In the study of building emergency evacuations, emergencies such as fires, earthquakes, and security threats have a crucial impact on occupant safety during evacuation. Especially in the face of these incidents, rational and effective evacuation strategies can significantly ensure safety. This study was located in Wuhan, Hubei Province—Wuhan is not in an earthquake zone and does not face security threats such as campus shootings. Therefore, considering this context, the focus of this study is on the analysis and optimization of fire evacuation simulations, aiming to provide scientific evidence for occupant evacuation during a fire.
2.2. Simulation Methods
2.2.1. Software
Currently, a variety of simulation software is used to simulate the evacuation process of people in various situations, such as Simulex, Cellular Automata (CA), Building-EXODUS, Pathfinder [
21,
28,
29,
30] etc. Pathfinder, developed by Thunderhead engineering, delivers agent-based simulation through an intuitive interface to output clear and detailed results. Each occupant in a Pathfinder model is aware of their surroundings and constantly recalculates their next step based on present information. These decisions are informed by academic research and validation testing. This process allows the Pathfinder simulation engine to model realistic human behavior. Pathfinder software is widely used in the field of emergency evacuation simulation.
Pathfinder uses a 3D triangulated mesh to represent the model geometry. As a result, Pathfinder can accurately represent geometric details and curves. Triangulation also facilitates the continuous movement of persons throughout the model, compared to other simulators that subdivide the space into cells that can artificially constrain the movement of occupants.
Pathfinder supports two simulation modes. In steering mode, agents proceed independently to their goal, while avoiding other occupants and obstacles. Door flow rates are not specified but result from the interaction of occupants with each other and with boundaries. In SFPE mode, agents use behaviors that follow SFPE guidelines, with density-dependent walking speeds and flow limits to doors. SFPE results provide a useful baseline for comparison with other results, but SFPE calculations do not prevent multiple persons occupying the same space. Optionally, Pathfinder allows you to specify door flow rates in steering mode to obtain a superior visualization in a constrained model. You can freely switch between modes in the Pathfinder user interface.
2.2.2. The Validity and Reliability of the Simulation Software
Actual building fire evacuation drills have many limitations. First, drills require significant personnel and venue support, making them costly and difficult to implement, especially in high-density crowds and complex buildings. Second, the number of drills is limited, and the conditions of each scenario are difficult to standardize, restricting the repeatability and comparability of the results. Furthermore, drills cannot precisely control details such as individual behavior and evacuation route choices, which may lead to discrepancies and affect the evaluation. To overcome these limitations, this study uses Pathfinder simulation software for evacuation modeling. Pathfinder can simulate individual behaviors during a fire, considering various factors (e.g., passage width, walking speed, density), ensuring consistency in results within a virtual environment, and exploring the impact of different factors on evacuation efficiency, thus avoiding biases in real-world drills.
Pathfinder, as a mature simulation tool, has been widely used in various fields, particularly in fire and emergency evacuations. Several studies have shown that Pathfinder can effectively simulate factors such as individual behavior, obstacle avoidance, and path selection, and its reliability has been validated through experimental data. Especially in complex environments such as low visibility, smoke, and fire, the numerical simulation results show a high degree of consistency with experimental data. Research has demonstrated that under low visibility and smoke conditions, Pathfinder can accurately predict evacuation speed and behavior. For example, Cao et al. [
31] and Jeon et al. [
32] validated Pathfinder’s effectiveness through simulations and experimental studies, finding that it accurately reflects evacuation behavior under different environmental conditions. Additionally, Chen et al. [
33] and Cao et al. [
34] validated Pathfinder’s reliability in simulating evacuation speed, individual behavior, and the effects of smoke through experimental and modeling studies. Ivanov et al. [
4] further demonstrated Pathfinder’s application in fire evacuations in complex buildings, with simulation results aligning with experimental data, confirming its reliability in high-rise buildings. Cuesta et al. [
35] also validated the effectiveness of the Pathfinder model in school evacuation scenarios, with simulation results closely matching actual evacuation data, with errors typically around 5%, further confirming its accuracy and reliability in complex environments. These studies indicate that Pathfinder’s application results in various complex environments are highly consistent with actual experimental data, validating its reliability and accuracy in emergency evacuations.
