Two ammonia leaks prompted evacuation of between 700 and 800 employees at the Schneider Corp. plant in Kitchener that is now owned by Maple Leaf Foods Inc.
The plant which is scheduled for closure later this year when all operations will be moved to a new plant in Hamilton has both an office tower and meat processing facilities.
Both parts were affected by the ammonia leaks.
The ammonia leak was in the office tower and spread throughout the building, said Maple Leaf senior supervisor Rick Vogel.
One person was taken to hospital and the health of two others was checked at the site on Courtland Avenue.
Two people were assessed at the scene by EMS workers and a third was taken to hospital.
"The air monitoring that we've done is at safe and acceptable levels," said Kitchener Fire Chief Tim Beckett who also said there were two leaks.
"We've got a good wind going and the ammonia is dissipating," he told CBC Kitchener.