Fire and explosion hazards

India has witnessed several devastating fires, explosions and toxic releases which not only claimed the life of hundreds but also huge property loss. In spite of the existence of the National Building Code of India and several fire safety regulations enacted by various state governments and local bodies, the fires and explosions are mounting day by day through out the country. Hence, sincere efforts are to be made by one and all to prevent the fire and explosions in the country.
– R. R. NAIR

1. INTRODUCTION :

There are three types of hazards viz., fire, explosion and toxic release, occur in industry in particular chemical process industries. In many instances, more than one of these hazards occurs in tandem of each other.

Fires occur in industry, more frequently than explosions and toxic releases, although the consequences in terms of loss of life are generally less. Hoverer, if the ignition of escaping flammable material is delayed, an unconfined vapour cloud of flammable material may be formed, which if ignited, can cause violent explosion, resulting in extensive damage. The fire is the first major hazard in the chemical / process industries and causes more serious accidents than explosions or toxic release, although the accidents in which the greatest loss of life and the damage occur are generally caused by explosion.

Fire is normally regarded as having a disaster potential less than explosion or toxic release. It may be remembered here that the world’s worst industrial disaster – Bhopal Gas Tragedy – occurred on the night of 2 – 3 December 1984, due to toxic release of the chemical “methyl isocyanate” and over 5,00,000 people were exposed to this chemical. However, ‘toxic releases’ are not dealt in this article. The scope of this article is confined to Fire and Explosion hazards only.

2. FIRES AND EXPLOSIONS IN INDIA :

Fire is a serious hazard in India and on an average about 25,000 people dies every year due to fires and explosions. India has witnessed several devastating fires and explosions that have claimed hundreds of innocent lives and property damages. Some of the major fires and explosions occurred in India are given below along with few images of the incidents (See Fig. 1 to 6).

Selected Major Fires and Explosions in India
April 14, 1944 : A major explosion occurred in the Victoria Dock of Bombay when the freighter SS Fort Stikine carrying mixed cargo of cotton bales, gold, and ammunition including around 1400 tons of explosives, caught fire and destroyed in two giant blasts, scattering debris over 2 square miles, sinking 27 other ships in Victoria Dock and neighboring Princes Dock and setting fire to the area killing around 800 people and injuring about 3000.

November 9, 1988 : A fire occurred on a light naphtha storage tank of BPCL Refinery at Mumbai. The tank was overfilled and consequentially over pressurized because of the faulty indication tank level gauge, which was repaired a couple of days prior to the incident. The tank roof ruptured releasing a large amount of hydrocarbon vapour spread over an extended area and ignited. – 35 persons killed and 23 injured. Out of the 20 tanks located in the farm area, 5 were damaged.

Fig. 1 – The devastated venue of he DAV School functions in Dabwali, Haryana – Photo by Shanker Chakravarty – (Courtesy:frontlineonnet.com)

November 6, 1990 : A leak occurred on a pipeline transporting ethane and propane to the gas cracker complex of IPCL petrochemical plant at Nagothane, Maharashtra. A vapour cloud formed and ignited at an off site gas treatment plant and compression facility. The cracker was not damaged by the resultant vapour cloud explosion, but serious damage was done to off site units – 31 persons killed.

December 23, 1995 : A fire broke out at the Rajiv Marriage Palace in Mandi Dabwali, Haryana, where the DAV School was holding its annual prize distribution function. A synthetic tent which had been setup inside the building caught alight, when an electric generator short-circuited. The fire spread quickly and blocked the main entrance. Many of the deaths were caused by the stampede as 1,500 people tried to escape through the single exit door. – 448 people including 230 children killed, and over 300 injured, (See Figure 1).

