The Portland Fire Department stopped an ammonia leak at a cold storage facility in a Portland industrial park five hours after large quantities of the noxious gas began spewing into the building early Tuesday morning.

No one was inside the building at the AdvancePierre Foods cold storage warehouse at 56 Milliken St. when the leak was reported at 5 a.m. by an employee of another business next door who smelled the gas and called 911, said Deputy Fire Chief Keith Gautreau.

Portland Fire Chief David Jackson said of the ammonia leak, "The good news is once it's in fresh air, it dissipates fairly quickly."

What remains unclear is why an AdvancePierre employee did not call the fire department after that person was notified of the leak by a private monitoring company that keeps tabs on the refrigeration system, much like a home security company.

“I have to look into why we weren’t notified immediately,” Gautreau said.

A spokeswoman for AdvancePierre did not answer questions about emergency procedures, and whether a plant manager should have called firefighters immediately.

The leak was stopped about 9:30 a.m. after firefighters from the hazardous materials team entered the plant five times to gather information before isolating the leak and stopping it. Gautreau said a faulty valve was the likely culprit in the leak.

The storage facility was previously owned by Barber Foods, which still operates a plant on St. John Street in Portland. AdvancePierre acquired Barber in 2011.

There is no record of violations on file with the federal Occupational Safety and Health Administration for the Milliken Street plant, according to the safety agency’s online database.

A spokeswoman for the Maine Department of Labor, which has oversight over public-sector workplace safety in the state, said that since the business is private, it would not be involved, however the federal workplace safety officials could investigate the leak.

Ammonia is used as a common industrial refrigerant. The AdvancePierre facility had 21,000 pounds of ammonia in its refrigeration system, but Gautreau said it is not yet clear how much leaked.

According to OSHA, an acceptable level of ammonia is 50 parts per million averaged over eight hours. During the leak, Portland hazmat teams were measuring between 3,000 parts per million and 5,000 parts per million, with readings peaking at about 9,000 parts per million, Gautrau said.

Ammonia is an extreme skin and eye irritant. At levels above about 12,000 parts per million, it becomes flammable. Prolonged exposure to high concentrations can be fatal because the gas displaces oxygen, causing asphyxiation and pulmonary edema, when fluid accumulates in the lungs.

After the leak, an emergency system automatically vented the gas out of the building. Although typical wind patterns would have brought the pungent smell toward a neighborhood about 250 yards from the plant, a weather system off the Maine coast pushed the odor in the opposite direction.

“The good news is once it’s in fresh air, it dissipates fairly quickly,” Fire Chief David Jackson said.

Jackson said he knows of no prior safety issues at the company’s Portland location.

He also said the alarm system that detects ammonia leaks appears to have functioned properly.

AdvancePierre Foods supplies proteins and sandwich products to schools, food service and retail outlets across the country. In 2011, the company purchased Portland-based Barber Foods. The company is headquartered in Cincinnati, Ohio.

CORRECTION: This story was updated at 10:28 a.m. on May 25, 2016 to clarify that Maine Department of Labor would not be involved with investigating the leak for the private business.