Nine residents — including five children aged 6 months to 3 years — who live above a Port Washington restaurant were poisoned by carbon monoxide Wednesday after a contractor used a gas-powered pressure washer to clean the equipment in the eatery, fire officials said.

A resident living in one of two apartments above Eastern Strawberry Kitchen, at the corner of Port Washington Boulevard and David Avenue, smelled fumes and called 911 shortly after 8 a.m.

“They were very lucky,” said Bryan Vogeley, first assistant chief of the Port Washington Fire Department. “They were smelling the fumes that were given off from the power washer.”

Carbon monoxide, called CO by its scientific abbreviation, is a colorless, odorless gas that can build up indoors and poison people and animals who breathe it, according to the Centers for Disease Control and Prevention. It’s found in fumes produced when fuel inside cars, trucks, small engines, stoves, grills, fireplaces, gas ranges, or furnaces is burned.

The contractor, part of the crew hired to clean the restaurant’s equipment, had been operating the gasoline-powered pressure washer for about an hour before the fire department received the 911 call, Vogeley said.

When firefighters arrived, they measured the carbon monoxide inside the two-story building, as well as the basement, and found levels as high as 150 to 200 parts per million, Vogeley said. The Occupational Safety and Health Administration says the permissible exposure limit is 50 parts per million over an eight-hour period.

Two adults and four children were in one apartment. The residents are related, but Vogeley said he did not know how they are related. Two adults and a child were in the second apartment, and again Vogeley said he did not know if these residents are related to each other.

All nine residents and a Port Washington police officer were taken to Nassau University Medical Center in East Meadow. Although none of the injuries were deemed serious, seven residents had elevated CO levels in their blood, said Dr. Dean Olsen, attending physician in the emergency department at NUMC. They were treated by spending about two hours in hyperbaric chambers — which look like a submarine — and had pure oxygen pumped into their bodies.

“The increased oxygen drives carbon monoxide out of the blood faster,” Dr. Olsen said.

The building did not have carbon monoxide detectors, said Michael F. Uttaro, Nassau County’s assistant chief fire marshal. Summonses were issued to the landlord, the restaurant owner and the contractor hired to clean the restaurant.

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Although the building had been cleared of the dangerous gas, it’s not known whether the residents have moved back.