Fig. 2- Flames inside the Brihadeeswara Temple complex. Photo by K. Ganesan. (Courtesy: frontlineonnet.com)

June 7, 1997 : A fire broke out in the yagasala of the Brihadeeswara Temple, Thanjavur. Inflammable materials likes’ ghee, condiments and thatched roofs helped the fire spread fast. Most of the victims died after inhaling carbon monoxide; while a few were killed in a stampede. – 40 killed, 85 injured, (See Figure 2).

June 13, 1997 : A fire engulfed the Uphaar Cinema at Delhi due to a blast in a transformer in an underground parking area in a five story building, which housed the Cinema hall. Most of the victims were trapped in the balcony and suffocated to death when poisonous smoke engulfed the hall – 59 killed and over 100 injuring in the subsequent stampede, (See Figure 3).

Fig. 3- The burnt-out parking lot of Uphaar Cinema, in New Delhi.
Photo by Rajeev Bhatt. (Courtesy: frontlineonnet.com)

September 15, 1997 : A large LPG leak occurred at the manifolds area below a sphere containing about 1000 tones of LPG, at HPCL Refinery at Vishakhapatnam. The resulting vapour cloud spread to an area of about 250 m radius and exploded on ignition – 57 people were killed. The explosion damaged 4 other spheres a number of liquid petroleum storage tanks and several buildings.

April 10, 2000 : A devastating fire broke out at a tent of ‘Brand India Fair’ at Victoria Park, Meerut. The cause of the fire was due to an electrical short circuit within the structure. The fire also led to the explosion of gas cylinders at the makeshift kitchen at the site which soon engulfed the area turning the park into an inferno. At least 100 people were killed, (See Figure 4).

Fig. 4 -Inferno: Fire sweepingthrough the stalls of the trade fair in Meerut. (Courtesy: hindu.com)

January 23, 2004 : A major blaze engulfed Padmapriya Marriage Hall at Srirangam, near Tiruchi, in Tamil Nadu. The probable cause of the fire was due to a short circuit which resulted from a wire of videographer’s camera – 62 people including the bridegroom were killed and 45 severely injured.

July 16, 2004 : A major blaze raged through the Sri Krishna / Saraswati English Medium School at Kumbakonam when its thatched roof caught fire – About 93 children aged 6 and 10 were charred to death.

October 29, 2009 : A fire broke out at the Indian Oil Corporation’s oil depots giant tank holding 8000 kilolitres of oil, in Slopura Industrial Area on the outskirts’ of Jaipur, Rajasthan. The blaze continued to rage out of control over a week and during the period half a million people were evacuated from the area. The Meteorology department recorded a tremor measuring 2.3 in the Richer scale when the first explosion occurred which resulted in shattering of glass windows nearly 3 kilometers from the accident site – 12 killed and injuring over 200, (See Figure 5).

Fig. 5 – A massive fire at the Indian Oil Corporation’s (IOC) depot near Jaipur.
(Courtesy: ibnlive.in.com)

December 9, 2011 : A blaze started in the basement of building of AMRI Hospital, Dhakuria, Kolkata and quickly spread, trapping hundreds of people – 94 patients and staffers were killed.

July 30, 2012 : A coach of Delhi – Chennai Tamil Nadu Express caught fire near Nellor in Andhra Pradesh at the wee hours – 35 passengers were killed and 25 injured.

September 5, 2012 : A powerful explosion tore through one of the biggest fire works factories, Om Sakthi Fireworks Industries Crackers in Sivakashi, Tamil Nadu, triggering a major fire. The blast reduced 40 to 48 sheds in the fireworks unit to rubbles in no time. – About 50 people killed and more than 75 injured, (See Figure 6).

