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purification. The absence of fresh air delivery into the injunctions alone cannot stop private vehicles and trucks
below-grade structure can detrimentally impact that facil- from attempting to transport them. Hazardous materials will
ity's ability to support life and safety. enter the tunnel systems in varying quantities, and many will
· Stations (passenger tunnels only). A passenger station exit the system without incident or release. Through driver
may be made partly or wholly unsafe by a structural error or unfortunate circumstance, hazardous materials may
integrity loss. Falling debris, unsettled steps and walkways, leak or be released into the tunnel. Many hazardous materials
and uneven road or rail surface contribute to an unsafe require specialized remediation that will close a road or tran-
environment. sit tunnel to allow processing. The related assets are as follows:
· Substation. A substation may be disturbed or made non-
functional by a loss of structural integrity. Machinery or · Tunnel system and structure. The introduction of haz-
piping may be made uneven, thereby interrupting the ardous materials into a tunnel system constitutes a hazard
designed flow of the station. Power brought in by hard wire to the safe use of the tunnel and requires immediate reme-
may be interrupted by the movement or decay of the struc- diation. When a material is identified as potential or actual
tures on which they are tethered. hazardous material, the area containing the hazard must be
· Control centers. Control centers lose functionality when taken out of service for remediation. This closure adversely
a loss of structural integrity occurs in a tunnel system. affects the use of the tunnel system and disrupts traffic
Sensors, cameras, alarms, radio signals, and detectors are flow. The tunnel as a system is adversely disrupted. The
normally hard wired inside a tunnel system and tethered structural integrity of the tunnel may also be damaged by
to a wall, shaft, plenum, or stairway system. The partial the introduction of certain hazardous materials, thereby
collapse of a support for one of these remote communica- requiring heavy repair under closed conditions.
tion systems would disable the unit and eliminate its use · Portals. Hazardous material introduction may have the
to a control center. same adverse impacts to a portal as to the tunnel structure.
· Distribution channels. Similar to the operation of a control Certain hazardous materials require remediation, and
and detection system, distribution channels would be inter- remediation may require full or partial closure of the road
rupted or impaired by the whole or partial loss of the struc- or rail line. Closures will affect flow through the portals.
· Stations (passenger tunnels only). The introduction of
tures that they monitor or are attached to. Buried utilities,
located within the footprint of the tunnel structure or in hazardous materials may constitute an immediate safety
nearby corridors, may be affected by the geotechnical alter- hazard and require the partial or full evacuation of the sta-
tion to commence remediation efforts. Any evacuation
ation subsequent to a whole or partial collapse. Utilities con-
would be an adverse impact.
nected by piping or hard wire may be severed or cracked.
The collapse may allow water to intrude on soft wire net-
works such as fiber optic to corrode connectors. Power util-
2.3.2 Threat Scenarios in Relation to Assets
ities may also experience water intrusion that may result in
surges, overloads, and possibility of electrocution. Introduction of Small IEDs
Explosives are materials capable of violent decomposition,
which often takes the form of extremely rapid oxidation (i.e.,
Introduction of Hazardous Materials
burning). Explosions are the result of sudden and violent release
A tunnel system may be threatened by the accidental dis- of gas during the decomposition of explosive substances.
charge of hazardous materials into the confined space of the Small IEDs are defined as explosive or incendiary produc-
tunnels or the stations. Hazardous materials can take a liquid, tion materials or devices small enough to be easily concealed.
solid, or gaseous form. Even minimal quantities of some mate- Compact or small devices are easily concealed among a per-
rials can cause serious injury to tunnel system users. Hazardous son or personal belongings and may only be detected by
materials can range from common industrial cleaners used by deliberate use of equipment, processes, or close observation.
