The Process of Designing Emergency Exit Portals for Road Tunnel Evacuation
By Daniel Nilsson,1 Håkan Frantzich,1 Enrico Ronchi1 and Karl Fridolf 2
1Division of Fire Safety Engineering, Lund University, Lund, Sweden
2WSP Brand & Risk, WSP Sverige AB, Malmö Sweden
The design of emergency exit portals for tunnels might seem like a relatively straightforward task. In principle, you only need a door in the wall and possibly some markings or flashing lights to attract the attention of evacuees. But how do we make sure the exit is easily noticed and that people understand how and when to use it? If we use flashing lights to attract people’s attention, what should be the flashing frequency of these lights? A too low flashing frequency (slow flashing) might not attract people’s attention, but a high flashing frequency (fast flashing) might signal “warning” or “keep away.” And what about the color of the area around the door or the color of the flashing lights? We know that red light penetrates smoke more effectively due to the long wavelength, but how is a red flashing light interpreted? And how does the setup of the door, the area around it and the lights influence how the portal is perceived? Perhaps it is not that easy after all?
There are many illustrative examples of cases where evacuation safety measures have not worked as intended. One example, which relates to emergency exit portals, is the experiments in a smoke-filled rail tunnel in the METRO project.1 One of the objectives of the experiment was to study the effectiveness of different emergency exit portal designs. Figure 1 shows one of the tested portal designs, which consisted of a green frame around the door, green and white lights at the bottom part of the frame, a back-lit emergency exit sign above the door and strong illumination on the portal. These features were chosen to resemble the design suggested in Swedish guidelines for tunnels.
Figure 1. Schematic representation of the emergency exit portal used in the experiment (left)
and the actual exit in the smoke-filled tunnel during the experiment (right)
The portal design was studied by the involved researchers (i.e., trained experts) both with and without smoke before the experiment. Although six experienced evacuation researchers examined the portal design, none of them was able to predict how it was going to be interpreted by the participants in the experiment. However, post-experiment interviews revealed that some participants interpreted the portal as an oncoming train.1 This was a surprise to the researchers, who had all failed to recognize the context in which the participants viewed and interpreted the portal.
As shown by the example, design mistakes can easily be introduced when new evacuation safety measures are developed, and expert judgement is not necessarily a sufficient remedy. Instead, designs must be developed in an iterative manner and tested in realistic settings to ensure that they work as intended.2 This was also the idea behind a research project performed at Lund University to accommodate the needs of the Stockholm Bypass Project.3 The research, which was funded by the Swedish Transport Administration and the EU Trans-European Transport Network (TEN-T), aimed at deriving well-working evacuation safety measures for an 18-km–long road tunnel section. One of the safety measures that was explored in detail was emergency exit portals.
The emergency exit portal design for the Stockholm Bypass road tunnel section was developed through three consecutive phases, namely:
Part 1: Affordance-based evaluation of emergency exit doors4
Part 2: Virtual reality test of way-finding systems at emergency exit portals5,6
Part 3: Field test in a smoke-filled road tunnel7,8
In the first part, a Theory of Affordance analysis was performed to determine what color and configuration (window or no window) of the emergency exit door in the portal was most appro-priate.4 This type of analysis consists of a systematic review of previous research to identify potential designs and is followed by a ranking procedure based on identified affordances (senso-ry, cognitive, physical and functional). The approach, which can be used by fire safety designers to avoid common design mistakes, is described by Ronchi and Nilsson.4 In part 1, it was con-cluded that the doors should be a darker color green than the surrounding frame and that a window should be installed in the door (Figure 2).
Figure 2. Recommended emergency exit door design
In the second part of the research, experiments were performed in the Cave Automatic Virtual Environments (CAVE) at Lund University.5,6 The CAVE is a system that projects images on three 4-meter–wide screens and on the floor (Figure 3). The technology uses stereoscopy with polarized light, which together with polarization glasses creates the impression of being in a three-dimensional environment. Participants navigate the virtual environment using a game pad, and their position is monitored in real-time with head ultrasound tracking.
