this happened to me when i was a beginner in bbq-i think like what bigabyte posted you
got a build up of fatty oils and was not aware of it,thats why its important to clean the
smoker and grill after use. i use goggles and a steamer after i clean out the ashes a day
later-you have to watch out for coals tht can still be active in the ashes-i have had coals
still hot two day after i bbqed!
if you cook fatty meats like lamb or ribs untrimmed like i do its important to clean everything
also you should have a fire extinguisher near by the grill! i hope this helps