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ENRESA-URV Industrial Safety Chair

Historical Record of Catastrophes

Below is a description of the most important catastrophes that have occurred around the world in recent years.

Feyzin Refinery

The Feyzin refinery (a few kilometres south of Lyon) went into service in 1964. The storage facilities included, among others, a 2000 m3 butane sphere and a 1200 m3 propane sphere. Periodically, the spheres had to be purged in order to eliminate the water and caustic soda that had accumulated at the base of the sphere, through decanting. The operation was carried out with two shut-off valves located 5 cm apart from each other and which were adjusted using a square key. Sample taking operations were also carried out. By being so close, the two valves could become covered in ice, owing to the expansion of liquefied gas. In addition, adjustments using the square key were not easy to perform, and could be delayed if the key fell on to the ground.  The diameter of the pipes was too great to facilitate adjustment of the valves.

On 4 January 1966, at six-forty, a purging operation was carried out in order to drain the accumulated water from the base of the propane sphere. It was still nighttime and the location was poorly illuminated. The operator purged the sphere by opening the two valves completely. Then, in order to complete the purging he left the lower valve open and the upper shut-off valve half open. Since nothing came out, he opened the latter completely. Suddenly, a plug of ice (a mixture of water and hydrocarbon) was released, throwing the worker to the ground along with the upper shut-off valve handle, which the worker was unable to reposition. He could not close the lower shut-off valve either because it was frozen. He did not make any further attempts to close it. He alerted the refinery, but initially nobody outside it. There was no wind. The gas spread at ground level, at a height of one and half metres, moving towards the motorway. Between 6:55 and 7:05 several cars passed along the motorway but nothing occurred until 7:15, when, with the motorway now closed, a car travelling along a nearby local route ignited the cloud. The driver died two days later.

The first fire crews arrived from Lyon at 7:30 and more continued to arrive until 8:30. They tried to extinguish the fire with a dry powder fire engine and switched on the sprinklers of the two spheres and the two nearest tanks that contained liquefied hydrocarbons. Once the dry powder had run out, they tried to use another available fire engine but the fire fighting water system did not have sufficient pressure, owing to its poor design. What is more, the adjoining factory, which used the same system, was cooling its owing spheres.

There were more problems: a vehicle sent to be filled with water from the River Rodano got stuck and twenty minutes were lost.

At 7:45 the safety valves flew off and the escaping gas ignited. At this moment there were 170 people present. At 8:45 a BLEVE occurred in the sphere, an explosion that is characteristic of spheres containing liquefied petroleum gas: 17 people were killed and 84 injured. The site was totally evacuated. At 9:45 the second sphere exploded. There were no victims, but the material damage was immense, spreading as far as Vienne, located 16 km away. The two volatilized spheres left a crater 35 m long, 16 m wide and 2 m deep.

Flixborough

Flixborough is a small rural town located 260 km north of London. The factory was owned by Nypro Ltd and was designed to produce 70,000 tons of caprolactam, a basic raw material in nylon production. The process consisted of air oxidation of cyclohexane. This product has flammability characteristics similar to that of petrol. The cyclohexane oxidises to cyclohexanol and the latter to cyclohexanone, which is transformed into caprolactam.

The plant consisted of six reactors in series, each with a capacity of 45 cubic metres, some 20 tons, powered by gravity. The reaction occurred at 155 ºC and 8.8 bar abs. The output among the reactors was 250 to 350 metres per hour.

The accident sequence began some months previously. On 27 March 1974 a leak was detected in reactor 5. A vertical crack was observed in the stainless steel wall. The following day it was decided to continue the production of caprolactam by installing a temporary bypass between reactors 4 and 6, by joining two expansion pipes 700 mm in diameter. The factory only had 500 mm diameter tubes. No calculation was made of the forces these elements would need to withstand. No pressure tests were carried out.

The installation worked until 29 May. A leak was discovered, and the system was shut down, repaired and put back into service on 1 June. The same day at 4 o’clock in the morning the leaks reappeared. It was shut down once again and put back into service. The pressure and the temperature were evolving in a worrying manner, but the system was not shut down again.