Fig. 6 – One of the working sheds in fire at the Om Sakthi Fireworks Industries in Muthalipatti
near Sivakashi – Photo by R. Ashok (Courtesy: thehindu.com)

Fires can take several different forms, such as jet fires (flames), pool fires, running liquid fires, flash fires, fireballs, vapour cloud explosions and boiling liquid expanding vapour explosions (BLEVEs), which are outlined below:

3. JET FIRES :

There is a wide variety of situation in which a jet fire or ejected flame, can occur, either by design or accident. The principal situations in which flames occur by design are burners and flares. Ejection of flammable liquid from a vessel, pipe or pipe flange, can give rise to a jet flame if the material ignites. Jet fires dissipate thermal radiation away from the flame’s visible boundaries. The energy transmitted could be hazardous to both life and property.

Scenarios involving jet flames are not easy to handle, since a large jet flame may have substantial ‘reach’ sometimes up to 50 meters or more. A jet fire would appear as a long narrow flame through a small aperture / hole / orifice. In other cases jet flames from pressure relief valves have cost adjacent vessels to overheat and burst a boiling liquid expanding vapour explosion (BLEVE).

Fig. 7. – Example of Jet Fire -A large fire destroyed the Piper Alpha oil platform in the North Sea.
(Courtesy: exponent.com)

Jet fires or flames have been involved in a number of accidents. Perhaps the most dramatic were the large jet flames from the gas riser on the Piper Alpha Oil Platform in the North Sea (See Fig. 7). On the night of 8th July 1988, a series of violent explosions and a large fire destroyed the oil platform. Only 62 crew members survived out of the 229 persons on board. Many workers were trapped because rescue helicopters could not approach when confronted with flames 100 meters high. The majority of those who survived jumped from the platform into the rough sea.

4. POOL FIRE :

A pool fire occurs when a flammable liquid spills onto the ground and is ignited. A fire in a liquid storage tank is also a form of pool fire, as in trench fire. A pool fire may also occur on the surface of flammable liquid spilled onto water.

A pool fire is defined as “a pool of flammable liquid burning with a stationary diffusion flame or the combustion of material evaporating from a layer of liquid at the base of fire”.

A pool fire is a complicated phenomenon. A pool fire burns with a flame, which is often taken to be a cylinder with a height, twice the pool diameter. In still air, the flame is vertical, but in wind it tilts. Wind also causes the base of the flame to extend beyond the downwind edge of the pool, thus exhibiting flame drag. With some pool fires blowout can occur a wind speed of about 5m per second.

Fig. 8. – Example of Pool Fire (Courtesy: arshadahmad. wordpress.com)

The characteristics of pool fire depend on the pool diameter. The liquid burning rates increases with the diameter until for large diameters it reaches a fixed value. The heat radiated from the flame behaves similarly.

A pool fire can take place in a storage tank, as for example, in a tank, which has lost its top, as a result of either internal or external explosion (See Fig. 8). The fire may also take places in a bund. In both the above cases, the boundary of the pool is clearly defined and the shape of the pool may be circular or rectangular. Other types of pool fire occur after a liquid is discharged on the ground, the shape and depth of the pool being determined by the local contours.

Pool fires, especially in bunds, which are either circular or square, have an approximately cylindrical shape. In the absence of wind, this would be an upright cylinder. But usually wind is present and the cylinder is oblique / tilted / inclined. A notable feature of pool fire is that of down-wind ‘spill over’ or ‘flame drag’. This spill –over increases the effective diameter of the pool fire by 50% of the bund diameter.

The pool fires have occurred at many places and the one occurred at Cleveland, Ohio, USA, in 1944 is important to remember. In this fire about 3,000 T of LNG ‘spilled over’ from several storage tanks and caused large scale pool fires. The accident resulted in 128 deaths and 400 injuries.

5. RUNNING LIQUID FIRES :

A running liquid fire involves the spread of flame across the surface of a flammable liquid spillage. In spread and extent, the fire is greatly influenced by local topography. As the spread is often promoted by, drains and trenches, it is necessary to consider the radiative effects from fires spread in this way.

Thin flames are less radiative than thick flames. Hence, drains can be built with narrow necks, opening into larger volumes below the surface. The design shall allow for presence of firewater and for separating immiscible liquids when desired.

