It wasn't very big, relatively speaking. Of course, that really depends on what you're comparing it to. After 14+ yrs as a firefighter, it really wasn't as bad as it could have been.
I had my amnps going and then the smoke kinda quit. I opened the chip loader a little more in case it needed more airflow and the smoke looked good again. I walked out of the kitchen for a few minutes and when my wife and I walked back in to look out the back door at the smoker, there was LOTS of smoke and I kinda knew right then there was probably a fire inside.
I had a sheet pan on the next rack below the turkey and when I opened the door I noticed it was splattering when it hit the sheet pan. I took the sheet pan out and tossed it into the yard, which got the fire out of the smoker.
Looks like it was only the grease that was burning but I will investigate more later this afternoon.