At 16:50 the 500 mm diameter pipe exploded releasing 40 to 60 t of hot pressurized cyclohexane. It is estimated that 10 to 15 t formed a cloud approximately 15 m thick and several hundred metres in diameter. After 40-50 seconds, an explosion occurred, destroying the entire plant.  28 people were killed, 18 of them in the control room. There were 36 people injured inside the factory and 53 outside it. The effects were felt up to 50 km away. All the houses within a 600 m radius were destroyed. The fire lasted for 10 days. The explosion was the equivalent of 20 t of TNT. At its epicentre, the excess pressure was between 1400 and 1700 mbar, quite extraordinary values. The damage was estimated at 75 million euros.

The primary cause of the accident was the poor design of the modification. Furthermore, the volumes being stored were very high.

Cyclohexane cloud that did not ignite

Unlike the Flixborough case, there was no explosion, in spite of the fact that the quantity of fuel was greater.  However, the accident did take place and only good fortune prevented it from causing damage.

On 11 September 1971, in a caprolactam plant located in Pensacola, Florida, and similar to the one in Flixborough, a pipe used to circulate pressurised cyclohexane at a temperature above its boiling point burst, releasing 33,5 t of product, and forming a dense white cloud approximately 30 m thick and 600 m in length. There was no wind, only a slight breeze. Two lorries trapped in the middle of the cloud stalled owing to a lack of oxygen. The cloud was very rich in fuel. Part of the cloud entered an oven and ignited, generating thick black smoke from the chimney. Surprisingly, the cloud did not explode and gradually dissipated without causing major damage.

Bhopal

In the accident at Bhopal, in the state of Madhya Pradesh, Central India, on 2 and 3 December 1984, an unknown number of people were killed. The official figures speak of 1,754 deaths, while others claim 8,000, although the true figure is likely to be much less.

The plant belonged to Union Carbide. It was located 3 km from the town centre and 2 km from the nearest houses but surrounded by shanty dwellings.

The produced an insecticide, carbaryl, commercial name Sevin, as an intermediate product of methyl isocyanante (MIC). MIC is reactive, toxic, volatile and inflammable. Its TVL is 0.02 ppm. It has a boiling point of 39.1 ºC and its vapour pressure at 20ºC is 348 mmHg. The vapour of MIC has a density double that of air.

The reaction of MIC with water is highly exothermic despite occurring slowly. It is most important that storage tanks are refrigerated in order to prevent MIC boiling. The plant was not operative owing to a labour problem and because it was no longer profitable. Maintenance had been non-existent for some months.

There were three storage tanks, one of which was empty, and used as a safety deposit. They had to be kept refrigerated at 0ºC and pressurized at 2.4 bar. If the pressure increased, a automatically controlled valve opened at 3.8 bar and sent the MIC towards two neutralisation towers (scrubbers) for it to be neutralised with 20% caustic soda. The unneutralised gas was burned in a refinery flare.

On the day of the accidents several security systems were switched off because the plant had shut down and they wanted to prevent the alarms going off continuously. On the night of day 2, a team of operators started work on cleaning a pipe with water in order to remove any impurities that might enter the tanks storing the MIC. They closed the valves but did not position the blinds, causing water to enter tank 610, which contained 42 t of MIC. In addition to the water, metal residues entered, catalysing the exothermic reactions of the MIC with the water. Initially the product was at a temperature of 20ºC instead of 0ºC because the refrigeration system was not working. At 11 o’clock at night, the pressure rose from 1.14 bar abs to 1.69 bar. The worker thought this was due to the maintenance work being carried out on line N2. Furthermore, the pressure was below the nominal 2.4 bar. The manometers were not accurate.

At 00:20 on day 3, the pressure was 3.8 bar. The production manager was informed, and at one o’clock in the morning he gave the order to evacuate. The safety valve was opened and the gases were sent to the “scrubber”, which was working but too small for the emergency flow that was arriving. The safety valve of the tower opened and the MIC escaped. The refinery flare was out.

The atmosphere was stable. The “scrubber” was 35 m high. 25 tons of MIC escaped, killing thousands of people and poisoning hundreds of thousands. Union Carbide was obliged to pay 140 million euros in civil liability payments.

