Well, not in lab, but I had some close calls while cooking potassium nitrate and sucrose. Me and a buddy were trying to find the right mixture for an industrial size smoke bomb that would burn during paintball matches. My wife wouldn't let us do it inside, or use her pans. So, we did our best to make due on an old charcoal grill with pie tins. Using a heat source we couldn't control, the inevitable happened rather quickly. The mixture caught fire and proceeded to burn through the pan and grill, starting a small fire on my deck. After that ordeal, we thought maybe a propane burner would be more stable. We still managed to light the mixture on fire. Again, vaporizing the pie tin, and was on it's way down the makeshift rack when we noticed it was going directly to the propane tank. We kicked the thing over before any serious damage was done. At this point, we decided our attempts to use inappropriate equipment were doomed. Went out and got a hotplate and some cheap pans and finished without incident.