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CHAPTER 2
Hazards and Threats
Tunnel systems, in their design, have a safe environmen- equipment breakdown, utility disruptions, minor criminal
tal order and are capable of withstanding the assaults nor- acts, and medical emergencies--because tunnel operators
mally presented by everyday use. For example, below-grade have years of experience in handling such issues. The expe-
tunnels are watertight, with proper water evacuation capa- riences of tunnel operators in handling these minor inci-
bility and safety systems to move air into and out of the dents have been distilled into handbooks and readily
tubes. The tunnel structure is designed and built to exist available procedural reference materials. Where possible,
within the soil or seabed that it occupies. Mined tunnels notations for additional reference material concerning
similarly coexist within their surface environment to pro- these minor hazards have been included in this report.
vide safe, smooth operation. Despite these and other safety The focus of this guidance is, therefore, a combination of
features, however, damage or disruption to a tunnel, its major hazards that are not likely and threats--principally acts
operations, and/or occupants can result from the impact of of terrorism--that might be realized in a tunnel environ-
hazards or threats. ment. Unlikely, extraordinary threats have been excluded.
The tables in this chapter consist of a list of major hazards These include highly unlikely acts of terrorism that seem irra-
and threats that may adversely impact the normal operation tional or ineffective in a tunnel context (such as a nuclear
of a transportation tunnel and associated infrastructure. The detonation or airborne threats).
transportation tunnel and associated infrastructure include The hazards and threats discussed in this report have
all electrical and mechanical operations within the tunnel been assembled individually. With this format, the reader
environment, such as ventilation and fire suppression. Haz- can first absorb the details of each potential scenario and
ards and threats to the tunnel environment also include actual then read the recommended actions to mitigate the hazard
or perceived physical hazards and threats affecting the users or threat.
of the transportation system. The remainder of Chapter 2 discusses (a) the major hazards
The primary criterion used for the analysis of safety haz- and threats that will adversely affect the normal operation
ards and security threats was the level of impact that a major of a transportation tunnel and its associated infrastructure,
hazard or threat would have on the tunnel system. All hazards (b) the damage potential of these hazards and threats, and
and threats considered in depth are capable of closing a tun- (c) possible hazard and threat scenarios.
nel for an extended period of time (i.e., lasting more than 25
hours). These hazards and threats encompass potential inci-
2.1 Major Hazards and Threats
dents that have not been routinely encountered or planned
for by a tunnel operator. Table 1 presents a range of major hazards and threats that
Because the standard literature discusses hazard issues, may adversely affect a tunnel and its associated features. The
threats make up the major portion of the events examined hazards and threats are expressed in terms of generic scenar-
in this report, particularly threats related to the introduc- ios with potential to damage the normal operation of a trans-
tion of a foreign item into the tunnel environment to dis- portation system, including specific tunnel components.
rupt the tunnel and its users. This analysis excludes One of the concerns, "Fire," appears under the "Threat"
completely the range of safety hazards that are routinely heading as arson and under the "Hazard" heading as unin-
observed and handled by a tunnel operator--such as tentional. This distinction is made because, although the
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Table 1. Major hazards and threats to transportation tunnels and associated features.
Vulnerable Tunnel Feature
Tunnel Construction and Engineering Feature Tunnel System Feature
Distribution Channel
Hazard or Threat
Immersed Tube
Bored or Mined
Utility Building
Control Center
Cut-and-Cover
Substation
Vent Shaft
Station
Portal
Hazard
Fire (Unintentional)
Structural Integrity Loss by Natural
Causes
Introduction of Hazardous Materials
Threat
Introduction of Small IEDs
Introduction of Medium-Sized IEDs
Introduction of Large IEDs
Introduction of Chemical Agents
Introduction of Biological Agents
Introduction of Radiological Agents
Cyber Attack
Maritime Incident
Fire (Arson)
Sabotage of MEC Systems
IEDs = improvised explosive devices.
MEC = mechanical, electrical, and communications.
effects of an intentional fire and an unintentional fire may be · Introduction of medium-sized IEDs: explosive materials
similar, the defenses to the two kinds of fire may differ. delivered either by vehicle (car) or by multiple persons act-
There are three major hazards and 10 major threats. The ing in concert to transport the payload.
major hazards are the following: · Introduction of large IEDs: explosive materials delivered
either by vehicle (truck) or by multiple persons acting in
· Fire (unintentional), concert to transport the payload.
· Structural integrity loss by natural causes, and · Introduction of chemical agents.
· Introduction of hazardous materials. · Introduction of biological agents.
· Introduction of radiological agents.
The major threats are the following: · Cyber attack: a virtual aggression against the command
and control systems of a tunnel system with the intent of
· Introduction of small improvised explosive devices (IEDs): disabling systems.
explosive materials delivered via one to five aggressors · Maritime incident: a waterborne incident affecting a tun-
transporting the payload. nel shell from above and any exposed sides. Adverse
