Locomotive boiler explosion

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Rick A

Active Member
This is what could happen if you didn't have a reliable safety valve! Like an Ashton Valve

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I think what impresses me most is the driving wheels having been driven into the ground, along with the rails. And the boiler walls are gone. Yeesh!


This not caused by overpressure of the boiler due to a failed safety valve. Instead it is caused by low boiler water level. Water level over the crown sheet, top of firebox, keeps the crown sheet cool enough to maintain its strength. When the water level drops below the crown sheet it will heat up to the point the steel softens and pulls away from the stay bolts. When the interior of the boiler open to atmosphere all the water inside will try to boil instantly. It's the sudden expansion that blows the boiler off the frame.

Rick A

Active Member
The stats on boiler explosions are scary!

"Another explosion in July of 1894 at a lumber mill caused the death of 4 workers and did substantial damage to the mill. It was a horizontal tube type boiler and when the explosion occurred the pressure was probably about 500 psi. The boiler head was blown out and the rest of the shell left the boiler room and flew through the air for a distance of over 1200 feet. During it’s flight it passed through the mill and over several houses at a height of about 80 feet. The last 350 feet of it’s flight was through a dense and heavy woods where it cut off everything in it’s path including a tree which was 28 inches in diameter. The insurance company stated “the safety valve did not work.” It obviously wasn’t an Ashton Valve!
In May of 1894 many people living in the town of West Bay City were terrified by the explosion of a boiler in the local planing mill. Buildings in the area were badly shaken up and the sidewalks of buildings nearby were littered with the glass from broken windows. The mill itself was wrecked and the boiler blown into 4 pieces. The engineer was blown against a sawing machine, cutting his lungs and heart out. Brick was thrown for a quarter of a mile. The late engineer was known to have a habit of running boilers with low water, claiming it was more efficient. In the years between 1885 and 1895, there were an average of 200 boiler explosions a year. Between 1895 and 1905, there were 3216 boiler explosions in the United States, and average of one a day, resulting in 7600 deaths and countless injuries."
That's a LOT worse safety record than I knew! These days an occasional water heater gets launched through a roof. I hope it's due to far fewer boilers (and stored energy) and much more stringent safety enforcement. But imagine the stored energy in the larger coal-fired and even nuclear power plants that use steam turbines. Do water-tube boilers have a better safety record?

Rick A

Active Member
There was an old trade journal called "The Safety Valve". It's a great read and every month they had a full page feature on boiler explosions. Very graphic too.
I think the safety enforcement has a lot to do with it. Way back there seemed to be no rules. Or not many.

Rick A

Active Member
Here are some eye opening statistics from a Hartford Steam Boiler Inspection and Insurance report from 1890.

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Rick A

Active Member
Here are some eye opening statistics from a Hartford Steam Boiler Inspection and Insurance report from 1890.

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For over 150 years the Hartford Steam Boiler Inspection and Insurance Co. has been documenting (and insuring) boiler explosions in their quarterly journal, "The Locomotive"
Here is some information about the company and their journal.






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