Dozens of firefighters were called to an early morning fire and the situation could have been hazardous.
The blaze occurred at a vacant building near Central Avenue and Baseline Road Tuesday. At one time, the building was a church and a lodge.
Firefighters say there were signs that the structure had been treated with cyanide.
"There's a lot of pockets inside of there...they were able to reach in those areas and knock it down..at this point they don't see any danger to the public whatsoever," said Larry Nunez of the Phoenix Fire Department.
Crews say the cyanide was most likely used as a pesticide for rats.
Firefighters do not know what sparked the flames.