Being that humans are creatures of habit, an uneven stairwell challenges users, even those grown familiar with asymmetries in construction. The most critical components of a stairwell to avoid becoming a tripping or slipping hazard include a decent (and uniform) tread and riser value. In the case of International Building Code specifications, this is 11 inches or greater in tread depth and between 4 and 7 inches in riser height. Note that these are rather large ranges when taken as a % of one’s foot. That’s why another critical component to design is that the variations between steps and overall are minimal. The IBC gives the following tolerances: less than 0.375 in both tread and riser. Other issues in stair design include width, capacity, use, nosings, and surface friction. As with all safety codes, if there’s a specific standard that applies to a particular business’ use, those requirements supersede any conflicting standards under the more general requirements. See OSHA and NFPA for more information on workplace design and fire safety.