Update: Building at centre of chemical incident in Colchester to remain empty for 48 hours

INVESTIGATORS are baffled by the second mystery chemical incident at a council office in less than a fortnight.

More than 100 people were evacuated from the Essex County Council building in Colchester Business Park and 11 people were treated by medics for nausea, dizziness and headaches yesterday morning.

Last night the Health and Safety Executive launched another investigation after an identical episode 11 days ago when more than 25 people became unwell after inhaling noxious fumes.

Essex Fire and Rescue Service crews spent several hours investigating the cause of the leak at Essex House in The Crescent but were unable to find a trace of any chemicals that could have caused the problem.

A specialist Detection Identification and Monitoring (DIM) vehicle attended the incident in an attempt to identify the source of the problem.

Firefighters were initially investigating reports the boiler system underwent a chemical clean and that a chemical may have been picked up by the air-conditioning system.

Assistant divisional officer Steve Foster said: “Crews have conducted their final tests inside the building with the air-conditioning system running and found no sign of any chemical which could have caused the problem.

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“The building remains empty and staff will not return for at least 48 hours.”

East of England Ambulance Service crews, specialist officers and the trust’s hazardous response team (HART) also attended the incident and treated 11 people at the scene with oxygen therapy.

A spokeswoman for Essex County Council said the building would now be closed until it was found to be safe and a review would be carried out.

She added: “Essex Fire and Rescue Service has confirmed there is no indication of what the cause of yesterday’s incident might have been.

“Despite the building being handed back to us we see the health and safety of our staff as paramount and have taken the decision to close the building until we can reassure our staff that it is a safe place to work.

“We recognise this is the second incident that has occurred at Essex House in the last month and would like to reiterate that the health and safety of our staff is paramount at all times.

“A complete and independent review will now be undertaken.”

A Health and Safety Executive spokeswoman confirmed it is making initial inquiries into the incident.