Evacuation Patterns of Occupant Groups in Super High-Rise Building Stairwells Under Different Visibility Conditions

Abstract

Stairwells constitute critical escape routes for emergency evacuation during building disasters. The spread of fire smoke and the failure of lighting systems can significantly reduce visibility within stairwells, thereby adversely affecting evacuation speed. This issue is particularly pronounced in super high-rise buildings. In this study, a typical super high-rise building was selected as the experimental site. The variation laws of key parameters such as evacuation time, speed, and heart rate were investigated for groups with different gender proportions in stairwells under different visibility conditions. The experimental results show that: First, collaboration within multi-person groups can effectively mitigate the adverse impact of reduced visibility on evacuation speed. Second, different gender proportions within groups affect evacuation speed, with groups having a higher proportion of males demonstrating relatively faster evacuation speed. Third, under identical visibility conditions, the heart rates of multi-person groups during evacuation are generally lower than those of individual groups; in low-visibility environments, the heart rates of members within the same group are significantly higher than those under normal visibility conditions. Accordingly, this study proposes a mixed-gender group evacuation strategy under low-visibility conditions. The findings provide empirical data support for the formulation of emergency evacuation response strategies in super high-rise buildings.

1. Introduction

In super high-rise buildings, the safe evacuation of occupants has always been a core issue in both pre-construction design and post-construction operation management. Their inherent characteristics—including considerable vertical height, high occupancy density, and long evacuation routes—expose them to severe challenges in emergency evacuation during sudden disasters such as fires. Among various evacuation routes, stairwells stand as the sole vertical evacuation channels independent of power systems, and their evacuation efficiency directly determines the level of life safety protection for occupants [1]. Once a sudden disaster occurs, stairwells become the primary means of escape and critical channels for emergency evacuation.

Regarding occupant evacuation behavior in stairwells, numerous scholars have conducted extensive research on descending movement characteristics under normal visibility conditions. For instance, researchers explored the features of occupants’ free descending movement [2], investigated the average descending speed of occupants [3], and analyzed the impacts of factors such as travel distance, gender, age, and congestion level on speed [4]. Existing studies have demonstrated that movement speed in stairwells is influenced by multiple factors, including evacuee characteristics [5], age structure [6], merging effects [7,8], staircase type [9], exit placement [10], and the use of handrails [11].

Regarding the impacts of visibility on evacuation decision-making and behaviors, scholars have adopted diverse research methods and conducted studies across different scenarios. The relevant findings can be categorized into two core directions. On the one hand, research focuses on the basic laws and methodological innovations of evacuation in low-visibility environments: Nagai et al. [12] verified the significant impact of exit layout on evacuation efficiency in zero-visibility rooms; Isobe et al. [13] conducted experiments and simulations on evacuation in zero-visibility rooms, and observed that occupants are prone to “herd gathering” and unbalanced exit selection; Xue et al. [14] confirmed that the “wall-following” behavior under limited visibility can improve evacuation safety and efficiency; Son et al. [15] systematically investigated the effects of door opening direction, handle type, and low visibility on the door opening process through controlled variable experiments; Lotero et al. [16] proposed an evacuation route optimization method under low visibility in the context of underground coal mines; Akizuki [17] discussed evacuation route design based on visibility to reduce evacuation delays. On the other hand, relevant research has been further extended to different evacuation scenarios and building types: Schmidt-Polonczyk et al. [18] verified the significant impact of low visibility on evacuation efficiency through full-scale experiments in road tunnels; Zeng et al. [19] confirmed that group collaboration can mitigate the adverse impacts of evacuation in tunnels under zero-visibility conditions; related studies have also analyzed the speed changes in occupants traversing smoke-filled corridors [20] and the evacuation behavior patterns in stairwells under different visibility conditions [21,22], verifying that smoke-induced low visibility can significantly reduce the movement speed of occupants [23,24]. Meanwhile, aiming at various types of buildings such as tunnels [25,26], metro stations [27,28], pre-school education institutions [29], seasides [30], cruise ship theaters [31] and retail stores [32], scholars have explored the evacuation rules under different visibility conditions and put forward optimization schemes. However, current research on evacuation rules in stairwells of super high-rise buildings under different visibility conditions remains relatively scarce. Most stairwells in super high-rise buildings are located in the core area of the building plan and generally lack natural lighting. In the event of sudden disasters such as fires, smoke can easily spread, and emergency lighting systems may malfunction, leading to a significant decrease in stairwell visibility and thereby greatly increasing the risk of safe occupant evacuation.

