Reno, NV – Two weeks ago, 64-year-old Sherry Madsen called a repairman to work on the water heater in the mobile home she shared with her daughter and was waiting for a part before it could be fixed.

On Sunday, relatives picking up the pair for church found Madsen dead and her daughter, Kathy Cassinelli, 45, critically injured from carbon monoxide poisoning caused by a gas leak in that water heater, police said.

Madsen was pronounced dead at the scene and Cassinelli was taken by medical helicopter to an undisclosed military hospital that specializes in treating carbon monoxide poisoning. Police said that if Cassinelli survives, she likely will have brain damage.

The women’s pets, a dog and a bird, also died, police said.

Carbon monoxide replaces oxygen in the blood, causing tissue damage and potentially death, according to the Centers for Disease Control and Prevention.

According to CDC, 500 Americans annually die from unintentional carbon monoxide poisoning and more than 2,000 people commit suicide by intentionally poisoning themselves.

In Washoe County, one person a year died between 2000 and 2002 from unintentional carbon monoxide poisoning, according to the coroner’s office. In 2003, two people died. So far this year, the coroner’s office has one death suspected to be unintentional carbon monoxide poisoning.

About 11 a.m. Sunday, Madsen’s older daughter and 9-year-old granddaughter came to the home at 2301 Oddie Blvd., No. 41, to pick up Madsen and Cassinelli for church, police said.

No one answered the door and a strong odor of gas was detected, according to a police report. Madsen’s daughter broke out a window and saw her mother and sister unconscious. A neighbor helped bring the women outside and the young girl called 911.

Police said they were told Madsen had called a repairman two weeks earlier to work on her water heater. The worker arrived and had to order a part before it could be fixed, according to a police report.

Even after the mobile home was ventilated, authorities said there still were toxic levels of carbon monoxide inside it.