6. FLASH FIRE :

Flash fire is also known a vapour cloud fire. Flash fire is defined as “the combustion of a flammable vapour and air mixture in which flame passes through the mixture, at less than sonic velocity (speed of sound in the medium), such that negligible over pressure is generated”. A flash fire, occurs when a vapour cloud forms from a leak and is ignited, but without creation of significant overpressure. If such overpressure occurs, the event is a vapour cloud explosion (VCE), rather than a vapour cloud fire (VCF).

Release of flammable vapour from a process plant followed by ignition is not uncommon occurrence. If the ignition is prompt, the cloud may be modest in size, but if the cloud has time to spread over an appreciable part of the site and is then ignited, a major cloud fire may result. This occurs in only a very small proportion of ignited release.

In a flash fire, the gas burns, but does not explode. The heat radiation or the flames may cause severe burns. It may also cause sudden depletion of oxygen. When controlled quickly, the flash fire may not cause serious damage to the main plant and equipment, but can extensively damage electrical cables and other vulnerable items of equipment.

In the petrochemical industries, flash fire can occur at collection points, compressor stations, refineries, etc. Industrial flash fire and explosions result from the accidental release and ignition of flammable fuels. The size and duration of the flame that result from this ignition is determined by the amount of fuel available, the efficiency of combustion, and the environmental and physical characteristics of the site of the flash fire or explosion. The temperatures attained by flash fire have been estimated to range from 550 to 1050?C, although higher temperatures are believed to occur. If the flash fire or explosion is sufficiently intense, the heat produced may cause regular clothing to melt or begin burning. Large and destructive vapour cloud fires occurred at Port Newark, New Jersey, in 1951 and at Mexico City, in 1984.

Fig. 9. – Example of Fire Ball (Courtesy: FESA)

7. FIRE BALLS :

A fireball burn at about 1400 ?C, and are extremely dangerous because of their rate of burn and amount of radiant heat generated. A fireball is inevitable from BLEVE’s involving flammable liquids. It is the radiant heat from the fireball that makes the consequences of a BLEVE involving flammable liquids so hazardous. The bulk of the cloud is too fuel rich, so they can only burn around the outer envelope. The cloud will also be lighter than air because of its heat content so that it will lift off to give the appearance of a mini – atomic bomb; complete with mushroom cloud and stem made up of burning fuel reaching up to it from the ground ( See Fig. 9).

According to Leith Higgins, Principle Scientific Officer of Fire and Energy Services Authority (FESA) of Western Australia, a BLEVE involving 50 tonnes of LPG would produce a fireball of 200 meters in diameter that would burn for about 14 seconds. During that time it would have a radiant heat content output of about 1, 70,000 megawatts.

There are two types of events, which may give rise to fireball. One is, the ignition of a release on a liquefied gas pipeline, where the jet flame is preceded, by a fireball in which un-ignited gas is burned. The other is an eruption in hot oil giving rise to release of burning vapour.

A distinction needs to be made between fireball resulting from the bursting of a pressure vessel and one resulting from a formation of a vapour cloud. In the first case, the bursting many occur under fire conditions and be part of a BLEVE or it many occur in the absence of fire. Momentum forces predominate if a fireball is formed from the bursting of a vessel, and buoyancy forces predominate in one formed from a vapour cloud.

Incidents involving fireballs are not uncommon. They normally occur as part of a BLEVE when vessel ruptures after it has been engulfed in fire or has been subjected to a directed flame. The vessels principally liable to such conditions are storage vessels, rail tank cars, and road tankers.

A massive BLEVE fireball occurred at Crescent City, Illinois, USA in 1970 with an estimated diameter of 150 – 200 m. The diameter of BLEVE fireball incidents at Houston, Texas, USA in 1971; Kingman, Arizona, USA in 1973 and Bet, Montane, USA, in 1976, was about 300m. The disaster at Mexico City, in 1985, involved a series of fireballs from BLEVEs. The estimated diameter of fireballs at Donnellson, Iowa, USA was 610 m.

