To avoid problems, they recommend investing in a carbon monoxide detector. The potentially lifesaving devices cost about $30 and are sold at home improvement, hardware and many other retail stores.

"This is a timely reminder that carbon monoxide [CO] can kill, and people need to take preventive measures like having a carbon monoxide detector," said Jess Gomez, spokesman for LDS Hospital.

In the first CO cases the hospital's doctors have treated this year, Jennifer Morrison, 21, called 911 on Sunday after feeling ill and finding her grandparents also sick and disoriented. She was staying at the Salt Lake City home of Richard and Carol Morrison when she experienced nausea, a pounding headache, cold feet and faintness.

"Be aware that these symptoms can mean something very serious is happening," Jennifer Morrison said.

All three were treated with hyperbaric oxygen therapy, in which patients are placed in a chamber while pressurized oxygen is pumped in. LDS Hospital has offered the therapy off and on since the 1960s for patients with CO poisoning and other conditions, including severe wounds, diabetes and the bends.

Lindell Weaver, the director of hyperbaric medicine at LDS Hospital, was instrumental in a study from 1992 to 1999 that found hyperbaric treatments reduced the frequency of cognitive problems in CO poisoning patients by almost 50 percent.

Any type of heater that burns fuel, such as propane, butane and charcoal, can produce carbon monoxide. The gas can shut down the blood's ability to circulate oxygen.

It is the leading cause of accidental poisonings and is blamed for an estimated 1,000 deaths a year nationwide, according to the U.S. Centers for Disease Control and Prevention.

Steps to keep your home safe

* Make sure appliances are installed according to the manufacturer's instructions and local codes.

* Have your heating system, including chimneys and vents, inspected and serviced annually by a trained service technician.

* Examine vents and chimneys regularly for improper connections, visible cracks, rust or stains.

* Install carbon monoxide detectors and inspect them regularly to make sure they are working.

* Never burn charcoal inside a home, garage, vehicle or tent.

* Never use portable fuel-burning camping equipment inside a home, garage, vehicle or tent.

* Never leave a car running in an attached garage, even with the garage door open.

* Never service fuel-burning appliances without proper knowledge, skills and tools.

* Never use gas appliances, such as ranges, ovens, or clothes dryers for heating your home.