Check: Coil Slitting Machines/Systems- Safety Requirements for Construction, Care and Use
Document Number: ANSI B11.14-1996
American National Standards Institute
Your guarding issues depend on what kind of slitters you have. Do you have stationary knives where the material is forced across the knives, or do you have rotary knives where the material goes between two rolling cutters?
Realistically, you need to guard in both instances. If they are stationary knives, they are likely to be sharp in which case they create a hazard because their surface is hazardous. Also with material flowing into cutting area, there is an opportunity for the material to convey a person into the cutters. If you have rolling slitters, you need to guard the entrance to the cutting heads because it creates a pinch point. Without more specifics, I have be fairly general.
