Emergencies such as vehicle crashes, fires, hazardous waste spills, or terrorist activities can be particularly hazardous when they occur inside long underground tunnels. The enclosed environment of a highway tunnel can concentrate heat, smoke, or other toxic gases resulting from the incident; limited right-of-way means that even a partially blocked lane can potentially trap vehicles and hinder access for emergency responders. As a result, tunnel users may need to evacuate themselves on foot via emergency exits. This research study examined emergency exit signs, markings, and messages intended for use in highway tunnels. The study’s three primary objectives were as follows: • To evaluate the effectiveness of emergency messages and their delivery methods (i.e., visual, audible, or both) to encourage drivers to leave their vehicles and evacuate a tunnel on foot. • To evaluate the effectiveness of sign messages, as well as signing and marking formats, to lead people to emergency tunnel exits. • To evaluate the visibility of different sign and marking materials and technologies for use in highway tunnel environments, in particular when a tunnel is filled with smoke. Studies of past tunnel emergencies have found that tunnel users often do not act independently to evacuate themselves on foot, instead choosing to remain in or near their vehicles. Some reasons for making the potentially fatal decision not to evacuate are the lack of awareness of an unfolding hazard, uncertainty about the appropriate course of action, reluctance to leave the perceived safety of the vehicle, and reluctance to abandon property. During an emergency, people have a tendency to wait for information or instruction rather than seeking it out. If and when people do decide to exit a tunnel in the face of a recognized danger, a common tendency is to try to reach the main tunnel portal entrance through which they drove into the tunnel, rather than emergency exits for pedestrians, which may be nearer. In fact, drivers may not be aware of the existence of emergency exits or cross passageways and therefore may not recognize the purpose of exit doors along the tunnel wall. Additionally, people tend to overestimate the amount of time they have to evacuate during a fire, a potentially fatal mistake since fire and smoke can spread more quickly in a tunnel fire than in a building. In the absence of emergency responders to give directions, in-tunnel signs, marking systems, lighting, and/or audible signals must provide direction to tunnel users. Both the need to evacuate and the location of the nearest emergency exits must be clearly communicated. Additionally, the signs and markings must be visible to pedestrians under potentially adverse viewing conditions, including darkness and smoke. Existing guidelines that address aspects of emergency exit signs and markings for highway tunnels include the following: • Directive 2004/54/EG of the European Parliament establishes minimum safety requirements for all roadway tunnels on the Trans European Roadway Network that are longer than 500 meters. One of the objectives of the guidelines is to improve conditions for self-rescue from a tunnel in an emergency, including guidelines for evacuation lighting and signing. • The National Fire Protection Association (NFPA) is a non-profit organization with members from nearly 100 nations. As part of its mission, NFPA has developed approximately 300 codes and standards for mitigating the risk and effects of fires. Three NFPA codes that directly address emergency exit signs and markings for highway tunnels are NFPA 502, Standard for Road Tunnels, Bridges, and Other Limited Access Highways; NFPA 170, Standard for Fire Safety and Emergency Symbols; and NFPA 101, Life Safety Code. • The International Building Code’s (IBC’s) guidelines do not directly apply to exit door and exit pathway signs and markings in tunnels; however, they represent a standard for exit signing in buildings that is consistent and recognized throughout the United States. • The International Commission on Illumination’s (CIE’s) 193-2010 Emergency Lighting in Road Tunnels provides guidelines for emergency lights and markings for pedestrians in highway tunnels, including marking recommendations for emergency exit doors. Building on prior research and existing U.S., European, and international standards for emergency exit signs and markings, researchers tested selected messages, sign and marking formats, and sign and marking technologies with volunteer participants. Research activities included focus group discussions and a simulation of a tunnel emergency situation involving smoke. The expert panel discussion included tunnel operators and emergency responders, and their responses were used to revise the focus group discussion and tunnel fire simulation, as well as to identify potential maintenance or other technical issues associated with signs and markings. Two focus group discussions were conducted to gain a better understanding of how tunnel users might respond to various tunnel incident scenarios and warnings. Participants were presented with pictures, videos, and audio clips pertaining to a hypothetical emergency involving fire inside a highway tunnel. Participants discussed how they might react to a similar situation, what types of information and messages would be most effective, and what might influence their decisions to either stay in their vehicle or evacuate the tunnel on foot. The results of the focus group discussions included the following: • Participants indicated that uncertainty about what is happening might lead to a delayed or incorrect response, so it would be important to relay to tunnel occupants details about the emergency or at least instruct the drivers to evacuate the tunnel. • The messages that participants found most useful included a brief statement about the emergency, followed by a direct action statement. Examples of this type of message, displayed on an electronic message sign, included “Emergency–walk to exits” and “Fire in tunnel–walk to exits.” Audio messages including the same information elements were also considered effective. The tunnel simulation tested individual responses to a tunnel emergency scenario similar to those discussed by the focus groups and tested several sign and marking formats and technologies within the simulated tunnel environment, both for participants’ comprehension of and confidence in various formats and for detection and legibility distances through smoke. Stage 1 of the tunnel exercise simulated a vehicle trip through a highway tunnel that was stopped by a traffic jam, followed by the appearance