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130 AccidentâAn incident followed by the development of unsafe situations for people in a tunnel. Alternative fuelâA motor vehicle fuel other than gasoline and diesel. BacklayeringâThe reversal of movement of smoke and hot gases counter to the direction of the ventilation airflow. CombustibleâCapable of undergoing combustion. CCTVâClosed circuit television. Combustible liquidâAny liquid that has a closed-cup flash point at or above 100°F (37.8°C), as determined by the test procedures and apparatus set forth in Section 4.4 of NFPA 30, Flammable and Combustible Liquids Code. Combustible liquids are classified according to Section 4.3 of NFPA 30. Critical velocityâThe minimum steady-state velocity of the ventilation airflow moving toward the fire within a tunnel or passageway that is required to prevent backlayering at the fire site. Deluge systemâAn open fixed fire fighting system acti- vated on a zone-by-zone basis. Operation can be automatic or manual. Fire emergencyâThe existence of, or threat of, fire or the development of smoke or fumes, or any combination thereof, that demands immediate action to correct or alle- viate the condition or situation. Fire growth rateâRate of change of the fireâs heat release. Fire suppressionâThe application of an extinguishing agent to a fire at a level such that open flaming is arrested; however, a deep-seated fire will require additional steps to assure total extinguishment. Fixed water-based firefighting system (or fixed fire suppression system; FFSS)âA system permanently attached to the tunnel that is able to spread a water-based extinguishing agent in all or part of the tunnel. Flammable liquidâAny liquid that has a closed-cup flash point below 100°F (37.8°C), as determined by the test pro- cedures and apparatus set forth in Section 4.4 of NFPA 30, Flammable and Combustible Liquids Code, and a Reid vapor pressure that does not exceed an absolute pressure of 40 psi (76 kPa) at 100°F (37.8°C), as determined by ASTM D 323, Standard Test Method for Vapor Pressure of Petroleum Products (Reid Method). Flammable liquids are classified according to Section 4.3 of NFPA 30. FlashoverâA sudden transition from localized to generalized burning where all of the items inside a vehicle or compart- ment ignite. Heat release rate (HRR)âThe rate at which heat energy is generated by burning expressed as Btu/s or megawatts (MW). Length of tunnelâThe length from face of portal to face of portal that is measured using the centerline alignment along the tunnel roadway. Point of safetyâAn exit enclosure that leads to a public way or safe location outside the structure, or an at-grade point beyond any enclosing structure, or another area that affords adequate protection for motorists. Road tunnelâAn enclosed roadway for motor vehicle traffic with vehicle access that is limited to portals. Scenario analysisâThe analysis of the consequences of a wide range of accidents in a tunnel. Self-rescueâPeople leaving the hazardous area or danger- ous situation without the help of trained or professional rescuers (tunnel personnel or fire fighters). Standpipe systemâAn arrangement of piping, valves, hose connections, and allied equipment installed in a building or structure, with the hose connections located in such a man- ner that water can be discharged in streams or spray patterns through attached hoses and nozzles, for the purpose of extin- guishing a fire, thereby protecting a building or structure and its contents in addition to protecting the occupants. Tenable environmentâAn environment that supports human life for a specific period of time. Water mist systemsâFixed fire fighting systems that oper- ate by discharging very small droplets of water. GLOSSARY