A Beltsville woman was taken to the hospital in serious condition and her dog died when a malfunctioning water heater created hazardous carbon monoxide levels in her home, authorities said.

The incident began about 4:30 p.m. Sunday after the woman’s daughter discovered her mother unconscious at a house in the 4900 block of Powder Mill Road, according to the Prince George’s County fire department.

The woman was taken to a local hospital, where she was being treated in a hyperbaric oxygen chamber, authorities said. Fire officials believe that if the woman’s daughter had arrived even a short time later, the woman would probably have died.

“Using gas-tracking meters, firefighters found 1,000 parts per million (PPM) of CO in the home’s interior atmosphere,” according to a prepared statement from county fire officials. “Anywhere from 0 to 35 ppm is considered normal, any reading over 35 is considered unhealthy.”

Fire officials warned that homeowners should have a CO detector in every level of their homes.