Well SmokinOkie, you got me thinking now. Not always the best thing for me to do, but anyway, here are a few of my rambling thoughts on the subject.
This morning I put 2 racks of ribs in the 009 and 1 chunk of wood (no bark). After 35 minutes I could smell a little of the smoke in the shop, which is normal since I left the door open to the garage where the smoker is. I went out to make sure the exhaust fan was drawing out the smoke and it was, as usual. While I was standing there looking right at the smoker it put on a show for me. There was a whooooosh and pop, and then a lot of smoke came out the top hole and around the door. After a few minutes the smoke was back to normal.
Now here are some details. The smoker was on for 35 minutes, it was 55 degrees in the garage and the ribs were right out of the fridg and cold. So the meat was not warm enough to produce grease. The hickory wood was some I had for 3 years so it was extremely dry.
I believe that what is happening is similar to what happens when burning coal in a stove. Gasses are released or produced as the wood starts to burn. The amount of gas varies depending on the type of wood and most of all the moisture content of it. I suspect the process starts at the bottom of the smoker where the fresh air comes in and mixes with the gasses, this gas/air mixture is the ideal environment for a mini explosion, which is ignited by the heating element.
Okay, I'm done, is anybody still with me?