Group size is also a crucial factor affecting evacuation speed, and some scholars have conducted a series of studies on the evacuation effects of group behavior. In high-rise office building scenarios, three sets of stairwell evacuation experiments found that cooperative behavior in multi-person groups can effectively reduce evacuation conflicts, optimize travel order, and exert a significantly positive effect on improving evacuation efficiency [33]. Subsequent studies have further analyzed the movement characteristics and coordination mechanisms of multi-person groups from multiple dimensions: Haghani et al. [34] explored the dynamics of social groups’ decision-making in evacuations; Mitsopoulou et al. [35] used Cellular Automata to analyze the impacts of spatial games and memory effects on crowd evacuation behavior; Fachri et al. [36] proposed a multi-agent system-based crowd evacuation scheme with leader-following behavior—these studies together provide solid theoretical and methodological support for systematically understanding group evacuation rules [37]. Vecliuc et al. [38] further verified the positive effect of collaborative behaviors in emergency evacuation through targeted empirical analysis, and Zablotsky et al. [39] supplemented research on the imitation of cooperative behavior in pedestrian evacuations. Regarding the combined effects of visibility and group coordination, the academic community has carried out more targeted empirical research: through a series of controlled experiments, scholars explored the quantitative impact of visibility conditions on group movement trajectories, coordination efficiency, and overall speed [40]. Although existing studies have initially revealed the positive impact of group size and cooperative behavior on evacuation efficiency [41], there remains an obvious research gap: current academic discussions on the internal structure of multi-person groups mostly focus on the dimension of size, while empirical research on how the gender proportion—a key structural characteristic within groups—affects evacuation speed is relatively lacking. Considering the inherent differences between men and women in physiological functions, emergency responses, and decision-making preferences, their interaction modes and behavioral choices during group evacuation may vary significantly, thereby influencing overall evacuation efficiency. Therefore, the underlying mechanism of this issue urgently requires further in-depth exploration.

Accordingly, this study conducted emergency evacuation experiments under different visibility conditions in a super high-rise building located in Xinyang City, Henan Province, China. Three experimental scenarios were established: individual evacuation, two-person group evacuation, and three-person group evacuation. For each scenario, emergency evacuation experiments under three visibility conditions were carried out, respectively: ① normal lighting in the stairwell (simulating a smoke-free normal environment); ② wearing eye masks with 18% light transmittance (simulating a low-visibility environment affected by mild smoke); ③ wearing eye masks with 6% light transmittance (simulating an extremely low-visibility environment affected by dense smoke). The aim is to deeply explore the evacuation characteristics of groups with different gender proportions under various visibility scenarios. During the experiments, key parameters such as evacuation time, speed, heart rate, and group behavioral characteristics were focused on collecting to accumulate empirical data on emergency evacuation of super high-rise buildings. The innovativeness of this study is mainly reflected in the following three aspects: First, it breaks through the limitation of existing studies that mostly focus on group size, takes gender as a variable to systematically explore the differences in evacuation efficiency of groups with different gender proportions in low-visibility environments, and reveals the potential impact of gender proportion on group evacuation behavior. Second, it conducts a coupling analysis of visibility gradient and group characteristics, and constructs a multi-dimensional variable system of evacuation scenarios, which provides a more refined research framework for analyzing the laws of group evacuation in complex environments. Third, it carries out experiments based on the stairwells of real super high-rise buildings, which makes up for the deficiency that existing studies are mostly concentrated in conventional scenarios such as tunnels, corridors and underground spaces, and provides key empirical data for the formulation of emergency evacuation strategies for super high-rise buildings, a high-risk scenario. This study further explores the optimization of group size and organizational structure to accommodate evacuation requirements under varying visibility conditions through the aforementioned innovative experimental design. It not only provides support for deepening the research on group evacuation characteristics in stairwells under different visibility conditions and improving the effectiveness and safety of emergency evacuation strategies but also offers a scientific basis for optimizing emergency evacuation plans of super high-rise buildings and improving the theoretical system of occupant evacuation in stairwells.

2. Experimental Design and Analysis Methods

2.1. Experimental Site

This study was conducted in Building B of a super high-rise building located in Xinyang City, Henan Province, China, which was selected as the experimental site. The building consists of 27 storeys, with an overall height of approximately 135 m and a standard floor height of 4.30 m. Floors 9 and 19 serve as refuge floors, each with a floor height of 5.60 m. The building functions as an office complex and adopts a typical frame–core tube structural system. The building plan is square in shape and symmetrically distributed along the east–west axis. The selected building exhibits representative characteristics of high-rise office complexes in China with heights of approximately 100 m, thereby providing a certain degree of generality. Based on these architectural and structural features, this building was chosen as the research object to provide reference value for construction safety management and evacuation studies in similar types of high-rise buildings.

