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Problem Statement

Due to non-compliances to the Code of Practice for Fire Precautions in Buildings (2007) for the development a combination of prescriptive approach and alternative solutions supported by performance-based fire engineering analysis was used. The main non-compliance for the multi-storey development is to Clause 7.6.1 for the natural engineered smoke control to the high atrium space.

Challenge

Total Evacuation Time = Pre-movement Time + Movement Time The code compliant stipulation for exit widths ensures that during a fire the occupants are able to safely evacuate the building in a timely manner. An inadequate exit width will increase the movement time due to the possible bottle necks at the existing designated exit doors. This will increase the total evacuation time and may compromise the ability of occupants to egress the building before the conditions become untenable. To mitigate this increase in timing due to increased occupant load, the Pre-movement Time must be reduced.

Solution

Pre-movement Time = Alarm Time + Delay Time The existing building design depends on the sprinkler system to activate the fire alarm. If a fast growth fire is considered, the time to trigger the sprinkler (and consequently the fire alarm) is 131s. On the other hand, if a smoke detector is used to detect the fire, the alarm activation can be reduced to 19s (for a fast growth fire). Therefore, it was proposed to use a smoke detector (in addition to the sprinkler system) to reduce the Pre-movement Time.

Results

The evacuation modelling clearly shows that the movement time increases by 50s when the occupant load per level is increased from 600 people to 720 people. However, introducing a smoke detection system to reduce alarm activation time, results in an overall reduction in Total Evacuation Time (regardless of the fire growth rate). In conclusion, the use of smoke detectors is be able to provide a mitigation of the inadequacy in the capacity of exit provisions and facilitates a Total Evacuation Timing that is at least 21s faster.

Fig. 2: Screen Capture of Evacuation Simulation at Level 1

 

Activation Time(s) Delay Time(s) Movement Time (s) Total Evacuation Time(s)
600 people/level w/o Smoke Detectors 358 36 887 1281
720 people/level with Smoke Detectors 49 36 937 1022

Table 1: Total Evacuation Timing for Slow Fire Growth Rate

 

Activation Time(s) Delay Time(s) Movement Time (s) Total Evacuation Time(s)
600 people/level w/o Smoke Detectors 214 36 887 1137
720 people/level with Smoke Detectors 29 36 937 1002

Table 2: Total Evacuation Timing for Medium Fire Growth Rate

 

Activation Time(s) Delay Time(s) Movement Time (s) Total Evacuation Time(s)
600 people/level w/o Smoke Detectors 131 36 887 1054
720 people/level with Smoke Detectors 19 36 937 992

Table 3: Total Evacuation Timing for Fast Fire Growth Rate

 

Activation Time(s) Delay Time(s) Movement Time (s) Total Evacuation Time(s)
600 people/level w/o Smoke Detectors 85 36 887 1008
720 people/level with Smoke Detectors 14 36 937 987

Table 4: Total Evacuation Timing for Ultrafast Fire Growth Rate