I think moisture content is the trigger. Same with sawdust/wood shavings/mulch. I helped change a cab on a truck that burned from a load of wood shavings parked overnight that caught fire.
when you see the "long" rope is so they can set the load on the ground and still be above the top of the trees.I assume there must be some regulation or rule of thumb determining the length of a rope used to lift a load by helicopter. Anybody know what that is and what determines it? The ropes seem quite long at times. Is it some multiple of the main rotor diameter?