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4
Health and Safety Underground
“It is important to note the significance of human behavior on tunnel safety.
The final outcome of some incidents may depend more on the quick and
right reaction of individuals than on the technical safety level in the tun-
nel.” (OECD, 2006, p. 15)
We design, build, and operate all manner of underground infrastructure,
but doing so must occur with due consideration of the abilities and behaviors of
the underground infrastructure operators and occupants to minimize risks and
increase efficiencies (see Box 2.1). George Bugliarello described the need to bal-
ance the human and mechanical elements of urban living to create modern, envi-
ronmentally sustainable, and emotionally satisfying environments (Bugliarello,
2001). Safety is also a necessary part of this vision. Underground infrastructure
systems are complex and have elements similar to what Bugliarello described
as biosoma systems—systems that include biological (individuals that create,
manage, or use the system), social (organizational aspects), and machine compo-
nents (the engineered artifacts). Bugliarello acknowledged the interfaces of these
elements in transportation systems to be points of vulnerability that ultimately
impact system resilience (Bugliarello, 2009). This committee contends the same
could be said more generally as humans move into the underground where the
infrastructure will be critical to support this movement.
Taking the idea further, it can be said that urban sustainability is as much
dependent upon human activities, ideas, and behaviors as it is upon the robustness
and resilience of physical infrastructure. Resilience of a community is tied to the
resilience of physical infrastructure (e.g., Miles, 2011), but an understanding by
the people who design, operate, use, or benefit from underground infrastructure
105
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106 UNDERGROUND ENGINEERING FOR SUSTAINABLE URBAN DEVELOPMENT
of the role each structure and system element serves in the proper functioning of
the urban system is important to address the robustness, resilience, and sustain-
ability of the urban system.
Real hazards and risk to humans in the underground exist, and engineers
have been largely successful in addressing many of them. Earlier chapters of
this report looked at how urban utilities and systems are highly integrated and
therefore interdependent. This chapter addresses human-technical system rela-
tionships, human response to hazards faced in the underground, and the hazards
and risks related to human use of underground space. This chapter recognizes
the people in the underground and considers the engineering necessary to keep
them healthy while also contributing to sustainability. The presence or absence
of naturally occurring phenomena in the underground may pose risk to humans.
Gases, radiation, temperature, water, and the lack of oxygen are among inherent
hazards to human underground occupation. Other hazards to people or infrastruc-
ture may result from human activity that creates, adds to, or intensifies naturally
occurring risks. These include risks associated with fire and smoke, hazardous
materials, intentional or accidental explosions, structural failure, human failure,
and extreme events.
It is important to fully understand the hazards and risks because a very key
part of long-term success (i.e., sustainability) of the underground is the ability
to regulate underground construction and activities to ensure minimum safety.
Although various standards exist that govern, principally, fire safety for under-
ground transportation and building and industrial facilities, there is a need for a
more comprehensive approach to safety against all hazards for all types of under-
ground facilities. The remainder of this chapter explores this need.
HUMAN FACTOR ENGINEERING
To create a functioning, sustainable, urban system that effectively links its
social, technical, and governing elements, the relationships between technolo-
gies, the people that construct, operate, and use those technologies, and the social
structures that govern them must be understood. In the manufacturing realm, this
area of research is referred to by several names including human factors, human
engineering, engineering psychology, and ergonomics. Licht and others (1989)
analyzed numerous definitions for terms and areas of study related to or syn-
onymous with “human factors” research and found that most definitions implied
a multidisciplinary approach including concepts related to behavioral science;
human performance capacity; manpower, personnel, and training; and biology,
physiology, and medicine.1 Information obtained through the study of human
factors can be applied to the “design of tools, machines, systems, tasks, jobs,
1 Biology, physiology, and medicine were more common in definitions associated with ergonomics
(Licht et al., 1989).
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HEALTH AND SAFETY UNDERGROUND 107
and environments for safe, comfortable, and effective human use” (Chapanis,
1991, p. 1) so that we may “optimize the relationship between technology and the
human” (Kantowitz and Sorkin, 1983; Licht et al., 1989, p. 27). The application
of Complex Adaptive Systems of Systems engineering as discussed in Chapter 2
would necessarily consider the relationships between humans and underground
infrastructure.
The military has long recognized the importance of integrating human and
technological system elements to make operations as effective, efficient, safe,
and sustainable as possible, and has promulgated these concepts through direc-
tives and guidance. For example, a Department of Defense (DOD) directive from
1988 required consideration of manpower, personnel, training, and safety in the
defense system acquisition process for the purpose of improving “all aspects
of the human-machine interface” (DOD, 1988: p. 1).2 In 2007, the National
Research Council published a report at the request of the Army Research Labo-
ratory, the Air Force Research Laboratory, and DOD to address approaches for
creating “an integrated, multidisciplinary, generalizable, human-system design
methodology” (NRC, 2007, p. 2). That report outlines principles considered criti-
cal to human-system development and evolution including those associated with
the need for stakeholder consensus on desired outcomes, regular reassessment of
plans based on lessons learned, and risk management.
