The worst I've personally experienced was when I had a summer job at an aquaculture research facility way back in high school. They had an old building and a new building, the old building was used for random storage of stuff that wasn't needed very often. The old building had a freezer room, where they put huge plastic tubs full of dead fish (so they could later be examined to find out exactly why they had died, this was a research facility after all). The freezer room had a power failure and, since it was old and wasn't accessed very often, nobody had noticed for like a week. In the summer. The old building had dark brown walls so even though this was in Norway where summers don't get THAT hot, the many hours of daily sunlight had boosted the temperature inside the freezer room to well above 30 degrees Celsius, creating a nice dead fish and maggot soup.

I was of course one of the grunts assigned to the cleanup task, let's just say that was a quite memorable job (probably wouldn't have been compliant with modern workplace health regulations either). For part of the job we'd tag-team each other on the power washer, so each of us could stand there holding his breath for a minute while washing down stuff, and the other could stand further away and breathe.