Fire crews investigating the cause of a suspected chemical leak at a council office that left nine people needing medical treatment have found no trace of any chemicals that could have caused the problem.
The Essex County Council building in The Crescent, Colchester, was evacuated this morning after reports of around a dozen people feeling ill.
It is the second time in less than a fortnight that the building has had a suspected chemical leak - it was first cleared by authorities on June 29 after reports of people falling unwell and reporting a strange smell.
Essex County Fire and Rescue Service said that shortly after the incident this morning nine people were given oxygen therapy and all other persons were accounted for.
Crews entered the building this afternoon to try and find the reason for the problem but have said there is no definitive cause.
A statement from the Fire Service said: "Crews have now 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.
"The building remains empty and staff will not return for at least 48 hours.
"Fire officers are now leaving the scene in the hands of the Health Protection Agency."
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 said: "Essex County Fire & Rescue Service has confirmed there is no indication of what the cause of today'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.
"A complete and independent review will now be undertaken.
"To minimise disruption to our customer's telephone calls, and as part of our business continuity plans, an alternative contact centre will be in place tomorrow from 9am to 5pm.
"Residents should check our website for up to date information about the contact centre opening times."
A specialist Detection Identification and Monitoring (Dim) vehicle from Epping - on its first emergency incident - was sent to the scene to assist in identifying the chemical involved.
Ambulance crews, specialist officers and the trusts hazardous area response team (Hart) were sent to the council office to deal with the incident after being alerted to a report of several people taken unwell at 10.40am, the East of England Ambulance Service said.
Assistant Divisional Officer Steve Foster said earlier: "Our crews treated nine people, all of whom were complaining of a bad smell, a feeling of nausea and metallic taste in their mouth. We gave all of them oxygen therapy."
A spokeswoman for Essex County Council said the cause of the incident last month was unknown and the building was declared safe 48 hours after it happened.
She said: "We can confirm that Essex House has been evacuated today following reports of employees feeling unwell.
"Emergency services are on the scene and responsible for leading initial investigations into this incident. We are aware of 11 members of staff currently being assessed.
"We are committed to making sure that our staff work in a safe and healthy environment and when emergency services dealt with the last incident, along with a specialist detection team, there was no indication of what the cause might have been - the building was handed back to Essex County Council by the emergency services 48 hours later, and was declared safe for employees to enter.
"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.
"We are taking necessary measures to ensure minimal disruption to our customers' telephone calls, with business continuity procedures currently in place.
"We would ask that emergency services as well as our own ECC teams are allowed to assess the situation and we will, of course update with further information and advice as soon as it is available."