Author(s): Kathleen Robinson. Published on December 29, 2014.

Looking Back

PERHAPS THE BEST THAT CAN BE said about the cyclohexane explosion at the Nypro plant in Flixborough, England, on June 1, 1974, is that the casualty count could have been much higher had it not occurred on a Saturday.

Originally built in 1938 as a fertilizer plant, the installation began manufacturing caprolactam, a chemical used to fabricate nylon, in 1967. A key ingredient in caprolactam is cyclohexane, a colorless, flammable liquid that occurs naturally in crude oil, volcanic gases, and cigarette smoke.

According to an investigation report published after the disaster by the British Secretary of State for Employment, the trouble began March 27, when a plant employee spotted a crack in one of six reactors through which the cyclohexane passed in succession during an oxidation process. By the next day, the crack was more than six feet long, and the plant manager took the reactor offline for inspection.

Because the plant was the only one in England producing caprolactam, however, production could not be halted for long. To get things flowing again, plant personnel built a makeshift bypass, connecting the two reactors on each side of the damaged one to each other with a pipe 20 inches in diameter, supported by scaffolding. Production resumed on April 1.

On May 29, another cyclohexane leak was discovered, and the plant was again shut down for repairs. Production resumed early on the morning of June 1, but was halted once more around 4 a.m., when several new leaks were found. An hour later, production began again but was stopped a short time later. The delay lasted until 7 a.m., when the plant went back online.

Things seemed to proceed normally through the day. But at 4:35 p.m., the makeshift bypass piping ruptured, producing a massive vapor cloud explosion and fire that could be seen more than 30 miles away. The force of the blast nearly leveled the entire installation, destroying the plant’s control room and killing all 18 employees inside. Another 10 employees died elsewhere in the plant, and 36 were injured. Fifty-three injuries were reported in the surrounding area. Had it not been Saturday, however, more than 500 employees would have been working at the plant, and the number of dead and injured could have been much higher.

The fire raged for days, eventually resulting in millions of dollars worth of damage. Every building within 650 yards of the reactors was flattened, and debris was later found as far as 20 miles away.

Despite protests from the surrounding communities, the plant was eventually rebuilt, incorporating a number of lessons learned as a result of the disaster. It closed a few years later due to economic reasons and was demolished in 1981.

KATHLEEN ROBINSON is NFPA Journal editorial operations manager.