After three trips to the hospital, the source of an elderly woman's ailment was finally discovered after her two daughters also became seriously ill after spending time in her home.

Carbon monoxide poisoning caused Ethel Browning, 95, to be taken from her Brownsville home to The Medical Center three times after she became extremely ill, said Brent York of Bowling Green, Browning's grandson.

After the second incident, York's aunt stayed in the home with her mother, who again became sick after turning up the heat early in the morning, York said. A few hours later his aunt became sick and was taken to the hospital.

York's mother was in the house cleaning later in the day and also became sick and was transported to the same emergency room, he said.

“My grandmother has a dog who lives with her and the dog even got sick. It was staggering around the house like it was drunk,” York said. “Carbon monoxide is known as the silent killer.”

The doctors couldn't figure out what was wrong with Browning, he said. They thought it was her advanced age and weak heart.

“If it wouldn't have been for my mother and aunt getting sick, my grandmother would have died,” York said. “They figured it out when three people came into the same emergency room on the same day from the same family.”

The carbon monoxide was coming from her gas heater - Browning would get sick every morning when she turned on the heat. She will probably never live in the house again, York said.

Browning suffered a mild heart attack during her second stay in the hospital because of the carbon monoxide poisoning, and left the hospital after several days. York's mother and aunt have been released from the hospital but are still weak.

“I want to make people aware they need to have either an electrical or battery-operated carbon monoxide detector in their house,” York said.

A lot of older people live in homes by themselves and don't have a lot of visitors, he said. Those people in particular need detectors.

Carbon monoxide detectors can definitely save lives, said John Weatherby, assistant chief of fire prevention at the Bowling Green Fire Department.

“I would not have a home with gas without having a carbon monoxide detector,” he said.

Carbon monoxide is an odorless gas that makes the person who's inhaling it groggy, Weatherby said.

“The blood likes carbon monoxide better than it likes oxygen, so it absorbs the carbon monoxide faster,” he said. “The gas also takes some time to be removed from the bloodstream.”

Even a one-time high-level exposure to carbon monoxide can potentially be fatal, Weatherby said. Repeated exposure to low levels also can cause problems.

The poisonous gas is produced by the incomplete burning of natural gas or other material containing carbon, including car exhaust, according to the Centers for Disease Control and Prevention.

The gas prevents the heart, brain and other vital organs from receiving oxygen, according to the CDC.

Every year in the U.S., more than 500 people die from unintentional poisoning, while more than 2,000 people use the gas to commit suicide, according to the CDC.

Carbon monoxide detectors can cost from $20 to several hundred dollars, depending on the features, Weatherby said.

In many new homes, the detectors are hard-wired into the electrical system, he said. As more homes have this feature, fewer people will experience carbon monoxide poisoning.