(CHICAGO) Nicor Gas is reminding customers that extremely cold temperatures—much like those expected Thursday—can pose a heightened risk of carbon monoxide poisoning.

Carbon monoxide is odorless, colorless and tasteless, earning the name “silent killer,” Nicor Gas said in a statement. It’s produced when a fossil fuel like natural gas is burned.

When these fuels do not burn properly, the gas can cause sickness or death, Nicor said.

Customers may look for different methods to stay warm as brutally cold temperatures blanket the Chicago area on Thursday. The high is a mere four degrees, with the low dipping to minus 6, according to the National Weather Service. The wind chill could drop as low as 23 degrees below zero, prompting a wind chill advisory for the area and surrounding suburbs.

To prevent carbon monoxide poisoning, customers should:

-Never heat home with a gas range or oven;

-Never burn charcoal inside home or garage;

-Always open the chimney flue when using a fireplace;

-Never run a combustion engine–such as your car, lawn mower or snow blower—in enclosed areas.

Symptoms of carbon monoxide poisoning include dizziness, nausea, a headache and coughing, Nicor said. Other warning signs include an irregular heartbeat or pale skin with cherry-red lips and ear tips.

Anyone who suspects they may have CO poisoning should step outside to get fresh air and call 911, Nicor said.

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