Steam explosion
Encyclopedia
A steam explosion
(also called a littoral
explosion, or fuel-coolant interaction, FCI) 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 the interaction of molten metals (e.g., Fuel-Coolant Interaction of molten nuclear-reactor fuel rods with water in a nuclear reactor
core following a core-meltdown
). Pressure vessels (e.g., Pressurized-Water (nuclear) Reactors
) that operate at above atmospheric pressure
can also provide the conditions for a rapid boiling event which can be characterized as 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 will 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
, and rely on release of stored superheat. But many large-scale events (e.g., 'Foundry Accidents') show evidence of an energy-release front propagating through the material (see description of FCI below), where the forces created fragment and mix the hot phase into the cold volatile one; 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 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). 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 reactor (an RBMK-1000 reactor
), is thought to have been due to such a steam explosion.
In a nuclear meltdown
the most severe outcomes would be those leading to 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 (e.g., the upper head) into, and through, the containment. Less onerous but still significant would be 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 coolable. See WASH-1400
for details.
Steam explosions are often encountered where hot lava
meets sea water. A dangerous steam explosion can 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.
and freezer production).
Steam explosions are naturally produced by certain volcano
s 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.
Explosion
An explosion is a rapid increase in volume and release of energy in an extreme manner, usually with the generation of high temperatures and the release of gases. An explosion creates a shock wave. If the shock wave is a supersonic detonation, then the source of the blast is called a "high explosive"...
(also called a littoral
Littoral
The littoral zone is that part of a sea, lake or river that is close to the shore. In coastal environments the littoral zone extends from the high water mark, which is rarely inundated, to shoreline areas that are permanently submerged. It always includes this intertidal zone and is often used to...
explosion, or fuel-coolant interaction, FCI) is a violent boiling or flashing of water into steam
Steam
Steam is the technical term for water vapor, the gaseous phase of water, which is formed when water boils. In common language it is often used to refer to the visible mist of water droplets formed as this water vapor condenses in the presence of cooler air...
, occurring when water is either superheated
Superheating
In physics, superheating is the phenomenon in which a liquid is heated to a temperature higher than its boiling point, without boiling...
, rapidly heated by fine hot debris produced within it, or the interaction of molten metals (e.g., Fuel-Coolant Interaction of molten nuclear-reactor fuel rods with water in a nuclear reactor
Nuclear reactor
A nuclear reactor is a device to initiate and control a sustained nuclear chain reaction. Most commonly they are used for generating electricity and for the propulsion of ships. Usually heat from nuclear fission is passed to a working fluid , which runs through turbines that power either ship's...
core following a core-meltdown
Nuclear meltdown
Nuclear meltdown is an informal term for a severe nuclear reactor accident that results in core damage from overheating. The term is not officially defined by the International Atomic Energy Agency or by the U.S. Nuclear Regulatory Commission...
). Pressure vessels (e.g., Pressurized-Water (nuclear) Reactors
Pressurized water reactor
Pressurized water reactors constitute a large majority of all western nuclear power plants and are one of three types of light water reactor , the other types being boiling water reactors and supercritical water reactors...
) that operate at above atmospheric pressure
Atmospheric pressure
Atmospheric pressure is the force per unit area exerted into a surface by the weight of air above that surface in the atmosphere of Earth . In most circumstances atmospheric pressure is closely approximated by the hydrostatic pressure caused by the weight of air above the measurement point...
can also provide the conditions for a rapid boiling event which can be characterized as 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
Scalding
Scalding is a process of burning using hot liquid such as boiling water. This may either be a deliberate treatment of material such as foodstuffs or accidental, resulting in injury....
and burning.
Steam explosions are not normally chemical explosions
Chemical explosive
The vast majority of explosives are chemical explosives. Explosives usually have less potential energy than fuels, but their high rate of energy release produces a great blast pressure...
