Thankfully we have yet to set fire to any of our kit. We just get staff phoning up saying their printers are on fire, usually first thing Monday morning after a cold weekend when the paper has absorbed a load of moisture. It takes a minute or two to convince them it's only steam. Never have understood why the phone us rather than hitting the fire alarm and legging it away from the fire!
In a previous job working as a technician in a University Physics dept a colleague managed to set a litter bin on fire. He had cleaned out an experiment containing what he though was oxidized sodium metal, he tossed the remains in a bin containing a banana skin. The sodium wasn't as oxidised as he thought and the next thing we knew was a lot of smoke coming out of the bin as the moisture in the banana skin reacted with the sodium. From that point on we tossed the remains in a beaker of water, it was much more fun as well as being safer.