1. Introduction
Fire is a type of major disaster that most frequently and universally affects public safety and social development [
1]. With the promotion and development of higher education, colleges and universities continue to increase enrollment, and the number of resident students continues to rise. Accommodation space generally does not increase at the same pace, increasing the density in student apartments [
2]. Meanwhile, many university buildings have inadequate hardware facilities, incomplete fire protection facilities, imperfect fire emergency systems, and structural designs that are inappropriate for satisfying the current student numbers situation due to their age [
3]. Additionally, some colleges and universities have poor management. Safety awareness in teachers and students is ignored, and they close and lock the safety exits of apartments for management convenience. Additionally, teachers and students illegally park electric vehicles or store items in the stairwells of apartment buildings, blocking safety passages and exits, which increases the difficulty of ensuring safe fire evacuation [
4]. The development of the internet has increased student use of electronic equipment considerably, increasing the electrical power demand in student dormitories. To overcome this, some students make illegal electrical connections or smoke in the dormitory, increasing the chances of starting a dormitory fire [
5]. In addition, a large number of flammable materials, such as bedding and clothing, are stored in limited spaces, creating favorable conditions for starting and accelerating the spread of fires. Furthermore, many teachers and students have a poor awareness of the need for fire protection and do not understand where fire protection facilities are located, or how they should be used. This makes it difficult for them to react appropriately at an early stage to ensure their safe evacuation [
6].
According to statistical data from the National Fire and Rescue Administration in 2021, 32,000 fires occurred in schools and other densely populated areas [
7], resulting in 422 injuries and 179 deaths. Student apartment buildings are difficult to evacuate once a fire has started, due to their high density, making them extremely dangerous. Therefore, an investigation into safe evacuation during a fire in an old multi-story student apartment building is critical to ensuring the safety of students and the sustainable development of building ecology.
There have been many studies conducted on fire-spread in buildings and safe evacuation. For instance, in terms of traditional methods, Hao [
8], Zhan and Chen [
9] used Pathfinder software to conduct fire evacuation simulations for dormitory buildings, finding that the evacuation time increased with a decrease in the number of floors. Liang et al. [
10] used Fire Dynamics Simulator software to simulate the fire scene in a university and found that the fire corridor on the same floor was more dangerous than the dormitory itself, noting that the risk decreased with increasing floor levels. Zou et al. [
11] studied the characteristics of visibility due to smoke, ceiling temperatures, and the safe evacuation time, finding that the effectiveness of fire-fighting facilities and the closure of ignition points in dormitory buildings have a considerable impact on safe evacuation. Joakim et al. [
12] used a questionnaire to study the sensory perception of different groups of people during the design of fire evacuation dissuasive signs, and relevant suggestions were proposed for sign designers. Miao [
13,
14] and Han et al. [
13,
14] analyzed the characteristics and influencing factors, such as building form and functions commonly existing in college dormitories, and then proposed fire prevention measures. Xu et al. [
15] and Jia et al. [
16] used a combination of BIM modeling and PyroSim to analyze the impact of changes in smoke visibility and other parameters of the evacuation process for different buildings, providing reference for evacuation design. Zhang et al. [
17] first optimized the public areas of the subway, and then imported the BIM model into PyroSim to simulate fires in different locations. They used Pathfinder to conduct safety evacuation research, which showed that optimizing the layout can improve the efficiency of safety evacuation. Fu et al. [
18] used PyroSim to simulate fires in confined spaces, exploring the variation patterns of different parameters under different working conditions. Based on the results obtained, they then proposed rectification suggestions for such places.
In terms of new methods, Gerges et al. [
19] and Minji et al. [
20] observed the impact of dynamic emergency clues on evacuation, and sent the evacuation instructions directly to the mobile phones of the evacuees through customization to intelligently find the best exit route for evacuation. Fang et al. [
21] discussed the advantages and disadvantages of current intelligent fire evacuation by using the Internet of Things. They discussed the development opportunities of 5G technology in future building fire evacuations. Yen Chern et al. [
22] designed and developed fire evacuation simulation software using a Belief-Desire-Intention agent plug-in, covering fire, building layout, human multi-agents, and other structural features. Lee et al. [
23] proposed a fire evacuation simulation method that can convert Fire Dynamics Simulator fire-spread data into a unit structure and map it to a FFM, which can quickly calculate the evacuation situation under different fire conditions. The results approximate to the actual situation.
