DOB Findings and Recommendations for WTC, Feb 2003

NYC 9/11 Public Portal Document ■!

4.2.1 Capacity and Location of Stairwells

In most areas related to egress capacity, further information and empirical investigation is required to warrant introduction of new. standards into the code. Despite having limited empirical I and modeling documentation, further evidence of a need for stair capacity increase on lower i floors would have to be provided to make a specific recommendation. The Task Force looks to NIST for a fnore comprehensive study of this issue. However, the goal of increased capacity, in absence of new workable design criteria could be addressed immediately with a change in the ( way developed space is calculated. To encourage the inclusion of more stairwells or wider stairwells in buildings, the Task Force recommends that the floor area of stairwells above the minimum requirements be excluded from total Floor Area, in the calculation of a building's potential maximum developable floor area. This recommendation would require a change in the Zoning Resolution.including environmental review and City Planning Commission Approval. Remote location of stairwells was also a concern to the Task Force, given the Building Performance Study conclusions. Currently, number and size of stairways, as well as remote location, are dictated by occupant load, determined by floor size and travel distance. The logic behind separating stairwells and placing them at a prescribed distance is predicated on redundancy (a lesson learned from many building tragedies), given the possibility of a catastrophic event isolating a portion of a floor. A building core organizes circulation, mechanical services, plumbing and power utilities, allowing for the necessary efficiency of an office floor "plate". Design of a building's core is not generic, but highly specific to a building, and thus, stair 1 quantity and location should be evaluated for the idiosyncrasies of individual building design and I risk profile. In reality, high-rise building design depends on this type of core construction. The Task Force believes that this issue should be examined by NIST. I I An additional building design efficiency includes the use of scissors stairs, two stairwells that adjoin one another and share a common shaft, but are separately enclosed. Such stairs are little used except in buildings with small floor plates, but allowable by the current code. The Task Force recommends that this design be limited to high-rise commercial buildings with a floor plate square footage under 10,000 square feet. I Recommendation 1

4. Work with the Department of City Planning to exempt floor, area of stairwells above minimum requirements from zoning Floor Area Ratio I I (FAR) calculations to encourage the inclusion of more stairwells or wider stairwells in buildings.

5. Prohibit the use of scissors stairs in high-rise commercial buildings with a floor plate of over 10,000 square feet.

I ' 4.2.2 Clarity of Egress Pathway The clarity or "readability" of the egress path is essential for a successful evacuation. When fire or another threatening condition impedes sensory perception, decision making for evacuees should be facilitated by systems that offer heightened comprehensibility. The Working Group concluded that improvements to the marking of the egress path, doors and stairs be implemented and that I existing buildings' exit signs should be retrofitted with either battery or generator backup power. It also concluded that overall lighting level was sufficient and that color coding stairwells could confuse the current requisite identification scheme.

Page 20 WTC Building Code Task Force February 2003 Findings and Recommendations

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