I fired up the propane burner today. I had 9 gal of wort in the kettle and another 4 gal draining into a bucket from my sparge. My flame quickly went from blue to yellow and then I smelled of something burning. I had put the kettle on my dining room table last night after giving it a good rinse and placed a pot holder under it to protect the table. I didn't notice the pot holder had stuck to the bottom of the kettle and now was being subjected to the flames.
I had to kill the burner, drain the kettle into some 5 gal buckets and I am glad I had enough. The pot holder must of had nylon or rayon in the weave and was burning and melting. Had to scrape if off the kettle and then drag it into the house to clean the bottom. No harm done except lost 30 - 45 minutes to resolve things.
I'll be checking the bottom of my kettle from now on.