Some considerations:

-A thorough inspection could have prevented the accident.

-The stored quantities of MIC should have been smaller.

-There is a manufacturing process for carbaryl that does not require MIC.

-The level of maintenance was negligible and should have been carried out by qualified personnel.

-The alarm and protection systems should have been working even though the plant was shut down.

-The plant should have been located further away from the population, bearing in mind the anticipated growth of the population, and, naturally, an exterior emergency plan should have existed.

Seveso, Italy

Seveso is a small town with 17,000 inhabitants, approximately 25 km from Milan. The plant is owned by the Icmesa chemical company. It manufactured hexachlorophenes, with trichlorophenol as the intermediate product. During the normal operation of hexachlorophene, a small quantity of TCDD is produced as an unwanted subproduct.

the TCDD is the most toxic product known to man, 10,000 more toxic than cyanide, insoluble in water and not degradable owing to the activity of bacteria. In tests carried out on animals lethal doses have been discovered as low as 10^(-9) the weigh of the animal. Its action on soil and plants is persistent over long periods of time.

On 10 July 1976, when performing a shut down, an uncontrolled reaction occurred in the trichlorophenol reactor, increasing the temperature to over 250 ºC, which led to an increase in pressure and the consequent opening of the bursting disc.  Furthermore, the increased temperature resulted in major production of toxic TCDD. With the breaking of the bursting disc 2 kg of TCDD was released, forming a white cloud over Seveso and TCDD rain over the region.

Attempts were made to warn the authorities but this was impossible, being the weekend. Subsequent communication with the local authorities was inadequate despite the deaths of many animals and the vegetation drying up. The population was not evacuated until 27 July. 250 cases of “chloroacne” occurred, 600 people were evacuated and 2000 had to undergo blood tests. The area surrounding the plant is still isolated.

Tacoa, Venezuela

This catastrophe took place on 19 December 1982 and claimed 200 lives. The Tacoa plant is located in Arrecife, on the coast of the Vargas Department, near Caracas. It is a thermal plant that uses fuel derived from petrol residues, mixtures of heavy crude, oils, kerosene, petrol, etc.

One of the tanks, number 8, exploded and ignited owing to causes that are still not known. At the time of the explosion fuel was being transported from an oil tanker, and there were two workers on the roof of the tank. The fire brigade arrived, and managed to bring the fire fully under control within two hours. Journalists approached tank 9, which was located further down at the end of a slope. Tacoa is located in a mountainous location, with houses on both sides of the mountain.

At 12:30 the water supply failed. The fire reintensified. The residues of tank 8 began to pour out over tank 9: a BOILOVER was taking place.

Suddenly, a huge explosion occurred. A ball of fire shot towards the sky and spread out over a radius of 1000 m. Everybody in the surrounding area was trapped by the volcano of fire. The ball of fire rose up the sides of the mountain, destroying everything in its wake.

Fire at the Sandoz warehouse

Warehouse 956 at the Muttenz plant was built in 1968 in order to house machinery and various equipment. Official approval was granted in 1979 for the building to store agrochemical and chemical products with an ignition point in excess of 21ºC. On 28 October 1986, four days before the fire, a fire inspection was carried out and everything was in order.

At 00:19 on 1 November 1986 the alarm was raised. The fire spread very quickly. The smoke caused by chemical products, such as phosphoric esters and mercaptans, resulted in the emergency group of Basel applying the © alarm (© for “Chemicals”). At 7 o’clock in the morning the emergency over alarm sounded.

To prevent the fire from spreading, large quantities of water were used. Approximately 1000 cubic metres of water, with 30 t of chemical products, including approximately 150 kg of highly toxic mercury compounds, ended up in the river Rin.

The greatest damage occurred in the Rin approximately 250 km away. Half a million fish, principally eels, died with the added aggravation that over the 15 preceding years, the surrounding regions had spent 1,800 euros on the environmental recovery of the river and the number of species had increased from 3 to 15.

The accident cost Sandoz 78 million euros in civil liability payments. Sandoz adopted a series of measures to prevent a repetition of such a catastrophe, by reducing the production of pesticides, reducing its stock to one third (21.300 t) and deciding against the storage of phosgenes.  Furthermore, at a cost of more than 9 million euros, its constructing to retaining dams, with capacities of 15.000 and 2.500 cubic metres in order to prevent fire water entering the river Rin.