The refuge floor of the experimental building selected in this study has two core characteristics: first, it has an independent physical space, which is separated from other areas by fire partition walls with a fire resistance rating of not less than 3.00 h, and the floor slab has a fire resistance rating of not less than 2.00 h, enabling effective fire and smoke isolation; second, it features a relatively high floor height, which can provide sufficient space for the temporary stay of personnel and the assembly and distribution of supplies, meeting the physical recovery needs during long-distance evacuation. Meanwhile, this refuge floor is equipped with smoke control and exhaust systems, emergency support facilities and life support facilities in accordance with relevant specifications, which can provide safe shelter for evacuees in disaster scenarios. From the perspective of actual evacuation scenarios in super high-rise buildings, occupants who evacuate via stairwells to refuge floors typically pause briefly to rest or adjust their subsequent evacuation strategies. Consequently, the stair segments between refuge floors can be regarded as relatively independent and complete evacuation units. Based on this consideration, the stairwell segment between the 9th and 19th floors was selected as the experimental scope of this study. This selection enables a focused investigation of stair-descending movement characteristics within a single refuge interval, while avoiding potential interference arising from the interaction of evacuation behaviors associated with different refuge floors. Moreover, it closely reflects the practical evacuation pattern of “segment-based evacuation” observed in real emergency situations. The detailed structural configuration of the selected stairwell segment is illustrated in Figure 1.

The total vertical height of the evacuation stairwell selected for the experiment was 47.9 m, with a stair width of 2.650 m. During the experiments, evacuation was conducted from the 19th floor down to the 9th floor. The floor-to-floor height from the 10th to the 18th floors was uniformly 4.3 m, and detailed dimensional information for each floor is provided in

Table 1. Stairwell dimensional information.

Floor No.	Floor Height	Entrance Landing Dimensions	Intermediate Landing Dimensions	Number of Stair Flights	Number of Steps per Flight
10–18	4.3	2.650 m × 1.780 m	2.650 m × 1.400 m	2	12
9	5.6	2.650 m × 1.520 m	2.650 m × 2.440 m	4	7

. The riser height and tread depth of all stair steps were 17.5 cm and 26 cm, respectively. Emergency evacuation signage was installed on each floor within the stairwell. The experiments investigated occupant movement during stairwell evacuation under the condition that the fire door on the fire-origin floor remained open.

2.2. Experimental Scheme Design

2.2.1. Experimental Equipment

A total of 22 high-definition cameras were employed in the experiment. One camera was installed at the landing of each floor to continuously record participants’ behaviors throughout the evacuation experiments. Through post-processing and analysis of the recorded video data, key parameters—including evacuation time, average movement speed, and movement preferences—were obtained. To avoid potential risks such as temporary malfunctions of the camera equipment, lens occlusion, or video frame loss during the experiment, each participant was also provided with a handheld stopwatch. Participants were required to hold the stopwatch in their non-dominant hand, and press the Lap button to record the arrival time upon reaching the marked position on each floor; upon arriving at the finish line, they pressed the Stop button to record the total evacuation duration. This operation not only prevents incomplete data caused by video loss or freezing, but also serves for cross-verification with the time stamps calibrated from the video footage. If the deviation between the two sets of data exceeds 0.5 s, the video footage must be reviewed frame by frame to ensure the accuracy of the experimental data. The instruments used for experimental data acquisition are listed in

Table 2. Summary of experimental data acquisition instruments.

Data Acquisition Instrument	Model	Usage	Image
Camera	WEA gun–dome linkage D13 (Digimerge Technologies Inc., New Jersey, United States)	Records the times at which participants pass each floor and their evacuation behaviors.
Stopwatch	M3-S100 (Shanghai Precision Instruments Co., Ltd., Shanghai, China)	Records arrival times at each floor and is used to calibrate video data to ensure the completeness and accuracy of participant data.
Illuminance meter	UT381A (UNI-T (Uni-Trend Technology (China) Co., Ltd.), Guangdong, China)	Measures stairwell illuminance and the light transmittance of eye masks to calculate the extinction coefficient.
Chest-strap heart rate sensor	Bigrun Team BRT PLUS (Zhejiang Dapao Technology Co., Ltd., Zhejiang, China)	Records heart rate variations in participants during evacuation.

, and the placement of the light-blocking eye masks and monitoring devices worn by participants is illustrated in Figure 2.

