to know what they are referring to. The word "balisage" suggests they are not talking about actual barriers, but "en dur" seems to imply barriers. Where "en dur" would refer to "physical barriers"

Then again, rather than simply painting yellow lines on the floor, say, to indicate danger spots (the paint might wear off), maybe they want metal studs set into the floor, or ribbed concrete flooring, or tactile spots, etc. Where "en dur" would refer to "concrete/substantial/three-dimensional markings", or maybe just "permanent markings" (more permanent than permanent ink though).