A man died and a woman was hospitalized from dangerously high carbon monoxide (CO) levels at a home in Baltimore County on Monday, according to the fire department.

Firefighters responded around 7:30 a.m. to the 11200 block of Old Carriage Road in Glen Arm for a hazardous carbon monoxide emergency where a man and a woman were found.

Investigators said a vehicle was left running in an attached garage which caused the CO to build up.

"The Baltimore County Fire Department reminds residents of the importance of carbon monoxide detectors in homes and the dangers of running vehicles in enclosed spaces," the Baltimore Fire Department said in a statement.

What are the symptoms of carbon monoxide?

According to the Mayo Clinic , carbon monoxide poisoning happens when carbon monoxide builds up in the blood. When too much of it is in the air, the oxygen in the red blood cells is replaced with carbon monoxide, which could lead to serious illness or death.

Carbon monoxide impacts the brain and the heart, according to the Mayo Clinic.

What causes carbon monoxide?

The Centers for Disease Control and Prevention says carbon monoxide is dangerous because it is an odorless and colorless gas.

The gas can be found in fumes produced any time you burn fuel in cars or trucks, small engines, stoves, lanterns, grills, fireplaces, gas ranges, or furnaces.

The CDC says that each year more than 400 Americans die from unintentional CO poisoning not linked to fires, more than 100,000 visit the emergency room, and more than 14,000 are hospitalized.

How do you prevent carbon monoxide poisoning?

Make sure you have a working, and up-to-date carbon monoxide detector, according to FEMA .

FEMA also recommends using portable generators outdoors in well-ventilated areas away from all doors, windows, and vents, along with making sure vents for the dryer, furnace, stove, and fireplace are clear of snow and other debris.

The CDC advises to have your heating system, water heater, and any other gas, oil, or coal-burning appliances serviced by a qualified technician every year, and make sure your gas appliances are vented properly.