Don Zets said he was taking a stroll Sunday through his West Middlesex neighborhood when he heard a noise that sounded like air being released from a tank.

"Then I heard sirens go off," the Main Street resident said. "I heard it but I paid no attention to it."

What Zets heard at about 7 p.m. was a nitrogen pressure valve letting loose at the Dairy Farmers of America, North Street, West Middlesex. Clouds of the white nitrogen puffed out as a result. Nitrogen is a non-flammable gas that is used to process cheese, an unidentified official at the scene said.

It was unknown Sunday night if the gas posed any danger to residents.

Neighbors along North Street watched as police and fire crews blocked vehicles from entering the end of the road. Firefighters also kept pedestrians yards away, warning them to stay back.

An assistant fire chief, who was at the scene, refused to comment on the incident and refused to allow the press near the scene.

A Mercer County 911 supervisor said a call of an explosion came in at 6:57 p.m., but the rupture turned out to be nothing serious.

"Just a tank blowing off steam," she said.

A hazardous materials team was not called out, she added.

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