I witnessed this a couple of times over a few years. More and more techs have switched to battery powered tools, such as drills and impact guns instead of air powered. As the tools get dirty they would clean them by spraying brake clean or contact cleaner on them over trash cans. Both of these cleaning solvents are extremely flammable and being heaver than air, the solvents collect in the trash can. The earlier versions of these tools utilized brushes that produce an electrical arc when the tool is energized which can cause the concentrated solvents to burst into flames if accidentally energized while cleaning. I've seen this happen twice, with one tech getting burned pretty bad. Some of the newer versions of this type of tool are brushless and do not produce sparks when used, they seem to cost more and many guys buy stuff based on price. Sorry this topic got a little long, but be careful if you opt to clean parts/tools over trash cans with solvents, the residue hiding in the trash can linger there for a while and can be ignited when you least expect it.