I saw a fire like this start along the DS edge of a stage, the band had used a 1/4'' instrument cable to jump in between 2 wedges and it heated up to the point of flames. It was quickly seen and extinguished but it's easy to see how some of these things happen. Imagine if that cable had been up stage next to a bunch of drape, fabric or scenery.
It was just a 3 piece band using a little sound system, one wouldn't think you could wire it up and create a fire hazard like this but it just goes to show the endless possibilities of accidents that can happen. Always be thinking of "what if" scenarios and plan and place thins accordingly.