The above studies used traditional methods, such as PyroSim and Pathfinder software, or new technologies such as the Internet of Things and 5G to describe the problems of the fire-spread phenomenon and evacuation times. There are few in-depth studies into fire characteristics, such as horizontal and vertical diffusion of fire-spread, as well as the impact of poor visibility, ceiling temperatures, and other factors. Previous studies also failed to propose targeted and constructive advance prevention and improvement measures during and after a fire event.
In this study, a multi-story student apartment building in a university in the Shandong Province was used as an example. PyroSim software was used to simulate the fire-spread characteristics (visibility due to smoke, ceiling temperatures, and smoke layer heights) on different floors, analyzing the diffusion characteristics of smoke spread during a fire and its impact on safe evacuation. Pathfinder software was then used to simulate and analyze the safe evacuation of personnel and compare the evacuation effectiveness of different safe evacuation plans to obtain an optimal evacuation plan after a disaster for the selected condition. Finally, measures were proposed for dealing with apartment fires in terms of the three dimensions of pre-prevention, emergency startup during a fire event, and post-event summary. These proposals can provide an important theoretical reference for the fire safety and emergency evacuation of college students from apartment buildings, and also provide important guidance for building ecological safety protection and sustainable development.
3. Comparison and Optimization of Safe Evacuation Performance
3.1. Pathfinder Model Construction and Parameter Selection
3.1.1. Introduction to Simulation Software
According to the above analysis of fire smoke spread characteristics, the student apartment building has many rooms and a dense population, aspects which can have a substantial impact on safe evacuation in the event of a fire. The process of safe evacuation embraces the whole process, from fire ignition to the movement of people to an area that is removed from any fire threat. This is mainly determined by the available and required safe evacuation time [
37]. Hence, to intuitively reflect whether people can be evacuated safely, this section describes the building of a Pathfinder evacuation model. In addition, evacuation routes and times are analyzed by customizing the number, speed, and evacuation behavior of personnel. This is then combined with computer graphics simulation and 3D role modeling [
38].
3.1.2. Simulation Parameters Setting
The Pathfinder software is compatible with the AutoCAD
® and PyroSim model file formats and can import PyroSim models directly. Using the situation of the apartment building described in
Section 2, the model was directly imported and rooms and floors were divided, while doors, stairs, emergency exits, etc. were set up and the visibility due to smoke, temperature, and other parameters obtained from the PyroSim simulation were imported, resulting in a close approximation to the actual fire situation.
Because the research object is a male apartment building, the male height follows the normal distribution
N (170, 4) (unit: cm), with the maximum height being 190 cm and the minimum 165 cm, with 42 cm shoulder width. The disorderly and orderly movement speeds are 1.4 m/s and 1.7 m/s, respectively [
39]. The fire was simulated in daytime. Each dormitory can accommodate a maximum of six people; however, people are continually coming, going and washing. Therefore, four people are randomly arranged in each dormitory, six people are arranged in the corridor, eight people are arranged in the washroom, and one person is on duty at the exit of the first floor, totaling 379 people in the dormitory building.
The characteristics of human behavior are set as moving to the nearest safe evacuation staircase immediately or after a certain time. The time follows the normal distribution
N (35, 5) (unit: s). According to the 3σ principle, 99.74% of the people start to evacuate according to the normal distribution
N (35, 25) (unit s), and 0.26% of the people start to evacuate directly [
40]. To simulate the congestion phenomenon caused by human congestion, when evacuation congestion occurs, the diameter of the personnel cylinder becomes 70% of the set diameter, meaning that the diameter reduction factor to prevent congestion is 0.7.
Figure 12 shows the 3D evacuation model built by Pathfinder.
3.2. Evacuation Capacity Analysis for Different Floors
In the previous section, the safe evacuation time through the staircases depended on the fire ignition point. In this section, the simulation analysis as to whether the apartment personnel can complete a safe evacuation is conducted based on the design conditions of the three floors above. The simulation of each working condition was repeated 10 times to improve the accuracy of the simulation results, and tthe number of people safely evacuated and the number of people remaining on the staircases within the safe evacuation time of each plan were monitored. Data with large deviations were eliminated, and its average value was used to analyze the ability to evacuate people.
(1) Evacuation analysis with R2-205 ignition
The safe and unsafe evacuations were monitored separately, and the statistical results are shown in
Figure 13a, where the Exited (Total) represents the total number of people safely evacuated, Floor
i (
i = 2, 3, 4, and 5) represents the number of people remaining on Floor
i after the safe evacuation time has been reached, and Stair (
j –
j + 1) (
j = 1, 2, 3, and 4) represents the number of people remaining on the staircases between Floor
j to
j + 1.
