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An explosion at an industrial chemical plant in southeast England on Thursday led to a leak of caustic soda, forcing local people to stay indoors for hours until the situation was deemed safe by the emergency services.

At about 8:00 pm on Sept. 26 an explosion was heard at the Industrial Chemicals Ltd plant in West Thurrock, Essex, BBC News reported. The facility is a chlorine scrubbing plant and the smell of chlorine caused serious concern among members of the local community. Witnesses reported seeing plumes of thick smoke over the facility right after the explosion.

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Five fire engines were sent to the site and the fire was put out about two hours after the blast. An investigation was immediately started by police officers and officials with the Health and Safety Executive (HSE). It was later announced by the Essex Fire and Rescue Service that a small tank of diluted caustic soda had been the cause of the blast.

According to a spokeswoman for the Essex Police, quoted by the Evening Standard, two people were slightly injured in the incident but were treated on site. A fire service spokesman stated that an assessment by chemical experts on site had found that there were no health or environmental risks for the community.