2.2.2. Experimental Parameter Design

• Extinction coefficient

To ensure participant safety, eye masks with different light transmittance levels were adopted to simulate different visibility conditions [28]. When a light beam with a wavelength of λ passes through smoke, the extinction coefficient can be described according to the Lambert–Beer law as follows:

$$C_S={\displaystyle \frac{1}{L}}\ln \left({\displaystyle \frac{I_{\lambda 0}}{I_{\lambda }}}\right)$$

(1)

By transformation, the expression for the light transmittance of the eye mask can be derived as follows:

$$T[\%]={\displaystyle \frac{I}{I_0}}\times 100=100\times \exp (C_{S}L)$$

(2)

where $I_{\lambda 0}$ denotes the intensity of the incident light (cd); $I_{\lambda }$ denotes the intensity of the transmitted light (cd); $C_s$ denotes the extinction coefficient (${\mathrm{m}}^{-1}$); $L$ denotes the distance between the light source and the object (m); and T denotes the light transmittance of the eye mask.

According to the above equations, under a given visibility condition (i.e., a fixed eye-mask light transmittance), the extinction coefficient of smoke is inversely proportional to the average incident light path length. In this study, visibility was adjusted by different levels of the eye-mask light transmittance (T), thereby restricting the viewing distance of participants. The relationship between the extinction coefficient ($C_s$) and the average incident light path length (L) is presented in

Table 3. Relationship between extinction coefficient (Cs) and distance of light source and object (L).

18% Light Transmittance Eye Masks				6% Light Transmittance Eye Masks
L/(m)	Cs [m−1]	L/(m)	Cs [m−1]	L/(m)	Cs [m−1]	L/(m)	Cs [m−1]
1	1.705	5	0.341	1	2.813	5	0.563
2	0.852	6	0.284	2	1.407	6	0.469
3	0.568	7	0.244	3	0.938	7	0.402
4	0.426	8	0.213	4	0.703	8	0.352

.

As indicated in Table 3, when participants wore eye masks with 18% light transmittance, objects could be recognized within a distance range of approximately 3–7 m, which corresponds to smoke density conditions in the range of 0.244~0.568 m⁻¹ within this spatial interval. When participants wore eye masks with 6% light transmittance, objects could be recognized within a shorter distance range of approximately 2–5 m, corresponding to smoke density conditions of 0.563~1.407 m⁻¹ in the same spatial context.

2.

Calculation of Evacuation Distance and Speed

The evacuation distance of occupants in stairwells should consist of two components: the evacuation distance along the stair treads and that on the landings [42]. The calculation method is expressed by the following equation:

$$L_L=\sum _{i=9}^{n=18}\left(L_{\mathrm{landing},i}+L_{\mathrm{tread},i}\right)$$

(3)

$$L_{\mathrm{landing},i}=\left\{\begin{array}{cc}\pi r,i=10\text{-}18& \\ 2\pi r,i=9\hfill & \end{array}\right.$$

(4)

$$L_{\mathrm{tread}}=n\sqrt{\left(d^2+h^2\right)}$$

(5)

where r denotes the width of the stair flight; d denotes the tread depth; h denotes the riser height; n denotes the number of steps in a stair flight, i = 9, n = 32; i = 10, 11, 12, ……, 18, n = 24.

Based on the above data, the calculated evacuation distances are presented in

Table 4. Evacuation distance.

Stair Flight	Evacuation Distance (m)
S9–10	12.93
Si–j	11.56

Note: In the table, i = 10, 11, 12, ……, 18; j = i + 1.

.

The evacuation speed of occupants on each floor can be calculated using the following equation:

$$v_i=L_i/t_i$$

(6)

where $v_i$ denotes the evacuation speed on the i-th floor, $L_i$ denotes the evacuation distance on the i-th floor, and $t_i$ denotes the walking time along the stair flight on the i-th floor.

The total evacuation movement speed of occupants can be calculated as follows:

$$V={\displaystyle \frac{L_L}{T}}={\displaystyle \frac{{\sum }_{i=9}^{18}(L_{\mathrm{tread},i}+L_{\mathrm{landing},i})}{T_{\mathrm{end}}-T_{\mathrm{start}}}}$$

(7)

where T denotes the total evacuation time of occupants in each experimental group.

2.2.3. Experimental Methods

The objective of this study was to investigate the movement patterns of downward evacuation for individual occupants and multi-person groups in stairwells of super high-rise buildings under different visibility conditions. Three evacuation configurations were established: individual evacuation, two-person group evacuation, and three-person group evacuation. For each configuration, evacuation experiments were conducted under three visibility conditions: ① normal stairwell lighting, simulating a smoke-free environment; ② wearing eye masks with 18% light transmittance, representing a low-visibility environment under mild smoke conditions; ③ wearing eye masks with 6% light transmittance, representing an extremely low-visibility environment under dense smoke conditions. Experimental simulations were carried out separately for individual evacuees, two-person groups, and three-person groups, and the corresponding evacuation speeds were calculated. The effects of group size and visibility conditions on evacuation time were subsequently analyzed. The experimental scenarios are summarized in

Table 5. Experimental conditions.