Many applications of human factors engineering are related to human inter-
action with a single manufactured item or technology. Underground systems
as part of total urban environments are more complex, and the need to under-
stand, design, regulate, and operate for human-technology relationships becomes
amplified. The impact of failure of key infrastructural components—including
human—and or systems can be devastating to sustainable functioning of the
urban environment (see discussion of cascading failures in Chapter 2). Human
behavior is not always predictable in the face of adverse and extreme events,
and regardless of how resilient to hazards underground infrastructure and safety
systems may be, infrastructure and system failure could have significant nega-
tive consequences. All forms of underground engineering not only must consider
what training and safety guidelines are necessary for the smooth functioning of
infrastructure in the best of circumstances, but also must anticipate the behavior
of underground occupants during both normal and worst-case operation sce-
narios. Design must be holistic and create an integrated environment that allows
people to almost intuitively understand how to remain safe should adverse con-
ditions arise. Sustainability of the urban setting is dependent on optimization of
human-technical relationships in ways that provide at least minimum safety while
remaining consistent with long-term societal visions.
Industry also addresses safety in underground infrastructure. The International
Tunneling Association (ITA), for example, established the Committee on
2 This directive has since been replaced by other directives that also emphasize human factors.
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108 UNDERGROUND ENGINEERING FOR SUSTAINABLE URBAN DEVELOPMENT
Operations Safety of Underground Facilities (COSUF)3 to address operational
concerns of safety and security in underground structures. COSUF has developed
risk assessment guidelines (Molag and Trijssenaar-Buhre, 2006) and, with an
ITA working group on health and safety,4 focused on increasing safety practices
during construction. The European Construction Technology Platform (ECTP)
acknowledges that safety and security must be designed into every element of
infrastructure, including the interfaces between every element, with consideration
of the entire life cycle of the infrastructure (ECTP, 2005).
MANAGING SAFETY THROUGH REGULATION
It may be expected that safety in underground infrastructure will be equal
to that of surface infrastructure, and if not, then the expectation may be that one
is fully informed of potential risks. However, although engineers have been suc-
cessful in reducing many types of risk associated with underground space use,
risk in underground infrastructure has not received the same level of regulatory
scrutiny as risk associated with surface infrastructure, and the levels of certain
risks may not be well understood. Existing codes tend to be prescriptive in
nature—prescribing specific procedures or materials—but underground space
poses different safety challenges that codes intended for surface space were
not designed to address. For example, most people know that simply leaving a
building that is on fire is adequate to reach safety. Exiting a tall building during
an emergency, for example, usually requires its occupants to climb down several
flights of stairs rather than use elevators or escalators. However, leaving an under-
ground structure on fire may only move occupants to a different underground
space also contaminated by smoke, and occupants may have to exit up several
flights of stairs—a physically challenging task for some. Hazards associated
with elevators and escalators are partially addressed by the American Society
of Mechanical Engineering Safety Code for Elevators and Escalators (ASME,
2010a) that covers design, construction, installation, operation, maintenance,
alteration, inspection, and testing of elevators and escalators. Guidelines also
provide information on how Department of Justice requirements related to the
Americans with Disabilities Act will be met by the performance of elevators or
escalators (ASME, 2010b).
Safety sometimes needs to be created operationally rather than through
technical solutions (e.g., no hazardous materials unless appropriate sprinkler or
other systems are in place). Safety codes are most often written in response to
lessons learned from incidents or litigation rather than in response to research.
A responsible risk management strategy includes identifying and understanding
3 Seehttp://cosuf.ita-aites.org/ (accessed June 15, 2011).
4 Forexample, the Health and Safety in Works working group of the International Tunneling As-
sociation has released multiple publications related to safe working practices (see ITA-AITES, 2011).
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HEALTH AND SAFETY UNDERGROUND 109
hazards and risks and applying appropriate mitigation strategies. Once recog-
nized, underground risks may be avoided, transferred, or reduced to tolerable
levels. In some cases the cost for mitigation may be substantial or prohibitive
either in terms of capital costs for construction or in operational costs. This could
mean a project is never started, or that minimum systems put in place may not be
optimally maintained due to the costs. Assuming that avoiding or transferring risk
is not feasible, reducing risk through appropriate safety regulations and education
may be the best approach. Safety standards for surface infrastructure have been
developed at the federal, state, and local levels and refined over generations to
cover a broad array of activities. Such standards serve a key role in preventing
or mitigating risks.
