Many busses would be taken off the road if age/condition were a factor!
They are full of flammable seating, etc.
Buses are not the worst - coaches have more soft furnishings, are not designed for rapid emptying, and have passengers who are (even) more likely to be old and slow-moving, plus they are more likely to be asleep.
BEA-TT does cover a few of the most serious road vehicle accidents in France. Their report on the Puisseguin bus fire (2015) was in some ways the most shocking accident report I have read. Nothing like the violence of some derailments, but 41 of the 49 passengers died in a bus that was barely damaged and with all the doors promptly opened, and while there was burning diesel on the ground it did not come near the doors.
Does that name mean anything to anyone here? Obviously it is better known in France, especially as a kind of "Axminster plus" - the passengers came from a couple of tiny villages, so a number of families lost two or more members and the older members of the population knew almost all of them.