SARANAC LAKE — The only reason to take the batteries out of a carbon monoxide detector is to make space for the new batteries you’re putting in.

This should be self-explanatory — but chimney sweep Michael McNulty warned that he’s seen people making the possibly fatal error.

“People have carbon monoxide detectors, and they go off on them sometimes, and they look around and they can’t see anything wrong, and it keeps going off,” he said. “Instead of calling National Grid or the fire department to find out what’s happening, they take the batteries out.”

McNulty, who works for North Country Chimney Service and has been in the industry for nearly 30 years, said that he’s seen disabled detectors in three or four homes this year. People become frustrated with a detector’s beeping, so they take it apart.

“It’s not a case that they did it on purpose,” McNulty said. “It’s just a misunderstanding of what’s going on.”

On a call earlier this week, McNulty said he “popped open the clean-out door” on a fireplace, “and the flue was totally blocked, I mean, I couldn’t even see.” McNulty cleaned it out — but after talking with the customer, learned that their carbon monoxide detector had been wailing, “and they couldn’t find anything — so they took the battery out.”

McNulty’s message to residents: if the sensor is beeping, always call the fire department or National Grid, as that blocked flue could have filled their home with poisonous gas.

“People die from carbon dioxide because it displaces the air and they suffocate,” McNulty said. “Carbon monoxide, on the other hand, is lighter than air. They’re both colorless, odorless and tasteless so you can’t see them smell them or taste them. But carbon monoxide attaches to your hemoglobin, and it takes the oxygen away from your body.”

Hemoglobin is an iron-containing protein in your red blood cells. Simply put, it is responsible for transporting oxygen throughout your body. However carbon monoxide, when taken into the body, binds to the heme iron, instead of the oxygen, stopping the O2 from getting where it needs to go.

This results in carbon monoxide poisoning that produces flu-like symptoms — headaches, muscle weakness, confusion and nausea are all common effects. Long-term exposure can cause a loss of consciousness, brain damage and suffocation.

About 200 people per year in New York are put in the hospital because of CO poisoning, according to the state Department of Health — and most occur in the home.

McNulty said when was working as a chimney sweep in Syracuse, he went on a call where a squirrel had climbed into a family’s chimney and wriggled down the hot water heater’s exhaust vent to an elbow before dying.

“Completely sealed off the pipe,” McNulty said. “So all the carbon monoxide that was normally coming out was just flooding into the basement. Everyone else in the house was sick.”

With a carbon monoxide leak, generally the cause is a furnace or hot water heater, McNulty said. Though sometimes, especially up here where there are 100-plus-year-old-homes, the problem can be in old chimneys.

Pieces of brick and mortar joints degrade and fall can fall into the chimney pipe, potentially filling a home with poison gas. McNulty said its important to get both heating appliances and chimneys serviced.

“If your carbon monoxide detector goes off, call the fire department, National Grid, whoever you’ve got.”