8. VAPOUR CLOUD EXPLOSIONS :

The relative importance of the vapour cloud explosion (VCE) hazard has grown in recent years. Until the early 1980’s, a vapour cloud explosion (VCE) was generally referred to as unconfined vapour cloud explosion (UVCE). However, since the combustion of a vapour cloud, the occurrence of overpressure tends to occur due to the presence of structures and obstacles and of partial confinements, the term “unconfined”, is now generally omitted.

A vapour cloud explosion is defined as “an explosion of a cloud made up of a mixture of flammable vapour or gas in air”. In other words, when a cloud of flammable vapour burns, the combustion may give rise to an overpressure or it may not. If there is no overpressure, the event is vapour cloud fire, or flash fire, and if there is overpressure, it is a vapour cloud explosion.

A vapour cloud explosion is one of the most serious hazards in the process industries. Vapour cloud explosions do occasionally occur and they tend to be very destructive. A feature of vapour cloud is that it may drift some distance from the point where the leak has occurred and may thus threaten a considerable area.

A vapour cloud explosion occurs when a sufficient amount of flammable or combustible material is released, mixes with air and is ignited. When the flammable vapour cloud is ignited, it can explode, producing a blast wave which can cause major destruction at a large distance.

Vapour cloud explosions could be of the two types viz., (1) Confined explosions – these are the ones, which occur within some sort of containment, such as a vessel or a pipe work. Explosions in building also come under this category, and (2) Unconfined explosions – these are the ones in, which the cloud burns in the space or open air, with sufficient rapidity. Normally, the peak pressures of confined explosions are higher and may reach hundreds of kN/m².

The difference between a gas explosion and vapour cloud explosion has to do whether the material is a gas or liquid at ordinary temperature and pressure. Methane and propane would be considered as a gas but fuels such as gasoline, hexane, and cyclohexane are liquids which can vaporise forming a vapour cloud.

Fig 10 – On 1 June 1974, a vapor cloud explosion destroyed the Nypro cyclohexane oxidation
plant at Filxborough. (Courtesy: isssource.com)

The shape of the vapour cloud before ignition is not spherical but is influenced by wind or air movement and by nearby structures. The fire will burn at all locations where the vapour cloud concentrations are about half the lower explosive limit or higher; however, ignition takes place between the lower and upper explosive limit values.

The peak overexposure within the vapour cloud when ignited probably does not exceed 15 psi above atmospheric. At the edge of the cloud the overexposure is likely to be 10 psi or less. The Table No. 1 gives some of the major industrial vapour cloud explosions.

The term “Unconfined Vapour Cloud Explosion” apparently was carried following the 1st June 1974 accident at a chemical plant near Flixborough. U.K. The accident involved the rupture in a 20 inch bypass pipe dumping almost 40 tons of cyclohexane which vaporized. The resulting vapour cloud found an ignition source; the blast and fire destroyed the entire chemical complex killing 28 people and injuring 89 (See Figure 10).

Fig.11-Houston (Pasadena) Texas 1989 Petrochemical Vapor Cloud Explosion and Fire.
(Courtesy:ww.mpri.lsu.edu/workshop/Phillips66Talk.pp)

On October 23rd 1989, a vapour cloud explosion and fireball occurred at the Philips 66 Petroleum Chemical Complex at Pasadena near Houston, Texas, killing 23 workers, one worker missing and injuring more then 130 others, (See Figure 11). The accident was investigated by the Occupational Safety and Health Administration (OSHA), the Environmental Protection Agency and other agencies. According to OSHA report, the vapour cloud resulted as a sudden gas release of an estimated 85,000 Ibs of a flammable gas mixture (hydrogen, ethylene, hexane, and isobutylene) through an 8 inch open valve. The vapour cloud (estimated to be roughly 1100 feet long, 800 feet wide, and 5 feet high) drifted downwind for about 90 to 120 seconds before contacting an ignition source. The vapour cloud plus additional flammable gas inside tanks at the valve source exploded with a force equivalent to 2.4 tons of TNT based on blast damage. Windows were shattered and bricks were ripped out in an administration building 0.5 miles away. Fragments were thrown as far as six miles away.

