These are the guys hooking up valves, fixing pipes, monitoring how chemicals are loaded from the trucks into the plant systems... doesn't much matter that's flowing through the pipes- the workers can read the data sheets and procedures and work on anything.
Again, these are blue collar jobs. High school education at best. Mostly a manual labor job. They're not designing the plant, just operating and repairing it according to plans designed by someone else.
EDIT: Here's a list of chemicals used in meat processing: https://www.osha.gov/meatpacking/hazards-solutions. Ammonia for refrigeration. Chlorine, hydrogen peroxide and peracetic acid for disinfectant. The chemicals are delivered to the plant in concentrated forms and diluted for use.