of smoke in the tunnel and sounds of stopped traffic and tunnel ventilation. One-third of participants received only these visual and auditory cues to the situation, another one-third also saw a dynamic message sign (DMS) with the message “Fire in tunnel–walk to exits,” and a final one-third heard a longer audio message: “Attention–there is a vehicle fire in the tunnel. Turn off your engine and leave your keys in the vehicle so that it can be moved by emergency personnel. Leave your vehicle and walk quickly to emergency exits.” Results of Stage 1 included the following: • While all three groups included participants who indicated that they would stay in their vehicle as well as participants who indicated they would leave the vehicle, the two groups of participants who received a message about the incident (either visually or audibly) were much more likely to say they would leave the vehicle and exit on foot (81 percent of those who saw the DMS and 73 percent of those who heard the audio announcement) versus the group who received no message (20 percent). • When asked what additional information they would want or need regarding the situation, participants who had not received a message were most likely to request information about the nature and seriousness of the situation, as well as instructions about what they should do. Participants who had received either of the two messages were most likely to ask about the locations of the exits and how to identify them. Participants viewed nine signs. Three of the signs were symbol-only signs: a “running man” symbol-only sign, a “refuge point” sign, and an emergency telephone sign. Researchers asked participants what they thought each of these signs meant. The other six signs all incorporated the word “EXIT,” and participants were asked where they would expect to find an exit door based on each sign. Some of the principal results from the comprehension testing included the following: • The stand-alone running man symbol was identified correctly by 48 percent of participants as an exit sign, while another 38 percent assumed that the sign indicated a direction or path for them to follow. • All signs that included the word “EXIT” were correctly identified by all participants as indicating a tunnel exit. Comprehension scores for signs with “EXIT” text, therefore, measured participants’ understanding of an exit’s location relative to the location of the sign. • Once the running man symbol was paired with the word “EXIT,” most participants thought that the running man sign (with or without the word “EXIT”) indicated a direction, even without a supplemental arrow. Therefore, participants most frequently assumed that the running man symbol indicated an exit to the side of the sign or farther away in the direction that the running figure was facing. However, participants saw the est signs in the context of a wall-mounted frame and so did not have the added context of a visible doorway. • A small number of participants did not recognize the chevron arrows on a text-only EXIT sign as directional arrows. All participants recognized tailed arrows as indicating a direction. • When the running man sign was paired with a (tailed) directional arrow and a distance, comprehension of the exit’s location relative to the sign was perfect among nearly all participants. • When a running man exit sign included an arrow but no specified distance, many participants assumed that an exit was nearby in the direction of the arrow; if no distance was provided, they assumed the distance to the exit was very short. Participants were presented with four pairs of exit path/door marking formats and asked to select the option from each pair that they would feel most confident about following to an exit: • Steady-state light-emitting diode (LED) lights vs. LED lights flashing in unison. • Unison-flash LED lights alone vs. unison-flash LED lights plus an audio beacon saying, “Exit here.” • Unison-flash LED lights vs. traveling LED lights that illuminated in a left-to-right sequence. • Unison-flash LED lights plus an “exit here” audio beacon vs. traveling LED lights. In general, participants preferred flashing lights over steady-state lights, and traveling lights that indicated a direction over unison-flash lights. An audio beacon was a favored option to indicate the location of doorway; however, when the audio beacon was compared against traveling/directional pathway lights, many participants indicated that the traveling lights would be more useful farther away from an exit door, and the audio beacon would be helpful close to the door. To assess the visibility of the signs tested, researchers measured the luminance of each sign’s positive (brighter) and negative (darker) areas, as well as of the gray walls and frames surrounding the signs. Measurements were conducted in clear conditions and in smoky conditions with smoke opacity levels of 4, 5, 10, 12 and 23 percent, and in both low ambient light and darkness. The measurements were used to calculate the contrast ratio of each sign compared to the tunnel wall, and also the contrast ratio of each sign’s positive and negative elements, i.e., sign legend versus sign background. Sign visibility was also measured during participant testing in the tunnel simulation by recording the distances at which participants could detect and read each sign. Some of the signs were internally illuminated by LEDs, while others were photoluminescent (PL). The luminance measurements showed that the overall luminance levels and the contrast ratios between signs and the tunnel wall, and between the sign legends and background, all diminished sharply when the signs were viewed through smoke. This significantly affected how far away signs could be seen and also reduced the contrast between their light and dark areas, which made text and symbols more difficult to read. The principal findings from the luminance measurements included the following: • In general, LED signs in clear conditions had much higher luminance levels than PL signs, and this difference continued when signs were measured in smoky conditions. However, these differences in luminance diminished as smoke opacity increased. • Under low levels of ambient light, the contrast of sign luminance with the tunnel wall diminished rapidly as smoke opacity increased. In general, LED signs slightly outperformed PL signs. When there was no ambient light, contrast between the tested signs and the tunnel walls was much higher, and PL signs displayed higher contrast ratios than LED signs. • Contrast ratios between sign legends and backgrounds were consistently higher for PL signs