2.3. Construction of Simulation Model Based on BIM
Based on public information, the teaching building consists of six floors, with a floor height of 5.1 m for the first floor and 3.6 m for the second to sixth floors. The gross floor area of the first floor is 9813.53 m
2, the second floor is 7141.61 m
2, the elevated platform area is 1049 m
2, the third floor is 6160.43 m
2, the fourth floor is 7295.30 m
2, the fifth floor is 7215.55 m
2, and the sixth floor is 7140.42 m
2. The 3D model of the teaching building and the local view are shown in
Figure 2.
This study utilized Revit 2018 software to establish a three-dimensional model of the teaching building. The floor plan and division of the first floor are shown in
Figure 3a, which is divided into three zones: A, B, and C, each serving a specific teaching function.
Figure 3b shows the three-dimensional model. Based on the floor plan and BIM model, the building is divided into three overall areas. To ensure that the simulation results are not affected and to achieve rapid modeling and reduced computation time, the model only includes basic building structures such as slabs, walls, door openings, and stairs. In the event of a fire, the safety of elevators cannot be guaranteed; therefore, the simulation employs an all-stair evacuation mode. The specific steps are as follows: ① the floor settings are specified, and in this case, the first floor has a height of 5.1 m, and the second to sixth floors have a height of 3.6 m; ② the grid is drawn and components such as walls, doors, and slabs are sequentially created according to the floor levels to form a complete floor structure; and ③ a 3D view is generated to display the overall effect.
2.4. Occupant Parameter Setting
To simulate the behavior of evacuees in specific locations and environments, a safety evacuation simulation system has been established. Evacuees, evacuation locations, and evacuation environmental conditions constitute the fundamental structure of the safety evacuation simulation system. The basic parameters of individuals in Pathfinder software primarily include shoulder width, height, evacuation speed, and the setting of population density. The accurate setting of shoulder width, in particular, enables the evacuation results to more closely resemble actual escape conditions during a fire.
The main evacuation groups in the teaching building are students and teachers, with the teacher group primarily consisting of middle-aged teachers, including a few elderly teachers. To assess the impact of the proportion of elderly teachers on the evacuation effectiveness, we set different ratios of elderly to middle-aged teachers: 0:10, 1:9, 2:8, 3:7, and 4:6. Based on age and response time, different priority levels were assigned: elderly teachers > middle-aged women > middle-aged men > young women > young men, with corresponding priority values of 4, 3, 2, 1, and 0. The total evacuation times for each ratio were 336.3 s, 333.3 s, 341.8 s, 337 s, and 337.8 s, respectively. The results indicate that as the proportion of elderly teachers changes, the evacuation time fluctuates slightly, suggesting that the proportion of elderly teachers has a limited effect on the total evacuation time.
Based on the above analysis, the evacuation groups are categorized as middle-aged women, middle-aged men, young women, and young men, with priority levels set as 3, 2, 1, and 0, respectively. The body parameters are based on the mean values from “Human
dimensions of Chinese adults” [
36] and the SFPE Fire Protection Handbook [
37]. The behavior mode for all individuals is set to “Goto Any Exit”, directing them to move towards any evacuation exit along the shortest available path. However, although the default behavior model is to evacuate along the shortest path, pedestrians in real situations may be influenced by various factors, such as visibility, group behavior, and evacuation pressure. These factors may lead them to choose non-optimal paths to avoid congestion or potentially hazardous areas. According to Zhang et al. [
38], pedestrians in high-risk environments may opt for detours rather than the shortest path. Additionally, Cao et al. [
31] found that under low visibility conditions, pedestrians not only evacuate along the shortest path but may also be influenced by group behavior, exhibiting dynamic path choices such as following others. The gender ratio is set according to Wuhan University of Science and Technology, a university specializing in science and engineering, with a male-to-female ratio of 6:4. The parameter settings are detailed in
Table 1.
