CT, I have a few bags of Royal Oak lump that have unuasually large pieces of lump. I poured some of that in, without any effort to get smaller pieces and I lit the fire in one place for a lo-n-slo, but just a couple of hours, to smoke a fattie. I thought the fire was stable, but the temp climbed to about 320 before the cook was over. I just left it on, because I was going to cook more later and when I went back it was about 420. Not exactly a runaway, but more change than I am used to. I just figured it was due to getting one a couple of pieces of lump going initially, that were really not touching others.....?