We (857) had some real flames on our robot back in 2002 while on in competition at the West Michigan Regional.
A non-electrical mentor put one of our old batteries (which I don't even know why we had it with us) on the robot without anyone noticing. He also installed it upside-down AND neglected to strap it down.
We hit a robot during the match, the battery popped up, and both contacts hit our aluminum chassis. The little electrical tape that was dangling from the connector caught on fire with dramatic foot-tall flames. Luckily, vinyl electrical tape doesn't burn well, and the flames quickly went out without the need of a fire extinguisher. The robot was disabled by the field judges out of concern over safety, but once back to the pit we found the damage was minimal (just a little soot).
I realized what happened, took off the battery and was shocked to see that the THREADS of the bolts holding the battery cables to the terminals were MELTED.
I cut off the battery cables so that mistake couldn't be made again.