They say practice makes perfect. But sometimes, it can be costly as well.

Charleston County recently learned that lesson to the tune of nearly $100,000.

That's the price tag of an emergency drill that ended with a worker mistakenly triggering the release of a pricey, fire-suppressing gas at the county's Leeds Avenue records center.

No one seems quite sure how the system got tripped, but it resulted in the warehouse being flooded with nearly 4,500 pounds of halon gas -- the building's entire supply.

While no records were damaged and no employees injured, the gaffe is costing the county $95,368 to refill the 10 halon tanks, according to Michael Filan, the county's director of internal services.

County officials are filing an insurance claim in hope of recouping that cost, an amount of money that would nearly cover the annual starting salaries of three sheriff's deputies or emergency medical technicians.

Halon gas is considered a very effective tool for fighting fires in museums, computer centers and other places where sensitive circuitry or vital records are stored because it leaves no damaging residue.

But production of the gas ceased in 1994 due to concerns about its effect on the ozone layer. You can still get halon, but it can be a costly proposition because tanks must be replenished from limited reserves, said Tom Cortina, executive director of the Virginia-based Halon Recycling Corp.

Halon usually sells for $10 to $15 per pound, on average, but that figure can vary considerably by region and availability, Cortina said.

The county uses the halon system to protect a trove of records from the Sheriff's Office, coroner, court system, auditor, treasurer, budget and finance office, Public Works Department and various other agencies, Filan said.

The release occurred when one of the center's 10 workers somehow activated the system's control panel during a fire-evacuation drill on the morning of Sept. 7, Filan said. He would not identify the employee, citing an ongoing personnel investigation.

The release was limited to the warehouse and no office areas were affected, Filan said. The tanks were expected to be refilled today, bringing the system back on line.

"It is unfortunate that the system activated," Filan said, "but it performed as it was designed."

Reach Glenn Smith at 937-5556 or on Twitter at @glennsmith5.