Els Alfacs

On 1 June 1978 the most serious accident in Spain with regard to the transport of hazardous goods occurred, claiming more than 200 lives, all of them, with the exception of the driver of the petrol tanker, tourists staying at the Els Alfacs campsite, in the Montsià region, approximately 70 km from Tarragona.

At 10:05 an empty tanker arrived at the Repsol Petrol Refinery at Pobla de Mafumet. Its weight on the scales was 16,180 kg. At 11:00 the operation to fill the tanker with propylene commenced, and lasted for 1h and 5m.  When the tanker left the Refinery at 12:35, it weighed 39,650 kg. Deducting the nitrogen carried by the tanker when it arrived at the complex, it had been filled with 23,169 kg of propylene. The legislation only permits 19,350 kg, in other words, 0.43 kg/l of tanker. This also breached Traffic Regulations, since it was carrying more than the permitted weight. However, the direct cause of the catastrophe was not solely the breach of the Legislation.

The accident – the explosion of the tanker – took place at 14:25, just as it passed by the Els Alfacs campsite. By depressurizing itself suddenly, it produced a propylene gas cloud which ignited with a stove on the campsite producing a blaze and an immense and devastating ball of fire.

The most likely hypothesis on the cause of the accident is that the cistern exploded as a result of being overloaded. At the end of the filling process, the temperature of the product was 1ºC and the pressure 5.5 atm, which corresponds to said temperature. The ambient temperature was very high that day, approximately 27ºC at midday. However, even at this temperature the tanker would not have exploded. In order to reach the pressure that would break the tanker, 49.95 kg/cm2, the temperature would have to reach 92ºC.

The tanker exploded as all the vapour condensed owing to a reduction in the density of the liquid, caused by the temperature increase. The mass of the propylene load was 23,619 kg. The volume of the tanker was 44.4 cubic metres. The specific weight of the liquid that would make all the vapour disappear would be 532 kg/m3. Assuming that the liquid was pure, the temperature that would correspond to this density would be just 8ºC. Afterwards the liquid would occupy the entire volume of the tanker and with the temperature increasing one delta T, without any possibility of the liquid expanding, the pressure would increase rapidly. The elastic limit of the tanker material was 70 kg/mm2, which would be reached when the volume was 44.54 m3, in other words, with a specific weight of 530,25 kg/m3. This value corresponds to a temperature of 9ºC, easily attainable in the atmospheric conditions of the accident.

Accident in Guadalajara, Mexico

On 22 April 1992, between 10 in the morning and 1 o’clock midday, in the Mexican city of Guadalajara 18 gas explosions left more than 200 dead and 100 injured, destroying 1,402 houses, 450 businesses, 600 vehicles and 10 km of road. The financial losses totalled 5,000 M €.

Initially, Pemex blamed an olive production company responsible for the escape of hexane the previous week. The residents had complained about the smell of gas up to the previous day. Consequently, the local council and technicians of Pemex took samples, detecting the risk of explosion at certain points. They removed the covers of inspection points in order to increase the ventilation but without evacuating the population or even alerting them.

The investigations carried out appeared to prove that Pemex had constructed a “polyduct” for gas and petrol and after a certain time placed a water pipe over it, which made contact at a specific point. The casings of the two pipes started to corrode over time and produced a leak which deteriorated in the final weeks with an orifice 1 cm in diameter. The leak spread to a drain where it concentrated the gases into an explosive mixture. The five main explosions were caused by large quantities of petrol combined with other fuels, such as hexane, industrial gases and organic material.

San Juan de Ixhuatepec, Mexico

On 19 November 1984, the LPG (liquefied petroleum gas) installation of Pemex was located in the Mexico City district locally known as San Juanico. 100,000 people lived in the valley, in houses or shanty dwellings or similar up to 130 m from the plant. It should be pointed out that when the plant was built in 1962 there were very few houses nearby.