Experimental Condition	Group	Visibility Condition	Code
Condition I	Individual (M/F)	Normal visibility	A
		Wearing eye masks with 18% light transmittance	B
		Wearing eye masks with 6% light transmittance	C
Condition II	Two-person group (MM/MF/FF)	Normal visibility	D
		Wearing eye masks with 18% light transmittance	E
		Wearing eye masks with 6% light transmittance	F
Condition III	Three-person group (MMM/MMF/MFF/FFF)	Normal visibility	G
		Wearing eye masks with 18% light transmittance	H
		Wearing eye masks with 6% light transmittance	I

.

A total of 72 participants without mobility impairments were recruited for the experiment, including 36 males and 36 females. The participants were aged 20–35 years, consisting mainly of young adults. The selection of this age group was based on two key considerations: first, the office population in super high-rise buildings is predominantly young adults, so the sample characteristics align with the actual user population of the research scenario; second, young adults have no obvious mobility impairments and their physical condition is relatively stable, which mitigates the interference of age-related physiological differences on indicators such as evacuation speed and heart rate. To simultaneously control the interference of the learning effect and individual physiological differences on the experimental results, we first divided the participants into 12 basic groups by gender proportion, with each basic group participating in only 3 mutually exclusive scenarios covering different visibility conditions and group sizes (e.g., A, F, I or B, E, H, etc.) to avoid the accumulation of skills in homogeneous scenarios. The interval between multiple experimental scenarios for the same participant was no less than 72 h to ensure memory attenuation and physical recovery. Finally, the execution order of the 3 scenarios within each basic group was determined via the random number table method to avoid errors caused by a fixed sequence. Subsequently, a one-way analysis of variance was conducted on the age, height and body weight of participants under Conditions I/II/III using SPSS 26.0. The results showed that there were no statistically significant differences in all indicators among the three groups (p > 0.05), and the coefficient of variation (CV) of each group was strictly controlled within 5%, which ensured a uniform distribution of the basic physiological characteristics of participants across all scenarios. Prior to the experiment, all participants were fully informed of the experimental objectives and procedures, and were required to refrain from engaging in strenuous physical activity for at least 24 h before testing. According to the assigned visibility conditions, participants were instructed to wear eye masks with the corresponding light transmittance and to undergo a 3 min adaptation period before entering the stairwell to formally commence the experiment. To facilitate identification and the collection of movement data, numbered tags ranging from 1 to 72 were affixed to both the front and back of each participant’s body. This arrangement enabled accurate identification during subsequent manual data extraction from the video recordings, as illustrated in Figure 3.

All participants were equipped with timing devices for time recording. Upon receiving the start instruction, participants initiated evacuation, with the start time and the times at which they reached the reference points on each floor being recorded, until timing concluded when they arrived at the reference point on the 9th-floor landing. Throughout the entire testing process, participants wore chest-strap heart rate sensors to continuously record heart rate data. During the experiments, participants were instructed to move as quickly as possible in order to simulate evacuation characteristics under emergency conditions. After the experiments, questionnaire surveys were administered to collect information on participants’ gender, age, height, weight, and subjective perceptions during the evacuation process. The full questionnaire is provided in Appendix A. Based on these data, statistical analysis and data organization were conducted, and the basic physical parameters of the experimental participants are summarized in

Table 6. Statistics of basic physical parameters of experimental participants.

Condition	Gender	Average Age (Years)	Average Height (cm)	Average Weight (kg)
Condition I (Individual)	Male	25.8	175.5	72.9
	Female	24.6	162.3	56.7
Condition II (Two-person group)	Male	27.1	174.9	71.1
	Female	25.3	164.8	54.3
Condition III (Three-person group)	Male	26.5	176.6	70.8
	Female	26.1	163.7	55.2

.

3. Experimental Results and Discussion

3.1. Evacuation Time on Each Floor Under Different Experimental Conditions

Table 7. Downward evacuation time of each group under three visibility conditions.

