Regarding Williams last post I have heard the vast majority of bursts on the old agricultural traction engines (steam) was from low water. If the area over the fire-box known as the Crown Sheet was allowed to get "Dry" as William said it soon became red hot & lost the strength to hold the pressure which caused it to blow down into the fire box, & of course the engineer was right there behind the firebox, possibly even with the door open feeding fuel at the time. A few years back an engine blew at a major steam threshers reunion & I believe this was decided to be the cause.

Miller/TN
I Didn't Say Everything I Said, Yogi Berra