Steam Explosion - Other Rapid Boiling Phenomena

Other Rapid Boiling Phenomena

High steam generation rates are possible under other circumstances, such as boiler-drum failure, or at a quench front (for example when water re-enters a hot dry boiler). Though potentially damaging, they are usually less energetic than events in which the hot ("fuel") phase is molten and so can be finely fragmented within the volatile ("coolant") phase. Some examples follow:

Steam explosions are naturally produced by certain volcanos especially a stratovolcano and are a major cause of human fatalities in volcanic eruptions.

When a pressurized container such as the waterside of a steam boiler ruptures, it is always followed by some degree of steam explosion. A common operating temperature and pressure for a marine boiler is around 950 P.S.I. (6.55 MPa) and 850 °F (454 °C) at the outlet of the superheater. A steam boiler has an interface of steam and water in the steam drum, which is where the water is finally evaporating due to the heat input, usually oil-fired burners. When a water tube fails due to any of a variety of reasons, it will cause the water in the boiler to expand out of the opening into the furnace area that is only a few P.S.I. above atmospheric pressure. This will likely extinguish all fires and expands over the large surface area on the sides of the boiler. To decrease the likelihood of a devastating explosion, boilers have gone from the "fire-tube" designs, where the heat was added by passing hot gases through tubes in a body of water, to "water-tube" boilers that have the water inside of the tubes and the furnace area is around the tubes. Old "fire-tube" boilers were known to fail due to poor build quality or lack of maintenance (such as corrosion of the fire tubes, or fatigue of the boiler shell due to constant expansion and contraction). A failure of fire tubes forces large volumes of high pressure, high temperature steam back down the fire tubes in a fraction of a second and often blows the burners off the front of the boiler, whereas a failure of the pressure vessel surrounding the water would lead to a full and entire evacuation of the boiler's contents in a large steam explosion. On a marine boiler, this would certainly destroy the ship's propulsion plant and possibly the corresponding end of the ship.

In a more domestic setting, steam explosions can be a result of incorrectly handled chip pan fires. When oil in a pan is on fire, the natural impulse may be to extinguish it with water. However, doing so will cause the water to become superheated by the hot oil. Upon turning to steam, it will disperse upwards and outwards rapidly and violently in a spray also containing the ignited oil. It is for this reason that the correct course of action for dealing with such fires is to either use a damp cloth or a tight lid on the pan; both help deprive the fire of oxygen, and the cloth also serves to cool it down. Alternatively, a non-volatile purpose designed fire retardant agent or simply a fire blanket can be used instead.