	Visibility Code	Gender	Evacuation Time Range (s)	Mean Time (s)	Standard Deviation (SD)	Time Increase Rate (vs. Normal Visibility)
Individual group	A	M	49.4–68.8	58.6	6.0	-
		F	60.3–80.1	69.9	6.4	-
	B	M	54.0–72.7	63.7	6.5	8.7%
		F	64.4–83.6	74.2	5.9	6.1%
	C	M	57.6–78.3	68.6	7.0	17.1%
		F	71.2–90.2	81.4	5.9	16.4%
Two-person group	D	MM	53.2–61.1	57.0	3.4	-
		MF	61.7–69.0	64.9	3.1	-
		FF	67.7–77.8	72.2	4.3	-
	E	MM	57.3–65.1	61.2	3.3	7.2%
		MF	66.1–75.6	70.4	4.0	8.5%
		FF	73.4–82.3	78.0	3.9	8.0%
	F	MM	61.1–69.0	65.0	3.4	14.0%
		MF	70.8–81.7	75.4	4.8	16.2%
		FF	77.3–87.3	82.7	4.3	14.5%
Three-person group	G	MMM	54.9–61.3	58.2	2.8	-
		MMF	61.9–67.0	64.6	2.2	-
		MFF	64.7–72.9	69.0	3.5	-
		FFF	73.2–81.1	76.8	3.4	-
	H	MMM	57.3–64.1	60.5	3.0	3.9%
		MMF	64.6–69.6	66.9	2.2	3.7%
		MFF	68.0–76.6	72.5	3.7	5.0%
		FFF	77.1–84.7	80.8	3.3	5.2%
	I	MMM	60.1–65.9	63.0	2.6	8.2%
		MMF	67.8–72.1	69.5	2.0	7.6%
		MFF	71.8–79.7	75.9	3.3	10.0%
		FFF	80.5–88.7	84.3	3.5	9.8%

Note: In the table, M represents male and F represents female. A–I represent the codes of experimental scenarios.

presents the evacuation time data for each group on each floor during downward evacuation from the 19th floor to the 10th floor under three different visibility conditions. As the 9th floor functions as a refuge floor and has a different floor height, the evacuation time associated with the refuge floor is not included in the analysis in this subsection.

Under normal visibility conditions, the variability of evacuation time progressively decreases with increasing group size. The experimental results show that the evacuation time ranges for individual participants were 19.4 s for males (M) and 19.8 s for females (F). For two-person groups, the corresponding ranges were 7.9 s for male–male (MM), 7.3 s for male–female (MF), and 10.1 s for female–female (FF) groups. A further reduction in variability was observed for three-person groups, with evacuation time ranges of 6.4 s for male–male–male (MMM), 5.1 s for male–male–female (MMF), 8.1 s for male–female–female (MFF), and 7.8 s for female–female–female (FFF) groups. These results indicate that, under constant visibility conditions, evacuation times become increasingly stable as group size increases. Larger groups exhibit more coordinated evacuation behavior, as group members are able to provide mutual assistance and jointly respond to unexpected situations during evacuation. This enhanced coordination effectively improves the consistency and efficiency of the evacuation process, highlighting the critical role of teamwork in emergency evacuation scenarios.

As visibility progressively decreases, evacuation times for groups with identical compositions exhibit systematic and consistent changes. Under the condition of wearing eye masks with 18% light transmittance, the mean evacuation times of all groups increased to varying degrees compared with those under normal visibility. Specifically, the mean evacuation times of individual groups (M, F) increased by 8.7% and 6.1%, respectively. For two-person groups (MM, MF, FF), the corresponding increases were 7.2%, 8.5%, and 8.0%, while for three-person groups (MMM, MMF, MFF, FFF), the increases were 3.9%, 3.7%, 5.0%, and 5.2%, respectively. When participants wore eye masks with 6% light transmittance, a more pronounced increase in mean evacuation time was observed across all groups relative to normal visibility conditions. The mean evacuation times of individual groups (M, F) increased by 16.5% and 15.8%, respectively. For two-person groups (MM, MF, FF), the increases were 13.5%, 15.6%, and 14.0%, while for three-person groups (MMM, MMF, MFF, FFF), the increases reached 8.0%, 7.4%, 9.7%, and 9.5%, respectively. The experimental results consistently indicate that mean evacuation time increases as visibility decreases across all group configurations, demonstrating that visibility is a critical factor influencing evacuation efficiency. Under the condition of wearing eye masks with 6% light transmittance, the increase rate of evacuation time of each group was 1.9–2.1 times that observed under the condition of wearing eye masks with 18% light transmittance. The lower the visibility, the more significant the prolongation of evacuation time. This effect is likely associated with multiple factors, including individual physical capacity, psychological tolerance, and emergency behavioral habits. Under reduced visibility conditions, movement is subject to greater constraints, and impaired visual perception may lead to decreased situational awareness and judgment accuracy, thereby prolonging evacuation time. In addition, heightened psychological discomfort and anxiety under low-visibility conditions may further interfere with decision-making and movement efficiency, ultimately reducing the overall effectiveness of the evacuation process. Furthermore, under the 18% light transmittance condition, the average increase rate of evacuation time for the three-person group (4.5%) was only 60% of that for the single-person group (7.4%). When the light transmittance decreased to 6%, the average increase rate of evacuation time for the three-person group (8.9%) accounted for merely 53% of that for the single-person group (16.8%). This suggests that the larger the group size, the smaller the impact of visibility on evacuation time.