Current federal-level safety regulations for underground infrastructure are
limited, do not apply to everyday usage of most types of facilities, and mostly
are intended to regulate construction safety through the Occupational Safety
Hazard Administration (OSHA). They include the OSHA regulations related
to underground construction (29 CFR 1926.800)5 that apply to construction of
underground tunnels, shafts, chambers, passageways, and cut-and-cover excava-
tions connected to underground construction to reduce hazards associated with
“reduced natural ventilation and light, difficult and limited access and egress,
exposure to air contaminants, fire, flooding, and explosion” (OSHA, 2003). The
regulations define a tunnel as a subsurface excavation, “the longer axis of which
makes an angle not greater than 20 degrees to horizontal.” Although applicable
to many types of underground infrastructure, the regulations are only intended to
protect underground construction workers during construction and do not address
safety issues once the infrastructure is in operation.
Each state in the United States has adopted fire and life safety codes to ensure
safety in structures, but the codes do not fully address underground structures.
Most states (45) have adopted the International Code Council (ICC)6 building,
fire, plumbing, and mechanical codes. The ICC codes refer to three National Fire
Protection Association (NFPA) standards—NFPA 130 (NFPA, 2010a), NFPA 520
(NFPA, 2010b), and NFPA 502 (NFPA, 2011)—that address underground fire and
life safety and that provide safety guidelines for road and passenger rail tunnels
and use of space created by underground excavation. Two of these standards have
been applicable to underground transportation facilities for decades. However,
the applicable NFPA standards cannot adequately address underground fire and
life safety for all underground space uses, and they will likely break down when
combining different types of occupancy in one underground space. Additionally,
the standards have limited legal authority unless adopted by states or local
jurisdictions.
5 See http://www.osha.gov/pls/oshaweb/owadisp.show_document?p_id=10790&p_table=STANDARDS
(accessed April 4, 2011).
6 See http://www.iccsafe.org/Pages/default.aspx (accessed June 9, 2011).
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110 UNDERGROUND ENGINEERING FOR SUSTAINABLE URBAN DEVELOPMENT
The inadequacy of safety standards results from their being developed with-
out due consideration of the growth of all types and large scales of underground
use. Innovation in underground design and construction may be bound by pre-
scriptive (and potentially ineffective) codes when performance-based mecha-
nisms that ensure designs will perform as intended are really needed.7 Further, as
is stressed throughout this report, underground infrastructure is only one element
of the total urban system that is increasingly interconnected and interdependent.
Decisions regarding safety of one infrastructural element need to be based on the
effects of that decision on the overall system. Demand for underground space
use is growing, and without carefully considered, research-based, national-level
guidelines or effective safety standards that account for the underground as part
of the larger integrated urban system, local jurisdictions are left to establish their
own safety standards that may not be fully informed if appropriate resources and
capacities are not available.
HAZARDS TO HUMAN HEALTH
The next sections discuss hazards to human health associated with occupy-
ing the underground, focusing on lack of adequate ventilation, smoke from fire,
and hazardous materials. Some hazards and risks can be prevented operationally,
others can be addressed through engineering solutions directly into infrastructure
design, and others can be controlled by systems. Careful analysis of underground
emergency scenarios for all hazards and risks—including those emerging as a
result of changes in technologies or use—could ensure that underground emer-
gency incidents do not escalate beyond the possibility of control or cause prevent-
able damage. For example, the current trend toward more electric vehicles could
be seen to reduce the risk of fires in tunnels, but the batteries in electric vehicles
present their own set of risks. Future fleets of vehicles powered by hydrogen or
natural gas present still different concerns.
Redundancy in fire and life safety systems is a key to controlling incidents.
For example, because underground smoke management is critical, it is essential
to ensure that the minimum ventilation scenarios to control smoke from a fire
are operational if any portion of emergency ventilation fails. Without this level
of redundancy in essential life safety systems, a simple mechanical failure could
jeopardize the underground occupants, contents, and physical structures.
Ventilation, Smoke, and Fire Control
Underground ventilation engineering entails providing breathable air to
people underground and removing hazardous gases (e.g., excess carbon dioxide,
7 Asia has more performance-based codes because contracting there is design-build rather than
design-bid-build, which is more common in the United States.
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HEALTH AND SAFETY UNDERGROUND 111
exhaust, fumes) from occupied space. Simply moving air from the surface to the
underground may not be adequate, because the air must contain enough oxygen
for the volume of people to be supplied and be free of contaminants. Hazardous
gases can be removed by cleaning the underground air or by safely (to those
underground and at the surface) routing contaminated air to the surface. NFPA
and ICC standards address many of these issues, but not explicitly for under-
ground spaces created for human use. Risks may be inadequately quantified.
One of the greatest hazards to human health and safety in the underground
is smoke from fire (ITA, 1998). It is well within current technical knowledge
and life safety system capacity to manage smoke in nearly all types of surface
structures. However, managing smoke in a complex underground structure—one
that can span multiple underground levels over several city blocks, be occu-
pied by thousands of people at any given time, and has many uses (e.g., retail,
office space, health care, residential) and therefore many potential hazards and
risks—may challenge the most sophisticated ventilation system designs. These
underground multi-use areas can be far more complex and difficult to ventilate
than, for example, some roadway tunnels that can be modeled as simple tubes of
air with, although long, relatively small cross-sections.
