But it’s the smokebox that’s blown up - that part doesn’t normally hold that much pressure, does it? Nor is there any gauge to measure that pressure.
Perhaps a steam leak pressurized the smoke box ?
Two different types of boilers:
1. Pipes with water/steam surrounded by fire/combustion gas, basically two tanks connected by a bundle of pipes.
2. Pipes leading combustion gas through a tank filled with water/steam.
If it is nr 1 the steam pressure can blow out the lid at the front or rear, the pipes end in an enclosed space at both ends. If the front lid blows it will take out the fire box. If the rear end blows it will take out the crew.
If it is nr 2 there will be steam pressure above the tubes and in the steam collection boxes located inside the smoke box (keeps the steam hot). A blowout there will also blast the smoke box.
There were also some older designs before they settled down to water tube or fire tube, links in the wikipedia article about nr 2 type (fire tube boilers)
Water tube boilers were not a success in locomotives, the were maintenance intensive, had requirements on water quality and didn’t like vibrations. Rumbling along on railroad tracks with joints, having to use water from local sources wasn’t the preferred environment
That lid with all the pipe ends could be the front of the water tank, all the pipes pass through it to exit into the smoke box. Too much pressure and the lid blows.
Fire tube boiler:
Trivia: There was water surrounding the fireplace so the tank had one surface towards the fire and one surface facing the outside world. The flat plates were held together by rods with a thin hole running the whole length or possibly with a thin wall in the middle. If the rod breaks water/steam will enter into the cavity and exit into the fireplace or out the side of the locomotive. In either case the water/steam will indicate which rod is broken.
The ballad of Casey Jones comes to mind.
IIRC most American locos used the “flue tubes in water tank” design. The tank extended over the top of the firebox roof, helping cool the steel so the fire didn’t soften it or allow the rivets to work loose. Trouble starts when the water level is allowed to run low, leaving dry hot air above the firebox, which eventually weakens until it springs a leak. Suddenly ALL of the superheated water in the boiler has an escape route, and it ALL wants to turn to steam at some 1300 times the volume! As the new hole is the only escape route, it forms a jet of steam down into the firebox, filling the cab with burning coal and scalding steam instantly, to the obvious detriment of the crew. It also forces the back end of the boiler upwards propelled by the jet, sometimes ripping the whole boiler off the frame and sending it somersaulting forwards. Depending on the strength of the boiler it might blow out the sides, or even travel the flues to blow out the smokebox at the front. Bad news for the crew regardless…
There is a photo somewhere of a Swedish locomotive which was being pressure tested after some repairs. The test was done inside the engine shed.
It failed.
The locomotive jumped through the roof and landed outside the shed …
The first days of April 1902.
Built 1869 by Hatcham Iron Works, George England & Co, London, England
Found a facebook discussion about it and this photo from the US was in that discussion.
May 12th 1948 5 miles east of Chillicothe Ohio
The inside of the shed where the accident occured.
The landing site
Apparently the damages couldn’t be buffed out so they scrapped it.
The cause was a blocked pressure gauge, they kept heating and heating but the pressure gauge didn’t show a pressure increase and then the bottom blew out and launched the locomotive through the roof.
That looks bad, but for really massive steam explosions you can’t beat when Chernobyl and Fukushima popped their corks…
M
P.S. Steam can be a problem even after it leaves the boiler/heat exchanger;
there is much fun (NOT!) to be had when a steam turbine fails…
That first pic looks like a parasite exploded inside that thing.