Fig. – 12 A vapour cloud explosion Devastating fire at the Buncefield oil depot may have damaged the environment for decades. (Courtesy: ziabuzz.com)

Another major conflagration caused by a series of explosions on 11 December 2005 at the Hertfordshire Oil Storage Terminal, Buncefield in England with a capacity of about 60, 000,000 imperial gallons fuel. The first and largest explosion occurred near tank 912 which led to further explosions which eventually overwhelmed 20 large storage tanks. The explosion measured 2.4 on the Richter scale. The incident described as the biggest of its kind in peacetime Europe (See Figure 12) and certainly the biggest such explosion in U.K. since 1974 Flixborough disaster.

9. BOILING LIQUID EXPANDING VAPOUR EXPLOSION (BLEVE) :

The term ‘BLEVE’ is an acronym for boiling liquid expanding vapour explosion coined by three Factory Mutual (FM) researches viz.: James B Smith, William S Marsh, and Wilbur L Walls. BLEVE has been defined and explained by various experts and some of them are quoted below:

Fig. 13 – Example of a Boiling Liquid Expanding Vapour Explosion (BLEVE) (Courtesy: gas-risk.blogspot.com)

Wilbur L. Walls while working with NFPA made many presentations on BLEVEs. According to Walls “for a BLEVE to occur, the container has to be under pressure, the pressure has to exceed the strength of the container, and the container has to be weakened in some way (impact, corrosion, fire)”. Walls further claims that BLEVEs occur with many types of liquefied gases, flammable and non flammable.

A Michael Birk, a professional engineer and a professor with Queens University at Kingston, Ontario, Canada, hold the view that a BLEVE occurs when a vessel holding a pressure liquefied gas fails catastrophically. According to Birk, “a BLEVE is a physical explosion of compressed vapour and rapidly vaporizing liquid. Upon vessel failure the vapour space sends out a shock wave from the liquid flashing to vapour. If the material is flammable, a fireball may follow it (See Fig. 13). The rapid explosion can also cause projectile effects.”

In the General Hazardous Materials Behaviour Model by Ludwing Benner, the BLEVE would be considered as a ‘release event’ as a result of the container’s failing. According to Benner, the magnitude of the release depends on the characteristics of the product, the state and quality of the product, the flow or release rate, the propulsion force, and even whether conditions.

David Lesak, a nationally known hazardous materials author, lecturer, and course developer, defines a BLEVE as a pressure release from catastrophic container failure. The result of a BLEVE is total devastation to the immediate area with potentially large loss of life and property.

The size of the BLEVE is dependent on the size and weight of the container along with the amount of liquid that remains inside the container at the moment of the BLEVE. Generally speaking, the bigger the container, the bigger the BLEVE.

BLEVE is an explosion caused by the rupture of a vessel containing a pressurised liquid above its boiling point. A BLEVE is a combination of fire and explosion with an intense radiant heat explosion within a relatively short time interval. In other words it is used to describe the sudden rupture of a vessel system containing liquefied flammable gas under pressure due to flame impingement. The pressure burst and the flashing of the liquid to the vapour, creates a blast wave and potential missile damage. It also results in immediate ignition of the expanding fuel – air – mixture leading to intense combustion, which ultimately results in a fireball.

The phenomena of BLEVE can occur within a vessel or a tank, in which a liquefied gas is kept above its atmospheric boiling point. If the pressure vessel fails as a result of a weakening of the structure, the contents are instantaneously released from the vessel as turbulent mixture of liquid and gas, expanding rapidly and dispersing in air as a cloud.

