MS in Fire Protection Engineering
College of Engineering
Frederick Mowrer and Christopher Pascual
The purpose of this report is to analyze and evaluate the prescriptive and performance-based criteria used to design the fire protection systems installed in the Gates Center for Computer Science and Engineering at the University of Washington, Seattle Campus. The Gates Center is a five-story building housing business and assembly spaces such as classrooms, workrooms, offices, a lecture hall, event center, and a café. The main architectural feature is a central atrium, which connects the ground, first, second, and third floors of the building.
Aspects of the prescriptive-based fire protection design include egress, automatic sprinkler systems, detection and notification devices, and structural elements. Egress capacity exceeded occupant load and an adequate number of exits were provided on each floor. One area of concern is the egress pathway for occupants on the first floor, east side of the building. In an emergency, architectural drawings show occupants egressing through the staircase as well as through the atrium due to the limited exit capacity of the staircase. However, if the fire is in the atrium, the conditions in which occupants will egress through will be worse than where they originated. Although the atrium has a smoke extraction system installed, a second staircase should have been added on the east portion of the building.
The smoke extraction system in the atrium is compliant with NFPA 92 and is comprised of six rooftop fans and makeup air pathways. Control logic enables the fans to operate upon detection of water flow or smoke. Once the fans initiate, motorized dampers are opened to allow for makeup air to infiltrate the space. Initiating devices such as sprinklers and smoke detectors are key to the operation of the smoke extraction system.
Analysis of the automatic suppression system revealed no deficiencies as the city’s water supply exceeded the building’s demand. The building demand was dictated by the most hydraulically remote area, which was the fourth-floor events space. Regarding hazard classification, the only space that could have been classified differently is the café pantry, which was classified as light hazard but ordinary hazard group one seems more fitting. Finally, installed sprinkler heads had proper spacing and flow characteristics.
Both fire alarm and notification system analysis and structural analysis concluded that the Gates Center complies with local codes. Voltage-drop calculations demonstrated the installed wiring complies with NFPA 72. Regarding structural analysis, the building construction type, allowable height and number of stories, and interior fire ratings all complied with local codes and university mandates. An aspect of passive protection that lacked documentation is interior finish ratings. The report reviews finish requirements, but no conclusion on whether the Gates Center complies was made.
For the performance-based design, a life safety analysis was performed using tenability criteria. Tenability criteria used in the analysis includes visibility, room temperature, smoke layer height, and toxic gas production. Two design fires were hypothesized and evaluated using fire correlations, Consolidated Fire and Smoke Transport (CFAST), and Fire Dynamic Simulator (FDS). The first design fire is an office fire, which was chosen to model an ultra-fast developing fire and analyze flashover effects. The office furniture has a peak heat release rate of 6900 kW, 375 seconds after the fire ignites, which corresponds to an alpha value of 0.049 kW/s2. The second design fire analyzed a 7-ft Christmas tree, having a peak heat release rate of 7.3MW, located in the events space. This design scenario represents a severe fire resulting from a large fuel load and analyzes the tenability criteria over time. The fourth-floor events space is also the most remote location in the building, representing the worst-case required safe egress time. For this design fire, the available safe egress time was calculated as the time to reach untenable conditions. In both cases, the available safe egress time is compared to the required safe egress time.
Recommendations to the Gates Center include added features to the egress and fire detection strategy. An additional staircase on the east end of the building would eliminate the need for occupants to egress through the atrium. In addition, all the stairs serving the second, third, and fourth floors terminate inside the building and discharge to hallways with the same fire rating as the staircase. However, having at least one exit discharge directly to the exterior on the first floor would be nice for occupants and fire fighters to access. Another recommendation includes the installation of a heat detector in the café pantry. Although classified as light hazard, ordinary group one is better suited for the fuel hazards stored in the space. From design fire results, sofas should not be allowed in offices unless the office is large enough for two sprinkler heads. This will limit the fuel load in a small space and help reduce the time to flashover. In addition, Christmas trees should not be displayed in the fourth-floor events space due to its high fuel load and remote location. The events space is most likely to house people who are unfamiliar with the building, which is not favorable for tenability criteria, nor egress time. However, it should be noted that the design fires were chosen to stress the fire protection system and the likelihood of having such large fuel loads is relatively small.