than for LED signs. This was the case with low levels of ambient light and was even more pronounced without ambient light. During the tunnel simulation, detection and legibility distances were recorded for each sign that participants viewed, as well as for a photoluminescent path marking square. Some of the findings from visibility testing of the signs with study participants included the following: • For all of the signs, smoke density/opacity was a significant factor in detection and visibility distances, as would be expected from the sharp drop in sign/marking luminance and contrast that was seen in the photometric measurements. • The LED signs that were tested could be seen from farther away than the tested PL signs, as would be expected from the LED signs’ higher luminance values. The findings from the study are summarized in a set of proposed guidelines for the format and placement of emergency exit signs and markings for highway tunnels. The guidelines also address considerations for selecting sign and marking materials and technologies, as well as some preliminary recommendations for public outreach and education pertaining to tunnel emergencies and exit plans. Highlights from the proposed guidelines include the following: • Emergency Exit Sign Formats. Emergency exit door and directional signs should include the running man symbol in combination with the word “EXIT,” as shown in Figure 1. Sign colors should be green and white. This sign should be placed on the exit door if possible, or on the tunnel wall immediately to the right or left of the door, preferably with the midpoint of the sign no higher than 1.5 meters (4.9 feet) above the floor. • Emergency Exit Directional Sign Formats. Signs indicating directions to emergency exits should be placed at least every 25 meters (82 feet) along the tunnel wall. These signs should include the running symbol and “EXIT” text, with the addition of a tailed directional arrow and the distance to the nearest exit in feet (see Figure 2). If exits are located in two directions relative to the location of the sign, two signs should be placed side by side to indicate the directions and respective distances to the two exits. • Exit Door Markings. The area around each exit door should be illuminated at a level that is three to five times brighter than the illumination of the adjacent walls. In addition, exit doors should be marked with strobe lights that activate only during an emergency. The lights should strobe at a frequency of between 1 Hertz and 2 Hertz; white strobe lights are specified under current NFPA guidelines, though further research may be warranted to compare white versus green strobe lights (recommended by some international guidelines) for this purpose. • Exit Door Audio Beacons. Auditory beacons may be used to supplement (not replace) illuminated exit door lighting. When used, auditory beacons should only contain a single message, such as “exit here” or “refuge shelter,” and may be in more than one language in addition to English. The primary benefit of an audible exit door beacon will be realized in the area close to the door. The decibel level used for the beacon should be calibrated to be audible to listeners within a relatively short radius of the door itself, and the use and type of auditory beacons should take into account the specific acoustic characteristics of the location in which it is used. • Exit Path Markings. Exit path markings can be static or dynamic. If feasible, path markers should indicate a direction to an exit door. This may be accomplished with a dynamic light array, controlled automatically or manually by tunnel operations staff, that lights sequentially to indicate a direction. If directional/sequential LED arrays are not a feasible option, LED lights that can be activated to flash in unison during emergency situations seem to be slightly more effective than steady-state lights for indicating an emergency exit path. Path direction to exit doors can also be accomplished with static markers that include a directional arrow. Pathway markings should be placed no more than 1 meter (3 feet) above the pathway floor. • Emergency Messages. In the event of an in-tunnel emergency or disruptive incident, it is beneficial to broadcast a message to drivers if possible, visually and/or audibly. In the case of an emergency that requires drivers to evacuate the tunnel on foot, an emergency message can be especially important for encouraging the evacuation. The message should contain, at minimum, the following pieces of information: o A brief statement about the nature of the emergency, e.g., “fire in tunnel” or “vehicle fire ahead.” o Direct instructions about the action to take, e.g., “walk to exits” or “leave vehicles, walk to exits,” if evacuation on foot is warranted. An evacuation direction (e.g., upstream of the fire) should be specified, if applicable. An emergency message broadcast via a dynamic message sign should be no more than two phases long, with a maximum of three lines/three bits of information per phase. Auditory messages may permit slightly longer messages than dynamic message signs; however, both loudspeakers and radio override systems can be problematic in a tunnel environment. Wireless emergency alerts may have potential for delivering emergency messages via driver cell phones. • Sign Material and Technology Considerations. Internally lit, externally lit, or photoluminescent signs are all options for tunnel environments. Sign spacing should take sign luminance and associated visibility distance into consideration. Any sign or marking must be capable of withstanding environmental and traffic conditions in a highway tunnel, as well as tunnel cleaning procedures (or should be capable of being removed prior to tunnel cleaning). This can mean waterproofing the housings around electrical components for internally illuminated signs and selecting water-resistant and corrosionresistant materials and coatings. Photoluminescent signs should be selected according to the availability of ambient light to charge them. • Public Education and Outreach. Public service announcements and/or other public outreach materials may be useful for educating drivers about safe behaviors associated with driving in highway tunnels, including information about tunnel incident procedures and tunnel emergency exits, such as cross passageways and refuge areas as applicable. This type of advance education may improve the responses of drivers in the event of a tunnel-related emergency and may also predispose them to look or listen for emergency announcements during an incident. (Author/publisher)
Samenvatting