There are important strategic distinctions in the management of smoke in
high-rise buildings versus large underground structures. For example, a 40-story
high rise that occupies a full city block (creating the equivalent of 40 city blocks
of floor space in a vertical alignment) is typically designed to control ventilation,
fire sprinklers, alarms, and exiting systems immediately for up to four floors of
the building where occupants are most at risk. Smoke management is typically
limited to stairwell and elevator shaft pressurization that require relatively small
fans. Occupants on other floors are protected by the structure’s intervening floors
for a short time until they can safely evacuate.
An underground structure of comparable size (the equivalent of 40 city
blocks of floor space) potentially can occupy a broader lateral space over fewer
levels, increasing the lateral exposure to fire and smoke that spreads throughout
the horizontal space. Smoke management in such a large-scale area—with few,
if any of the control tools available in buildings (e.g., windows to the outside)—
requires comparatively more complex design and more powerful ventilation sys-
tems, larger sprinkler systems, and carefully designed fire detection, alarm, and
exiting systems to protect occupants. Specialized emergency alarm information
need to be designed to notify people of the need to evacuate. High rise building
systems need only address one floor at a time. Underground systems necessarily
accommodate the equivalent of 20 or more floors simultaneously.
Preventing fire and inhibiting fire growth are possible through management
strategies including non-combustible construction, automatic fire suppression,
precise fire detection, compartmentalizing, control of hazardous materials,
heightened security, and careful occupancy restrictions (e.g., to prevent proximate
hazards such as factory work adjacent to hospitals). Underground structures may
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112 UNDERGROUND ENGINEERING FOR SUSTAINABLE URBAN DEVELOPMENT
have some advantages in terms of fire and life safety as compared to surface
structures. Underground structures with smaller enclosed spaces may permit
utilization of a fine water mist or gaseous systems to control fire and smoke,
thereby reducing the demand for water and drainage which can create other
problems in the underground. Simply ensuring that the occupants recognize the
hazard of fire in the underground may ensure that all occupants take fewer risks
associated with fire.
Hazardous Materials
Hazardous materials used in or created by manufacturing, processing, and
shipping pose special risks in the underground for reasons similar to those for
smoke and fire: the physical separations and ventilation systems that provide
adequate safety aboveground may not be adequate below grade. On the surface,
for example, a machine shop that employs cutting torches may be permitted
to operate in a building next to a residential structure provided that a firebreak
such as an open air gap exists between the walls of the two structures. A suf-
ficient air gap ensures that a fire in the machine shop does not readily spread to
adjoining structures, and allows easy air exchange to the outside so that gases
used in cutting processes do not displace oxygen and create an oxygen-deficient
atmosphere. On the other hand, engineering and operational measures may be
needed to ensure safety in underground structures. Proper firewalls, ventilation,
and procedures may be necessary for safe cutting in the underground. Similarly,
underground spillage of hazardous liquids may pose long-lasting health risks
if they migrate via underground ventilation and drainage systems or penetrate
adjoining soils and porous rocks to contaminate other spaces or water supplies.
SECURITY FROM VIOLENCE
Underground infrastructure is often designed to make underground facili-
ties attractive and easier for the public to access and use. Even underground
public utilities, although not designed for access by the general public, need to
be designed to accommodate access by workers and equipment. Infrastructure
design often includes security elements to prevent crime and vandalism or to pro-
tect against fire or similar emergencies. Unfortunately, design elements that allow
easy access to the underground by ordinary public citizens also allow access to
those with dangerous or destructive intent. It is impossible to foil all attempts
of violence against people or infrastructure (Jenkins and Gersten, 2001). Even
so, ridership trends of underground metros in large U.S. cities have risen in the
past 10 years (e.g., WMATA and Cambridge Systematics, Inc., 2009; DiNapoli
and Bleiwas, 2010), indicating that need and convenience outweigh immediate
concerns over personal safety for at least some percentage of the population. Few
studies have documented underground use patterns following terrorist events, but
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HEALTH AND SAFETY UNDERGROUND 113
studies of public transit ridership in the aftermath of the 2005 London bombings,
the 2004 Madrid bombings, and the 1995 Sarin gas attacks in Japan revealed that
behavior is influenced by cultural beliefs, characteristics of the attack, factors
associated with the transportation system itself, and social perceptions of risk
(von Winterfeldt and Prager, 2010). For example, London underground and bus
(also targeted in the attack) ridership dropped but slowly recovered after the inci-
dent there, but ridership in Japan did not seem to change (Prager et al., 2010b).
Security and resilience to violence in an urban community can be enhanced
through a variety of planning, design, and operational functions that reduce the
frequency or severity of hazardous events. This section first discusses the safety
of individuals from personal violence and then discusses violence against larger
numbers of people and infrastructure itself.
