Design Fires in Road Tunnels (2011) / Chapter Skim
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Pages 53-77
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From page 53... ...
An effective fire protection design for life safety and property protection in tunnels requires a systematic assessment of a number of component "sub-systems," which contribute to the overall safety of the design. These sub-systems are: • The initiation and development of fire spread • Spread of smoke and toxic gases • Detection of fire and activation of active fire life safety systems • Tunnel users' evacuation • Fire service intervention.
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From page 54... ...
Fire-resistant equipment Failure management Reduction of accident importance Fire-fighting equipment Rescue teams Drainage Road surface (non-porous) Emergency action plan Escort Reduction of the consequences on the tunnel Fire-resistant structure Explosion-resistant structure Source: Safety in Tunnels (2001)
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From page 55... ...
Response to Fire: Structural Fire Resistance and Fire Protection One of the serious consequences of a fire is damage to the tunnel structure and its ultimate collapse. By suitable design of the tunnel structure and by passive fire and/or fixed fire suppression protection, the tunnel can withstand the relevant fire scenario and tunnel rehabilitation and repair costs can be reduced or eliminated.
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From page 56... ...
Design fire scenario for ventilation and other systems (e.g., fixed fire suppressions) design and assessment -- Smoke ventilation in tunnels needs to be designed on
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From page 57... ...
• Road tunnel fires cannot be completely eliminated until vehicle fires are eliminated. DESIGN FIRE SIZE Design fire size is one of the most important parameters for tunnel fire engineering.
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From page 58... ...
, or a – Ventilation-controlled fire, giving rise to large amounts of toxic fumes and products of incomplete combustion. Essentially, all the oxygen is consumed within the combustion zone and fuel-rich gases leave the exit of the tunnel (e.g., extremely severe tunnel fires, such as the Mont Blanc fire where oxygen is limited)
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From page 59... ...
EXPLORING THE EMERGING ISSUES OF ALTERNATIVE FUEL VEHICLES ON DESIGN FIRES Environmental issues such as climate change and scarcity of resources have stimulated the development of new energy carriers for vehicles. This also means that there will be an increase in the number of vehicles running on these new energy carriers in tunnels and other confined spaces.
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From page 61... ...
• In France and the United Kingdom vehicles running on gas are prohibited in the Euro Tunnel. • In Austria, LPG and CNG are not permitted in the Tauern Tunnel.
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From page 63... ...
However, seeking the worst case scenarios is important when new energy carriers are developed. It is also important to realize that all risks are not eliminated by introducing PRDs.
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From page 64... ...
This makes a detailed review of all aspects of risks associated with new energy carriers and safety in tunnels beyond the scope of this study. On the other hand, this is exactly why this issue is so important.
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From page 65... ...
Basically, it can be said that as a result of the heat released around the fire site and thermal buoyancy, the smoke is lifted up to the ceiling near the fire site and spread in the upper area of the tunnel. The smoke continues its flow in one direction when the longitudinal velocity is high (with or without backlayering)
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From page 66... ...
For 100–150 MW (341–512 MBtu/hr) fires, the entrainment of fresh air does not compensate for the very strong reduction of smoke temperature 50 to 100 m (164 to 328 ft)
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From page 67... ...
; and u (m/s) is a unified longitudinal ventilation velocity across the tunnel cross section A (m2)
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From page 68... ...
Additional testing results are needed. TEMPERATURE OF FIRE GASES AND TUNNEL WALLS Tunnel fires significantly increase the air temperature in the tunnel roadway and in the exhaust air duct.
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From page 69... ...
bJet fans located 170 ft (52 m) downstream of fire site.
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From page 70... ...
On the other hand, the Mont Blanc and Nihonzaka fires lasted significantly longer. The EUREKA and Runehamar tests showed a steep decline of temperatures just after the hot phase.
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From page 71... ...
. The relatively low temperatures generated create less buoyancy in the combustion products, and thus decreases the likelihood of smoke stratification under the tunnel roof as with hotter fires.
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From page 72... ...
Figure 20 represents different fire growth quadratic growth curves. The ultrafast fire growth curve with the fire growth coefficient of 0.178 kW/s2 meets most of the Runehamar Tunnel fire tests.
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From page 73... ...
Usual tunnel fires are fuel-controlled fires; however, in a severe fire such as the Mont Blanc fire, with multiple vehicles involved, the fire was a ventilation-controlled (oxygen-limited) fire.
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From page 74... ...
. The duration of the hot phase of a fire normally covers a time interval of about 30 to 60 min after ignition stage, unless there are unusual circumstances such as a big pool fire caused by a gasoline tanker or a situation similar to the Mont Blanc fire.
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From page 75... ...
A design fire scenario is the interaction of the design fire with its environment, which includes the impact of the fire on the geometrical features of the tunnel, the ventilation and other fire safety systems in the tunnel, occupants, and other factors. Nobody can precisely predict every fire scenario given the range of variables and people behavior.
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From page 76... ...
They can be categorized as: • Ultrafast growth rate • Fast growth rate • Medium growth rate • Slow growth rate. The ultrafast fire growth curve with the fire growth coefficient of 0.178 kW/s2 meets most of the Runehamar Tunnel fire tests.
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From page 77... ...
Tunnel fires significantly increase the air temperature in the tunnel roadway and in the exhaust air duct. Therefore, both the tunnel structure and ventilation equipment are exposed to the high smoke and gas temperatures.
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