Freedom Tower to include advanced high-rise
fire safety features
By Samuel S. Dannaway, PE,
President, S.S. Dannaway Associates, Inc., Honolulu
One World Trade Center will have 108 floors and a total floor area of 2.6 million square feet. The building will have a total height of 1776 feet. There will be a ledge at 1368 feet marking the height of WTC 1.
According to the website of the New York Port Authority, the tower currently stands at a height 961 feet at 78 floors. The topping off of the tower is expected to occur in the first quarter of 2012.
The building will incorporate advanced fire safety features exceeding those required by the building code of the City of New York, creating a new standard for high rise buildings.
The key element is a hardened central core with three foot concrete walls. It will protect essential building systems, including exits stairs, sprinkler and standpipe risers, HVAC shafts, elevators, and power supply and communication risers. Elevator evacuation will be incorporated into the elevator system. Elevator lobbies will be enclosed by one hour smoke barrier sized to accommodate 25% of the floor occupant load, be equipped with two-way communications and have direct access to an enclosed exit.
The tower also will include the additional fire safety requirements in the 2009 International Building Code for high rise buildings exceeding 420 feet in height. Many of these provisions are the direct result of recommendations contained in the NIST WTC Investigation Report. These features include:
• IBC Section 403.5.2 Additional Exit Stairway. For buildings other than Group R-2 that are more than 420 feet height one additional exit stairway shall be provided in addition to the minimum number of exits and minimum total exit capacity required. It is noted that the IBC has an exception to this requirement if elevators designed for occupant self-evacuation are provided. One WTC will have both. The additional stair provided to enable the first responders to commander one of the available stairs for their use during fire fighting operations without affecting the required egress capacity for building stairs.
• 1005.1 Minimum Required Egress Width. The reduction for sprinkler protection of the egress capacity factors have been eliminated in the 2009 edition of the IBC. Stairs must be calculated based on 0.3 inches per person rather than 0.2 inches per persons previously allowed for sprinkler building. This will result in wider stairs in many buildings.
• 403.5.1 Remoteness of stair enclosures. Stair enclosures shall be separated a minimum of 30 ft. or one-fourth the maximum diagonal dimension of the building or area served.
• 403.5.5 Luminous Egress Path Markings for exit enclosures.
• 403.6.1 Fire Service Access Elevator. A dedicated elevator for the fire service is required for buildings with 120 feet or more in height. The elevator must open into a protected elevator lobby with a minimum 150 square feet and the lobby must have direct access to an exit stair.
• 403.4.4 Emergency Responder Radio Coverage. An emergency responder radio communications system must be installed in all high-rise buildings.
• 403.4.6 Smoke Removal System to facilitate smoke removal in post-fire salvage and overhaul operations.
• Bond strength of sprayed fire-resistive material (SFRM): The minimum bond strength for SFRM in buildings more than 420 ft. in height will be 1,000 psi.
• Fire command center size: An increase the minimum size of the fire command center from 96 sq. ft. to 200 sq. ft. with a minimum dimension of 10 ft.
• Dual fire sprinkler risers. Buildings more than 420 ft. in height tall shall have dual fire sprinkler risers arranged so that risers supply alternating floors. This is the correct way to ha a design to avoid progressive collapse, biological and chemical filters on the air supply system, a hardened exterior glazing system and increased set backs from West Street.
Though the Freedom Tower will not be completed to by the 10th anniversary of September 11, the Port Authority indicates that the Visitors Orientation and Education Center and the Memorial Museum with its Memorial Wall will be officially opened on that day.
It is wonderful that after these many years there will stand
Samuel S. Dannaway, PE, is a registered fire protection engineer and mechanical engineer with bachelor’s and master’s degrees from the University of Maryland Department of Fire Protection Engineering. He is past president and a Fellow of the Society of Fire Protection Engineers. He is president of S. S. Dannaway Associates Inc., a 15-person fire protection engineering firm with offices in Honolulu and Guam. He can be reached via email at SDannaway@ssdafire.com.