Safety from Crime
A sense of personal safety—the freedom to function in a city with a low
expectation of violent attacks against one’s person—is important for the smooth
functioning of society. The physical design of and the number of people pres-
ent in an occupied space contribute to safety of individuals and the sense of
personal safety. Certain types of underground structures, for example pedestrian
underpasses, may have a poor reputation with respect to safety, perhaps due to
poor lighting or limited occupation, as compared to metro systems where higher
levels of security are in place to manage passenger organization (for example,
through the use of shorter trains and platform use at night to increase the number
of passengers in occupied areas). Mixed underground use offers different sorts
of problems. How is the security, for example, of a retail operation located in
a public transportation concourse assured when the retail space is closed for
business at night but when public transportation is still in use? How is public
access to transportation assured if an underground shopping area is closed for
the day? Engineering solutions may come in the form of enhanced monitoring
(see Chapter 6).
Attacks against Infrastructure and Urban Populations
The underground has long been and still is suggested or used for either con-
tainment or security. For example, the underground is used to protect the security
of a nation’s leadership (McCamley, 1998; Barrie, 2000). With the advent of
weapons of mass destruction, a great deal of engineering work was done in the
1950s and 1960s on underground military and defense facilities in the United
States that served to advance technologies related to the environment, security,
and fire protection in underground facilities. Examples include the Cheyenne
Mountain alternate command facility deep in a granite mountain and the bunker
at Greenbrier in West Virginia for the continuity of government in the event of
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114 UNDERGROUND ENGINEERING FOR SUSTAINABLE URBAN DEVELOPMENT
an attack. Additionally, there is continued interest worldwide in placing nuclear
power plants and their waste underground to increase isolation of radioactive
materials as well as to increase security of the facilities (e.g., Myers and Elkins,
2009). The feasibility of long-term storage and safety continues to be an active
field of investigation. In recognition of the security offered by the subsurface, the
Svalbard Global Seed Vault in Norway was constructed in a mountain to protect
global crop diversity in the event of climate- or war-related regional or global
catastrophe (Fowler, 2008).
The September 11, 2001, (9/11) terrorist attacks on the United States, how-
ever, fundamentally changed the way safety and security are addressed in this
country, including the design and operation of underground structures. Prior to
9/11, vandalism and criminal activity were the main concerns for underground
security. Terrorist threats against people and infrastructure were considered
anomalies. Underground infrastructure, especially mass transit systems, is now
recognized as a vulnerable target by those individual wanting to do large amounts
of damage to infrastructure or to inflict harm on large numbers of people. The
effects of explosions, fire, gases, and other airborne toxins and health hazards can
be more concentrated and deleterious in confined underground structures. Acts
of terrorism have occurred in several underground locations with serious conse-
quences, for example, the 1995 attack with the nerve gas, Sarin, in Tokyo, Japan
(Tu, 1999), the 2005 bombings in London, England (HC, 2006), and the 2010
bombings in Moscow, Russia (Rogoza and Zochowski, 2010). All of these events
were perpetrated using devices carried by hand into underground infrastructure.
Approximately 87 percent of terrorist attacks around the world in 2003 were
perpetrated through bombings (U.S. Department of State, 2004), which may be
delivered as vehicle-borne improvised explosive devices, devices employed as
booby traps, remotely detonated devices, or devices delivered by human bomb-
ers. There also is a conceivable threat of targeted ground-penetrating explosive
devices delivered by missiles. However, underground installations have been rec-
ognized as providing the “most effective physical protection available” and can
be designed so that critical infrastructure elements are protected against physical
attack and hardened against electronic attack (Linger et al., 2002). Underground
placement of facilities makes them harder to damage from the outside (i.e., from
the surface) and limits points of entry. Linger and others (2002) describe the
cost of that protection as “competitive” with aboveground structures hardened to
similar levels. Unfortunately, classification of military technologies has resulted
in a lack of standards or practices in civilian infrastructure (Gui and Chien, 2006).
Recognizing the need to address such hazards, multiple organizations have
initiated research related to many aspects of underground security and safety. The
American Association of State Highway and Transportation Officials (AASHTO)
Transportation Security Task Force sponsored the preparation of a guide to assist
transportation professionals as they identify critical highway assets and take
action to reduce their vulnerability (SAIC, 2002). The Transportation Research
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HEALTH AND SAFETY UNDERGROUND 115
Board of the National Research Council has released many reports related to
transportation safety and security, including many related to underground trans-
portation.8 These reports provide guidelines and recommendations on topics such
as permanent enhancements to underground infrastructures that will improve
security as well as the usable life of the underground structure and support sys-
tems (TRB, 2006). Similarly, the Federal Highway Administration and AASHTO
jointly sponsored a panel to develop “strategies and practices for deterring, dis-
rupting, and mitigating potential attacks,” recommending that interagency and
stakeholder coordination occur so that security assessment methodologies and
solutions are consistent with needs of all involved and that federal- and state-level
legal responsibilities are clarified (BRPBTS, 2003). From a technical point of
view, the panel recommended that critical bridges and tunnels be identified and
prioritized, and funds allocated to cover security of those structures. The panel
further recommended that security should be an engineered element of design and
that appropriate research and development should inform technical standards for
structures in consideration of security threats.
