In Tallahassee a few years ago a local insurance agent had several unexplained electrical fires in his office suite. Photos in the paper showed an electrical outlet with the wall above it burned as if the romex cable had burned. He hired an EE professor from FSU who postulated that EM waves from a nearby cellular tower were concentrating energy into his office! I think more likely he had those backstabbed outlets and the office workers were plugging an electric heater into the outlets.