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The research project also focused on the design of tunnel information signs (TIS), acoustic alarms and way-finding aids in the tunnel, but these measures are not described in this publication.
Figure 3. A participant in the VR environment inside the CAVE
The aim of the VR experiment was to investigate the color, flashing frequency and type of flashing lights at emergency exit portals, as well as the influence of the configuration of flashing light sources. A total of 96 participants took part one at a time, which means that social inter-action was not included in the study. Participants first performed an evacuation of the virtual tunnel and were then repeatedly placed in front of different emergency exit portals and asked to rate the designs using Theory of Affordance-based questions. The most striking results were that green or white flashing lights were perceived as better than blue flashing lights and that a flashing frequency of 1 Hz or 4 Hz was preferred compared to 0.25 Hz.
In the third part, the refined emergency exit portal from part 2 was tested in a real road tunnel, the Norra Länken tunnel in Stockholm.7,8 A total of 66 participants took part one at a time and moved approximately 100 meters in a smoke-filled environment before reaching the emergency exit portal. All participants moved along the right-hand wall, and the portal was located along the left-hand wall. In addition to testing the portal design, the experiment also aimed to explore the effectiveness of different way-finding aids, such as arrows in the pavement, distance signs along the right-hand wall and an acoustic alarm at the emergency exit portal. The experiment revealed that the portal design from part 2 performed as expected but that the performance could be further increased by using additional way-finding aids.
Introducing a novel evacuation safety measure, such as a new design of an emergency exit portal, is not as easy as it might initially seem. It is difficult to ensure that it performs as intended, and the only way to make sure is to evaluate the design in a systematic way. The current paper has illustrated the process of evaluation and development of an emergency exit portal design for the Stockholm Bypass project. More detailed information can be found in the referenced re-ports and papers. 3–8
References
[1] Fridolf, K.; Ronchi, E.; Nilsson, D.; and Frantzich, H. (2013). Movement speed and exit choice in smoke-filled rail tunnels. Fire Safety Journal, 59, 8–21.
[2] Nilsson, D. (2014) “Interaction between people and evacuation systems in tunnels,” Proceedings of the 6th International Symposium on Tunnel Safety and Security, Marseille, France.
[3] Nilsson, D.; Frantzich, H.; Ronchi, E.; Fridolf, K.; Lindgren-Walter, A.; and Modig, H. “Integrating Evacuation Research in Large Infrastructure Tunnel Projects—Experiences from the Stockholm Bypass Project.” Proceedings of the 7th International Symposium on Tunnel Safety and Security.
[4] Ronchi, E. and Nilsson, D. (2013) “Traffic Information Signs, colour scheme of emergency exit portals and acoustic systems for road tunnel emergency evacuations.” Report 3173, Lund: Department of Fire Safety Engineering, Lund University.
[5] Ronchi, E. and Nilsson, D. (2015) “A virtual reality experiment on the design of flashing lights at emergency exit portals for road tunnel evacuations.” Report 3180, Lund: Department of Fire Safety Engineering, Lund University.
[6] Ronchi, E.; Nilsson, D.; Kojić, S.; Eriksson, J.; Lovreglio, R.; Modig, H.; and Lindgren-Walter, A. (2015). “A Virtual Reality Experiment on Flashing Lights at Emergency Exit Portals for Road Tunnel Evacuation,” Fire Technology, 1–25.
[7] Fridolf, K. and Frantzich, H. (2015). ”Test av vägledande system i en tunnel—Slutrapport.” Report 3189, Lund: Department of Fire Safety Engineering, Lund University.
[8] Fridolf, K.; Ronchi, E.; Frantzich, H.; Nilsson, D.; Lindgren-Walter, A. and Modig, H. (2016). “Full scale tunnel evacuation experiment to determine appropriate emergency exit por-tal designs in road tunnels,” Proceedings of the 7th International Symposium on Tunnel Safety and Security.