Figure 4 presents line charts illustrating the evacuation times of participants on each floor during downward evacuation from the 19th floor to the 10th floor under different experimental conditions. From these plots, differences in evacuation time across floors can be observed for different group configurations under different visibility conditions.

3.2. Floor-by-Floor Variations in Evacuation Speed Under Different Experimental Conditions

3.2.1. One-Way Analysis of Variance (ANOVA)

One-way analysis of variance was conducted using SPSS 26.0 software in this study, with the core objective of examining whether the effects of visibility and group size on evacuation speed were statistically significant. The data in

Table 8. Univariate ANOVA of Visibility on Evacuation Speed.

Visibility Condition		Sum of Squares	Degrees of Freedom (df)	Mean Square	F	Significance (p)
A	Contrast	0.516	1	0.516	24.098	<0.001
B	Contrast	0.338	1	0.338	15.778	<0.001
C	Contrast	0.362	1	0.362	16.871	<0.001
D	Contrast	0.296	2	0.148	21.793	<0.001
E	Contrast	0.274	2	0.137	20.189	<0.001
F	Contrast	0.237	2	0.118	17.433	<0.001
G	Contrast	0.392	3	0.131	31.344	<0.001
H	Contrast	0.397	3	0.132	31.737	<0.001
I	Contrast	0.378	3	0.126	30.203	<0.001

and

Table 9. Univariate ANOVA of Group Size on Evacuation Speed.

Group Size		Sum of Squares	Degrees of Freedom (df)	Mean Square	F	Significance (p)
F	Contrast	0.275	2	0.138	6.420	0.003
M	Contrast	0.410	2	0.205	9.568	<0.001
FF	Contrast	0.065	2	0.033	4.809	0.016
MF	Contrast	0.096	2	0.048	7.035	0.003
MM	Contrast	0.100	2	0.050	7.357	0.003
FFF	Contrast	0.029	2	0.015	3.519	0.040
MFF	Contrast	0.036	2	0.018	4.313	0.021
MMF	Contrast	0.029	2	0.014	3.380	0.046
MMM	Contrast	0.036	2	0.018	4.366	0.020

correspond to these two analytical dimensions, respectively. First, the core data from all experimental scenarios were extracted, with the floor evacuation speed of each participant as the dependent variable; the data were then grouped and classified by visibility condition and group size, laying a data foundation for subsequent dimension-specific analyses. Table 8 was divided into 9 analytical units according to the experimental scenarios. In each unit, visibility was set as the sole independent variable, and only the speed differences among different groups under this specific visibility condition were compared. Intergroup variation was tested via the Contrast test, followed by the calculation of the sum of squares, degrees of freedom, mean square, and F statistic. SPSS 26.0 outputs the significance p-value, where a value of p < 0.05 indicates a statistically significant difference in evacuation speed among different groups under the corresponding visibility condition [43]. Table 9 was also divided into 9 analytical units, in which group size was designated as the sole independent variable to compare the speed differences in the same group size under different visibility conditions. After quantifying intergroup variation through the Contrast test, the above calculation processes for the sum of squares, mean square, and F statistic were repeated. Finally, the p-value was used to determine whether the effect of group size on evacuation speed was statistically significant.

In Table 8, the dependent variable is evacuation speed, and the independent variable is visibility level. Across different groups, the effect of visibility on evacuation speed is statistically significant (p < 0.001). Comparison of the mean square values indicates that, as visibility decreases, the mean square values also decrease, suggesting that the speeds of both individual and multi-person groups tend to become more homogeneous under low-visibility conditions. In Table 9, the dependent variable is evacuation speed, and the independent variable is group size. Under different visibility conditions, the effect of group size on evacuation speed is statistically significant (p < 0.05), indicating that gender proportion and group size influence evacuation speed. Groups with a higher proportion of males exhibit relatively larger mean square values, implying greater variability in evacuation speed among these groups. Overall, both visibility and group size have significant effects on evacuation speed; moreover, visibility exerts a more pronounced influence on speed than group size.

3.2.2. Effects of the Interaction Between Group Characteristics and Visibility on Evacuation Speed

Figure 5 shows that cooperative interactions among multi-person groups can improve evacuation efficiency under low-visibility conditions. Under normal visibility, as group size increases from the individual group to the two-person group and then to the three-person group, the mean evacuation speeds are 1.63 m/s, 1.60 m/s, and 1.56 m/s, respectively, exhibiting a clear trend in which evacuation speed gradually decreases with increasing group size. When participants wore eye masks with 18% light transmittance, the corresponding evacuation speeds were 1.51 m/s, 1.49 m/s, and 1.48 m/s, respectively, indicating that the effect of group size on evacuation speed is not pronounced under this visibility condition. Under extremely low-visibility conditions, represented by wearing eye masks with 6% light transmittance, the evacuation speeds were 1.39 m/s, 1.40 m/s, and 1.43 m/s, respectively, showing an opposite trend in which evacuation speed increases with increasing group size. Therefore, the influence of group behavior on evacuation speed is strongly dependent on visibility conditions. Under normal visibility, group behavior leads to a significant reduction in evacuation speed, whereas under low-visibility conditions, increasing group size can instead enhance evacuation speed.

