The Gwinnett County 911 call center re-opened late Monday afternoon, several hours after being evacuated when the building’s fire suppression system activated. The county’s emergency response was not affected, the county’s police department said.

“There was no disruption in service,” Cpl. Michele Pihera told the AJC.

Late Monday afternoon, investigators had not determined what caused the fire system to activate. But a clean-up crew was allowed inside and operations resumed around 5:30 p.m., according to Cpl. Jake Smith. Call center operations shifted to police headquarters for several hours Monday.

Shortly before 10 a.m., the call center’s fire system activated for unknown reasons, police said. A communications supervisor also smelled smoke, Smith said. The call center staff members have the opportunity to halt the system from activating, but did not because of the smoke smell, he said.

A chemical substance is released from the system, rather than just water, according to Smith. The extinguishing agent is a gas, which causes short-term irritation.

“The fire suppression system is not a typical water sprinkler system used in most buildings,” Smith said.

The building was evacuated, and five employees were transported to the hospital for evaluation of respiratory issues after the fire system was activated, Smith said. Another person was treated at the scene and released, he said.

A ceiling tile fell on an employee, possibly due to the fire system being activated, according to investigators. The employee was not seriously injured. All but one county employee had been released from the hospital by Monday afternoon.

The call center’s operations were shifted to the adjacent police headquarters and mobile operations center, Smith said.

Investigators were working to determine what caused the fire system to activate. There was no sign of a fire, Smith said.