A HSE spokesperson said: "HSE has launched a full investigation into the incident at Millennium Inorganic Chemicals Ltd near Grimsby on 5 March 2010. HSE inspectors were on site throughout the weekend and will continue to be on site throughout next week.
"Specialist HSE inspectors with knowledge in mechanical engineering, process safety, electrical engineering, control and instrumentation and photography have also been assisting with the investigation.
"The cause of the incident is still to be determined and the investigation will take a number of months to complete.
"HSE is continuing to liaise with the police, fire service and the Environment Agency."
A HSE spokesperson said: "HSE was informed early this morning of an incident at Millennium Inorganic Chemicals Ltd near Grimsby shortly after midnight. HSE sent two inspectors on site this morning, and is liaising with the police, fire service and the Environment Agency.
"HSE has launched an investigation. The cause of the incident is still to be determined and HSE staff are likely to be at the site throughout the weekend.
"The area around the site has since been made safe and poses no danger to the nearby community."
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