On June 1, 1974, at approximately 4:53 PM, there was an explosion of catastrophic proportions equivalent of 15 to 45 tons of dynamite when part of reactor system used in the production of cyclohexane ruptured at the Flixborough Works of Nypro Ltd plant in Flixborough, England.
The explosion took the lives of 28 people and with another 36 persons being injured. Ironically, the amount of casualties were decreased given the explosion occurred on a weekend.
Prior to the explosion, on March 27, 1974, there was a discovery of a vertical crack in the Number 5 reactor leaking cyclohexane. The plant was subsequently shut down and an investigation revealed a serious problem in the Number 5 reactor. The plan was then to take it out of service for repair; and installed a bypass conduit system in it's place between reactor Number 4 and Number 6 so that production could resume.
In the afternoon, on June 1, 1974, the 20 inch in diameter bypass conduit system ruptured causing the release of a large volume of cyclohexane. The cyclohexane formed a flammable mixture which then found an ignition source causing a vaporous cloud explosion resulting in extensive damage and fires to the plant structure.
Of the 28 people who died in the explosion, 18 persons who were plant control room perished due to a collapse of the floor structure.
The cause of the accident was believed to be the result of a series of calculation errors related to installing the 20 inch bypass conduit system between Reactor Number 4 and Number 6.
The reactor system consisted of six vessels which were situated in a step-like formation. On March 27, 1974, the Number 5 reactor was taken out of service and a 20 inch bypass assembly system was added. The bypass assembly consisted of 20 inch in diameter pipe; and bellows 28 inches each in diameter that were connected to Reactor Number 4 and Number 6.
For approximately two months, the bypass assembly system operated properly; however, on the afternoon of the accident, it is believed the pressure within the reactor system was elevated enough causing the bellow extensions to rupture from the sheer force. This rupture led to holes in the bellows and subsequent escape of cyclohexane resulting in a large vapor cloud and subsequent explosion.
Key errors with the Flixborough Disaster:
The modification was carried out without a full assessment of the potential consequence.
No pressure testing was carried out on the bypass assembly pipeline.
The control room should be able to withstand major hazards; however, in this disaster, it was the area that had the most casualties.
The large scale of flammable product at the plant contributed to the scale of the explosion.
Download Report of Court of Inquiry (3.65 MB file)