Martin, it does interest me, I like to know what happened.
As an engineer at ICI we had chemicals, pressure, and highly inflammable compounds, every man and woman on the site had to attend the on site Fire Station for an up date each year which included fighting some sort of fire. The lads knew me so I usually got the bad one, often as I worked forward knowing the fire behind me was out it would self ignite from the heat of the surface it was on. Most of the explosions we had were pressure causing the initial blast then some outside element firing it up.
Rotting vegetation gives off methane which is why an open compost bin is better than a closed one it also depends on where it is full sun or shade.
Having lived in a house that used peat for fires you find it takes a while to fire up which was why we damped them down at night rather than let them go out.
The posters on here had a problem without cause, one a peat fire one an explosion, it would shake them and be a mystery but as you will know there is always an explanation, and as soon as Ash or carbon was added the light started to come on for me, we had to be very careful about the storage of Nitrates, which end up in most fertilizers.