When this cloud is ignited, a fireball occurs, causing an enormous heat, radiation intensity within a few seconds. This heat intensity can cause several skin burns and deaths at several hundred meters from the vessel depending on the quantity of the gas involved. A BLEVE can therefore be caused by a physical impact on a vessel or a tank which is already over-stressed or damaged. It can also be caused by fire impinging upon or engulfing a vessel and thus weakening its structure.

Thus the essential features of a BLEVE are: (1) the vessel fails (2) the failure results in flash – off of vapour from the super heated liquid and (3) if the liquid is flammable, the vapour ignites and forms a fireball. The effects are: (1) BLEVE (2) fragments and (3) for flammable liquids, a fire ball. The BLEVE create an over pressure. The phenomena associated with this are: (i) the expansion of this vapour (iii) for flammable liquids, the combustion of the vapour. These events are not completely simultaneous, but have been measured as separate effects. A BLEVE usually generates missiles. There may be fragments created by the rupture event and also the body of the vessel itself. The pressure at the instant of burst is high and the reaction force is often large enough to cause the main part of the vessel to rocket. A BLEVE arising something from the fire engulfment of a vessel containing a flammable liquid also gives rise to a fireball.

Although most BLEVEs involve a liquid, which is flammable, this is not a necessary feature of a BLEVE. Even rupture of a vessel containing super heated water can constitute a BLEVE. Likewise, although engulfment in fire is the common cause of BLEVE, it too is not a necessary feature. Any rupture of a vessel containing a superheated liquid may be traced a BLEVE. The events that can lead to a BLEVE are : (1) Fire exposure, (2) Vapour space explosion, (3) Overpressure (4) Mechanical damage, (5) Collisions, (6) Overfilling, (7) Runaway reactions, (8) Overheating and, (9) Corrosions. The highest frequencies of BLEVE incidents were due to explosions and damage to tanks. Explosion and damage BLEVE incidents resulted in high injuries. Overfilling and fire BLEVE incidents resulted in high fatalities.

Over the years many BLEVE’s have occurred and have taken many lives including fire fighters. Some of the BLEVE incidents are outlined below:

Fig. 14 – In the San Juanico Disaster (Mexico), 54 of these spherical type LPG containers exploded into huge fireballs (Courtesy: http://en.wikipedia.org)

The BLEVE at Feyzin refinery in France on January 1966 has received particular attention. In this accident an operator when drawn water from the bottom of a propane sphere control, a vapour cloud formed, ignited and flashed back to the vessel. The pressure in the vessel rose and the relief valve lifted, but the metal of the vessel lost strength and some 90 minutes after ignition the vessel burst. The accident killed 18 and injured 81 people and caused the destruction of five of the spheres.

There have also been instances where release from one storage vessel has led to a fire which has caused BLEVE of an adjacent one such as the case at Texas city, Texas in 1978, where overfilling of an LPG sphere led to a fire which caused the BLEVE of an adjacent sphere which resulted the death of 7 and injury of 10 people. In another case BLEVEs have occurred due to engulfment in a vapour cloud fire.

Such a fire occurred at Port Newark, New Jersey, in 1951 and led to the destruction of over 73 horizontal bullet tanks, many by BLEVE. Engulfment in a vapour cloud fire was also the cause of destruction, largely by BLEVE of 6 storage spheres and 48 horizontal cylindrical vessels holding LPG at the PEMEX storage (bottling) plant at Mexico City, on 19th November 1984, which killed 650 people and injured about 7000 (See Fig. 14.)

Fig. 15 – Example of BLEVE (Courtesy: arshadahmad.wordpress.com)

BLEVES also happen in transport, when flammable material is released and ignited following an accident, so that transport tank cars, often when a jet flame from the relief valve on one tank has played on another. A derailment of rail tank cars at Crescent City, Illinois in 1970 caused a release of propane, which led to a fire and caused a succession of tank car BLEVE’s. The BLEVE’s were accompanied by, large fireballs and missiles, including rocketing tanks (See Fig. 15).

