Firefighters respond to a call of a structure fire, which turned out to be a hazardous materials incident, at Wells Concrete in unincorporated Cary Tuesday morning. | Photo: CFPD

70 employees were evacuated after chemicals were mixed incorrectly and caused a vapor plume inside a manufacturing plant near Cary Tuesday morning, fire officials said.

The Cary Fire Protection District responded around 7:47 a.m. Tuesday to Wells Concrete, 4012 Northwest Highway in unincorporated Cary, for a call of a structure fire.

Firefighters arrived in five minutes and met with employees, who initially reported there was a fire in the building, according to Cary Fire Protection District Lt. Michael D. Douglass.

A further investigation revealed that there was no fire but instead a hazardous materials incident.

Firefighters respond to a call of a structure fire, which turned out to be a hazardous materials incident, at Wells Concrete in unincorporated Cary Tuesday morning. | Photo: CFPD

The incident resulted in a vapor plume within the building.

Douglass said Wells Concrete employees were mixing chemicals in a 55-gallon drum as part of their normal work process.

They did not mix the right concentrations, which caused a chemical chain reaction.

The chemical began leaking out of the drum and produced a vapor plume in the production area of the building, Douglass said.

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Employees, prior to evacuating, dumped an absorbent over the spilled area which stopped the chemical chain reaction.

Several overhead doors were left open so that the plume would ventilate from the building.

Firefighters respond to a call of a structure fire, which turned out to be a hazardous materials incident, at Wells Concrete in unincorporated Cary Tuesday morning. | Photo: CFPD

There were 70 employees in the building at the time and they were able to evacuate safely.

Hazardous materials technicians met with company representatives to review the chemicals involved, Douglass said.

The building was ventilated after the leak was mitigated and crews monitored to verify the building was safe.

The Wonder Lake Fire Department was specially requested to the scene with their airboat.

Douglass said the airboat has a large fan and was placed by an overhead door to ventilate the entire building.

Firefighters from the Algonquin-Lake in the Hills, Village of Barrington, Barrington-Countryside, Fox River Grove, Nunda Rural and Wauconda fire departments also responded to the scene.

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