A boiling liquid expanding vapor explosion (BLEVE, /ˈblɛviː/ BLEV-ee) is an explosion caused by the rupture of a vessel containing a pressurized liquid that is or has reached a temperature sufficiently higher than its boiling point at atmospheric pressure. [1] [2] Because the boiling point of a liquid rises with pressure, the contents of the pressurized vessel can remain a liquid as long as the vessel is intact. If the vessel's integrity is compromised, the loss of pressure drops the boiling point, which can cause the liquid to convert to gas expanding rapidly. BLEVEs are manifestations of explosive boiling.
If the gas is flammable, as is the case with e.g., hydrocarbons and alcohols, further damage can be caused by the ensuing fire. However, BLEVEs do not necessarily involve fire.
On 24 April 1957, a process reactor at a Factory Mutual (FM) facility underwent a powerful explosion as a consequence of a rapid depressurization. It contained formalin mixed with phenol. The burst damaged the plant. However, no fire developed, as the mixture was not flammable. In the wake of the accident, researchers James B. Smith, William S. Marsh, and Wilbur L. Walls, who were employed with FM, came up with the terms "boiling liquid expanding vapor explosion" and its acronym "BLEVE". [3] [4] The expressions did not become of common use until the early 1970s, when the National Fire Protection Association's (NFPA) Fire Command and Fire Journal magazines started publishing articles using them. [5]
There are three key elements in the formation of a BLEVE: [6]
Typically, a BLEVE starts with a vessel containing liquid held above its atmospheric-pressure boiling temperature. Many substances normally stored as liquids, such as carbon dioxide, propane, and other industrial gases have boiling temperatures below room temperature when at atmospheric pressure. In the case of water, a BLEVE could occur if a pressure vessel is heated beyond 100 °C (212 °F). That container, because the boiling water pressurizes it, must be capable of holding liquid water at very high temperatures.
If the pressurized vessel ruptures, the pressure which prevents the liquid from boiling is lost. If the rupture is catastrophic, i.e., the vessel becomes suddenly no longer capable of holding any pressure, then the liquid will find itself at a temperature far above its boiling point. This causes a portion of the liquid to instantaneously vaporize with extremely rapid expansion. Depending on temperatures, pressures and the material involved, the expansion may be so rapid that it can be classified as an explosion, fully capable of inflicting severe damage on its surroundings.
For example, a tank of pressurized liquid water held at 350 °C (662 °F) might be pressurized to 10 MPa (1,500 psi) above atmospheric (or gauge) pressure. If the tank containing the water were to rupture, there would for a brief moment exist a volume of liquid water which would be at:
At atmospheric pressure the boiling point of water is 100 °C (212 °F). Liquid water at atmospheric pressure does not exist at temperatures higher than 100 °C (212 °F). At that moment, the water would boil and turn to vapor explosively, and the 350 °C (662 °F) liquid water turned to gas would take up significantly more volume (≈ 1,600-fold) than it did as liquid, causing a vapor explosion. Such explosions can happen when the superheated water of a boiler escapes through a crack in a boiler, causing a boiler explosion.
The vaporization of liquid resulting in a BLEVE typically occurs within 1 millisecond after a catastrophic loss of containment. [7]
For a BLEVE to occur, the boiling liquid must be sufficiently superheated upon loss of containment. For example, at a pressure of approximately 1 MPa (150 psi), water boils at 177 °C (351 °F). Superheated water released from a closed container at these conditions will not generate a BLEVE, as homogeneous nucleation of vapor bubbles is not possible. [8] There is no consensus about the minimal temperature above which a BLEVE will occur. A formula proposed by Robert Reid to predict it is:
where TC is the critical temperature of the fluid (expressed in kelvin). The minimum BLEVE temperatures of some fluids, based on this formula, are as follows: [9]
Substance | Tmin,BLEVE | ||
---|---|---|---|
K | °C | °F | |
Water | 579 | 306 | 583 |
n-Octane | 509 | 236 | 457 |
n-Heptane | 483 | 210 | 410 |
n-Hexane | 454 | 181 | 358 |
n-Pentane | 421 | 148 | 298 |
Ethyl eter | 418 | 145 | 293 |
Phosgene | 407 | 134 | 273 |
n-Butane | 381 | 108 | 226 |
Chlorine | 375 | 102 | 216 |
Ammonia | 363 | 90 | 194 |
Propane | 331 | 58 | 136 |
Propylene | 327 | 54 | 129 |
Ethane | 273 | 0 | 32 |
Carbon dioxide | 272 | –1 | 30 |
Ethylene | 253 | –20 | –4 |
Methane | 171 | –102 | –152 |
According to Reid, BLEVE will occur, more in general, if the expansion crosses a "superheat-limit locus". In Reid's model, this curve is essentially the fluid's spinodal curve as represented in a pressure–temperature diagram, and the BLEVE onset is a manifestation of explosive boiling, where the spinodal is crossed "from above", i.e., via sudden depressurization. However, direct correspondence between the superheat limit and the spinodal has not been proven experimentally. In practical BLEVEs, the way the pressure vessel fails may influence decisively the way the expansion takes place, for example causing pressure waves and non-uniformities. Additionally, there may be stratification in the liquid, due to local temperature variations. Because of this, it is possible for BLEVEs to occur at temperatures less than those predicted with Reid's formula. [10]
