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6 impacts may be due to sunken ships, misguided anchors, source of power or method of communication between a or explosives. tunnel system and a utility terminus. Fire (arson): an intentionally set conflagration with the Control center: any facility designed, constructed, and intent of causing physical harm or damage to property. equipped with systems intended to monitor and control Sabotage of mechanical, electrical, and communications the tunnel environment and the movement of vehicle and (MEC) systems: the intentional impairment or destruction rail traffic over and through a tunnel section. of MEC systems necessary to the safe, efficient operation of Substation: any facility specifically designed to relay a tunnel system. power, water, or sewer connections between the tunnel and the central utility building. The substation is con- The right side of the table notes the affected vulnerable nected to the utility building and the tunnel via distribu- tunnel features, also referred to in this report as "assets." The tion channels. vulnerable tunnel features have been divided into two types: Utility building: Any facility specifically designed to pro- tunnel construction and engineering features and tunnel sys- vide power to the tunnel system. This facility is operated tem features. continuously to achieve its mission and is connected to Tunnel construction and engineering features include both substations and the tunnel through a distribution the type of tunnel facility constructed and the major channel. A utility building may also be designed to provide engineered features, which are typically immovable. There water or sewer removal from the tunnel. are six categories of tunnel construction and engineering features: 2.2 Damage Potential Immersed tube: employed to traverse a body of water. Tun- nel sections, usually 300 to 450 feet (91 to 137 meters) long, The damage potential of hazard and threat scenarios-- are placed into a pre-excavated trench. often a sequence of physical events (such as fire or flooding) Cut-and-cover: tunnel construction method involves and their secondary impacts (such as injuries, fatalities, or braced, trench-type excavation ("cut") construction of loss of function)--determines the key characteristics of structures and placement of fill materials over the finished countermeasures that can mitigate the impact of hazards and structures ("cover"). threats, if not prevent them. Table 2 presents the damage Bored or mined: bored tunnels are often excavated using potential of the hazards and threats listed in Table 1. mechanical equipment such as road headers or tunnel bor- Except for radiation, the types of damage listed in Table 2 ing machines (TBMs), while mined tunnels may be exca- and considered throughout this report are visible to emer- vated using manual or mechanical methods. gency responders and the tunnel operator. All types of dam- Vent shaft: any at-surface or above-grade air intake or age, including radiation, may be mitigated. Possible damage exhaust facility servicing a below-grade road, transit, or rail includes the following: section. Portal: any engineered entranceway or boat section to a Fire/smoke: any active conflagration or post conflagration below-grade road, transit, or rail section. condition of smoke and harmful vapors. Station: any facility in regular use by nonemployees of a Flooding: the condition of excessive water inflow to a tun- passenger rail or transit system. Unlike the other categories nel area exceeding the pumping capacity of the tunnel of construction and engineering features, this category is systems and causing a hazard or threat to people and applicable to passenger rail and transit only. property. Structural integrity loss: any decrease in the fitness of the Tunnel system features include the major components tunnel to carry passengers or freight that requires inspec- designed and installed to support the efficient operation and tion by the tunnel owner and major repair prior to its safe environment of a tunnel. Mechanical, electrical, ventila- reopening for beneficial use by the public. tion, and communication systems are the major sections Contamination: the condition of being unfit for nor- designed to support the tunnel system. These systems are mal habitation due to the presence of radiation, biologi- capable of update or replacement over time. The categories of cal agents, harmful chemicals, hazardous airborne tunnel system features are as follows: particles, or sewage sufficient to require professional remediation. Distribution channel: any conduit, sheath, piping, fiber Utility disruption: loss of power, air, steam, water, or com- optic, or metal line designed and installed to provide a munication service for more than 25 hours.