Posted: Friday, July 20, 2012 --- 9:10p.m.

FOND DU LAC, Wis. (AP) -- Residents are back in their homes after an ammonia leak at a milk processor forced an evacuation in Fond du Lac.

Fire Chief Peter O'Leary says the leak was reported just after 4 p.m. Friday at Milk Specialties. Firefighters arrived to find employees were evacuating.

Fire crews smelled ammonia outside. All employees were able to get out of the building safely.

Several residents were evacuated as a precaution. Many residents called 911 to report the odor.

Members of the Fond du Lac hazardous materials team began testing air quality outside and inside the plant.

The fire chief says a seal had failed on an ammonia tank compressor, activating an automatic pressure relief valve. Once the air was declared safe, workers went back into the plant to repair the machine.

Copyright 2012. The Associated Press.