WINDHAM (AP) – A father and his 16-year-old son died from carbon monoxide poisoning after being overcome by the deadly fumes that came from a portable generator in the basement of their home, officials said Friday.

Stewart Townsend, 35, was dead when a friend checked on him at 10:40 a.m. Friday, and his son Nicholas died several hours later at Maine Medical Center in Portland, said Paul Cox, a patrol officer from the Windham Police Department.

The gas-powered generator was used to run the lights and to provide heat, Cox said. The home’s electricity was cut off by Central Maine Power last summer, a spokesman said.

Firefighters arrived to find carbon monoxide levels of greater than 900 parts per million, high enough to render a person unconscious within minutes, Cox said.

While there’s no agreed-upon indoor standard for safe levels of carbon monoxide, the U.S. Environmental Protection Agency recommends that people’s outdoors exposure to the odorless gas be limited to eight hours at 9 parts per million.

A family friend, Scott Benoit, discovered the body of Stewart Townsend on the first floor of the home and performed CPR on the teenager, who was in bed upstairs, Cox said. Benoit, along with a paramedic, were taken to a hospital for observation.

All of the windows in the house were closed, and firefighters had to ventilate the home for 45 minutes before police officers could safely enter, he said. The Townsends routinely used the generator, and the generator’s switch was in the “on” position when police arrived, Cox said. It had run out of gas.

The deaths were the third and fourth in Maine in just over a month attributed to carbon monoxide poisoning from a portable generator.

Two men working on the interior of a house under construction in the Somerset County town of Smithfield died in November after being overcome by fumes from a generator. The bodies were discovered by the father of one of the victims.