What Happened?

Rev Jim

Last night I was preparing dinner for the love of my life and our three offspring - - steaks on the egg! I use a large egg with the ceramic fire grate replaced with an iron trivet. I stirred the old coals, loaded humpty with new lump, and plugged in the electric charcoal starter. All seemed to be going well - - the top was off, the damper was wide open, and I knew I would be up to 750* in no time. Well, 30 minutes later I had crept up to 300*. I looked in the top of humpty (I NEVER open the top)and was just backing away when WHOOMP! three feet of flame shot out the top and from the damper. In about 45 seconds the temp rose to 500*[p]The only thing I can figure out is that the fire was somewhat oxygen-starved. It must be that just enough of the holes in the trivet were blocked to keep the temp from climbing higher, but enough were open to keep it going and slowly climbing. Perhaps one or more of the holes cleared allowing the air flow to increase and causing a back draft. But, it must have been one heck of a coincidence. It was the darnest thing I've seen, and it nearly took my eyebrows off. It scorched the legs of my jeans from the damper, and raised my heartrate for a few minutes.[p]So, all you physicists out there, what happened?[p]Eagerly awaiting your wisdom,[p]Rev. Jim

Bama Fire

Rev. Jim,
I read about that sort of thing happening the day a took my baby (large BGE) home. [p]Sounds like a tale of the classic Whoosh! If you check the archives, there is a long thread discussing this event -- check Sept. 99.[p]Bama Fire

Grumpa

Rev. Jim,[p]Ain't those Woomps fun :~)[p]The temp rose sharply afterwards because you had flames in the coals. When we say that we are cooking at the higher temps it is the flame that is being measured and not the "oven" temp necessarily. You are right about the fire being oxygen starved and that is what caused the whole process. [p]I usually raise my lid and let the coals get good and hot with as much burning in there as possible. That gets the temp up much quicker and helps avoid what you experienced.

MAC

Rev. Jim,
IT MUST BE THE NIGHT FOR "BACK ...........DRAFT”! ! ! ! I too was doing the same thing. My cheap store gave mea centigrade thermometer. It started going backwards. So I being a neophyte opened the lid. Well a large orange ball of flame came out the top and tried to eat me. Well it got half my mustache some of my hair and a little of the eye brows. Not the smell I was looking for in a steak. Well the steaks turned out well but my features are a little fried. That is NOT what I call a HOT Valentines Day.[p]MAC

King-O-Coals

Rev. Jim, hot dog,, I get to give the physics class again. Back-draft is eggsactly what it is. Solids and liquids don't burn. Even gasoline. Only the vapor of flammable and combustable solids and liquids will burn. When you ignite a pool of gasoline, only the vapor, which is slightly above the liquid is what you see burning. The heat inturn causes the liquid to release vapor more and more rapidly and the fire will intensify. Disturb the surface and more surface is created, thus more fire. Wood, charcoal, plastics, and other solids are consumed the same way. Heating of the surface creates vapors, which is the smoke. That is the ignition temperature of that substance. Enough vapor coupled with the right ignition temp and oxygen and "whoomp" the redily available fuel ignites. That's the flash point. (it's been a long time, I hope I didn't reverse those terms) In your case, charcoal was being vaporized at a rate faster than O2 was being introduced and not enough heat was present. I know you have sprayed charcoal lighter fuel on hot briquets and noticed the bright white vapor,, which usually "whoomps" too. Same thing. I have observed my egg during startup, breathing in and out at the bottom vent, even with the top vent (daisy slide wheel) fully open. The egg dosen't start drafting real good until the inner surface is heated. Sometimes this results in more available fuel that there is oxygen. This happens at relatively low dome thermometer readings. I was using Cat's method the other day and with a small hot spot, I closed the dome, opened the daisy slide, and closed the bottom vent down. The smoke started boiling. It was doing very well until I got to the part where I needed to put my chickens (yes "those" chickens) in. Knowing full well what to expect, I just opened the dome slightly and closed it to allow physics to do it's thing,, but I wasn't fast enough. It cleaned all the hair off of my left arm (except for that under my watch), and ruffled my sweatpants from the bottom vent. Well that's my idea and it's much longer than I had planned. Let's be careful out there. :^)

Mark

Rev. Jim,
Try removing all the old charcaol and make sure all the air holes are clean as well as the area under the grate. It has been my experiance that ash has a way of clogging up the world. Good air flow is the key.
Mark

MAC

King-O-Coals,
Your last line is a great line from Hill Street Blues

King-O-Coals

Mark, agreed. I too have noticed after a performing a very good stiring before doing a total clean out, when I remove the old coals down to the fire grate, there is a ton of ash and tiny pieces of charcoal still there and that definately restricts the airflow.

Dr. Chicken

King-O-Coals,
Me thinks therz some guys out der dat need to go thru a "snot wringing" fire to respect the phenomena! Wat does you dink?[p]Dr. Chicken

King-O-Coals

Dr. Chicken, if it's an eye-opener on the egg,,, they should see it happen in a 10,000 sq.ft. building. It'll make you re-thunk your profession, values, and morals..

Brant

Rev. Jim,[p]Is your Egg on a wooden deck or something that might shake a little bit when you walk on it? If so, it might have disturbed some coals, unclogging some vent holes or something. Just a thought.[p]I agree with Bob about the flames licking the thermometer as being the reason for the fast temperature climb once the "event" happened.[p]Brant

The Colonel

Rev. Jim, Whoa, dude--another flaming experience from humpty. aren't you glad the damper isn't any higher. Hummmmm
yours in the egg--The Colonel

Grumpa

The Colonel,[p]Whoooosh! You keep those thoughts up and we are going to have to rate this place PG :~)

Char-Woody

MAC, seems we all have to do that..it's a learning experience. Try as we may to explain the venting proceedure to prevent it, things happen. Once the technique of proper venting is a habit, then that problem is nearly eliminated.[p]Your status of Pro..is now raised to Pro first class..:-)
C~W[p]

Mike Oelrich

King-O-Coals,[p] Yup, by stirring, you send the smaller parts to the bottom of the pile. Inevitably, small chunks of lump wedge in the holes and the ash fills around them. I usually try to get the lump to one side of the firebox and look to make sure the holes are open; then push he lump to the other side.[p]MikeO