||This article includes a list of references, but its sources remain unclear because it has insufficient inline citations. (May 2013)|
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. 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 M Pa (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 2005 Buncefield fire.
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 (three 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 filmstock news 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 personnel who were not experienced in high-pressure pipework, no plans or calculations had been produced, the pipe was not pressure-tested, was mounted on temporary scaffolding poles that allowed the pipe to twist under pressure and had not been reviewed by appropriate chartered engineers. The by-pass pipe was a smaller diameter (20 inches) than the reactor flanges (28 inches), 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.
New theories on the causes of the disaster
In April 2007 new evidence was presented by Dr John Cox at a one-day symposium at University College London. Cox argued there were two explosions, a smaller one, which was overlooked, happening before the massive blast. An eyewitness backed the claims and explained how she had tried to contact the police but the incident was never followed up. 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".
In 1999, allegations of cover-up had been unveiled by a whistle-blowing scientist sacked from the original inquiry, Ralph King. 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 experiments. The test results released in November 2000 seemed to back up King's theory that the presence of water inside the reactors and the simultaneous shutting down of crucial equipment, generated a massive build-up of pressure that blew the valve apart.
A BBC Radio 4 programme reported that in order to save costs and cut electricity use due to a fuel crisis, routine stirring of the tanks, previously performed to prevent the buildup of condensation of water in the tanks, was severely curtailed, and the hypothesis was that the over pressure was caused by some of this water flashing to steam.
- List of United Kingdom disasters by death toll
- Health and Safety Executive
- 2005 Hertfordshire Oil Storage Terminal fire
- "Flixborough (Nypro UK) Explosion 1st June 1974: Accident summary". Health and Safety Executive. Retrieved 28 September 2011.
- Chartres, John; Kershaw, Ronald; Osman, Arthur (3 June 1974). "Fire rages on after one of the worst disasters in world chemical industry". The Times (59105) (London). p. 1.
- "Nypro: New Theories". Scunthorpe Telegraph.
- "Double explosion may have destroyed the plant". Scunthorpe Telegraph.
- Lashmar, Paul (25 November 1999). "Secret tests clear workers of blame for Flixborough blast". The Independent.
- The Flixborough Disaster, Report of the Court of Inquiry, 1975
- Summary of the official inquiry into the accident
- Flixborough memories on h2g2
- Flixborough: 20 years on, Loss Prevention Bulletin issue 117, 1994