Figure 13 shows that the people began to evacuate in a relatively short time and continued to transfer from each floor to the stairs, which showed that the change curve of the number of people on the staircases lagged behind that for those remaining on the floor. In addition, the floor characteristics of evacuation capacity show that the safe evacuation was faster for the higher floors. The complete evacuation of the fifth floor only took 78 s, while that of the fourth and third floors were 134 s and 165 s, respectively. According to the results in
Table 4, the safe evacuation time of the WCS and ECS following R2-205 ignition was 170 s and 172 s, respectively. After 172 s, both staircases could not be safely used for evacuation; however, the stairs on other floors were available. Data statistics show that people on floors 3–5 and corridors, and stairs 1-2/3-4/4-5 could be safely evacuated after 172 s. The 315 people that are reflected by the Exited (Total) were safely evacuated, with only a few people remaining on Floor 2 (26 people) and stairs 2-3 (38 people). The above 64 people were not able to safely evacuate, as shown in
Figure 13b If no emergency measures were taken, they would be affected by the fire.
(2) Evacuation analysis with R3-310 fire
As shown in
Figure 14, after ignition in R3-310, the centralized evacuation and floor characteristics were similar to those for R2-205 ignition.
Table 4 shows that the WCS and ECS were affected by fire smoke and temperature after 181.2 s and 132 s, respectively, but after 181.2 s, people on floors 3–5 and the corresponding staircases had been safely evacuated, and only a few people on Floor 2 and stairs 1-2 remained. However, because the fire smoke on this floor had significant vertical upward diffusion characteristics (
Table 1), only Floor 2 and stairs 1-2 were located below Floor 3, and the delayed people who were still transferring would complete the safe transfer within 210 s, leading to 379 people in the whole building being completely transferred safely. Hence, based on the simulation scenario and parameters, ignition in R3-310 could complete the safe evacuation of all people, although there was no slack in the evacuation time (the complete evacuation of stairs 2-3 took approximately 180 s, which is equivalent to the actual safe evacuation time). If the occurrence of overcrowding or other adverse conditions is considered, there is the possibility of incomplete evacuation.
(3) Evacuation analysis with R5-516 ignition
Because the fire smoke has significant horizontal and vertical upward diffusion characteristics, the smoke and temperature have a relatively small impact on the bottom floor when the fire is on the top floor. Therefore, when simulating the top floor fire, the main investigation focuses on the people evacuation from the top floor (Floor 5) and its adjacent stairway (stairs 4-5). Evacuation below the fifth floor can be considered as successful. It can be seen from
Figure 15 that it takes 70 s for people on Floor 5 to complete the evacuation, while the time for complete evacuation of stairs 4-5 is approximately 103 s, which is within the available time for safe evacuation (
Table 2 shows that the safe evacuation time of stairs on the west and east sides is 168.1 s and 70 s, respectively). Finally, after 183 s, the statistics show that 379 people in the whole building completed the evacuation, indicating that, under this simulated working condition, in the event of a fire on the top floor, all of the people in the building can be evacuated safely.
To summarize, for ignition on the middle (R3-310) and top floors (R5-516), all of the people can complete safe evacuation under design conditions. Some safe evacuation can be completed with bottom floor ignition (R2-205), which is shown by the increasing difficulty of safe evacuation when fire ignition changes from the top to the bottom of the building. The safe evacuation takes progressively longer (the complete safe evacuation time for ignition on floors 5 and 3 are 180 s and 210 s, however safe evacuation could not be completed for ignition on Floor 2).
3.3. Optimization Analysis of Safe Evacuation Drill Plan
In the above simulation scheme, the emergency exit at the bottom (first floor) of the east side is set to be closed, resulting in the safe evacuation of all people being unachievable. In fact, two important factors affecting safe evacuation are the number of emergency exits and whether evacuation is orderly. Hence, to ensure the fire emergency treatment and improve the evacuation efficiency, the number of emergency exits available must be considered, as should whether the evacuation is orderly. The evacuation emergency plan needs to be studied in advance and an optimal safe evacuation plan determined, as only then can the fire emergency plan and emergency path be determined, with a view to providing targeted prevention strategies after the fire.
Based on the above description analysis and the actual situation of the apartment building, in addition to considering the number of emergency exits (one or two) and whether the evacuation is orderly (orderly or disorderly), a total of four fire evacuation drill schemes were established, as shown in
Table 5. The Pathfinder simulation software was also used to monitor and count the number of people evacuated and the evacuation time in each of the four schemes. This enabled the number of people still in the building and still transferring in the evacuation stairways to be determined for each scheme, as shown in
Figure 16.
