Harrisburg, PA – Seven people were taken to an area hospital to be evaluated after a Harrisburg duplex filled with carbon monoxide gas early Saturday.

City firefighters were called about 6:35 a.m. to the 800 block of North 18th Street, where residents reported illnesses consistent with carbon monoxide poisoning, said Brian Enterline, Harrisburg Bureau of Fire’s chief.

“They were feeling sick,” he said. “They had all the signs of carbon monoxide poisoning.”

During an investigation, firefighters found that one half of the duplex showed a carbon monoxide level of 300 parts per million, and the other half showed a much higher level at 1,800 parts per million, Enterline said.

“That is extremely high,” he said.

Seven people living in the duplex reported illnesses, and they were transported from the home to an area hospital for treatment, Enterline said.

Their illnesses were not life threatening, Enterline said, but carbon monoxide poisoning can be fatal.

Enterline went on to explain that carbon monoxide is a threat because it cuts off access to oxygen.

When a person is first exposed to carbon monoxide they often experience symptoms like nausea and headaches. Eventually, they will feel tired, and that is when they can lose consciousness, Enterline said.

“It essentially puts you to sleep,” he said. “It just shuts your system down.”

In Saturday’s case, the carbon monoxide issue was the result of a malfunctioning heating system, he said.

Carbon monoxide is created as a byproduct of combustion in gas an oil furnaces, Enterline said, explaining a malfunctioning flue, or exhaust pipe, could cause a home to fill with the gas.

In cold winter months, the problem is more common, but carbon monoxide is a threat all year, he said, explaining some water heaters also release the gas.

“It’s exacerbated in the winter,” he said. “It’s not just a wintertime thing.”

On Saturday, neither side of the duplex was equipped with a carbon monoxide detector, Enterline said.

Enterline said firefighters installed carbon monoxide detectors before leaving the scene. He also pointed out that free carbon monoxide and smoke detectors are available through the Bureau of Fire. Enterline said anyone interested in receiving a detector should call 717-255-6464.