ive seen spontaneous combustion in the coal pile at fairfield texas, and in a hopper car inbound as well. it's not a "fire" so to speak, just a smoldering, slow burn, that creates lots of smoke, but no open flame. bnsf had to bring a fire engine in, and a car was set out, and hosed for two days, in an attempt to put out a smoldering fire in the car. the powerplant didnt want to dump the burning coal onto the belts, for fear of a bigger fire, i guess. it seems strange to see a coalpile burning, knowing the coal is damp, and nothing but the coal itself caused the fires. the fire we found in the car wasnt even showing visible smoke. the heat was discoloring the aluminum carbody, and radiating heat off of it. there wasnt any other indication the car was burning, and that car was simply dumped, with the waterjets inside the hopper being run wide open, as that car was dumped. the bnsf burning car, was a visible burn, with large amounts of heavy white smoke pouring from the car. it does seem the longer the coal sits, the more likely an opportunity for a spontaneous burn.
as for the latex sprayed on the coal, thats done for dust abatement. the amount of damage done by coal dust, to the roadbed, is staggering. it wouldnt seem like it, but the dust from the top, and that fine particulate that seeps out of the doors, fouls the ballast, creating the ability to retain moisture, and causes the roadbed to "pump", causing slow orders. the prb mainline was out of commission a couple of years back, for a massive undercutting/ballast cleaning project, to reverse the damages done by coal dust. it created giant mow windows, causing trains to be delayed, or sent in fleets, of trains running as close as possible, one after the other. "gluing" the coal in place, with sprayed on coatings, is seen as a cheaper than having to clean the ballast, across an entire division.