The London Fire Department (LFD) was dispatched for a hazmat call at the Kinsmen Arena on Wednesday.
According to the fire department, the building had to be evacuated at around 2 p.m. due to an ammonia leak.
No injuries were reported.
Emergency crews used natural and mechanical ventilation to improve the air quality while waiting for repair technicians to arrive.
By 4:20 p.m., LFD reported that the leak had been contained.
The arena is expected to be reopened after 6 p.m. after mandatory repairs are completed.