In a past life, I was an operations engineer on a coker process unit (it upgrades bitumen to gas oils and naphtha by thermally cracking it). Even when the unit is running (and 100x worse when the unit is shutdown), you get filthy with coke dust... it gets in any exposed crack or crevice (yes there too). It comes out of your nose for days afterward, even breathing through a mask. Anyway, the guys who basically jackhammer the coke off the walls of the reactor during shutdown are kindly referred to as coker rats. And as the cokers weren't quite the unit of choice for some of the engineers (for some reason they liked the "clean" units like hydrotreaters and stuff...bah!!), the operations engineers on the cokers were called that too. It was fun, I actually sorta miss it some days.