tunnel workers to a canister of pepper spray set off by a com- The destructive pattern of any explosive device has the poten-
muter. In both circumstances, it is unlikely that the mainte- tial to damage every object within its blast radius. A small
nance worker or the commuter entered the tunnel system with conventional explosive has the capacity to kill or injure any-
the intent of discharging hazardous material into the air. Mate- one within its blast radius. The related assets are as follows:
rials may also include hazardous liquid, debris, or waste prod-
uct moved into the tunnel system by a vehicle, truck, or rail car. · Tunnel structures. A hand-carried IED will damage the
Public vehicular tunnel systems may forbid the transport portion of the tunnel located within the blast radius. The
of dangerous materials through below-grade areas, but these portion of the structure damaged may be relatively small
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or extensive. The hand-carried IED will cause the tempo- delivery. Vehicle-borne delivery systems are noticeable to
rary closure of the tunnel for evacuation and repair. defenders. The related assets are as follows:
· Portals. Similar to the tunnel structure, the portal may be
damaged if it is within the blast radius of the hand-carried · Tunnel structures. A vehicle-borne explosive will damage
IED. The portal will be closed temporarily for repair. a significant portion of the tunnel located within the blast
· Vent shafts. Similar to the tunnel structure, the vent shaft radius. The vehicle-borne explosive will cause a long-term
may be damaged if it is within the blast radius of the hand- closure of the tunnel for evacuation and repair. A well-
carried IED. The shaft or intake structure will be closed placed large explosive may cause the tunnel structure to
temporarily for repair. collapse and require rebuilding. A large explosive may also
· Stations (passenger tunnels only). A hand-carried IED set cause a mass casualty incident.
to detonate in a passenger station will likely cause more · Portals. Similar to the tunnel structure, the portal may be
damage to persons than to property. A device set to explode damaged or destroyed if it is within the blast radius of the
in a passenger station will have been intended to harm or vehicle-borne explosive.
frighten people. The relative space difference between a sta- · Vent shafts. Similar to the tunnel structure, the vent shaft
tion and a tunnel will allow a greater physical area to may be damaged or destroyed if it is within the blast radius
absorb the blast, thereby lessening the physical damage to of the vehicle-borne explosive. The shaft or intake struc-
the station. A mass casualty incident will likely lead to the ture may require reconstruction.
closure of the station for an extended period, but not · Stations (passenger tunnels only). A vehicle-borne explo-
permanently. sive set to detonate in a passenger station will cause signif-
· Substation. Similar to the tunnel structure, the system's icant damage to persons and property. A mass casualty
substation may be damaged if it is within the blast radius incident will likely lead to the closure of the station for an
of a hand-carried IED. The substation will be closed tem- extended period, if not permanently. Reconstruction of the
porarily for repair. station will need to occur.
· Control centers. Depending on the placement of an explo- · Substation. Similar to the tunnel structure, the substation
sive device, the blast may throw the facility off line or may be damaged or destroyed if it is within the blast radius
threaten the facility's ability to safely hold persons and of a vehicle-borne explosive. A substation will require
equipment. A control center located many miles from the reconstruction if the damage is significant.
scene of an explosion may be physically unaffected but still · Control centers. Depending on the placement of a vehicle-
see a loss in monitoring capacity to the affected area. A con- borne explosive, the blast may throw the facility off line or
trol center located at the site of an explosive blast may be threaten its ability to safely hold persons and equipment. A
directly affected, evacuated, and possibly destroyed. control center located many miles from the scene of an
· Distribution channels. A small blast will damage or explosion may be physically unaffected but still see a loss in
destroy wiring, piping, or vents located within the blast monitoring capacity to the affected area. A control center
zone. Loss of these distribution channels may force the clo- located at the site of an explosive blast may be directly
sure of the tunnel system for repair. affected, evacuated, or possibly destroyed.
· Utility terminus building. A building may be partially · Distribution channels. Any explosive blast will damage or
closed for repair as the result of the successful delivery of a destroy life safety and monitoring systems located within
small IED. Loss of a utility may have a cascading effect on the blast zone. Interconnected distribution channels will be
downstream systems, thereby debilitating service in the severed, thereby limiting or destroying their usefulness to
tunnel system. another part of the tunnel system not directly affected by
the blast. Systems will need to be reconstructed.
· Utility building. Utility lines and connectors may be dam-
Introduction of Medium-Sized and Large IEDs
aged or destroyed if they are within the blast zone. Loss of
Medium-sized and large explosives typically rely on a a utility will have a cascading effect on downstream sys-
mobile delivery system, such as a car, truck, or rocket, or are tems, debilitating service in the tunnel system and adjoin-
stealthily placed in a chosen area prior to detonation. The ing areas.
power of a medium-sized or large explosive is wholly
destructive to persons and property. In the confined atmo-
Introduction of Chemical Agents
sphere of a tunnel system, the force of a blast will be
absorbed by the components of the tunnel system, causing According to the Federal Emergency Management Agency
casualties and destruction. Large quantities of explosives (FEMA), as promulgated in Emergency Response to Terrorism
require efforts at interdiction prior to their placement or Job Aid (which is available online at http://www.usfa.dhs.
