“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 tunnel.” (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 balance the human and mechanical elements of urban living to create modern, environmentally 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 components (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
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 relationships, 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 infrastructure 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 underground transportation and building and industrial facilities, there is a need for a more comprehensive approach to safety against all hazards for all types of underground facilities. The remainder of this chapter explores this need.
To create a functioning, sustainable, urban system that effectively links its social, technical, and governing elements, the relationships between technologies, 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 synonymous 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).
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 directives 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 Laboratory, 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 critical 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 interaction with a single manufactured item or technology. Underground systems as part of total urban environments are more complex, and the need to understand, 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 negative 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 scenarios. Design must be holistic and create an integrated environment that allows people to almost intuitively understand how to remain safe should adverse conditions 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.
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).
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 successful 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 underground 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
4 For example, the Health and Safety in Works working group of the International Tunneling Association has released multiple publications related to safe working practices (see ITA-AITES, 2011).
hazards and risks and applying appropriate mitigation strategies. Once recognized, 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 excavations 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).
The inadequacy of safety standards results from their being developed without due consideration of the growth of all types and large scales of underground use. Innovation in underground design and construction may be bound by prescriptive (and potentially ineffective) codes when performance-based mechanisms 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.
The next sections discuss hazards to human health associated with occupying 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 emergency incidents do not escalate beyond the possibility of control or cause preventable 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.
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 underground 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 occupied 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 systems, 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
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 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 sufficient 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.
Underground infrastructure is often designed to make underground facilities 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 protect 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
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 incident 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 present 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 containment 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
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, however, 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 consequences, 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 bombers. There also is a conceivable threat of targeted ground-penetrating explosive devices delivered by missiles. However, underground installations have been recognized 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
Board of the National Research Council has released many reports related to transportation safety and security, including many related to underground transportation.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 systems (TRB, 2006). Similarly, the Federal Highway Administration and AASHTO jointly sponsored a panel to develop “strategies and practices for deterring, disrupting, 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 comprehensive 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 damage 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 behavior and to guide threat recognition, decision making, and action under stress are called for. New materials and their behaviors for this application must be considered
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.
(e.g., to prevent injury from fragments and flying debris and the development 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 safety codes and guidelines applicable to underground infrastructure 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 underground 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 (European 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 factors 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).
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 environment 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.
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, responders 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 processes 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.
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 satellites and are not functional underground. Alternatives have yet to be developed for underground use, and emergency responders must rely on old technologies
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 several European countries related to tunnel safety, operations, and emergency response. The following are recommendations and some implementation strategies 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 studies 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 Transportation 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 tunnel 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.
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 appropriate 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 aesthetically 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 situations 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 inspection 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 distance 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 motorists discern the roadway edge and determine safe following distances. SOURCE: Ernst et al., 2006.
(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 underground 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).
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 including 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, potentially from many agencies, and the ability to communicate on multiple frequencies 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 section, 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. Continued
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.
Anecdotal evidence suggests that many people, especially those unaccustomed 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, unpleasant 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, productive, 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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