The term BLEVE is often associated to explosive fires from pressure vessels containing a flammable liquid. However, a BLEVE can occur even with a non-flammable substance such as water, [11] liquid nitrogen, liquid helium or other refrigerants or cryogenics. Such materials can go through purely physical BLEVEs, not entailing flames or other chemical reactions. In the case of unignited BLEVEs of liquefied gases, rapid cooling due to the absorption of the enthalpy of vaporization is a hazard that can cause frostbite. Asphyxiation from the expanding vapors is also possible, if the vapor cloud is not rapidly dispersed, as can be the case inside a building, or in a trough in the case of heavier-than-air gasses. The vapors can also be toxic, in which case harm and possibly death can occur at relatively low concentrations and, therefore, even far from the source.
If a flammable substance, however, is subject to a BLEVE, it can ignite upon release, either due to friction, mechanical spark or other point sources, or from a pre-existing fire that had engulfed the pressure vessel and caused it to fail in the first place. In such a case, the burning vapors will further expand, adding to the force of the explosion. Furthermore, a very significant amount of the escaped fluid will burn in a matter of seconds in a raising fireball, which will generate extremely high levels of thermal radiation. While the blast effects can be devastating, a flammable substance BLEVE typically causes more damage due to the fireball thermal radiation than the blast overpressure.
BLEVEs are often caused by an external fire near the storage vessel causing heating of the contents and pressure build-up. While tanks are often designed to withstand great pressure, constant heating can cause the metal to weaken and eventually fail. If the tank is being heated in an area where there is no liquid (such as near its top), it may rupture faster because the boiling liquid does not afford cooling in that area. Pressure vessels are usually equipped with relief valves that vent off excess pressure, but the tank can still fail if the pressure is not released quickly enough. [1] A pressure vessel is designed to withstand the set pressure of its relief valves, but only if its mechanical integrity is not weakened as it can be in the case of an impinging fire. [12] In an impinging fire scenario, flammable vapors released in the BLEVE will ignite upon release, forming a fireball. The origin of the impinging fire may be from a release of flammable fluid from the vessel itself, or from an external source, including releases from nearby tanks and equipment. For example, rail tank cars have BLEVEd under the effect of a jet fire from the open relief valve of another derailed tank car. [13]
The main damaging effects of a BLEVE are three: the blast wave from the explosion; the projection of fragments, or missiles, from the pressure vessel; and the thermal radiation from the fireball, where one occurs. [12]
Horizontal cylindrical ("bullet") tanks tend to rupture longitudinally. This causes the failed tank and its fragments to get propelled like rockets and travel long distances. [14] At Feyzin, three of the propelled fragments weighed in excess of 100 tons and were thrown 150–350 meters (490–1150 ft) from the source of the explosion. One bullet tank at San Juanico travelled 1,200 meters (0.75 mi) in the air before landing, possibly the farthest ever for a BLEVE missile. [15] Fragments can impact on other tanks or equipment, which may result in a domino effect propagation of the accidental sequence. [7]
Fireballs can rise to significant heights above ground. [14] They are spheroidal when developed and rise from the ground in a mushroom shape. [7] The diameter of fireballs at San Juanico was estimated at 200–300 meters (660–980 ft), with a duration of around 20 seconds. Such massive fires can injure people at distances of hundreds of meters (e.g., 300 m (980 ft) at Feyzin and 400 m (1310 ft) at San Juanico). [14]
An additional hazard from BLEVE-fireball events is the formation of secondary fires, by direct exposure to the fireball thermal radiation, as pool fires from fuel that does not get combusted in the fireball, or from the scattering of blazing tank fragments. [15] [7] Another secondary effect of importance is the dispersion of a toxic gas cloud, if the vapors involved are toxic and do not catch fire upon release. [7] Chlorine, ammonia and phosgene are example of toxic gases that underwent BLEVE in past accidents and produced toxic clouds as a consequence. [7]
Notable BLEVE accidents include:
Propane is a three-carbon alkane with the molecular formula C3H8. It is a gas at standard temperature and pressure, but compressible to a transportable liquid. A by-product of natural gas processing and petroleum refining, it is often a constituent of liquefied petroleum gas (LPG), which is commonly used as a fuel in domestic and industrial applications and in low-emissions public transportation; other constituents of LPG may include propylene, butane, butylene, butadiene, and isobutylene. Discovered in 1857 by the French chemist Marcellin Berthelot, it became commercially available in the US by 1911. Propane has lower volumetric energy density than gasoline or coal, but has higher gravimetric energy density than them and burns more cleanly.
