The Flixborough disaster was an explosion at a chemical plant close to the village of Flixborough, England, on 1 June 1974. It killed 28 people and seriously injured 36.[1]
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The chemical plant, owned by Nypro UK (a joint venture between Dutch State Mines and the British National Coal Board) and in operation since 1967, produced caprolactam, a precursor chemical used in the manufacture of nylon.[2] Residents of the village of Flixborough were not happy to have such a large industrial development so close to their homes and had expressed concern when the plant was first proposed.
The process involved oxidation of cyclohexane with air in a series of six reactors to produce a mixture of cyclohexanol and cyclohexanone. Two months prior to the explosion, a crack was discovered in the number 5 reactor. It was decided to install a temporary 50 cm (20 inch) diameter pipe to bypass the leaking reactor to allow continued operation of the plant while repairs were made.
At 16:53 on Saturday 1 June 1974, the temporary bypass pipe (containing cyclohexane at 150°C (302°F) and 1 MPa (10 bar)) ruptured, possibly as a result of a fire on a nearby 8 inch (20 cm) pipe which had been burning for nearly an hour. Within a minute, about 40 tonnes of the plant's 400 tonne store of cyclohexane leaked from the pipe and formed a vapour cloud 100–200 metres (320–650 feet) in diameter. The cloud, on coming in contact with an ignition source (probably a furnace at a nearby hydrogen production plant) exploded, completely destroying the plant. Around 1,800 buildings within a mile radius of the site were damaged.
The fuel-air explosion was estimated to be equivalent to 15 tonnes of TNT (60 gigajoules) and it killed all 18 employees in the nearby control room. Nine other site workers were killed, and a delivery driver died of a heart attack in his cab.
Observers have said that had the explosion occurred on a weekday it is likely that more than 500 plant employees would have been killed. Resulting fires raged in the area for over 10 days. It was Britain's biggest peacetime explosion until the Buncefield Depot explosion in 2005.
Substantial destruction of property was recorded in Flixborough itself, as well as in the neighbouring villages of Burton-upon-Stather and Amcotts. Significant structural damage affected Scunthorpe (eight miles away) and the blast was heard over thirty miles away in Grimsby.
Although the area was quite remote, graphic images of the disaster were soon shown on television due to BBC and Yorkshire Television film crews who had been covering the Appleby-Frodingham Gala in Scunthorpe that afternoon.
The official inquiry into the accident determined that the bypass pipe had failed because of unforeseen lateral stresses in the pipe during a pressure surge. The bypass had been designed by engineers who were not experienced in high-pressure pipework, no plans or calculations had been produced, the pipe was not pressure-tested, and was mounted on temporary scaffolding poles that allowed the pipe to twist under pressure. The by-pass pipe was a smaller diameter (20") than the reactor flanges (24") and in order to align the flanges, short sections of steel bellows were added at each end of the by-pass - under pressure such bellows tend to squirm or twist. These shortcomings led to a widespread public outcry over industrial plant safety, and significant tightening of the UK government's regulations covering hazardous industrial processes. See COMAH Regulations.
Despite protests from the local community the plant was re-built but, as a result of a subsequent collapse in the price of nylon, it closed down a few years later. The site was demolished in 1981, although the administration block still remains. The site today is home to the Flixborough Industrial Estate, occupied by various businesses and Glanford Power Station.
The foundations of properties severely damaged by the blast and subsequently demolished can be found on land between the estate and the village, on the route known as Stather Road. A memorial to those who died was erected in front of offices at the rebuilt site in 1977. Cast in bronze, it showed a number of mallards in flight landing on water: When the plant was closed the statue was moved to the pond at the parish church in Flixborough. During the early hours of New Year's Day 1984 the sculpture was stolen. It has never been recovered and those responsible for the crime have never been found.
The plinth it stood on, featuring a plaque listing all those who died that day, can still be found outside the church.
In April 2007 new evidence was presented by Dr John Cox at a one-day symposium at University College London. Dr Cox argued there were two explosions, a smaller one, which was overlooked, happening before the massive blast.[3] An eyewitness backed the claims and explained how she had tried to contact the police but the incident was never followed up.[4] Dr Cox criticised the Health and Safety Executive (HSE) for "[coming] up with the safe conclusion to allay public fears, rather than a significant conclusion which is that it was quite a complex issue".[3]
Previously, in April 2000, allegations of a cover-up had been unveiled by a whistle-blowing scientist earlier sacked from the original investigation team. His name was Dr Ralph King, an eminent author of chemical engineering text books and an expert in the thermodynamics of large scale chemical reactions. He carried out numerous and complex calculations which suggested a build up of water in the base of the cyclohexane reactors could have led to a sudden explosive release of pressure which displaced the temporary by-pass pipe causing it to fail due to twisting and rupture of the bellows. This became known as the "water theory", an alternative explanantion to the causation set out in the Official Inquiry Report. The significance of Dr King's findings was that the disaster did not occur due to a failure of the local engineering team in constructing the temporary by-pass pipe (even though their methods might have been lacking in finesse), but was esentially a failure in the design of the process by the factory owners (Dutch State Mines)who failked to take account of the possibility of water build up in the reactors, especially at start up. He said the original inquiry was wrong to blame a simple mechanical failure: "I realised that what we were really there for was to come up with a cause which would not embarrass the company". His criticism led to the HSE ordering laboratory scale experiments at their Buxton Research Centre. The early laboratory experiments were inconclusive but seemed to indicate that Dr King's "Water Theory" might have some merit. Since the design fault suggested by Dr King, if correct, could have an impact on other similar reactors currently operating in the UK and overseas, HSE decided to scale up the experiments to take place in a stainless steel pressurized reactor at their Buxton site. The HSE research facilities at Buxton possesses features which can allow potentially dangerous experiments to be carried in 'bunkers' shielded by earth bunds with the controls for the experiment located in a concrete blockhouse a safe distance away. A miniaturized version of the Flixborough cyclohexane oxidation reactor was operated within such a safe facility at Buxton. After numerous test runs, HSE were unable to replicate Dr King's findings and the test results released in November 2000 did not seem to support Mr King's theory that even if water had been present inside the reactors at start up it could not have generated a level of build-up of pressure that would have caused the bypass pipe to fail. In spite of these findings by HSE (which are still questioned by some who have personal knowledge of the Flixborough Disaster) it is remarkable that Dr King managed to keep his "water theory" on the agenda for the best part of 20 years unflaggingly raising the isuue with politicians, civil servants, trade union leaders, heath and safety experts and many others until at last, he was finally taken seriously by HSE. Dr King's main concern was not one of personal vindication or status, simply a genuine concern that unless his theory was tested, another similar disaster would one day take place somwhere in the world. Unfortunately Dr King was never to learn whether his theory was proven or not by HSE, since he sadly died just a few months before the larger scale experiments were carried out.