MS in Fire Protection Engineering
College of Engineering
Frederick Mowrer and Christopher Pascual
This report examines the fire protection and life safety features of a new, 3-story plus basement, hotel on California’s Central Coast. These features are examined from both a prescriptive, code-driven perspective, as well as from a performance-based design point of view.
The prescriptive analysis includes exit configuration and capacity, the NFPA 13 sprinkler system, the NFPA 72 fire alarm system, and the building construction types. All were found to be acceptable when compared against the applicable codes the building is subject to, with the exception of some of the load- bearing exterior walls.
The performance-based component examines the affect two fire scenarios could have on the building structure. The fire scenarios chosen are considered a reasonable representation of the risks such a property could face. The first scenario considers the risk posed to the building structure created by the use of car stackers in the basement parking garage. In this evaluation, Fire Dynamic Simulator (FDS) is used to determine the elevated temperature applied to the bottom surface of the concrete floor/ceiling assembly separating the basement and first floor levels. This temperature rise is driven by the hypothetical combustion of six passenger vehicles, which are modeled in the simulation as gasoline pool fires. The resulting temperature/time data returned by the FDS model was then incorporated into a Microsoft Excel spreadsheet which approximated the heat spread through the 1’-4” (0.4 m) thick concrete floor/ceiling assembly as one-dimension conduction. When subjected to this six-car design fire, the center of the concrete floor/ceiling assembly was found to experience less than a 10 °C temperature rise. As a check, this same one-dimension conduction spreadsheet was supplied with a temperature/time curve representing the ASTM E119 furnace test applied for 3-hours, consistent with fire resistance time called out for the floor/ceiling assembly in the project documents. Subjected to this heat input, the spreadsheet reports a maximum temperature at the center of the concrete slab of approximately 150 °C. From these two evaluations, it is concluded that the thickness of the floor/ceiling assembly is ultimately driven by structural requirements, and not fire resistance.
The second scenario considers a fire within a guest room. Again, we are considering the effects of elevated temperatures upon the structural elements of the floor/ceiling assembly above the room of fire origin. Here a CFAST model representing a burning couch is used to determine the resulting ceiling temperature. With this determined, one-dimension conduction through the gypsum wallboard ceiling and into the composite wood floor/ceiling joist is considered. After computing that the joist’s strength is reduced to the point of failure at temperatures exceeding 220 °C, it is determined, after several iterations, that a layer of gypsum wallboard at least 1” thick will limit the temperature in the joist to approximately 180 °C for the selected fire scenario. This finding is consistent with the project architectural details which call out two layers of ½” thick gypsum wallboard, for a total thickness of 1”, at the guest room ceilings. The performance-based analysis confirms that the structural assemblies specified in the construction drawings are adequate for this property.
While the performance-based analysis returned favorable results for the chosen fire scenarios, consideration should be given to potential increased fuel loads in the future. Given trends towards greater plastic content in cars, as well as the increasing prevalence of electric vehicles, the threat of vehicle fires with greater heat release and posing more difficulty to extinguish seems likely to materialize. In addition, policy should be put in place for the guest rooms to regulate the quantity and combustibility of furniture placed within them – particularly when a remodel is considered.