If you decide to use salt or ice melt crystals on your parking lot or sidewalks you should also use something to remove the crystals before people step onto carpet. Salt and ice melt rocks can get into carpet and break it down. Removing chemicals and abrasives from your shoes and boots will save the life of commercial carpeting.
Ice melt is typically made from Calcium Chloride, a chemical that melts ice and leaves a slimy residue. Ice melt is corrosive to metal and will damage metal door thresholds and door moldings. Rock salt is made from sodium chloride and is also corrosive to metal.
The solution to keeping ice melt and rock salt off commercial carpet and away from metal doorways is using a special rug that brushes salt from the bottom of shoes. These types of rugs have deep rubber pile or bristles that brush the salt from the bottoms of footwear and collect debris in the mat.
Placing such a mat both outside and inside the door will help prevent winter chemicals from being tracked into your carpet. Remember to periodically shake outside mats in particular to keep them fully functional. Runners from the doorway down the hall will help collect any additional debris.