Security, like safety, is enhanced by collaborative systems thinking among all
stakeholders throughout the life cycle of the infrastructure. Interaction between
urban planners and underground engineers during development and operation
can focus on how underground infrastructure can improve or impede protection
of critical facilities and their occupants. Security issues and needs constantly
change as technologies change, known hazards are successfully addressed, or
new hazards evolve. Sustainability requires applying innovative and compre-
hensive technologies, and, as often described in the security arena, technologies
must include the concepts of prevention, deterrence, detection, and delay (e.g.,
Rowshan et al., 2005), as well as the concepts associated with response, recovery,
and evaluation of lessons learned from incidents or “near misses” that do occur.
Massive loss of life and grave structural, economic, and even political dam-
age may result if security threats are not appropriately assessed and addressed.
Ensuring the safety of people and physical assets and minimizing disruption of
the physical, social, and economic infrastructures of the total urban system must
be considered. However, each underground system element is unique and requires
specific measures to mitigate a range of anticipated threats. Passive hardening
is, in reality, the last line of defense in providing a safe and secure facility, and
passive structural hardening techniques applied to reduce vulnerability will not
necessarily increase sustainability.
Introduction of human factor engineering to prevent panic and errant behav-
ior and to guide threat recognition, decision making, and action under stress are
called for. New materials and their behaviors for this application must be consid-
8 See http://onlinepubs.trb.org/Onlinepubs/dva/CRP-SecurityResearch.pdf (accessed June 15, 2011)
for a status report of cooperative research programs related to security, emergency management, and
infrastructure protection.
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116 UNDERGROUND ENGINEERING FOR SUSTAINABLE URBAN DEVELOPMENT
ered (e.g., to prevent injury from fragments and flying debris and the develop-
ment of airborne toxins from chemical changes due to heat and fire). In addition,
the risk assessments need to include aspects of evacuation, rescue, and recovery
to minimize impacts and assist in post-incident activities.
INTERNATIONAL UNDERGROUND TUNNEL SAFETY CODES
International safety codes and guidelines applicable to underground infra-
structure are not enforceable in the United States, but comparison to U.S. codes
can be helpful to reveal inadequacies in practice and guide future practice in
the United States. The U.S. Federal Highway Administration (FHWA) sought
to learn what underground systems, equipment, and procedures were employed
internationally to improve underground safety, operations, and response (Ernst et
al., 2006) and ultimately made recommendations for implementation strategies
in nine areas in which U.S. standards and regulations could be improved (see
Box 4.1).
The most comprehensive international safety information related to under-
ground infrastructure deals with road tunnel construction and operation, and the
United Nations Economic Commission for Europe (UNECE) has found that there
are fewer traffic accidents in long tunnels than on similar length stretches on the
open road, which is attributable to protection from the elements and consistent
lighting (UNECE, 2001). However, incidents that do occur in tunnels are likely to
have greater impact in terms of harm to people and infrastructure. UNECE states
that improving motorist behaviors, their vehicles, tunnel operator efficiency,
and the infrastructure itself are ways to decrease the number of tunnel incidents.
UNECE findings are acknowledged in a directive from the European Union on
minimum safety standards for tunnels in the trans-European road network (Euro-
pean Parliament and Council, 2004).9 The World Road Association (PIARC)10 is
another international forum that considers an array of road and transport issues
from the point of view of sustainability. Its standing technical committee is tasked
with exploring management and improvement of tunnel safety, influencing user
behavior in tunnels, and evaluating, organizing, and communicating knowledge
on tunnel operations and safety. PIARC has produced several safety documents
including those related to controlling fire and smoke in road tunnels, human fac-
tors and road tunnel user safety, and integrated approaches to road tunnel safety.
9 All tunnels longer than 500 meters belonging to the road network are to meet minimum safety
requirements related to organization, roles, and responsibilities of various administrative bodies in
charge of tunnel safety, and related to technical standards for tunnel infrastructure, operation, traffic
rules, and user information. Approximately 500 tunnels in Europe in operation, under construction, or
at the design stage are affected. Retroactive requirements for safety are also detailed in the directive.
10 PIARC Technical Committee. 3.3 Road Tunnel Operations. Available: http://www.piarc.org/en/
Technical-Committees-World-Road-Association/ (accessed June 27, 2012).
