Paramedics treated 17 people and took 11 to hospitals on Monday when a safety valve released ammonia in the air at Schneider's Dairy in Whitehall.
No one had life-threatening injuries, said Allegheny County Department of Emergency Services Chief Alvin Henderson. Those transported to hospitals went as a precaution, said Whitehall police Chief Donald Dolfi.
Dairy employees reported the valve released about 50 pounds of ammonia, emergency officials said. The valve released the foul-smelling and -tasting gas when pressure in a tank rose to unsafe levels, Dolfi said.
The tanks, where ammonia is stored as a liquid, are designed to release the chemical when pressure rises to prevent an explosion.
"The system appeared to work as it was designed," Dolfi said.
Inspectors from the Pittsburgh office of the Occupational Safety and Health Administration will investigate the incident, said Chris Robinson, the agency's area director. It was too soon to determine a cause.
Dairy management was not available to comment on the ammonia release. Flanked by single-family homes and manicured lawns, the Schneider's Dairy facility on Frank Street serves as a headquarters and processing plant, according to the dairy's website.
Employees in the offices upstairs said they had to evacuate the building during the afternoon but later returned to work. Ambulances were called to the facility about 1:45 p.m.
Dolfi said pressure in the tank rose because Pennsylvania American Water shut off water on Frank Street while doing work. Water company employees were replacing a valve nearby and had notified all customers on the street of a planned outage, said Gary Lobaugh, a spokesman for the company.
Ron Bouvy, who owns Bouvy Heating & Air Conditioning Services, was working on an air-conditioning unit across the street from the dairy and noticed a pungent smell and sour taste in the air shortly after noon. Bouvy works with ammonia, which is used as a cooling agent, and recognized the smell and taste.
Paramedics evaluated 17 employees at the scene. The 11 patients went to Allegheny General, UPMC Presbyterian and UPMC Mercy hospitals.
The Allegheny County Health Department responded to check air quality and dairy products. No food products were contaminated by the ammonia, Henderson said.