The Knoxville Fire Department said crews found two men dead from suspected carbon monoxide poisoning inside a South Knoxville duplex.

KFD said it happened at the 1200 block of Moody Avenue Wednesday around 11:30 p.m.

When firefighters and paramedics arrived on a medical call, they found two men dead inside the duplex. The men were identified later as 53-year-old James Arthur and 45-year-old Charles Elmore.

Crews entered the duplex equipped with a self-contained breathing apparatus to protect themselves and CO monitors.

They said they detected abnormally high levels of carbon monoxide -- 8 times higher than normal levels. KFD said it appeared the two had tried to rig a propane fuel container up as a heater.  

Firefighters checked if anyone else was inside the duplex, but only found the two victims before opening the windows to ventilate.

The medical examiner will determine the final cause of death as the investigation continues.