Mechanical Consulting Group Inc.
2208 Magnolia Lane
Elgin, IL 60120
Ph: (630) 830-2083
Fax: (630) 830-0630


Most steam explosions are involved with a boiler. The boiler can be either a hot water boiler or a steam boiler. A steam boiler is more likely to explode than a hot water boiler.

Most boiler explosions are a result of the boiler running dry or running out of water (dry fired) and then water from either the water feeder, boiler feed water pump, or condensate return enters the boiler. When water enters the boiler which is probably red hot the water turns to steam instantly and it is likely that there will be a boiler explosion. Contrary to popular belief a pressure relief will not stop the explosion. The amount of heat that is built up into the boiler and the amount of steam that is instantly generated is more that the pressure relief can handle.

The most common cause of a steam explosion is the failure or lack of a low water cut off. It is also possible that the low water cut off was bypassed or jumped out.

Low water cut off controls are required on all steam boilers and hot water boilers that have an input of 400,000 BTU per hour or more.

In a steam explosion the boiler sections that contain the steam and or water are damaged.

There are also cases many cases where there is not enough heat and or water to cause the boiler to explode. Fortunately there is no explosion. In these cases the cast iron boiler section cracks and leaks water. This is typical of boilers with cast iron boiler sections. The cause is often due to the malfunction of the low water cut off.

If there is a natural gas or propane explosion with a boiler the damage is in the burner area and generally the flue pipe is damaged or blown apart. The cabinet of the boiler may also be damaged if the boiler has burners (ribbon burners) similar to those of an older style home furnace

There are two types of boilers. One type is for steam and the other is for hot water. A steam boiler has a vertical glass sight glass or tube so that the water level in the boiler can be observed. There is also a low water cut off control and a boiler feed water control for a steam boiler. A hot water boiler will have one or more pumps driven by electric motors. A hot water boiler also has an expansion tank. The expansion tank may be as small as 12 inches in diameter by 12 inches long or as large as 36 inches in diameter by 10 feet long. The small tank is generally located on the water piping that goes to the boiler. Larger expansion tanks are typically hung from the ceiling of the boiler room.





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