The Belvedere had a very interesting starter system for each engine. Their lordships of the Air Council decreed that the aircraft should be independent in the field, of any external starter aids, so the BTH cartridge initiated Avpin system was fitted.
The only trouble was, the Avpin tank was above the cartridge breech, so if there was a seal leak over night, Avpin would fill the cartridge chamber.
The result of this, was that when you went to do the first start in the morning, the whole thing would explode.
The fix for this was to armour plate the co-pilots seat, the rear engine was no problem, as you had enough time to evacuate.