1. Introduction
In recent decades, the use of computer agent models in managing evacuation procedures and crowd movement is on the rise, as it is considered as the most efficient way to accurately simulate the effects of evacuation in all types of structures and assess occupants’ safety. Human behavior in evacuation procedures is the most unpredictable and therefore difficult aspect to predict and simulate, as people’s characteristics, such as psychology and companionship, do not follow a standard pattern. Evacuation simulation software have adopted some basic human parameters including, size, walking speed, behavior, assistance and more in order to mimic human behavior during emergency events.
Globally accepted regulations and standards include, among other parameters, the maximum unimpeded travel speed of occupants in case of emergency evacuation.
The Society of Fire Protection Engineers (SFPE) has adopted a relation between people’s density and walking speed as well as a maximum travel speed [
1] that is used widely in conventional and computer modeling evacuation simulations in order to calculate the evacuation time.
A very useful data collection for movement speed during a fire drill evacuation in a high-rise building has been achieved by Peacock et al. with the collected data by the National Institute of Standards and Technology (NIST) [
2]. The study shows that the average movement speed along the whole building is equal to 0.48 ± 0.16 m/s which is quite similar to the range of literature values. However, the local movement speed as occupants traverse down the stairwell seem to vary widely within a given stairwell, ranging from 0.056 m/s to 1.7 m/s. Thus, using a distribution of movement speed rather than a single value should provide more realistic representation of movement speed in stairwells.
In order to investigate human movement in emergency situations and crowded areas, Kiyono and Mori [
3] compared simulations of the evacuation behavior using elliptic elements with real pedestrian flows. The simulation results showed a good agreement with the actual phenomena.
Moreover, Kobes et al. [
4] studied the ability of virtual reality in studying human behavior in fires and attempted to determine the walking speed by measuring the (approximate) walking distance and divide it by the movement time. They used the ADMS—BART, a pre tested simulation platform by emergency training organizations.
Xie et al. [
5] indicated that the body mass index (BMI) has a significant effect on ascending evacuation speed and proposed an evacuation model to predict the best evacuation path in fire stairways. The effect of occupant characteristics on crawling speed in evacuations has been studied by Kady and Davis [
6], who showed that the mean crawling speed is 0.77 m/s, significantly higher than other studies which propose a crawling speed of around 0.3 m/s [
7,
8]. This finding is vital in order to improve the reliability of evacuation models. Even more, the effect of trim and heel angle of a ship corridor on walking speed during an extreme-conditions evacuation has been studied in a ship corridor simulator and showed that average individual walking speed could be greatly attenuated [
9].
Other studies subject the outdoor human speed in case of emergency, such as the simulation study to observe the walking speed of evacuees in the case of tsunami evacuation in Indonesia [
10], in which the results show an average speed of 1.419 m/s. In this real-scale experiment, the volunteers were asked to hurriedly walk from a specified point to a specified point near to shelter and observers were placed at 6 points along the travelling route to observe the time when the volunteers passed their position.
Other studies that include travelling speed under limited visibility such as smoke-filled environments proved that the travel speed may be reduced up to 70% of normal speed with regard to visibility and smoke type (irritant and non-irritant). Among these studies, Jin conducted an experiment in a 20 m-long corridor where a highly irritant white smoke and a less irritant black smoke were produced. He created a graphic relation between extinction coefficient and walking speed for irritant and non-irritant smoke. For example, for an extinction coefficient of 0.5, which corresponds to a visibility of approximately 6 m for irritant and 12 m for non-irritant smoke, the walking speed is 0.3 m/s and 1 m/s, respectively [
7,
8,
11]. In addition, Fridolf et.al reveal that the crucial visibility limit is set to 3 m, and for values below that, speed decreases radically; they also provided a variation of unimpeded walking speed according to population characteristics [
7].
As mentioned before, underground spaces have special requirements as they differ from a typical surface building: there is an absence of physical lighting; exit route paths are always ascending and thus cause fatigue to evacuees; and the users have a limited orientation awareness, which affects the travelling speed in contrast to conventional buildings. The National Fire Protection Association suggest that the maximum means of egress travel speed is equal to 0.628 m/s along platforms, corridors, and ramps in more congested areas in contrast to 1.017 m/w in less congested areas and 0.243 m/s for stairs in underground transit systems (in cases of vertical travelling, speed and distance are defined in terms of the vertical change in elevation bridged by the facility), in order to calculate the Request Safety Egress Time (RSET) in case of emergency [
12]. It should be mentioned that these values are meant to be used in the hand calculation method.
Studies concerning underground movement behavior are limited to those on tunnel experiments (both railway and road) [
13,
14,
15]. In a full-scale experiment in a road tunnel by Seike et al. [
16,
17], the normal walking speed (“walk in the tunnel as you normally walk”) and emergency evacuation speed (“please decide to evacuate, and do it extremely urgently”) were investigated under different visibility limitations and revealed a variation between 3.55 m/s and 1.1 m/s, respectively. More specifically, the maximum normal speed was observed from 2 m/s to 1 m/s (approximately) and the evacuation speed from 3.55 m/s to 1.41 m/s. In the presence of smoke, the value of maximum speed decreases linearly to 2.53 m/s and the minimum value to 1.24 m/s. Summarizing, evacuation experiments in a smoke-filled tunnel show that the maximum, minimum and mean values of normal walking speed are almost constant regardless of the extinction coefficient, but maximum emergency evacuation speed decreases rapidly as smoke density increases. In addition, the mean emergency evacuation speed is not severely influenced by smoke density.