, although a number of substances will react chemically with steam (for example, zirconium
Zirconium
Zirconium is a chemical element with the symbol Zr and atomic number 40. The name of zirconium is taken from the mineral zircon. Its atomic mass is 91.224. It is a lustrous, grey-white, strong transition metal that resembles titanium...
and superheated graphite
Graphite
The mineral graphite is one of the allotropes of carbon. It was named by Abraham Gottlob Werner in 1789 from the Ancient Greek γράφω , "to draw/write", for its use in pencils, where it is commonly called lead . Unlike diamond , graphite is an electrical conductor, a semimetal...
react with steam and air respectively to give off hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
, 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
A boiling liquid expanding vapor explosion occurs when a vessel containing a pressurized liquid above its boiling point ruptures.-Mechanism:...
, and rely on release of stored superheat. But many large-scale events (e.g., 'Foundry Accidents') show evidence of an energy-release front propagating through the material (see description of FCI below), where the forces created fragment and mix the hot phase into the cold volatile one; 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
Water hammer
Water hammer is a pressure surge or wave resulting when a fluid in motion is forced to stop or change direction suddenly . Water hammer commonly occurs when a valve is closed suddenly at an end of a pipeline system, and a pressure wave propagates in the pipe...
. This was the mechanism that caused the SL-1
SL-1
The SL-1, or Stationary Low-Power Reactor Number One, was a United States Army experimental nuclear power reactor which underwent a steam explosion and meltdown on January 3, 1961, killing its three operators. The direct cause was the improper withdrawal of the central control rod, responsible for...
nuclear reactor vessel to jump over 9 feet (2.7 m) in the air when it was destroyed by a criticality accident
Criticality accident
A criticality accident, sometimes referred to as an excursion or a power excursion, is an accidental increase of nuclear chain reactions in a fissile material, such as enriched uranium or plutonium...
. 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). 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
Chernobyl disaster
The Chernobyl disaster was a nuclear accident that occurred on 26 April 1986 at the Chernobyl Nuclear Power Plant in Ukraine , which was under the direct jurisdiction of the central authorities in Moscow...
, a graphite-moderated, light-water-cooled reactor (an RBMK-1000 reactor
RBMK
RBMK is an initialism for the Russian reaktor bolshoy moshchnosti kanalniy which means "High Power Channel-type Reactor", and describes a class of graphite-moderated nuclear power reactor which was built in the Soviet Union. The RBMK reactor was the type involved in the Chernobyl disaster...
), is thought to have been due to such a steam explosion.
In a nuclear meltdown
Nuclear meltdown
Nuclear meltdown is an informal term for a severe nuclear reactor accident that results in core damage from overheating. The term is not officially defined by the International Atomic Energy Agency or by the U.S. Nuclear Regulatory Commission...
the most severe outcomes would be those leading to 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 (e.g., the upper head) into, and through, the containment. Less onerous but still significant would be 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 coolable. See WASH-1400
WASH-1400
WASH-1400, 'The Reactor Safety Study, was a report produced in 1975 for the Nuclear Regulatory Commission by a committee of specialists under Professor Norman Rasmussen. It "generated a storm of criticism in the years following its release"...
for details.
Steam explosions are often encountered where hot lava
Lava
Lava refers both to molten rock expelled by a volcano during an eruption and the resulting rock after solidification and cooling. This molten rock is formed in the interior of some planets, including Earth, and some of their satellites. When first erupted from a volcanic vent, lava is a liquid at...
meets sea water. A dangerous steam explosion can 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.
