Minnesota officials warn that emergency visits for carbon monoxide poisoning drastically increase during the colder months when people use fuel-burning heaters more often. But most unintentional poisoning of the odorless, colorless gas could be prevented.

The danger period is now, when people begin to turn on their furnaces and other appliances as the temperature begins to dip.

The number of emergency room visits for CO poisoning more than doubles between September and November, the Minnesota Department of Health (MDH) said in a news release Tuesday.

“Just as we turn back our clocks in the fall or put on the storm windows, part of preparing our homes for winter should be to make sure heat sources and carbon monoxide alarms are in good working order,” Dan Tranter, supervisor of the indoor air program for MDH, said in the news release. “When the temperature drops, we begin to see an uptick in carbon monoxide poisonings.”

Death and illnesses can be prevented if Minnesotans make sure they have working CO alarms and have their furnace or wood-burning stove inspected each year. State law requires alarms in all single- and multifamily residences within 10 feet of each bedroom.

The Health Department warns people to never leave a vehicle on idle inside a closed area, such as a garage. Generators should be at least 20 feet from the home and the agency warns people not to run a gasoline or propane heater, or a gas or charcoal grill indoors.

“Any heating system that burns fuel produces carbon monoxide,” according to the news release.

The symptoms of overexposure to the gas include headaches, dizziness, shortness of breath and confusion.

Health officials say to get fresh air and call 911 if the alarm sounds or you think you are experiencing carbon monoxide poisoning.