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OCR for page 102
103 FIGURE 32 Time-of-tenability sample graph with no ventilation (67). in the tunnel and helps to decide what needs to be done to Design of emergency exits achieve fire life safety goals. In this figure the pre-movement Choice of a fire-detection system time is the time between discovery of a fire and the start of Choice of ventilation and fire suppression systems egress travel. Tunnel structural engineering Specification requirements for tunnel structures and Figure 32 illustrates how longer detection and pre- equipment movement times with greater fire hazards can lead to casual- Operation of the tunnel ties. Figure 33 illustrates the impact of longitudinal ventilation Training of operators and first responders dealing with on fire life safety and structural protection. It shows no casu- tunnel fires. alties and much safer fire fighting. Tunnel spalling danger is eliminated on the upstream side and significantly reduced on Fire scenarios usually include: the downstream side. Governing standards and guidelines SUMMARY Description of the scenario Thorough definition of the fire parameters (e.g., HRR/ A fire scenario must be designed to get an optimum fire life temperature versus time) safety strategy for road tunnels. Fire scenarios are used for Traffic scenario operation during fire emergency and the following: tunnel ventilation operation FIGURE 33 Time-of-tenability sample graph with longitudinal ventilation (35, 68).

OCR for page 102
104 Guidelines for structural protection It is necessary to add times for detecting and alert- Specifications for materials, equipment, and structure. ing, reaction and leaving the vehicles, and walking to a safe place, to know if people can escape the fire If the specific fire scenario is known, such as with a truck safely. with a specific load, it is suggested that a predetermined Spacing between emergency exits shall be justified by timetemperature curve be used when designing the tunnel calculations. It is impossible to take fire and smoke structure and equipment. There is a number of known time under control immediately; therefore, for several min- temperature curves used worldwide. The Dutch RWS temper- utes, fire and smoke will be driven by natural factors. ature curve includes the most stringent temperature require- This is the most important time for evacuation. The ments and is referenced in NFPA 502 for structural design. This sooner smoke and fire are under control, the sooner there curve is based on the assumption that, in a worst-case scenario, will be a tenable environment for evacuation. The dis- a 50 m3 (1,765 ft3) fuel, oil, or gasoline tanker fire with a fire tance that people can safely travel to an exit depends on load of 300 MW (1024 MBtu/hr) occurs, lasting up to 120 min. the fire development and system activation. The primary role in system activation is fire detection. Thus, spacing Simple heat transfer equations do not allow for the making between cross passages will largely depend on the fire- of a direct correlation between the timetemperature curve and detection system. the timeheat release curve. It appears that the known fire 3. Equipment activation time consists of the following growth rates follow the super fast (highest increasing rate mea- phases for supervised tunnels: sured) temperature rise in the timetemperature curves. How- Fire-detection time ever, the use of HRR curves is often allowed for the design. Fire alarm and operator reaction time Time to bring the first group of fans to full speed For fire life safety an integrated approach is to be taken. Time to activate the fixed fire suppression system if Time-of-tenability can be understood by analyzing the entire desired system with all components working together. To develop a Achieve a full operational mode for ventilation time-of-tenability final curve, the project must develop: system. For unmanned tunnels, the system is usually designed 1. A fire heat release curve as a function of time. to be fully automatic or operated by the local fire 2. A design evacuation (egress) curve as a function of time. department. 3. A design systems response curve as a function of time. Based on fire development, emergency egress, and equip- 1. The development of fire or a fire heat release curve is ment activation timeline, it is possible to create a combined a function of: heategress system activation time curve. This curve allows Maximum FHRR, for the analysis of the design HRR at every evacuation and Fire growth rate (quadratic curve for either super fast, system activation phase and aids in making the correct fast, medium, or slow fire growth rate), and decisions. Fire decay rate. 2. The egress timeline depends greatly on human behavior. A tenability map shows all time steps and the resulting For design purposes, there is a need to: impact on casualties and tunnel structure. It allows one to Assume that people will realize the danger, be noti- predict for how long the environment will be tenable in the fied to evacuate, make the right decision on the direc- tunnel and helps to decide what needs to be done to achieve tion for evacuation, and go to the point of safety. fire life safety goals.