Firefighters and a Nassau County Fire Marshal’s Office hazmat team responded to the Merrick Post Office Thursday morning after a 911 caller reported smoke from a possible fire in a work area of the building on Merrick Road, Nassau fire officials said.

But a spokesman for the Merrick Fire Department said no fire was found and said that a “meticulous” multi-hour inspection of the property finally located the cause of the smoky haze that filled the building: a leaking air conditioner unit.

Spokesman Ron Luparello said the call reporting the incident was received at 5:58 a.m. and said that even after firefighters found there was no fire the haze still filled the air. “Considering what the building is, you can never be too careful these days,” he said, adding that the decision was made to call both the hazmat unit and the postal inspector.

A search, under the direction of Merrick Chief Patrick Gavigan, determined the haze was not only not related to any fire or combustible source, but that it was not from postal-related packages being stored, sorted or processed at the facility. It was finally determined that the source was leaking refrigerant from the old building’s air conditioning system, which was causing a thick mist and haze when it vaporized in the moist air.

The system was shut down, Luparello said.

Repairs are ongoing.

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The building was finally cleared around 8:30 a.m.

There were no injuries and no customers were affected. The building does not open to the public until 9 a.m.