Emergency services in Essex said they had been called to Industrial Chemicals Limited, Stoness Road, in West Thurrock.
Fire crews found there had been an explosion of chemicals in a chlorine scrubbing unit.
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Atlantic frontal systems spread rain in from the northwest on both weekend days. Windy - with gales across the north and west but mild.
The band announced at a free concert on Friday that they would take over the event's Pyramid stage on Saturday June 25.
The victims were collecting permits and escorts a day after their home town was liberated from the extremists.