Liquefied petroleum gas, also referred to as liquid petroleum gas, is a fuel gas which contains a flammable mixture of hydrocarbon gases, specifically propane, n-butane and isobutane. It can sometimes contain some propylene, butylene, and isobutene.
A steam explosion is an explosion caused by violent boiling or flashing of water or ice into steam, occurring when water or ice is either superheated, rapidly heated by fine hot debris produced within it, or heated by the interaction of molten metals. Steam explosions are instances of explosive boiling. 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 solid or 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, creating a danger of scalding and burning.
The Weyauwega derailment was a railroad accident that occurred in Weyauwega, Wisconsin, United States, in the early morning hours of March 4, 1996. The derailed train was carrying a large quantity of hazardous material, which immediately caught fire. The fire, which involved the train cars and an adjacent feed mill, burned for more than two weeks after the actual derailment, resulting in the emergency evacuation of 2,300 people for 18 days, including the entire city of Weyauwega, with about 1,700 evacuees.
A gas explosion is the ignition of a mixture of air and flammable gas, typically from a gas leak. In household accidents, the principal explosive gases are those used for heating or cooking purposes such as natural gas, methane, propane, butane. In industrial explosions, many other gases, like hydrogen, as well as evaporated (gaseous) gasoline or ethanol play an important role. Industrial gas explosions can be prevented with the use of intrinsic safety barriers to prevent ignition, or use of alternative energy.
The Waverly, Tennessee tank car explosion killed 16 people and injured 43 others on February 24, 1978, in Waverly, Tennessee. Following a train derailment a two days earlier, a cleanup crew had been sent into the area. At approximately 2:58 in the afternoon, a tank car containing 30,161 US gallons of liquefied petroleum gas (LPG) exploded after an action taken during the cleanup related to the derailment.
The Los Alfaques disaster was caused by the explosion of a road tanker near a holiday campsite on 11 July 1978 in Alcanar, Spain. The exploding truck, which was carrying 23 tons of highly flammable liquefied propylene, killed 215 people and severely burned 200 more. Several individuals from the company that owned the vehicle were prosecuted for criminal negligence. The disaster resulted in new legislation in Spain, restricting the transit of vehicles carrying dangerous cargo through populated areas to night time only.
Oxy-fuel welding torch and oxy-fuel cutting are processes that use fuel gases and oxygen to weld or cut metals. French engineers Edmond Fouché and Charles Picard became the first to develop oxygen-acetylene welding in 1903. Pure oxygen, instead of air, is used to increase the flame temperature to allow localized melting of the workpiece material in a room environment.
The San Juanico disaster involved a series of fires and explosions at a liquefied petroleum gas (LPG) tank farm in the settlement of San Juan Ixhuatepec, a municipality of Tlalnepantla de Baz, State of Mexico, Mexico, on 19 November 1984. The facility and the settlement, part of Greater Mexico City, were devastated, with 500–600 victims killed, and 5000–7000 suffering severe burns. It is one of the deadliest industrial disasters in world history, and the deadliest industrial accident involving fires and/or explosions from hazardous materials in a process or storage plant since the Oppau explosion in 1921.