Figure 16 shows that, after the fire, the number of people in the evacuation stairway for each of the four plans changes in a similar way as the time after ignition increases, which is characterized by a rapid increase
–flat
–rapid decrease. This is due to the phenomenon of rapid accumulation
–a large amount of accumulation or congestion
–a rapid evacuation.
By comparing and analyzing
Figure 16a,b, it can be seen that, when the emergency exits on both sides are open, the gentle phase of the change curve of the number of people in the orderly evacuation is significantly shorter than that in the disordered state, while the overall completion of the evacuation takes 104.7 s in the orderly state and 117.3 s in the disordered state. This indicates that the evacuation time is shorter for an orderly evacuation, which is more conducive to the rapid and safe complete evacuation of people. Similarly, comparing
Figure 16c,d, the orderly evacuation is more conducive to safe evacuation; however, when only the west emergency exit is open (the simulation software is programmed to only open the west emergency exit by default, so that the best evacuation route is to transfer to the west emergency evacuation staircase), the evacuation times of the two plans are 175 s and 147.3 s, respectively. These times are much longer than when the emergency exits on both sides are opened, showing that the number of emergency exits has a significant impact on the success of safe evacuation. Therefore, the comparison analysis of personnel evacuation in the above four schemes shows that the evacuation time is the shortest when the emergency exits on both sides are open and orderly evacuation takes place. Hence, Plan 2 is the best one for evacuation and should be strengthened in the future.
In
Section 3.2, when ignition occurred in R2-205, not all evacuations could be completed safely. Using this condition as an example, the safe evacuation time after the fire was 172 s; however, according to the above four evacuation plans, Plan 3 only opens the west emergency exit and takes 175 s for disordered evacuation, which does not achieve complete evacuation. The other three schemes can achieve a completely safe evacuation, but the effect of improving the evacuation efficiency differs. As shown in
Table 6, the evacuation efficiency of plans 1 and 2 has been improved by 31.8% and 39.13% compared with that of ignition in R2-205. The efficiency of Plan 4 has been improved by only 14.36%, which also indicates that opening the emergency exits and orderly evacuation are the best factors for ensuring safe evacuation. In addition, to obtain the importance order of the number of emergency exits and whether the evacuation is orderly, the effects on safe evacuation of varying the number of open exits, as well as orderly and disorderly exits were calculated and compared. It was found that the improvement to the evacuation efficiency of opening the second exit door was approximately 30% on average. The improvement of orderly over disorderly movements increased the efficiency by 15% at most, which is far less than the number of exit doors. This confirms that the impact of the number of safe evacuation exits is more significant than orderly evacuation, as shown in
Figure 17. The above results also provide theoretical guidance for the improvement of safety awareness and measures in the apartment building.
To summarize, based on the actual apartment building situation and comparing the four evacuation drill schemes, the optimized plan 2 (open two emergency exits and orderly evacuation) has the best evacuation efficiency, and the evacuation effect is significantly improved by 39.13% for the planned R2-205 ignition. Meanwhile, it was found that the number of emergency exits has a more significant impact on the evacuation effect than whether the evacuation was orderly or not.
4. Proposed Fire Prevention and Evacuation Measures
It has been shown above that the evacuation time of a student apartment building is relatively short once the fire starts, which brings great challenges for the safe evacuation of students due to the high student density. Therefore, considering the time characteristics of fire development, fire prevention and evacuation measures are proposed in the three dimensions of pre-fire incident, during-fire incident, and post-fire incident, which is also a better implementation of the policy of “prevention first, prevention combined”.
(1) Prevention measures
Optimize fire protection design and improve fire safety. This apartment building is an old building, and should therefore be updated with added mechanical smoke exhaust systems to reduce the diffusion of smoke inside the building, thus increasing the safe evacuation time [
41]. Fire prevention measures such as smoke and temperature sensors and sprinkler systems should be added. The sensors can detect and sound an alarm timeously. Adding fire doors can establish separate fire compartments and limit the fire to finite elements. Adding to and inspecting firefighting equipment, such as fire extinguishers, and ensuring all staff learn how to use the equipment effectively is imperative, as is [
42] improving the apartment building training and management systems, as well as the management, emergency, and psychological comfort of the management personnel [
43].
