"Every year, thousands of people are injured or killed in stairway-related accidents. The model building and fire codes provide requirements for handrails along most stairs to give people traversing them a stable and continuous surface to grip. In all but a few cases outlined in the codes, stairways are required to have handrails on each side." This document details the requirements for handrails as stated in building and fire codes.
Coffee Break Training - Fire Protection Series No. FP-2014-49
United States Fire Administration: http://www.usfa.fema.gov/