The arrival of cold weather means that people are starting up their furnaces and fireplaces for the season. And when the snow flies and the power goes out, people find creative ways to cook their food and heat their homes. Together, these factors spell an increased risk of carbon monoxide poisoning.

Carbon monoxide, or CO, is a product of all kinds of combustion, from candles and cookstoves to gasoline engines. It is invisible and has no odor or taste, and can kill quickly in high concentrations by attaching to red blood cells, taking the place of the oxygen molecules that those cells should deliver.

Depending on the air concentration of CO and the duration of exposure, symptoms can include headaches, dizziness, nausea, weakness and shortness of breath. If the person isn’t immediately removed to fresh air, it causes suffocation and death. While CO exposure is the leading type of fatal poisoning in the United States, it is completely preventable.

Chatham Fire Inspector Richard Shevory said that Chatham has experienced tragedy from CO poisoning in the past, and urged people to consider the danger it poses. When Chatham firefighters respond to a medical emergency, the first equipment bag they bring with them contains a carbon monoxide detector. If it goes off, responders have a good indication of what might be causing the medical emergency, and they also know to evacuate everyone to fresh air.

When power goes out, some people light up a charcoal or gas grill to cook their food, and if it’s kept too close to the house, it can cause a dangerous CO build-up indoors.

“Some people put their generators in the garage and shut their doors,” he said. Or they place the generator outside but keep it too close to an open window, “so it’s blowing the CO inside the house.”

There’s also a significant danger from people leaving their vehicles running in the garage, Shevory said. Particularly with modern vehicles with keyless ignitions, it is easy to forget to turn off the engine, especially with hybrid or other very quiet vehicles.

Care needs to be exercised with natural gas-fired fireplaces, as well. Many exhaust to the outside through a vent that is only a few feet off the ground; if the vent is covered by a snow drift, the CO will back up inside the home, he said. There are also “ventless” gas fireplaces on the market that meet safety codes, but still pose a risk. “If you read the fine print in the manual, it says to leave your window open a little bit,” Shevory said.

With so many potential sources of CO, the most important line of defense is a working carbon monoxide detector.

“By code, they should be on every level of the house, including the basement, and within 10 feet of bedroom doors,” he said. Various types are available, but the best have recorded voice prompts that issue a spoken warning when carbon monoxide is detected. Particularly with combination smoke and CO detectors, “they have to tell you the difference between smoke and CO,” Shevory said. Otherwise, people may hear the beeping and ignore it because they don’t smell smoke, though dangerous CO can be present.

Because CO spreads evenly through the air in a confined space, CO detectors can be placed on the ceiling or at any height on a wall, Shevory said. And while it’s important to replace the batteries twice a year, preferably along with smoke detector batteries when the clocks change for Daylight Savings Time, it’s also important to know when to replace the whole unit. Most CO detectors have to be thrown out and replaced every five or seven years.

“There’s a date on the back of them,” he said. “If it’s older than that, replace it.”