Based on preliminary research into the functions of the teaching building’s zones, Zone B is the main teaching area, consisting of 87 classrooms, including 29 large classrooms (60 students per classroom) and 58 small classrooms (30 students per classroom), characterized by high foot traffic, relatively concentrated personnel distribution, and high density. Zones A and C primarily consist of student offices, research rooms, activity rooms, consultation rooms, etc., with relatively low foot traffic and more dispersed personnel distribution. Considering the seating capacity of each classroom and the teaching activities, we estimated the population distribution on each floor based on the class schedule and an actual survey. Specifically, since not all classrooms are fully occupied, we selected peak time slots as the initial population setting by analyzing the student scheduling data for different weekdays over the course of a week. This approach ensures that the estimates are more aligned with actual conditions and have greater research significance. The classroom occupancy for floors 1 to 6 is as follows: 5, 8, 9, 12, 12, and 12 classrooms, respectively. For research rooms, activity rooms, offices, etc., the population was distributed randomly based on actual conditions, and the total population for each floor and the entire building was estimated (
Table 2). The initial personnel distribution on the fourth floor and the stairway numbering (S1, S2, S3, …, S10) are shown in
Figure 4a, while the local personnel distribution in Zone B is presented in
Figure 4b, providing a clear visualization of the initial distribution across different areas.
2.5. Simulation and Optimization for Evacuation
Assuming that all safety exits and the passages between areas A, B, and C of the teaching building are open, adjustments were made to the number and distribution of the occupants within the building. Based on the initial personnel numbers and parameter settings, the changes in evacuation and congestion are shown in
Figure 5a. The results indicate that the total evacuation time is 336.3 s. The figure reflects the trend of the number of evacuees and remaining individuals over time. The curve shows the congestion and evacuation efficiency at different time points, revealing potential bottlenecks at key evacuation points. By observing the dynamic process of the evacuation simulation, significant personnel congestion was observed near the evacuation staircases in Zone B, with varying degrees of blockage in the staircase areas during the evacuation, especially on the fourth floor and above, where personnel experienced delays. Due to the large number of classrooms in Zone B, personnel movement was restricted during evacuation, leading to severe congestion, which significantly impacted the overall evacuation time.
Figure 5b presents the four-floor evacuation route diagram at 100 s generated by Pathfinder software, visually illustrating the movement of people on the fourth floor. It is evident that congestion occurred in specific areas (e.g., stairwells) due to high density, resulting in evacuation delays. These congested areas are critical bottlenecks in the evacuation process, and optimizing the evacuation strategy in these areas can significantly improve overall evacuation efficiency. To further investigate the key factors affecting the safe evacuation of the teaching building, the above simulation results were used as the baseline model condition (M). All subsequent adjustments and optimizations were based on this model, with in-depth analysis and improvements through modification of related parameters or conditions.
2.5.1. Pedestrian Flow
According to on-site surveys, some classrooms in the teaching building have low utilization rates. The number of students varies greatly on different workdays, with higher foot traffic during certain periods and more vacant classrooms at other times, leading to the uneven distribution of personnel in the building. In the event of an emergency, the uneven distribution of foot traffic across different workdays may significantly affect evacuation efficiency. To study the impact of different pedestrian distributions on evacuation efficiency, a key area reduction method was used, reducing the number of students on the 4th to 6th floors of the main teaching area (Zone B), and adjusting the distribution of one classroom also requires adjusting one teacher. Six scenarios (PF1 to PF6) are set, with specific adjustments shown in
Table 3. In this study, the adjustment of occupants within the teaching building was made in accordance with the “Building Fire Protection Design Code [
39]”, ensuring that the occupant density met the regulatory requirements. Specifically, the occupant density in classroom areas was controlled at 0.5 persons/m
2, in office areas at 0.6 persons/m
2, and in laboratory areas at 0.4 persons/m
2. Based on these standards, subsequent adjustments to occupant distribution (including vertical distribution and optimization of horizontal functional zoning) adhered to the corresponding density limits to ensure safety and efficiency during the evacuation process.