The Feyzin disaster occurred in a refinery near the town of Feyzin, 10 kilometres south of Lyon, France, on 4 January 1966. An LPG spill occurred when an operator was draining water from a 1,200m³ pressurised propane tank. The resultant cloud of propane vapour spread, until it was ignited by a car on an adjoining road. The pool of propane in the bund caused the storage tank to be engulfed in flames, which produced a Boiling Liquid Expanding Vapour Explosion (BLEVE) when the tank ruptured. This resulted in a fireball which killed and injured firemen and spectators. Flying missiles broke the legs of an adjacent sphere which later BLEVE'd. Three further spheres toppled due to the collapse of support legs which were not adequately fire protected. These vessels ruptured but did not explode. A number of petrol and crude oil tanks also caught fire. The conflagration took 48 hours to bring under control. This incident resulted in the deaths of 18 people, the injury of 81 and extensive damage to the site.
A gas carrier, gas tanker, LPG carrier, or LPG tanker is a ship designed to transport LPG, LNG, CNG, or liquefied chemical gases in bulk.
A Horton sphere, also referred to as a spherical tank or simply sphere, is a spherical pressure vessel, which is used for industrial-scale storage of liquefied gases. Example of materials that can be stored in Horton spheres are liquefied petroleum gas (LPG), liquefied natural gas (LNG), and anhydrous ammonia.
The Kingman explosion, also known as the Doxol disaster or Kingman BLEVE, was a catastrophic boiling liquid expanding vapor explosion (BLEVE) that occurred on July 5, 1973, in Kingman, Arizona, United States.
The Williams Olefins Plant explosion occurred on June 13, 2013 at a petrochemical plant located in Geismar, an unincorporated and largely industrial area 20 miles (32 km) southeast of Baton Rouge, Louisiana. Two workers were killed and 114 injured. The U.S. Occupational Safety and Health Administration (OSHA) and the U.S. Chemical Safety and Hazard Investigation Board (CSB) launched investigations to determine how and why the heat exchanger failed. The Chemical Safety Board concluded that a standby heat exchanger had filled with hydrocarbon. This heat exchanger was isolated from its pressure relief; shortly after the heat exchanger was heated with hot water, the hydrocarbon flashed to vapor, ruptured the heat exchanger, and exploded.
On December 23, 1988, a tractor-trailer tanker truck hauling liquefied propane crashed on an exit ramp at the Interstate 40/Interstate 240 (I-40/I-240) interchange in downtown Memphis, Tennessee, US. The crash ruptured the tank; the leaking gas exploded, setting multiple vehicles and structures on fire. The explosion propelled the tank 125 yards (114 m) into a residential complex and started additional fires. The accident caused nine deaths and ten injuries. The interchange where the accident occurred was considered unsafe and poorly designed, and had been the site of several previous accidents; it was completely rebuilt in the 2000s.
The Chala LPG tanker disaster was a road transport accident that occurred on August 27, 2012, on Indian National Highway 17 at Chala in the Kannur District of India's Kerala State. The accident occurred when an Indian Oil Corporation Limited (IOCL) LPG road tanker hit a road lane divider, overturned and exploded, starting several building fires between 9:30 p.m. and 11 p.m. The accident killed 20 people.
In the early morning of June 21, 2019, a fire and multiple explosions occurred at the Philadelphia Energy Solutions (PES) refinery in Philadelphia, Pennsylvania. A release of hydrocarbons and hydrofluoric acid in the refinery's alkylation unit caused a ground-hugging vapor cloud which rapidly ignited, leading to three separate explosions minutes apart from each other. The largest explosion, a BLEVE, sent a vessel fragment flying 2,000 feet (610 m) across the Schuylkill River. Five employees sustained minor injuries, but there were ultimately no fatalities. The refinery announced it would shut down operations the same month, and filed for bankruptcy a month later.
On 6 August 2018, the collision of a liquefied petroleum gas (LPG) road tanker with an articulated lorry carrying flammable solvents and a car transporter resulted in a huge explosion on the A14 motorway within Borgo Panigale, a neighbourhood of Bologna, Italy. It was a case of boiling-liquid expanding-vapour explosion (BLEVE), where nearly all the road tanker cargo combusted in a matter of seconds upon release, generating a tremendous amount of thermal radiation. The accident killed two people, injured 145 and caused significant damage to the surrounding commercial and residential area. One span of the viaduct where it happened collapsed and a gash opened in the motorway.
Roberts, Michael W. (2000). "Analysis of Boiling Liquid Expanding Vapor Explosion (BLEVE) Events at DOE Sites" (PDF). Energy Facility Contractors Group (EFCOG). Archived from the original (PDF) on 20 October 2012.