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HEALTH AND SAFETY UNDERGROUND 117
EMERGENCY RESPONSE CHALLENGES
Response to underground emergencies of all types poses distinct challenges
to emergency responders who typically develop strategic and tactical plans
and train for response scenarios. Response time to underground emergencies is
increased, access and way finding may be difficult, and the complex environ-
ment makes intuitive decision making more challenging. Emergency responders
require specific training and practice to use the more complex fire and life safety
systems that manage, for example, smoke, fire suppression, access, exiting, and
fire notification in the underground.
Response Times
Fire and medical services are mandated to respond to calls as quickly and
safely as possible. For example, NFPA 1710 establishes a 4-minute minimum
response time by firefighters to the “front door” of the structure for 90 percent
of all incidents (NFPA, 2010c). However, the “front door” of an underground
structure could be its street level access portal, possibly several blocks distant
from the emergency site. The distance increases the time firefighters can respond
to the actual emergency. If lengthy response times are unacceptable, respond-
ers and equipment may need to be located underground or closer access points
included in design. For larger underground complexes, underground emergency
resources may include emergency apparatus (fire engines, ladder trucks, and
medical vehicles) and law enforcement.
Accessing an underground fire or other hazard may require a difficult descent
through rising smoke unless alternate access routes or methods are designed,
built, and maintained. Fire fighting activities are difficult because normal pro-
cesses for visual assessment of a situation on the surface, typically accomplished
through inspection of at least three sides of the incident building, may not be
practical underground. Emergency ventilation by vertical or horizontal methods
may be limited by lack of exterior windows or access to the exterior by a ‘roof’
where smoke can be released to the outside.
Wayfinding
The ability of emergency responders to orient themselves is critical. Extra
steps are necessary to ensure use of a comprehensive methodology that provides
exact and rapidly recognizable locations. Many emergency response departments
now use satellite technology to locate response units and employ computer aided
dispatch (CAD) to identify the units with the shortest possible response time.
However, these technologies depend on line-of-sight communication with satel-
lites and are not functional underground. Alternatives have yet to be developed
for underground use, and emergency responders must rely on old technologies
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118 UNDERGROUND ENGINEERING FOR SUSTAINABLE URBAN DEVELOPMENT
BOX 4.1
Recommendations and Implementation Strategies for
Improved U.S. Tunnel Safety from the International
Technology Scanning Program
The U.S. Federal Highway Administration and the American Association
of State Highway and Transportation Officials and the National Cooperative
Highway Research Program sponsored a study to explore practices in sev-
eral European countries related to tunnel safety, operations, and emergency
response. The following are recommendations and some implementation strat-
egies excerpted from the resulting report (Ernst et al., 2006).
1. Develop Universal, Consistent, and More Effective Visual, Audible,
and Tactile Signs for Escape Routes.
Recommendations include uniformity of signage that could be understood by
all people and minimizes confusion in locating an exit in case of an emergency.
Sounds and simple verbal messages and tactile messages could make visual
signs more effective in low light situations. National Fire Protection Association
(NFPA) guidelines applicable to fire protection and life safety designs should
be reviewed, and current technologies and results from human response stud-
ies should be incorporated into the design of escape portals, escape routes,
and cross passages (See Figure 1).
2. Develop AASHTO (American Association of State Highway and
Transportation Officials) Guidelines for Existing and New Tunnels.
A single AASHTO reference for engineers and operators to facilitate consistent
U.S. criteria coordinating AASHTO, FHWA, NFPA, American Public Transpor-
tation Association, and National Research Council Transportation Research
Board standards and guidelines for tunnels.
3. Conduct Research and Develop Guidelines on Tunnel Emergency
Management That Includes Human Factors.
Learn from European human factor design experience for more effective tun-
nel planning, design, and emergency response. Work through AASHTO to
FIGURE 1 Example from Mont Blanc Tunnel (between France and Italy) of tunnel escape
route signage, typical of the uniform signage used throughout many countries in Europe.
SOURCE: Ernst et al., 2006.
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HEALTH AND SAFETY UNDERGROUND 119
fund and develop tunnel emergency management guidance. Collaborate with
academe to study human response in tunnel incidents.
4. Develop Education for Motorist Response to Tunnel Incidents.
5. Evaluate Effectiveness of Automatic Incident Detection Systems
and Intelligent Video for Tunnels.
Computer systems connected with video surveillance systems can be used
to detect, track, and record incidents and signal operators to take appropri-
ate action, decreasing response time. Because widespread public use of
closed-circuit television is not readily accepted in the United States, outreach
explaining the benefits and possibilities of this technology would be necessary.
6. Develop Tunnel Facility Design Criteria to Promote Optimal Driver
Performance and Response to Incidents.
Innovative tunnel design with improved geometry or that is more aes-
thetically pleasant enhances driver safety, performance, and traffic operation.
7. Investigate One-Button Systems to Initiate Emergency Response
and Automated Sensor Systems to Determine Response.