Flash boiling in cooking
There is also a cooking technique called flash boiling, in which a smaller amount of water is used so as to quicken the process of boiling. An example of this technique is used to melt a slice of cheese onto a hamburger patty, whereby the cheese slice is placed on top of the meat on a high-heat surface (e.g., a hot frying pan), and a small quantity of cold water is thrown onto the surface near the patty. A vessel (such as a volume-rich small pot or frying-pan cover) is then used to quickly seal the steam-flash reaction, which disperses much of the steamed-water on the cheese/patty, which results in a large release of heat in a transfer resulting from the vaporized water condensing back into a liquid, resulting in an energy release (a principle also utilized in refrigeratorRefrigerator
A refrigerator is a common household appliance that consists of a thermally insulated compartment and a heat pump that transfers heat from the inside of the fridge to its external environment so that the inside of the fridge is cooled to a temperature below the ambient temperature of the room...
and freezer production).
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 volcano
Volcano
2. Bedrock3. Conduit 4. Base5. Sill6. Dike7. Layers of ash emitted by the volcano8. Flank| 9. Layers of lava emitted by the volcano10. Throat11. Parasitic cone12. Lava flow13. Vent14. Crater15...
s especially a stratovolcano
Stratovolcano
A stratovolcano, also known as a composite volcano, is a tall, conical volcano built up by many layers of hardened lava, tephra, pumice, and volcanic ash. Unlike shield volcanoes, stratovolcanoes are characterized by a steep profile and periodic, explosive eruptions...
and are a major cause of human fatalities in volcanic eruptions.
When a pressurized container such as the waterside of a steam boiler
Boiler
A boiler is a closed vessel in which water or other fluid is heated. The heated or vaporized fluid exits the boiler for use in various processes or heating applications.-Materials:...
ruptures, it is always followed by some degree of steam explosion. A common operating temperature
Operating temperature
An operating temperature is the temperature at which an electrical or mechanical device operates. The device will operate effectively within a specified temperature range which varies based on the device function and application context, and ranges from the minimum operating temperature to the...
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
Fire-tube boiler
A fire-tube boiler is a type of boiler in which hot gases from a fire pass through one or more tubes running through a sealed container of water...
" designs, where the heat was added by passing hot gases through tubes in a body of water, to "water-tube
Water-tube boiler
A water tube boiler is a type of boiler in which water circulates in tubes heated externally by the fire. Fuel is burned inside the furnace, creating hot gas which heats water in the steam-generating tubes...
" 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
Metal Fatigue
Metal Fatigue , is a futuristic science fiction, real-time strategy computer game developed by Zono Incorporated and published by Psygnosis and TalonSoft .-Plot:...
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
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
, and the cloth also serves to cool it down. Alternatively, a non-volatile purpose designed fire retardant
Fire retardant
A fire retardant is a substance other than water that reduces flammability of fuels or delays their combustion. This typically refers to chemical retardants but may also include substances that work by physical action, such as cooling the fuels; examples of these include fire-fighting foams and...
agent or simply a fire blanket
Fire blanket
A fire blanket is a safety device designed to extinguish small incipient fires. It consists of a sheet of fire retardant material which is placed over a fire in order to smother it ....
can be used instead.
See also
- BLEVEBLEVEA boiling liquid expanding vapor explosion occurs when a vessel containing a pressurized liquid above its boiling point ruptures.-Mechanism:...
- Boiler explosionBoiler explosionA boiler explosion is a catastrophic failure of a boiler. As seen today, boiler explosions are of two kinds. One kind is over-pressure in the pressure parts of the steam and water sides. The second kind is explosion in the furnace. Boiler explosions of pressure parts are particularly associated...
- multiphase flowMultiphase flowIn fluid mechanics, multiphase flow is a generalisation of the modelling used in two-phase flow to cases where the two phases are not chemically related or where more than two phases are present In fluid mechanics, multiphase flow is a generalisation of the modelling used in two-phase flow to...
- 2007 New York City steam explosion2007 New York City steam explosionThe July 18, 2007 New York City steam explosion sent a geyser of hot steam up from beneath a busy intersection, with a 40-story-high shower of mud and flying debris raining down on the crowded streets of Midtown Manhattan in New York City, New York, United States.It was caused by the failure of a...