MS in Fire Protection Engineering
College of Engineering
Frederick Mowrer and Christopher Pascual
The subject building is an approximately 180,000 SF technology office; the location and some details are omitted for privacy of the project and client. It is a 3-story heavy timber frame (Type IIIA) over 1 level of concrete basement stepped into a hillside.
The building is compliant with the prescriptive building code for egress, fire alarm, and fire sprinkler systems. A NFPA 72 compliant fire detection, notification and communication system is provided. The building is fully sprinklered with a system that is hydraulically designed per NFPA 13, 2016 Section 11.2.3 Water Demand Requirements – Hydraulic Calculation Methods. Water supply is provided by the City.
It is largely compliant for passive protection features, with the exception that a performance-based design is used to justify exposed cross laminated timber (CLT) panels.
Three design fires, based on considerations outlined in NFPA 101, are used to stress the building’s fire protection systems assuming that sprinkler do not activate to control or suppress a fire.
Three deign fires, in accordance with NFPA 101, are selected. Assuming failure of the sprinkler system, based on typical occupancy specific use, and the most severe fuel load (workstations in open office areas, largest conference room table and chairs, and kitchen equipment), the following design fires are used:
NIST Office Workstation Fire (6 MW @ 5 min) Large Conference Room Fire (6 MW @ 25 min) Café Kitchen Fire (2 MW @ 15 min)
Based on the large conference room fire, a performance-based design confirms that life-safety is met by demonstrating that an available safe egress time (ASET) of 7.5 minutes exceeds the 3 minutes required safe egress time (RSET).
The ASET time of 7.5 minutes is governed by untenable visibility at 6 ft above finished floor (AFF), and the RSET time is comprised of time to detection and alarm, pre-movement time, and travel time. This ASET over RSET comparison results in a factor of safety over 2.
Additionally, it is confirmed that under the NIST office workstation fire that the actual temperatures and heat flux experienced by the exposed CLT panels is less than that which would generate prescriptive code char rates, allowing for these panels to remain exposed as an architectural feature.
Research into various char rates corresponding to different temperature profiles would assist in evaluation of exposed heavy timber in similar applications.