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See also: Boiler explosion and BLEVE
Littoral explosion at Waikupanaha ocean entry at the big island of Hawaii was caused by the lava entering the ocean

A steam explosion is a violent boiling or flashing of water into steam, occurring when water is either superheated, rapidly heated by fine hot debris produced within it, or heated by the interaction of molten metals (as in a fuel-coolant interaction, or FCI, of molten nuclear-reactor fuel rods with water in a nuclear reactor core following a core-meltdown). Pressure vessels, such as pressurized water (nuclear) reactors, that operate above atmospheric pressure can also provide the conditions for a steam explosion. The water changes from a liquid to a gas with extreme speed, increasing dramatically in volume. A steam explosion sprays steam and boiling-hot water and the hot medium that heated it in all directions (if not otherwise confined, e.g. by the walls of a container), creating a danger of scalding and burning.

Steam explosions are not normally chemical explosions, although a number of substances react chemically with steam (for example, zirconium and superheated graphite react with steam and air respectively to give off hydrogen, which burns violently in air) so that chemical explosions and fires may follow. Some steam explosions appear to be special kinds of boiling liquid expanding vapor explosion (BLEVE), and rely on the release of stored superheat. But many large-scale events, including foundry accidents, show evidence of an energy-release front propagating through the material (see description of FCI below), where the forces create fragments and mix the hot phase into the cold volatile one; and the rapid heat transfer at the front sustains the propagation.

If a steam explosion occurs in a confined tank of water due to rapid heating of the water, the pressure wave and rapidly expanding steam can cause severe water hammer. This was the mechanism that, in Idaho, USA, in 1961, caused the SL-1 nuclear reactor vessel to jump over 9 feet (2.7 m) in the air when it was destroyed by a criticality accident. In the case of SL-1, the fuel and fuel elements vaporized from instantaneous overheating.

Events of this general type are also possible if the fuel and fuel elements of a liquid-cooled nuclear reactor gradually melt. Such explosions are known as fuel-coolant interactions (FCI).[citation needed] In these events the passage of the pressure wave through the predispersed material creates flow forces which further fragment the melt, resulting in rapid heat transfer, and thus sustaining the wave. Much of the physical destruction in the Chernobyl disaster, a graphite-moderated, light-water-cooled RBMK-1000 reactor, is thought to have been due to such a steam explosion.

In a nuclear meltdown, the most severe outcome of a steam explosion is early containment failure. Two possibilities are the ejection at high pressure of molten fuel into the containment, causing rapid heating; or an in-vessel steam explosion causing ejection of a missile (such as the upper head) into, and through, the containment. Less dramatic but still significant is that the molten mass of fuel and reactor core melts through the floor of the reactor building and reaches ground water; a steam explosion might occur, but the debris would probably be contained, and would in fact, being dispersed, probably be more easily cooled. See WASH-1400 for details.

Steam explosions are often encountered where hot lava meets sea water. Such an occurrence is also called a littoral explosion. A dangerous steam explosion can also be created when liquid water encounters hot, molten metal. As the water explodes into steam, it splashes the burning hot liquid metal along with it, causing an extreme risk of severe burns to anyone located nearby and creating a fire hazard.

Practical uses[edit]

Steam turbines[edit]

A water vapor explosion creates a high volume of gas without producing environmentally harmful leftovers. The controlled explosion of water has been used for generating steam in power stations and in modern types of steam turbines. Newer steam engines use heated oil to force drops of water to explode and create high pressure in a controlled chamber. The pressure is then used to run a turbine or a converted combustion engine. Hot oil and water explosions are becoming particularly popular in concentrated solar generators, because the water can be separated from the oil in a closed loop without any external energy. Water explosion is considered to be environmentally friendly if the heat is generated by a renewable resource.

Flash boiling in cooking[edit]

A cooking technique called flash boiling uses a small amount of water to quicken the process of boiling. For example, this technique can be used to melt a slice of cheese onto a hamburger patty. The cheese slice is placed on top of the meat on a hot surface such as a frying pan, and a small quantity of cold water is thrown onto the surface near the patty. A vessel (such as a pot or frying-pan cover) is then used to quickly seal the steam-flash reaction, dispersing much of the steamed water on the cheese and patty. This results in a large release of heat, transferred via vaporized water condensing back into a liquid (a principle also utilized in refrigerator and freezer production).

Other rapid boiling phenomena[edit]

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.

The 1986 Chernobyl nuclear disaster in Soviet Union was feared to cause major steam explosion (and resulting Europe-wide fallout) upon melting the lava-like nuclear fuel through the reactor's basement towards contact with residue fire-fighting water and groundwater. The threat was averted by frantic tunneling underneath the reactor in order to pump out water and reinforce underlying soil with concrete.

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 causes 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 often failed 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 trying to extinguish burning oil with water. 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.

See also[edit]

Bibliography[edit]


Original courtesy of Wikipedia: http://en.wikipedia.org/wiki/Steam_explosion — Please support Wikipedia.
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426 news items

newtoncitizen

newtoncitizen
Tue, 25 Nov 2014 13:56:15 -0800

Frying a frozen turkey will cause a steam explosion. ##• Never overfill a fryer pot, and keep a fire extinguisher nearby in case of an emergency. Additionally, never let children near a fryer. ##• Once the turkey is done cooking, precautions for the ...

MinnPost

MinnPost
Thu, 20 Nov 2014 07:37:57 -0800

Just getting the raw material down to digestibly small particle sizes can require treatment with acids, heat, high-pressure "steam explosion." So there's been interest in learning how this happens in low-intensity biological venues like, say, the ...
 
WDBJ7
Fri, 31 Oct 2014 21:07:30 -0700

The United States Department of Agriculture has asked Virginia Tech to find an environmentally friendly way to kill these invasive snails. Researchers have come up with what could be called a portable steam oven. Scientists call it their steam ...
 
Washington Business Journal (blog)
Tue, 26 Aug 2014 07:48:45 -0700

Companies contracted by the GSA have been embroiled in two lawsuits for the last decade, after two workers were killed in an explosion during modifications to steam and water systems under 17th Street NW. Commuter's Dream on 2 Acres 15 photos ...
 
JD Supra (press release)
Wed, 19 Nov 2014 09:26:15 -0800

In G&S Metal Consultants, the insured filed suit challenging the amount of insurance proceeds paid for property damage and business interruption resulting from a November 29, 2007 steam explosion at one of its facilities. During the beginning stages of ...
 
Business Standard
Thu, 30 Oct 2014 05:28:57 -0700

According to unconfirmed reports, China's first aircraft carrier appeared to suffer a steam explosion during the recent trials that temporarily knocked out the carrier's electrical power system. Yang however declined to answer questions regarding the ...

Hydrocarbon Processing

Hydrocarbon Processing
Mon, 03 Nov 2014 13:04:27 -0800

A steam explosion occurred at Total's Antwerp refinery, resulting in two fatalities. There is a limited basis for comparison with the steam explosion at an LNG plant in Algeria in 2004. If steam was the lethal agent in the Antwerp explosion, then ...

OnEarth Magazine

OnEarth Magazine
Thu, 21 Aug 2014 09:17:15 -0700

Another Icelandic volcano is primed to erupt. What can these events teach us about climate change? by Brian Palmer @PalmerBrian • August 20, 2014. It's not quite a sharknado, but the possible impending eruption of a mile-high volcano under Iceland's ...
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