Ever seen the movie “Backdraft” ? It’s a movie about firefighters and an arsonist who builds fires that are starved for oxygen and eventually create a flashback when a rush of air is introduced to the smoldering embers. This can (and does) happen when cooking low and slow. I can’t speak for all the different types of cookers on the market, but for sure the Big Green Egg can create this event.
A friend of mine, a fellow Egger and a pretty darned good photographer, caught the phenomenon with his camera.

Thanks to Phydeaux Deauxmayne for the photo
This usually occurs when you’re attempting to reduce the cooking temperature by tightening the vents on your cooker and reducing air flow. You can minimize the liklihood of this happening by “burping” your egg before opening it wide. To do this, raise the lid just slightly in order to control the rush of air into the cooker. Hold the lid there for about a three count before completely opening it.
If you’re not in the habit of burping your egg when opening it, you’ll get in the habit quickly once you’ve had your first flashback. I only had to loose the hair on my arms once before I learned my lesson! 8>)
Cheers,
Braddog