MS in Fire Protection Engineering
College of Engineering
Frederick Mowrer and Christopher Pascual
The report evaluates the fire protection features of a K-12 classroom building (Bldg. B) in San Bernardino County, California. Bldg. B is a two-story Type V-A light timber frame construction. At the time of this report’s composition, Bldg. B is undergoing modernization construction. The fire protection analysis of this building consists of prescriptive and performance portions.
The prescriptive analysis verifies the compliance of building egress, passive, and active protection features with the 2019 edition of California Codes of Regulations Title 24 (Title 24) and Title 24-adopted National Fire Protection Association (NFPA) standards. The analysis comprises of four sections: egress, structural analysis, fire alarm design, and sprinkler system analysis. The egress section describes the occupancy classifications and assesses the occupant loads, the required width for exits and exit access doorways, the number of available fire escapes, exit separation distance, and interior finishes. The structural analysis section focuses on the modernization expansion area increase, the building elements’ fire-resistance rating, and fire separation requirements. The fire alarm section surveys the location of alarm devices, determines the spacing requirements, identifies active smoke control in place, and diagnoses the secondary power supply. The sprinkler system analysis section checks the fire suppression device coverage and the required hydraulic pressure for the chosen remote design areas. Overall, the fire protection features in Bldg. B follow the prescriptive codes of regulation in effect at the time of modernization design, and implicit safety is accomplished.
The performance-based analysis gauges the effectiveness of prescriptive active fire protection systems in providing explicit safety to occupants in Bldg. B using three design fires. Locations of these fires are selected based on potential life safety impacts. The heat release rates of the design fires reference fuel load data from SFPE Handbook and Nuclear Regulatory Commission (NUREG) literature.
To achieve explicit safety, the available safe egress time (ASET) for a design fire must exceed the required safe egress time (RSET).
Before ASET is estimated, a set of tenability criteria on visibility, toxicity, radiant heat exposure, and flashover has to be established. The exceedance of any one tenability criterion signifies the expiration of ASET. Computational fire dynamics is used to find the ASET of a design fire.
RSET is based on egress component width, space density, occupant familiarity with the building, and population size. Using hydraulic flow model, NIST Egress Estimator, and Thunderhead Engineering’s Pathfinder software, the full-evacuation time for the entire building is predicted to be 4.87 minutes. RSET is then further refined for individual design fire scenario.
The first design fire (DF-1) is on the first-floor Flex Studio 2 137. Flex Studio 2 137 and the adjacent Flex Studio 1 136 are significant exit access areas where occupants of nearby classrooms and north wing 2nd-floor occupants must go through to reach building exits. If egress is disabled for the area, occupants in nearby spaces would be trapped. Using hydraulic flow model and Pathfinder, RSET for DF-1 is calculated to be 2.81 minutes. DF-1 is then put into Pyrosim to estimate ASET. After analyzing simulation results, DF-1 ASET is found to be visibility driven, as incapacitation, radiant heat exposure adverse outcome, and flashover are unlikely. When significant sub-4m visibility pockets appear along the wall around 3.14 minutes, visibility tenability expires for DF-1. As such, for DF-1, ASET (3.14 minutes) is greater than RSET (2.81 minutes); explicit safety is achievable. Another ASET vs RSET analysis is performed for the 2nd-floor because smoke may travel through the now unenclosed Stair B unimpeded and impair egress. Pyrosim predicts the visibility would remain above 30 meters during RSET. As such, ASET is also greater than RSET for the 2nd-floor spaces above DF-1.
The second fire (DF-2) is in the library reading area. An ASET vs RSET comparison is done, and occupants would be able to escape in time through the available exits. The concerns then become property damage mitigation and life safety in adjacent spaces. Using Pyrosim, the sprinkler system is predicted to activate at 61 seconds, keeping the HRR at 400 kW. With the activation of automatic fire sprinklers, the risks of flashover and property damage are low.
The third fire (DF-3) is in the first-floor electrical room near the elevator shaft and a main building exit. The concern is a possible flashover. A two-zone model is constructed in CFAST which predicts that the sprinkler system would activate 45 seconds and freeze the HRR at 130 kW, far below the lowest predicted flashover HRR of 1053 kW. Therefore, flashover is not expected and DF-3’s impact on adjacent space egress is minimal.
The results of performance analysis are favorable. Explicit safety is attainable with functional active fire protection systems.