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gov/downloads/pdf/publications/ert-ja.pdf), there are five aggressor would be able to introduce the agent into the
classes of chemical agents, all of which produce incapacitation, ventilation system. This method may also dilute the con-
serious injury, or death: centration of the chemical agent. An affected vent shaft
would need to be quarantined, decontaminated, and likely
· Nerve agents damage the nervous system of a person and decommissioned due to damage, public fear, or use as
are extremely effective in small doses. Exposure is achieved evidence in a criminal investigation.
through the respiratory tract and the skin. Nerve agents are · Stations (passenger tunnels only). Stations would be the
deadly and fast acting, and symptoms include difficulty likely scene of both introduction of the chemical agent and
breathing, seizures, headaches, and salivation. All nerve the mass casualty. The means to introduce a chemical agent
agents require handling and treatment with extreme care. into a station is relatively unsophisticated. An aggressor
Well-known nerve agents include sarin (GB), soman (GD), could enter the station with a vial, bag, or other carrier and
tabun (GA), and V agent (VX). open it on the platform, thereby exposing the tunnel users
· Blister agents, also known as vesicants, include phosgene to the chemical agent. The station would be designated as
and mustard gas. Vesicants are absorbed through the eyes, out of service; it would become a mass casualty treatment
skin, and lungs. They attack tissue and cause severe blister- area, crime scene, and site of an infected structure requiring
ing. They may lead to seizures, blindness, and pulmonary decontamination. Upon decontamination and release as a
edema. Blister agents are treatable and were first intro- crime scene, partial or full reconstruction may be necessary.
duced during World War I.
· Blood agents quickly diminish the ability of the body to
Introduction of Biological Agents
absorb oxygen into the bloodstream, thereby depriving the
organs of oxygen. Common types of blood agents include The introduction of a harmful biological agent into a tun-
hydrogen cyanide and arsine, both of which are used in nel transportation system is a threat of high damage potential
industrial applications. Blood agents enter the body and low probability. There is little historical data on the use of
through the skin or the respiratory tract and provoke biological agents in the United States as a threat against tun-
cherry red lip color convulsions, nausea, and respiratory nel transportation systems.
arrest. Affliction by a blood agent is treatable. Biological agents are weaponized versions of organisms that
· Choking agents interfere with the breathing process and, occur in the natural environment. Bacteria, viruses, and toxins
if left untreated, may induce asphyxiation. Choking agents can be manipulated to cause widespread contagion and infec-
include common compounds such as chlorine, ammonia, tion among a targeted population. Biological agents can be
hydrogen chloride, and phosphorous. Common symptoms released into the air of a tunnel system and provoke either an
include coughing; shortness of breath; and a burning sen- immediate or delayed response from the affected individuals.
sation in the eyes, nose, and throat. There are no known Biological agents are very difficult to manufacture, handle,
antidotes to choking agents, but successful medical treat- and deliver. Their effectiveness is impacted by wind, moisture,
ment is available. and air removal systems. Well-known biological agents
· Irritant agents are agents designed to temporarily inca- include botulism, smallpox, and anthrax. Symptoms of a
pacitate a person. They generally do not have long-term biological agent vary, but may include increasing fatigue or
effects or induce death. Common irritants include pepper flu-like symptoms. Victims may suffer localized paralysis,
spray, mace, and tear gas, all of which will induce tearing swelling, rashes, or fever. Treatment is possible for many, but
eyes, coughing, and throat irritation. These effects are tem- not all, biological agents.
porary and treatable. Introduction of a biological agent into a transportation
tunnel would likely cause a delayed medical treatment situa-
The agents' means of affliction and effects are outlined in tion. Travelers would begin seeking medical treatment hours
Emergency Response to Terrorism Job Aid and in the succinct or days after the exposure. Damage to the tunnel infrastruc-
Department of Health and Human Services's Terrorism and ture would be contained to directly affected equipment and
Other Public Health Emergencies: A Reference Guide for Media areas, all of which would require complete decontamination.
(which is available online at http://www.hhs.gov/emergency/ During the period of decontamination, all equipment must
mediaguide/PDF/00.pdf). be quarantined and replaced.
