction heat and start a fire. A. Chemical - Detonations propagate at the speed of sound.
Deflagrations propagate at subsonic speeds.
B. Mechanical - Steam explosions whether in boilers or pipes are awful. D. Thermal - unstable material decomposing in a closed environment. Gas and heat build up and are contained until they blow apart the container. 35,000 ppm-min is likely to be dangerous. Terrible irritant to eyes and upper respiratory tract with resulting impairment at 75 ppm.