Health and safety officials are reminding Minnesotans to follow carbon monoxide safety rules after a Duluth man and his dog died Friday, apparently after being poisoned by the deadly gas.

Michael Steen, 54, and his canine companion were found unresponsive in his home by a friend. St. Louis County sheriff’s deputies found high levels of carbon monoxide inside, suggesting they were poisoned by the gas. The Midwest Medical Examiner’s Office will determine the official cause of death.

No carbon monoxide alarms were sounding in the home when deputies arrived, prompting the Sheriff’s Office to remind residents to test their carbon monoxide detectors, particularly during the heating season, and replace batteries as needed.

Carbon monoxide (CO) is an odorless, colorless, tasteless gas found in fumes from cars, portable generators, heating systems, water heaters, clothes dryers, gas and wood-burning fireplaces, gas stoves and ovens and other appliances and equipment that burn gasoline, wood, propane, charcoal or other fuels.

CO can cause sudden illness or death when inhaled, the Minnesota Department of Health warns on its website. Unintentional CO poisoning kills an estimated 400 a year nationally, and 14 a year on average in Minnesota, especially in winter, according to the department. Another 300 people visit emergency departments each year for treatment of symptoms linked to unintentional CO exposure.

Men are about three times more likely than women to die of CO poisoning, state data show. Death rates also increase with age.

Symptoms of CO poisoning include headache, nausea, dizziness, vomiting, confusion and tiredness. If you suspect a CO leak or poisoning, leave the building immediately. Call the local fire department and, if needed, seek prompt medical attention.

CO poisonings are almost always preventable with proper use of equipment and maintenance of CO alarms. Never use a generator, charcoal grill, camp stove or other gasoline or charcoal burning device inside your home, basement, garage or near a window or inside a fish house. Do not use an oven to heat your home. Not only is it a CO hazard, it is also a fire risk. Do not run or idle your vehicle in an attached garage.

Improperly installed or maintained appliances can also emit the gas, the St. Louis County Sheriff’s Office said.

“Improperly ventilated appliances and engines, particularly in a tightly sealed or enclosed space, may allow carbon monoxide to accumulate to dangerous levels,” the Sheriff’s Office said in a news release.

Minnesota law requires that every home have at least one operational CO alarm within 10 feet of every room legally used for sleeping.

For more information about carbon monoxide safety — including how to tell the difference between CO poisoning and flu symptoms — see the Minnesota Department of Health website.