2.5.2. Vertical Distribution of Personnel
In the lower floors of Zone B, some classrooms are vacant, while classrooms on the 4th to 6th floors face evacuation pressure due to their distance from the emergency exits under high foot traffic. To address this, it is necessary to optimize the vertical zoning of Zone B by relocating some teaching functions from the 4th to 6th floors to the lower floors, improving the utilization of vacant classrooms and optimizing evacuation routes to enhance safety. Six scenarios (VD1 to VD6) are set, and the number of people on each floor of Zone B for each scenario is shown in
Table 4.
2.5.3. Horizontal Functional Zoning
The main functions of Zones A, B, and C in the teaching building are different. Zone A and Zone C primarily contain consultation rooms, material rooms, equipment rooms, research rooms, and student offices, with relatively low foot traffic. Zone B, as the main teaching area, houses a large number of classrooms, and teaching activities are highly concentrated, resulting in significantly higher foot traffic than other areas, leading to uneven resource utilization and safety risks. Therefore, adjustments to the functional zoning of the teaching building are necessary. The adjustment plan involves a gradual horizontal shift, starting from the 6th floor, where large and small classrooms in Zone B are gradually swapped with the functional areas in Zones A and C, proceeding down to the 3rd floor, optimizing the functional distribution in each zone. Four scenarios (HF1 to HF4) are set, and the total number of people in each zone after the functional zoning adjustments is shown in
Table 5.
2.5.4. Evacuation Personnel Priority Ranking
In Pathfinder, personnel behavior is defined by two states: Seeking and Idling. In the Seeking model, higher-priority individuals prioritize obtaining the optimal path and are granted priority access at the exits during evacuation. Lower-priority individuals must avoid or re-plan their paths. In the Idling model, lower-priority individuals may experience a delay at the start of evacuation, simulating scenarios where evacuation occurs in batches or there is a delay in personnel response. When an individual encounters someone with the same priority, their status remains unchanged. When encountering a higher-priority individual, their status changes to Idling, allowing the higher-priority individual to pass first. During the teaching building evacuation, different groups may significantly affect overall evacuation efficiency due to differences in shoulder width, speed, and reaction time. To further study the impact of priority settings on evacuation time, six different priority scenarios (EP1 to EP6) are set. The specific settings are shown in
Table 6.
2.5.5. Combination Strategies
By combining the above strategies, a random combination approach was used to investigate whether the optimized combination strategies have better evacuation efficiency than a single strategy. The effects of these combination strategies were simulated and evaluated. Five scenarios (CS1 to CS5) are set, with each combination strategy shown in
Table 7.
2.5.6. Psychological Factors of Individuals
In the above scenario, we focused on the influence of physical and architectural factors, but panic and leadership also played significant roles in the evacuation process. To analyze the impact of psychological factors on evacuation efficiency, this study simulated the evacuation process under different panic situations. Considering potential panic reactions during emergencies such as fires, we adjusted individual behavior parameters, including reaction time and walking speed, in Pathfinder software. In panic states, the reaction time was extended, and the walking speed was reduced. Based on these settings, the panic levels were categorized as mild, moderate, and severe to simulate the impact of panic on evacuation efficiency. Three scenarios (P1 to P3) were set. To further investigate the role of leaders in such situations, a “leader” role (e.g., teacher, class monitor) was introduced in the simulation to study its effect on improving evacuation efficiency under different panic levels. The leader’s reaction time was shortened, walking speed was faster than that of ordinary people, and their behavior was set to group guidance. The leader was given higher priority and a specific target path, ensuring they were the first to begin the evacuation. The remaining individuals were assigned lower priority, exhibiting group-following behavior rather than randomly or independently choosing paths. Three scenarios (P4 to P6) were set. The setup for each scenario is shown in
Table 8.