www.msstate.edu/dept/fst/Homepage/ RTE_Listeria1/sld018.htm

"Kill steps" are pre-determined variations which will kill (stop) a process or procedure. They are not restricted to physical characteristics, but also influenced by biological, Ph. and other factors. In this application the refernce probably is to increases / decreases or spikes either way in temperatures which would cause ink and roller temperatures to vary beyond normal boundaries, thus stopping whatever process in on-going.
It is a very difficult term to translate relative to this application, as it could also be refering to acidic changes (if applicable in vegetable / chemical based inks. See ref and judge for yourself.