You really don't want a standard steel rule for cutting, generally if you slip the blade will skid across the rule to where you are applying the pressure, you need a proper cutting rule, with grooves to trap the blade if it slips, similar to the attached image.
where I worked once Stanley knives were banned totally, I was the one exception as there was no other safer knife to cut the foam mounting boards I used in the drawing office, (the only thing we found able to cut them was over £4000) so when cutting I had to use the relevant cutting rule and wear a pair of Kevlar cut resistant gloves.
Grendel