Worst place I ever did any work in a rendering facility, they used a similar cooking process, but cooked up anything that that died on the farm, bits the butcher didn't want (inc out of date and rancid stuff) etc. They would produce materials such as tallow and bonemeal, there were different classes of it, class three was the least hazardous and could be used in pet food, etc, class 1was egenrated from dead farm animals, etc and could generally only be used for burning for fuel (I beleive the classes had been introduced in the wake of teh BSE crisis, or at least the restrictions tightened up)
Every part of that place was horrible, the cookhouse was more or less what I picture Hell would be like, hot, smelly, poorly lit, everything exceedingly dirty, the receieving sheds with their interlocked twin roller doors certainly weren't pleasant on a hot day, and the worst smell at all was the water treatment plant that seemed to fling greasy/****ty water everywhere, including at some pieces of switchgear.
I don't consider industrial enviromments covered in welding dust as particualy dirty anymore, its quite nice to just be able to wash some dust off rather than a smell that can linger for ages....