Emergency Egress from Buildings. Part 1: History and Current Regulations for Egress System Design. Part 2: New Thinking on Egress from Buildings

摘要

For most of history buildings were short enough that stairs provided for access were suf icient for rapid egress in the event of fire. Even in single stair (mostly residential) buildings, experience showed that this stair was sufficient for fire egress as long as the fire did not expose or block access to the stair. Fire resistant apartment doors shielded the stair from most fires and exterior fire escapes provided a second egress path beginning early in the 20th Century. The 1854 invention of the elevator safety brake enabling the passenger elevator is credited with facilitating increases in building height and the first so-called skyscraper in Chicago in 1885. These buildings utilized steel frames protected by masonry or tile and were dubbed 'fireproof construction' providing a (possibly false) sense of security. By 1914 authorities had begun to question these arrangements as evidenced by a move to change the term 'fireproof' to 'fire-resistive,' and description of egress provisions in regulations as 'exceedingly deficient.' Model building regulations in the US started with the National Building Code published by the National Board of Fire Underwriters (NBFU) following the Great Fire of Boston (1872). Property loss claims from this fire resulted in more than 70 insurance companies being driven into bankruptcy, causing insurance interests to form the NBFU and to develop building fire safety rules aimed at reducing property losses in fires. These rules became the first model building code, called the National Building Code (NBC), and first published in 1905. The NBFU was able to tie compliance with their rules to their Municipal Grading Schedule on which insurance rates are based. Cities needed favorable rates to attract investment, so they were motivated to adopt regulations consistent with the National Building Code. The first (1905) edition of the NBC required exit stairs to have a minimum width of 20 in (510 mm). The purpose of this paper is to document current regulatory requirements for means of egress in fires, their origins and scientific basis, and the approaches used in other countries. Then the paper will present an argument for why these approaches and requirements should be re-evaluated to reflect changes both in buildings and in their occupants. Finally the paper will make some suggestions for reasonable revisions to design practice along with a more holistic philosophy that takes better account of human behavior and is based on a more appropriate performance metric.