I cannot believe no one else is talking about this. How could the cameramen have known that fire was going to happen?
1. They zoomed in on the fire and on Butch's banner as the tribe members were leaving for the immunity challenge. It was just like foreshadowing in a feature film. Only the camermen should not have know this was going to happen.
2. The immunity necklace was only half burned. Why not fully burned or completely out of the fire? That was for effect. The producers thought it would look cool on TV if tribe members wore a half burned necklace.
3. Why would camera men remain at the scene when all the action was taking place at the challenge? Shots of an empty camp would not usually be appealing to a TV audience -- unless they knew there was going to be a fire.
I know it is all circumstantial but reason #1 is overwhelming. Watch it again. Too weird not to be set on purpose.