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102
TABLE 32
EXAMPLE OF PROJECT ESTABLISHED TIME-OF-TENABILITY CURVE
Self-Rescue FLS Systems Activation
A. Make a decision to evacuate 1. Detection Time
B. Disembark the bus 2. Operator Reaction Time (alarm)
C. Walk away from the fire effected zone 3. Systems Activation
D. Reach cross passage 4. All Fans Activated
5. Ventilation Mode in Full Operation
time for evacuation. The sooner smoke and fire will be taken For the unmanned tunnels, the system is usually designed to
under control the sooner there will be a tenable environment be fully automatic or operated by the local fire department.
for evacuation. The distance that people can safely travel to
an exit depends on the fire development and system activa- In any case, the first and the most critical element of the
tion. The primary role in system activation is fire detection. system is fire detection. Although many tunnels still rely on
Thus, spacing between cross passages will largely depend manual fire detection, this needs to be revisited. Operators
on the fire-detection system. For example, if the fire is not may require help in detecting a fire, which would allow them
detected, the smoke control systems are not activated and to take appropriate actions in a timely manner.
spacing between cross passages would be determined based
on the speed of the loss of visibility and smoke growth in the
path of evacuation. COMBINED CURVE FOR EVACUATION
AND SYSTEM ACTIVATION
Application of the tenability criteria at the perimeter of a
fire is impractical. The zone of tenability is defined by apply- Based on fire development, emergency egress, and the equip-
ing it outside the boundary, away from the perimeter of the ment activation timeline, it is possible to create a combined
fire. This distance will depend on the FHRR. heategress system activation time curve similar to the one
presented in Table 32. This curve allows one to analyze the
design HRR at every evacuation and system activation phase
EQUIPMENT ACTIVATION TIMELINE and to make the correct decisions.
It was discussed in previous chapters that it is not possible to
When the evacuation phase is concluded, fire fighting must
achieve a fully operating mode for all fire fighting equipment
be facilitated by proper smoke handling. A basic requirement
instantaneously. Equipment activation time consists of the
is to provide maximum opportunity for the fire fighting access
following phases for supervised tunnels:
in minimum smoke. During evacuation, the direction of smoke
1. Fire-detection time (from 2 to 3 min if reliable auto- flow must not change. With the arrival of the fire department,
matic fire-detection system is installed). it can be decided on-site which fan control is the best to facil-
2. Fire alarm and operator reaction time (from 60 to 90 s). itate the fire fighting.
3. Time to bring the first group of fans to full speed
(60 s for unidirectional and 90 s for reverse mode-- The time-of-tenability graph can be prepared as the result
NFPA 502). of fire life safety systems design and CFD analysis. A sam-
4. Activate fixed fire suppression system if desired (30 s ple of this graph is shown in Figure 31. This graph is called a
60 s if wet). tenability map and shows all time steps discussed earlier and
5. Achieve a full operational mode for ventilation system the resulting impact on casualties and tunnel structure. It allows
(180 s). one to predict for how long the environment will be tenable
FIGURE 31 Example of project established time-of-tenability curve (67 ).
