The chemical release and fire at the Associated Octel Company Limited, Ellesmere Port, Cheshire. 1st February 1994

Accident summary

At about 8.23 pm on 1 February 1994 there was a release of reactor solution from a recirculating pump near the base of a 25 tonne ethyl chloride (EC) reactor vessel at the factory of The Associated Octel Company Ltd, Ellesmere Port, Cheshire. The reactor solution was highly flammable, corrosive and toxic, mainly consisting of ethyl chloride, a liquefied flammable gas, mixed with hydrogen chloride a toxic and corrosive gas, and small quantities of solid catalyst, aluminium chloride. A dense, white cloud soon enveloped the plant and began to move off-site.

The on-site and external emergency services were called in accordance with pre-arranged procedures for major incidents involving chemical release. Over the next one and a half hours action was taken to isolate the leak, to suppress the further release of vapour and to prevent the cloud spreading.

In spite of these attempts a pool of liquid continued to collect and at 10.08 pm the flammable vapours of ethyl chloride ignited, causing a major pool fire which was most intense at the base of the reactor. As the incident developed there were also fires at flanges damaged in the fire, including jet flames at the top of two large process vessels on the plant. Although these vessels and the reactor were protected by a fire resistant coating, there was concern at one stage that the vessels might explode and the damage extend to chlorine storage vessels on the adjacent plant.

The leak occurred at a point between fixed pipework and the discharge port of a pump recirculating liquids to the reactor, as a direct consequence of either (a) the failure of a corroded securing flange on the pump working loose; or (b) the failure of a PTFE flexible connection ("bellows") connecting the pump discharge to the pipe. The HSE believes the first of these possible causes was the more likely. The most likely source of ignition was an electrical control box to a compressor nearby.

Failings in technical measures

• Either: Pipework failed due to a corroded securing flange on the pump working loose.
• Corrosion / Selection of Materials: Corrosion allowances, monitoring/inspection
• Or: Failure of PTFE bellows connecting the pump discharge to the pipe.
• Design Codes - Pipework: Use of flexible pipes
• No formal system of maintenance and fault reporting of the components.
• Maintenance Procedures: Maintenance systems, Fault reporting systems
• Manual isolation valves were difficult to reach and operate; ROSOV valves should have been in place.
• Isolation: Manual Isolation, Emergency isolation

References

Health and Safety Executive, 'The chemical release and fire at the Associated Octel Company Limited : A report of the investigation by the Health and Safety Executive into the chemical release and fire at the Associated Octel Company, Ellesmere Port on 1 and 2 February 1994', ISBN: 0717608301, 1996.