BLEVEs

Back when trains ran on steam engines, what would happen if the train, for whatever reason, ran out of water to boil in the middle of no-where?

Didn’t let it happen. What you get before you run out of water is a BLEVE.

It means Boiling Liquid Expanding Vapour Explosion. When the water level in the boiler sinks below the safe level, the water begins to boil all over, and in the end it explodes. The crown plate gives in, and the boiler expunges the superheater and the fire tubes off.

This is a steam engine boiler. The firebox, where the fuel is burned, is at the left. The boiler consists of hundreds of fire tubes, with gaps between them being filled with water.

Now the exhaust gasses go through the fire tubes to the smokebox and smokestack, and heat the water. Some of the water boils and rises to the stetson-like steam dome, from where it is led to the work cylinders to move the engine ahead.

The water jacket surrounding the fire tubes also cools the fire tubes and the crown plate. Now if the water level lowers down so that it exposes the fire tubes and/or the crown plate, their temperature is likely to rise extremely high, and as the tenacity of steel lowers with extreme heat, the result is a rupture.

Now the hot gasses from the firebox get directly in contact with the water. The water boils immediately - and it expands 1700-fold. One litre of water liquid produces 1700 litres of steam - yes, that is 1.7 cubic metres. If the crown plate gives way but the fire tubes stay intact, the result is a sudden drop in a pressure - and flash evaporation and boiling of the water in the boiler.

The result is a boiler explosion. Usually the engine crew on the footplate are scalded to death.

Source: Some or all of the content was generated using an AI language model