One man is dead and another hospitalized in critical condition after they were found unresponsive last week in an Almont Township pole barn, police said. An autopsy revealed carbon monoxide poisoning was the cause of the death, investigators said in a statement Wednesday.

The Butler County Coroner’s Office reports two men and a woman were found dead shortly before 5 p.m. Tuesday at the home in Butler, 35 miles north of Pittsburgh.

Called “the silent killer”, carbon monoxide can be extremely dangerous and completely unrecognizable at first. Upstate Medical’s director of poison control, Vincent Calleo, gave out some helpful tips on how to stay safe.

There’s a large emergency response at a Butler home after three people were found dead. Channel 11 saw firefighters, police and medics at a home on College Street on Tuesday afternoon. We’ve learned that three people were found dead from possible carbon monoxide poisoning. The deaths are under investigation.

AAA reminds drivers that it is never safe to start or leave a vehicle running in an enclosed space. The exhaust contains poisonous carbon monoxide gas that can cause severe injury or death if inhaled.

Three people were found dead in a home in Butler County from possible carbon monoxide poisoning, sources said. First responders were called to a home on College Street in Butler at around 5 p.m. on Tuesday.