Some human errors and the need for decision making in emergency situa-
tions may be avoided with a single button for operators to press that initiates
multiple critical response actions. Automated systems (e.g., using opacity
sensors) may help determine appropriate responses to certain situations.
Fans and vents may best be controlled through closed-loop data collection
and analysis systems that monitor atmospheric conditions, tunnel air speed,
and smoke density.
8. Use Risk-Management Approach to Tunnel Safety Inspection and
Maintenance.
Intelligent monitoring and analyses of data can provide information to allow
risk-based decision making with respect to scheduling inspections (and inspec-
tion frequency) and priorities.
9. Implement Light-Emitting Diode Lighting for Safe Vehicle Distance
and Edge Delineation in Tunnels.
Blue LED lights at specific intervals allows drivers to more easily gauge dis-
tance from tunnel walls and vehicles in front and to maintain safe driving
distances (see Figure 2).
FIGURE 2 Some European tunnels use evenly distributed light-emitting diodes to help motor-
ists discern the roadway edge and determine safe following distances.
SOURCE: Ernst et al., 2006.
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120 UNDERGROUND ENGINEERING FOR SUSTAINABLE URBAN DEVELOPMENT
(e.g., hard copy maps) to orient themselves in underground settings. Whereas
maps are a viable alternative, using more than one technology (e.g., satellite and
hard copy maps) may create confusion for responding units. Some technologies
for emergency communications and tracking that may have application in under-
ground infrastructure are being researched and tested through support provided
by National Institute for Occupational Safety and Health Office of Mine Safety
and Health Research. For example, the agency supports research for inertial
navigation for self tracking and wireless communication for use by miners and
rescue personnel.11 Advancement of these technologies may lead to eventual
improvements in underground infrastructure safety.
Response to terrorist events in underground infrastructure can be particularly
challenging for emergency responders because responders, along with key safety
systems (e.g., exits), also may be targets of attack. Low-occupancy (less than
500 people) above- and belowground infrastructure commonly require only two
exits according to the International Building Code (IBC, 2007) and therefore
have limited emergency access and egress. Choke points may be created when
emergency responders move down and occupants move up the same paths.12 A
coordinated terrorist attack may include plans to make exits impassable, creating
a greater problem than for surface buildings with windows and direct access to
fresh air. More information on terrorism for emergency responders is available
in several government sources (see, e.g., FEMA, 2004).
Communication
Surface radio often uses radio repeaters to cover large areas through open
air, a technology that may not work in the underground. However, emergency
responders critically rely on radio communication. When unable to use surface
radio communications technology, responders rely on other technologies includ-
ing radio repeaters and leaky feeder coaxial cable that functions as extended
antennae. These methods work underground, but must be coordinated and robust
enough to ensure intelligible coverage throughout the underground through, for
example, system redundancy. Interoperability among multiple responders, poten-
tially from many agencies, and the ability to communicate on multiple frequen-
cies are also important to ensure safety. The technology to communicate between
emergency responder departments with redundant systems exists today, but these
systems may not function in the underground. As mentioned in the previous sec-
tion, the mining industry is researching enhanced underground communication
(e.g., underground use of wireless technologies) between those occupying the
underground, and between those on the surface and those underground. Con-
11 A listing of current and past projects supported in this area of research can be found at http://www.
cdc.gov/niosh/mining/researchprogram/communicationstracking.html (accessed October 25, 2012).
12 The opposite of this happened at the World Trade Center on 9/11.
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HEALTH AND SAFETY UNDERGROUND 121
tinued research in these areas is needed to ensure reliable communications in
underground infrastructure.
INCREASING COMFORT AND MAXIMIZING SAFETY
Anecdotal evidence suggests that many people, especially those unaccus-
tomed to being underground on a regular basis, are uncomfortable with the idea of
being underground. The committee is not aware of data that quantify the extent of
negative perceptions. Negative attitudes may stem from safety concerns, unpleas-
ant personal experiences, or a belief that the underground is dank and dangerous,
rather than from specific knowledge about the benefits, risks, and relative safety
of underground facilities. Presumably, the public is not campaigning for removal
of existing underground systems and services, but it may seem unenthusiastic
about new underground applications, especially given their initial costs.13 Finding
ways to clarify and counterbalance negative perceptions can be as big an obstacle
as the most complex safety and technical challenges and requires a thorough
research focus of its own. The urban underground environment can be engineered
and managed—given good design—to be safe, attractive, stimulating, produc-
tive, and healthy (Carmody and Sterling, 1993; Meijenfeldt and Geluk, 2003).
Given appropriate attention to lighting, ventilation, visual cues for orienting,
fire prevention and other safety considerations, emergency egress, and aesthetic
considerations, underground space can be as enticing as surface space designed
for similar use. Creating underground space that enables and encourages safe,
economical, and sustainable use over the long-term is fundamental to that space
being part of sustainable and resilient development in the urban setting.
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