We were somewhere around Barstow, on the edge of the desert, when the
drugs began to take hold. I remember John Rumm
saying something like:

I was thinking of two - one where the plastic header tank got back
filled with hot and failed, and another where a cylinder ruptured and
dumped hot water on sleeping people below.

I thought they were both storage tank collapse incidents. What caused the
cylinder to rupture, do you know? Sounds almost as if it had gone
unvented.

The recentish one certainly was. I am not sure the older report actually
contained specific info - only "burst hot water cylinder".

Undersized vent scaling up, or inappropriate fitting of a gate valve in
the wrong place would seem like obvious culprits though.

There was one a few years back where the owner /renter had been nicking
power and the hot tank was on permanently. The stat had failed shut and
the chalky water over the years had closed the vent pipe down. Resulting
steam explosion took out the back wall of the house.