Not a lot it would appear.
I remember two, one in 1975 - a new SOAF (Oman) BAC 1-11 (1003) was being charged with oxygen at Muscat for the first time since delivery about 10 days previously. The Oxy cart regulator was sticky and suddenly opened with full, 3600psi, pressure. The charging adaptor had the wrong type of seal fitted and it caught fire. The cockpit was gutted by the fire and the aircraft was dismantled and returned by sea to the factory at Hurn for repair. Total aircraft hours was 78 hrs 45 mins at the time. I know this as I had to fill out the avionic component record cards when the aircraft returned to Muscat in 1976 after repair.
The other I know of was a Saudi DC-8-63 at Luxemburg about 1981. A friend of mine worked there. They had just completed a major check on the aircraft and when he came to work the day it was due to depart he found fire engines everywhere and the aircraft cabin was burnt out to the floor line.
In each case nobody was hurt.
Hopefully these events are very rare.