Finally, concerning evacuation in ascending stairways, Ronchi et al. investigated the effects of fatigue on walking speeds, physiological performance and behaviors in the case of a long ascending evacuation and revealed that physical work capacity affected walking speeds in the case of upwards stairway travelling [
18], with the mean value ranging from 0.62 m/s to 0.83 m/s. There are further studies that consider the evacuation in ascending stairways which reveal that a speed variation exists [
19,
20,
21,
22,
23].
A summary of studied research regarding the occupancy type is presented in
Figure 1. Moreover, representative regulations as well as past research concerning walking speed mainly in underground areas (road tunnels and METRO stations), as well as upward evacuation are presented in
Table 1.
As seen from the Table above, regarding the evacuation speed of occupants, there is a variation concerning the type of occupants, building type, visibility conditions, human psychology and more.
In
Table 2 various experiments are presented regarding the estimation of travel speed in smoke. Each experiment had its own particular characteristics. For example in Jin’s experiment people were called to walk in a corridor filled with smoke and their speed value was observed for various values of optical density [
8]. SFPE proposes speed values for specific optical density for irritant and non-irritant smoke [
30]. Seike et. al. conducted an experiment inside a tunnel where walking speed was measured for values of extinction coefficient below one (Cs < 1) [
17].
From all the above, it becomes obvious that there is still a high need for further research on evacuation behavior regarding travelling speed, both for the specification of studies by underground structure type, exit path and visibility conditions, as well as for the further development of the computer agent models.
The purpose of this paper is to describe an experiment of real-time evacuation, and present a data-set on walking speed both in a clear and smoke-filled environment. The results are related to horizontal and upward travelling speed, as well as participants’ age distribution.
5. Conclusions
Significant conclusions arise from this study concerning the evacuation speed and the need for clear information and guidance during evacuation.
The maximum travelling speed on the horizontal surface reduced with the presence of smoke from 1.70 to 1.08 m/s, while the minimum speed increased from 0.63 to 1.01 m/s. This observation, along with the fact that in the smoke environment the maximum value of travel speed almost coincides with the minimum value, leads to the conclusion that in “difficult” environments, people tend to act more as groups and their behavior is somewhat homogenized.
The same conclusion derives from the evacuation through the staircase exit route, where one can observe a small variation of travel speed values, regardless of factors such as occupants’ age. From the experiment, one can see that there is a remarkable difference between travelling on horizontal corridor and the staircase, only concerning the maximum travelling speed value, while the mean speed value is practically identical. Travelling by the staircase requires attention and causes fatigue, which makes it a “difficult” environment for the users of the underground space and people are obliged to travel as a group.
Since the development of underground facilities is on the rise, the need for research on ascending evacuation, especially in deeper constructions, is urgent.
The avoidance of the further reduction of the minimum speed value during the smoke-induced experiment is due to the guidance provided to the evacuees during the procedure by the trained personnel. This reveals the importance of an effective guidance system in underground spaces, the existence of an adequate evacuation plan for emergency situations and the continuous training of the working personnel as well as for the users of underground spaces.
The effective and continuous guidance improves the occupant’s psychology and minimizes stress which could lead to panic and unpredictable human behaviors that compromise their safety. This fact is also revealed from the answers that the participants gave to the questionnaire at the end of the experiment, where the majority claimed that they had no feelings of anxiety.
Regarding existing regulations and previous research, the unimpeded speed from the current experiment in wide corridor and ramp during evacuation in an underground space is within the proposed range, approximately 1–1.25 m/s. The same conclusion derives also for the stairway mean speed value, approximately 0.4–0.7 m/s. Therefore, the results of the experiment are generally in accordance with existing regulations. The speed value in a smoke-filled environment is, as mentioned above, strongly dependent on visibility conditions. The speed value derived from the experiment, 1.05 m/s, comes to an agreement with the value proposed by Jin’s experiment for non-irritant smoke and visibility conditions (approximately 6 m to 7 m), as observed from the cameras [
8].
As seen from the experiment, there is a significant difference in speed values among the distinctive exit paths of the underground space, tunnel ramp, horizontal surface and staircase. This difference directly affects the required egress time and the safety of the underground space. Therefore, occupants’ speed is a crucial parameter which should be taken into account along with other technical and economic factors, in order to decide the selection of the egress routes type, during the design of an underground infrastructure.
The need for evacuation procedure improvement is a continuous project. This experiment shows that if the occupants’ awareness through education and training is high, the evacuation can be completed on time and without any losses. Thus, the safety systems and guidance in workplaces constitute a major factor for the effectiveness of the evacuation procedure and should be taken into account when designing an underground space prior to construction.