A model for fire risk assessment of a mid-rise or high-rise buildings is developed considering seismic damage of six fire safety equipment systems including sprinkler system, mechanical smoke exhaust system, fire door, fire detector, fire extinguisher, and indoor fire hydrant. The model consists of three sub-models, namely, (a) the two-zone smoke transport model, (b) the model for fire-fighting activity of occupants, and (c) the network-based model for evacuation of occupants. The two-zone smoke transport model predicts smoke transport inside of a building until the fire ends either by extinguishment by fire-fighting activity of occupants or by burn out of entire fire load. Activation time of a sprinkler system and a fire detector is predicted based on the RTI model considering the effect of ceiling jet in the two-zone environment. The fire-fighting model determines success and failure of fire-fighting activity by comparing the maximum size of fire extinguishable by an equipment, Zcr, with the size of fire at the time fire-fighting starts, Z(tFF). Start time of fire-fighting activity by occupants, tFF, depends upon the activation time of fire detector. The evacuation model predicts movement of individual occupants on a route network with the room as a node and the door as a link. Failure of evacuation of an occupant is determined by comparing the smoke layer height, HS, with the critical smoke layer height. Damage of a fire door not only allows the leakage of smoke from a fire room to adjacent rooms, but may also block a passage of occupants. Availability of each fire safety equipment systems is analyzed by the fault trees and their probabilistic parameters such as damage ratio of the systems and occurrence probability of power outage under a certain seismic condition is modeled based on the records of past earthquakes.
As a case study, the model is applied to a hypothetical nine-story building with building area of 1,144m2 and its post-earthquake fire risk is assessed by the Monte Carlo simulation. Among the six fire safety equipment systems considered in the present model, availability of sprinkler system, mechanical exhaust system, and indoor fire hydrant were more sensitive to seismic shaking compared to the others. This is attributed not only to the damage of the system itself, but also to availability of power, water for fire-fighting, and probability of occupants engaging in fire-fighting activity. Exceedance frequency of the fire damage represented by the smoke vitiated area and the number of evacuation-failed occupants showed that the fire damage remains minor in most of the cases even if occurred. However, the proportion of major damage increases with the increase of seismic intensity. While the maximum smoke vitiated areas for each seismic intensity converged into a same degree, the maximum number of evacuation-failed occupants varied. This indicates that the range of human loss expands as the unavailability of fire safety equipment systems increases.
