The smell starts out like an old meat smoke house. The first pile started in the winter after a very hot,dry summer. I smelled it for weeks before small flames started up on the surface. The pile was started on the edge of a hill and piled out like a sand dune. It burned for a few weeks and could not be put so just burned away. Snow and rain kept it from being an issue. The next pile was moved to a more open location on a less steep hill where it was much easier to take out by truck load. The run off from the wash rack kept some of it pretty wet. It took 27 years for that one to catch fire and happened in the summer. The better location meant that it could be spread out and sprayed out. Manure has to be kept turned for Composting so the heat can be controled or removed and spread so that it cannot get hot. Fair barns and horses are burned every year because people can't seem to understand just how hot these piles get. Next time you go to the barn get a shovel and dig into what is about two weeks old. You my be surprised that it burns your hand. Please do not let the piles get very big or sit around for long or it could be deadly.