The storage was made up of: 2 spheres with a capacity of 2,400 m3, 4 spheres with a capacity of 1,600 m3 and 48 horizontal cylinders, of various capacities. In total, 16,000 cubic metres. On the day of the accident, 11,000 m3 were being stored and some tanks were being filled.

The plant stored LPG brought from the Pemex refinery in three underground pipes, for its subsequent distribution: Two 100 mm pipes transported propane and one 300 mm pipe transported various products.

The accident occurred at 5:45 in the morning: a large quantity of LPG ignited, having escaped after an 8” diameter pipe broke, probably due to overfilling. Witnesses say they saw LPG flowing over the walls of the 1m high retaining tray over which the tank was positioned.

The resulting cloud of LPG occupied an area of 200 x 150 m2, with a thickness of 2m; it ignited 5-10 minutes after the leak occurred, possibly from a flame located at ground level in the bottle filling section.

The gas cloud reached the nearest houses, where it produced fires and explosions. The University of Mexico, 25 km away, recorded 9 explosions from 5:45 until 7:01. The most intense, BLEVES, were the 2nd and the 7th.

Minor explosions continued until 11 o’clock in the morning and the fire continued until 6 o’clock in the evening. The first explosion was a VCE (vapour explosion) followed by a flash fire, which affected the vapour section of the spheres (it is possible that some of them were more vulnerable due to overfilling and affected structurally by the initial explosion). The second explosion was more violent: BLEVEs occurred in one or more spheres, with balls of fire 200-300 m in diameter. This explosion, described as an earthquake, destroyed numerous houses.

Following this, more BLEVEs occurred. In total, 4 spheres and 15 cylindrical tanks exploded with a BLEVE. Two cylinders were displaced some 1,200 metres by the explosion.

542 people were killed and 4,200 were injured, some of them seriously. Close to 10,000 people lost their homes. 5 plant workers died, and 200,000 people had to be evacuated. Virtually all the fatal victims were located within a 300 m radius of the centre of the plant.

When the plant was built, the nearest houses were more than 360 m away (still an insufficient distance), however the construction of houses up to 130 m from the boundary of the plant was permitted.

Explosion in the Urals gas pipeline

On 4 June 1989, the natural gas produced from a leak in a pipeline running from Tran-Siberia to  Russia formed a cloud and exploded near Ufa, some 115 km east of Moscow, destroying two passenger trains that were passing by the location of the explosion at the time. Of an estimated total of 1.200 passengers, 600 were killed. The gas had been deposited in the valley in order to let the trains pass. The main cause of the leak was the corroded pipeline material.

Piper Alpha Platform, North Sea

On 6 July 1988, at approximately 10 o’clock at night, an explosion was the beginning of the disaster that destroyed the Occident Piper Alpha Platform. A few seconds after the first explosion, the huge fire developed which generated a huge plume of black smoke that surrounding the entire platform, except the lower and upper sections.

Many of the 226 people on the platform were trapped in the accommodation areas. Twenty minutes after the fire started, one of the huge pipes that connected the Piper Alpha with Texaco’s Tartan Alpha platform broke. This produced a ball of fire more than 150 m in diameter on the platform, causing more pipelines to break and the collapse of the structure in just a few hours. The following morning, just a few of the modules remained in place.

167 people died. The financial losses were calculated at approximately 2,000 million euros. Of the 61 survivors, 5 jumped into the sea from more than 50 metres and 13 did so from 30 metres.

The immediate cause of the accident was as follows: the previous night the high pressure injection pump for the condensed propane was switched off either to carry out programme maintenance or to repair the variable speed connection, since it was producing vibrations. Furthermore, since the safety valve (PSV) had to be recertified, it was removed, without placing a blind in the pump. The work was left unfinished, in order to continue with it the following morning. But at 10 o’clock at night, during the following shift, the main condensation pump broke and the panel workers in the control room decided to put the reserve pump into operation unaware that it was under maintenance. This was what caused the major gas escape which 10 minutes later ignited and exploded. Unfortunately the automatic sprinkler system had been switched off in order to protect the divers close to the sea water outlet.

Apart from the above, the direct cause of the accident was certain shortcomings that were identified in the subsequent investigation. Many of the workers had been hired a short while before and were therefore almost new employees. Evacuation simulations had not been carried out for 3 years. Training on safety issues was highly inadequate. The escape routes to the lifeboats were blocked.