Strengthen safety education and formulate safety emergency plan. The above results show that orderly evacuation is more conducive to the safe evacuation than disordered evacuation. Therefore, the property department should carefully consider the current building evacuation performance, clarify the number and location of personnel, comprehensively develop a set of feasible fire emergency plans and regularly drill according to the optimal evacuation plan. They should also invite the local fire department to evaluate the plan and rectify it timeously if necessary. Evacuation routes should be clearly marked on walls and doors on each floor. Emergency exits and emergency exit indication signs should be added, and, to combat low visibility due to smoke, sound signals should be turned on to guide the evacuation [
44]. Improving the safety awareness and knowledge of all personnel, broadcasting videos of relevant accidents and safety training for display on screens around the building, and regularly training and evaluating student safety and psychological knowledge, while ranking them, could also be beneficial.
Strengthen safety patrol inspections and eliminate hidden dangers. The comparison of evacuation drill plans found that the number of safety exits has a significant impact on evacuation. Therefore, daily inspections of evacuation staircases and safety exits should be conducted to ensure the smooth flow of emergency evacuation routes. Regularly hiring third-party testing institutions or local fire departments to inspect and evaluate fire-fighting facilities in the building, registering and recording the location of hidden accident facilities, and ensuring that a responsible person makes the necessary rectification within a time limit; hiring a qualified fire protection equipment maintenance company for regular maintenance of fire protection facilities in the building to ensure the functionality of fire protection facilities and improving the completeness of fire safety management are all imperative.
Improve rules and regulations and strengthen institutional constraints. The fire department may carry out strict inventory spot checks periodically on the student apartment buildings in their jurisdiction and take reasonable measures to publicize, notify, rectify, and close down the problems found. The property should be divided into fire zones and responsible persons assigned to monitor each zone. Problems should be reported for rectification or suspension of use. In addition, the relevant rules and regulations should be studied, study meetings held, personnel fire knowledge assessments conducted, etc., to improve the fire control level. Establishing a multi-party linkage mechanism of organizations, including the fire brigade, property management, alarm points, and hospitals, and developing a fire warning and linkage platform under the auspices of big data technology is important, as is ensuring that all parties are connected to resolving and rectifying problems in advance, completing timely rescue operations, and providing feedback results on time to improve the speed and accuracy of action in the whole cycle of accident occurrence, as well as reducing the impact of fire accidents.
(2) Emergency response during the incident
Start the plan in time to evacuate people. After a fire occurs, the property management unit and dormitory management personnel should, according to the severity of the fire incident, launch an emergency plan timeously at an appropriate level, organize a team to extinguish the fire at the initial stage, notify the school security department and fire brigade, and report the fire situation and details of any trapped personnel. Evacuation leading and working groups should be established immediately to evacuate the people from the building. The evacuation leader and the group should maintain communication. If an exit cannot be used, the route shall be immediately reported and re-planned to prevent congestion and serious accidental injuries. If it is impossible to evacuate all of the people, attempts should be made to try to evacuate the floors above the ignition point to two floors below the ignition point to avoid casualties on the high floors. Evacuation of all other personnel should then be initiated according to the fire development situation until all people are accounted for.
Improve self rescue ability and increase chances of rescue. If the evacuation is not completed in a timely manner after an accident, the self rescue ability should be improved, the dormitory doors and windows should be closed in a timely manner, and moist materials should be used to block the gaps to prevent flames from spreading into the interior of the dormitory. When the fire situation decreases or there is an opportunity for evacuation, evacuation should be carried out quickly. No one should advance blindly in the process of escape, and everyone should evacuate according to the horizontal and vertical characteristics of smoke spread, always paying attention to the surrounding environment to cause damage by sudden flame.
(3) Post-incident Summary
Summarize the accident experience and timely feedback and study. The fire department should collect and assess recent accidents, sharing them with relevant units in the area to learn and summarize, especially those resulting in property losses and casualties. All colleges and universities should carefully study and comprehensively consider the occurrence and development of accidents and emergency evacuations, understand the lessons learned, learn from the experience, and compare whether there are problems in their own plans. The property management unit can establish a monthly fire control report to review the current problems checked by the fire department and focus on the fire control of evacuation routes and emergency exits.
Enhance rescue capabilities and enhance overall quality. For fire department and property management, it is necessary to update existing rescue equipment in a timely manner, rectify fire-fighting facilities within each jurisdiction, continuously conduct self drills, maintain a good level of business, and improve rescue capabilities after a fire occurs. At the same time, we will strengthen our publicity and education capabilities within our jurisdiction, utilize new technologies (such as VR) to conduct virtual reality rescue drills and fire prevention education, and improve fire safety from a practical perspective.