Centennial Ice Arena was evacuated Thursday afternoon after an ammonia leak was discovered.
The leak originated from a tank holding ammonia, a chemical used as a refrigerant, at the facility on Bench Boulevard, said Capt. Bill Michaelis of the Yellowstone County Sheriff's Office.
The odor from the leak was strong, Michaelis said, and forced about 50 people, arena employees and people attending a hockey practice, from the building.
A Billings Fire Department crew disconnected the ammonia supply around 4:20 p.m. Soon after, a hazardous materials team arrived to dissipate the fumes.
The cause of the leak has not been determined, Michaelis said.