You need to get a good hot coal bed before loading that much coal into it. Get your wood coals then add a layer of maybe 1 to 2 inches. Let this layer get hot and burning, then add another layer a little thicker. once this layer is caught and going, then add your coal to it. Keep your ash door damper open, but not the ash door. Whats happerning is your smothering the fire and producing alot of coal gas. Once the flames get to the gas whoosh. I had it happen to me 2 times, and that was 2 times too many. Once you add that last bit of coal, close the ash door, keep your damper open, and let it go for about 1/2 hour to 45 minutes, then check it. This should help. Good Luck.