The three BLEVE’s occurred at Albert – City, Iowa in April 9, 1998, Burnside, Illinois in October 2, 1997, and Ste. Elisabeth de Warwick, Quebec, Canada in June 27, 1993, was investigated by National Fire Protection Association (NFPA), USA. The NFPA Team, who investigated these accidents, made many observations. According to them in each case, the propane was used to heat building. In each case the tank’s relief valves were operating when fire fighters arrived, but they could not stop flames from impinging on the tanks and weakening the tank shells.

And in each case, tanks ruptured in BLEVE’s that sent pieces of metal flying at high velocities in random directions, killing those caught in their path. Further, when a BLEVE occurs, debris may travel hundreds of feet, with tremendous force, and the escaping fuel can ignite causing an expanding fire ball. Fireballs several hundred feet in diameter are not uncommon, and deaths from burns have occurred to persons as much as 250 ft from the larger containers. The size of a BLEVE depends upon the weight of the container pieces and upon how much liquid vaporizes when the container fails. Generally speaking, the bigger the container, the bigger the BLEVE.

The BLEVE Incident Simulator (BIS) software developed with the help of Dr. A. M Birk will be a very good guide for those who want to know more about BLEVE.

10. CONCLUSION :

There are several forms of fires and explosions. Jet fires or flames; have been involved in a number of accidents. A large jet flame may have a reach up to 50 m or more. A pool fire can take place in a storage tank and in a bund. The characteristics of pool fire depend on the pool diameter. A flash fire occurs when a vapour cloud forms from a leak and is ignited without creation of significant overexposure. The most dangerous and destructive explosion in the chemical process industries are vapour cloud explosions. Vapour cloud explosions and fires are responsible for most of the largest property loss events world wide.

A BLEVE occurs with many types of liquefied gases, flammable and nom flammable. The size of the BLEVE is dependent on the container and the bigger the container, the bigger the BLEVE’s. A fireball occurs as a part of BLEVE when vessel ruptures and generally occurs on storage vessels, rail tank cars and road tankers. Over the years many BLEVE’s have occurred and have taken many lives including fire fighters.

India has witnessed several devastating fires, explosions and toxic releases which not only claimed the life of hundreds but also huge property loss. In spite of the existence of the National Building Code of India and several fire safety regulations enacted by various state governments and local bodies, the fires and explosions are mounting day by day through out the country. Hence, sincere efforts are to be made by one and all to prevent the fire and explosions in the country.

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19. NFPA Fire Investigations: BLEVE. http://nesp.tamu.edu/reports
20. SHE Bulletin, January 10, 2011.
21. The First Responder – July, 2009 Vol. VIII Issue 7. www.aristatek.com
22. U.S. Fire Administration – Federal Emergency Management Agency (EFMA)/Technical Report Series – Phillips Petroleum Chemical Plant Explosion and Fire, Pasadena, Texas, USA – TR – 035 / October 1989.
23. U. S. Chemical Safety and Hazard Investigation Board – Investigation Report on Propane Tank Explosion at Herring Brothers Feather Creek Farm, Albert City, Iowa, April 9, 1988.
24. Wikipedia – Boiling Liquid Expanding Vapour Explosion. http://en.wikipedia.org

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Mr. R. R. Nair has more than 40 year’s exposure in Occupational Safety, Health & Fire Protection. He is author of 15 books & more than 60 articles in various topics on Safety, Health & Environment. He has carried out more than 45 safety audits in various industries and high rise buildings.
He can be contacted on:
M: +91 7045172050, Resi: +91 477 2266994
E-mail: [email protected] / [email protected]
Website: www.shib.co.inp