Amoco Cadiz

On 16 March, 1979 the Amoco Cadiz petrol tanker was heading towards the coasts of Limebay and Rotterdam. It leaked 200,000 tons of petrol, making it one of the biggest catastrophes in history. This tanker had been built three years before in Spanish dockyards.

The spillage covered the bay of Portsall, in the English Channel, with hydrocarbon. Thousands of cases of contaminated birds and marine fauna were recorded. Obviously this had a serious impact on the economic activities associated with the sea in the region.

This disaster will also be remembered for being the first time the courts had prosecuted a petrol company and forced it to compensate for the damage caused.

Chernobyl

The Chernobyl accident, which occurred on 26 April, 1986 in the Ukraine (then in the old Soviet Union), was the most serious nuclear accident in history, and is the only one to have reached level 7 (the highest level) on the International Nuclear Event Scale (INES).

The Chernobyl nuclear power station was made up of four RBMK-100 reactors each able to produce 1.000 MW. From 1977 to 1983 the first four reactors were progressively brought online. The accident meant that two reactors which were under construction were never finished. The design of these reactors did not comply with the safety requirements imposed Western civil nuclear reactors at the time and the most important of these is what was lacking in the containment tower.

On the day of the accident, a test was being carried out to improve the safety of the reactor and consequently they needed to ascertain how long the steam turbine would continue generating electricity once the flow of steam had been cut. In the case of a breakdown, the emergency cooling pumps needed a minimum amount of power to operate and the technicians did not know if, once the steam flow had been cut, the turbine would be able to keep the pumps working.

When carrying out the test the technicians wanted to keep the chain reaction in the reactor going so as to avoid a phenomenon known as xenon poisoning. The operators inserted the control rods to reduce the power of the reactor, which fell to 30 MW. At such a low level, the automatic systems can shut the reactor down and so the operators disconnected the power regulation system, the emergency core cooling system and other protective systems. At 30MW xenon poisoning began to occur, so in order to prevent this they increased the power of the reactor by raising the control rods. However, with the reactor about to come to a halt, the operators manually removed too many control rods. The safety regulations stated that at least 30 of the 170 boron steel rods in the core must remain lowered at all times, but on this occasion they only left 8 in place. With the emergency systems disconnected, the reactor underwent an extremely rapid power surge which the operators did not detect in time. At 1:23 am, four hours after the experiment had started, some of the operators realized that something was wrong.

When they tried to lower the control rods again there was no response, possibly because the heat had twisted them out of shape, and so the operators disconnected them so that they did not fall due to the pull of gravity. Loud noises were heard and these were followed by an explosion which was caused by a hydrogen cloud forming inside the reactor core. This took the 100 ton roof off the reactor, caused a fire in the plant and released gigantic emission of fission products into the atmosphere.

The quantity of radioactive material released was directly responsible for the death of more than 31 people and forced the Soviet government to evacuate more than 135.000 people. It also caused international alarm when radioactive material was detected in several eastern and central European countries.

In addition to the economic consequences, the long term effects of the accident on public health were also the object of various studies.  

Buncefield

On 11 December 2005 at 6:03 in the morning a series of explosions caused fires that destroyed the Buncefield fuel depot in Hemel Hempstead, some 40 km from London. The depot, operated by Total and Texaco, supplied fuel to Heathrow airport and other major facilities in the region.

The fire was considered the worst to have occurred in the United Kingdom and in Europe since the Second World War, and 15 million litres of water, 250,000 litres of foam and 26 fire engines were required to put out the flames.

According to the report published by Lord Newton de Braintree, chairman of the Buncefield Investigation Committee, one of the storage tanks overflowed, yet neither the workers nor the alarm system detected the high level of fuel vapour. The tank had been overflowing for more than forty minutes before the explosions occurred.

A complex of retail outlets close to the depot suffered serious material damage. Following the initial explosion it was necessary to check the structures of several buildings on the site. Even buildings located 800 metres away were affected. The force of the explosion was 2.4 on the Richter scale.

Historical record of accidents

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