The related assets are as follows: The related assets are as follows:
· Vent shafts. Similar to a biological agent, air intake facili- · Vent shafts. Air intake facilities may be the point of intro-
ties may be the point of introduction for a chemical agent. duction for a biological agent. By introducing a biological
By introducing a chemical agent into a vent shaft, an agent into the air shaft, an aggressor would be able to
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introduce the agent into the ventilation system. This successfully executed on an occupied passenger station
method may also dilute the concentration of the biologi- would be a mass casualty event and would lead to closure
cal agent. For a persistent agent, an affected vent shaft of the station for an extended period for abatement and
would need to be quarantined, decontaminated, and likely reconstruction. Severe contamination or severe damage
decommissioned due to damage, public fear, or use as evi- from the explosive delivery could result in abandonment.
dence in a criminal investigation. The impact to the system could be drastic. The station
· Stations (passenger tunnels only). Stations would be the might not be used as a transit way, entry point, or egress
likely scene of both the introduction of the biological agent point for a considerable amount of time.
and the mass casualty incident. The means to introduce an
agent into a station is relatively unsophisticated. An aggres- A NOTE ABOUT BIOLOGICAL, CHEMICAL, AND RADIOLOGICAL
sor could enter the station with a vial, bag, or other carrier ATTACKS: Biological, chemical, and radiological attacks may
and open it on the platform, thereby exposing the tunnel not be readily apparent at the site of introduction within the
users to the biological agent. Once identified as contami- tunnel system. The introduction of these agents may be dis-
nated, the station would be designated out of service; cernable only later, when victims seek medical treatment and
depending on the speed of onset of symptoms, it could the origin of their problems are traced to the use of a com-
become a mass casualty treatment area, crime scene, and mon tunnel. The effect of an attack would remain consistent
infected structure site requiring decontamination. Upon with the descriptions provided, yet the discovery of the attack
decontamination and release as a crime scene, partial or would be different than other primary hazards and threats
full reconstruction may be necessary. described. An extended discussion of chemical, biological,
and radiological agents and transportation system response
options is presented in NCHRP Report 525, Vol. 10: A Guide
Introduction of Radiological Agents
to Transportation's Role in Public Health Disasters.
A radiological attack would have a destructive impact on a
tunnel transportation system, nearby environments, and the
Cyber Attack
user community. Radiological contamination disrupts the
cell structure of a victim, causing sickness and death. A vic- Closed-circuit television (CCTV), air quality testing, and
tim may experience delayed symptoms and may mistake the traffic algorithms are commonplace to ensure the smooth,
cause of the symptoms for a flu-like illness. Radiological safe use of a tunnel. The deployment of a concerted effort to
material is difficult to manufacture, handle, and deliver. It can deny the use of digital technology to the tunnel operator is a
be as deadly to the attacker as to the victims. threat. The venue to attack the computer network of a tunnel
Facilities and equipment would both be placed out of ser- operator is remote and virtual. The introduction of a virus
vice and possibly abandoned. Extensive decontamination into a remote network is commonplace in today's environ-
efforts would be required to restore them to use. The related ment. Minimal technology is needed to launch a cyber attack.
assets are as follows: The related asset is as follows:
· Tunnel structure. A successful radiological attack would · Control centers. Technology is crucial to the monitoring
adversely affect the tunnel structure. Damage may be and safe operation of a tunnel. Control centers remotely
immediate (resulting from the explosive used in the deliv- view, test, and monitor a tunnel environment using digital
ery) or long term (resulting from the contamination of the transmission and other technology.
structure with radiological material). Immediate blast
damage may affect the integrity of the structure, including
Maritime Incident
supports, braces, and engineered works that withstand
water intrusion. The long-term effects of radiological con- The occurrence of a maritime incident, specifically a ship
tamination might require lengthy remediation, including sinking over a subaqueous tunnel or dropping a depth charge
replacement of sections or construction of alternative on the tunnel, is a threat to the safe operation of a water tun-
routes. These scenarios would require a long-term closure nel. Subaqueous tunnels located under navigable waterways
of that area of the system or abandonment. are potentially at risk. A maritime incident may result from a
· Portal. The portal would be similarly impacted as the tun- navigational error or mechanical defect aboard the ship. A
nel structure. Depending on the placement of the explosive maritime incident may also result from an intentional act by
delivery device, the portal may become unsteady and con- an aggressor.
taminated. Damage may require reconstruction, long-term An intentional maritime incident may be part of a more
closure, or abandonment. The effect of a radiological threat elaborate attack designed to simultaneously inflict damage on
