Empirical seismic fragility function for fire doors based on inspection data from the 1995 Kobe earthquake and its use in post-earthquake fire risk assessments

The seismic damage to fire protection systems heavily affects post-earthquake fire safety, an important requirement for seismic-resilient buildings. Quantitative fire risk assessments are useful in understanding and improving safety. Such assessments require modeling the seismic fragility of fire protection systems. As a starting point for rigorous risk assessments, this study focuses on fire doors, which contribute to compartmentalization during fires as an underlying principle in the fire safety design of buildings; accordingly, fire door inspection records for five mid-rise buildings that suffered slight to severe structural damage from the 1995 Kobe earthquake in Japan are analyzed. The objectives of this study are to (1) develop an empirical fire door seismic fragility function based on the inspection records and (2) discuss the post-earthquake fire risk of buildings via a hypothetical case study using the developed function in terms of the loss of life caused by fires. Structural response analyses based on synthetic ground motion waveforms and Japanese building models allow the fire door damage states recorded floor by floor to be correlated with the simulated peak inter-story drift angles. The developed fragility function indicates that 50% of fire doors fail to open or close at a peak inter-story drift angle of approximately 0.01 rad. For buildings with two exit stairways compartmentalized by smoke detector–activated fire doors, the case study reveals (1) that the post-earthquake fire risk can increase by up to 2000 times relative to normal periods because of the increased probability of ignition and the reduced reliability of the fire door system and (2) that, even if the structural response can be reduced by an improved seismic performance to less than a peak inter-story drift angle of 0.01 rad, the post-earthquake fire risk can still be high, up to 800 times higher than the normal level. These results indicate that, in addition to seismic designs aimed at reducing the structural response, the implementation of post-earthquake ignition prevention measures and the enhancement of occupant initial firefighting capabilities are essential for post-earthquake fire risk reduction. • Fire door seismic fragility function is developed from earthquake inspection records • 50% of fire doors fail to open/close at peak inter-story drift angles of ∼0.01 rad • Post-earthquake, ignition probabilities increase and fire door systems are unreliable • Fire risk can rise 2000 times, or 800 times even with improved structural responses • Ignition prevention and initial firefighting measures are crucial to reduce fire risk