As visibility decreases, evacuation speed across different groups is correspondingly affected. In terms of overall speed, under normal visibility conditions, individual evacuees exhibit relatively higher evacuation speeds. Because multi-person groups require coordination and communication among members, which introduces greater complexity, the mean evacuation speeds of two-person and three-person groups are comparatively lower. However, as visibility decreases, two-person and three-person groups may benefit from mutual support and cooperative interactions within the group, leading to an increase in their average evacuation speed, which can even exceed that of individual evacuees. Under such conditions, multi-person groups become more advantageous for evacuation than individual evacuees, with evacuation speeds that are relatively more stable and less sensitive to changes in visibility. Questionnaire survey results further indicate the presence of a positive motivational interaction among evacuees, whereby many participants reported being more easily encouraged and stimulated by other members of their group, thereby increasing their own evacuation speed. Overall, both visibility and group size exert significant influences on evacuation speed. Under low-visibility conditions, effective group cooperation can play a critical role in enhancing evacuation efficiency.

3.2.3. Effects of Gender Proportion on Evacuation Speed

Based on Equations (3)–(7), the mean downward evacuation speeds of participants under different visibility conditions were calculated for each experimental condition, and the results are summarized in

Table 10. Downward evacuation speeds of participants under three visibility conditions.

	Visibility Condition	Gender	Speed Range (m/s)	Mean Speed (m/s)	Standard Deviation (SD)	Speed Reduction Ratio (vs. Normal Visibility)
Individual group	A	M	1.39–2.38	1.78	0.18	-
		F	1.22–1.88	1.49	0.14	-
	B	M	1.27–2.11	1.64	0.17	7.9%
		F	1.13–1.74	1.40	0.12	6.0%
	C	M	1.22–1.94	1.52	0.16	28.1%
		F	1.07–1.60	1.28	0.10	14.1%
Two-person group	D	MM	1.56–2.12	1.82	0.10	-
		MF	1.35–1.84	1.59	0.08	-
		FF	1.22–1.66	1.43	0.08	-
	E	MM	1.50–1.94	1.70	0.09	6.6%
		MF	1.26–1.70	1.47	0.08	7.6%
		FF	1.18–1.53	1.33	0.07	7.0%
	F	MM	1.39–1.84	1.59	0.08	23.6%
		MF	1.20–1.60	1.38	0.08	13.2%
		FF	1.12–1.42	1.25	0.06	12.6%
Three-person group	G	MMM	1.64–2.03	1.81	0.07	-
		MMF	1.42–1.83	1.61	0.06	-
		MFF	1.47–1.76	1.51	0.09	-
		FFF	1.20–1.55	1.35	0.07	-
	H	MMM	1.55–1.95	1.75	0.06	3.3%
		MMF	1.38–1.76	1.55	0.06	3.7%
		MFF	1.37–1.64	1.44	0.09	4.6%
		FFF	1.13–1.45	1.29	0.06	4.4%
	I	MMM	1.51–1.83	1.67	0.05	7.7%
		MMF	1.33–1.64	1.49	0.05	7.5%
		MFF	1.35–1.56	1.37	0.07	9.3%
		FFF	1.08–1.39	1.23	0.06	8.9%

.

As the evacuation process progressed, the mean evacuation speeds of both male and female individual groups exhibited a decreasing trend. The magnitude of this speed reduction varied slightly across different visibility conditions; however, it generally remained within a comparable range (approximately 13.0–17.7%). Specifically, under normal visibility conditions, the mean speed of male participants from the 19th floor to the 8th floor was 1.78 ± 0.18 m/s, corresponding to a reduction of 15.0%, while the mean speed of female participants was 1.49 ± 0.14 m/s, with a reduction of 15.0%. When participants wore eye masks with 18% light transmittance, the mean speed of males decreased to 1.63 ± 0.17 m/s, representing a reduction of 17.7%, whereas the mean speed of females was 1.40 ± 0.12 m/s, with a reduction of 15.5%. Under the condition of wearing eye masks with 6% light transmittance, the mean speed of male participants was 1.52 ± 0.16 m/s, corresponding to a reduction of 15.6%, while the mean speed of female participants was 1.28 ± 0.10 m/s, with a reduction of 13.6%.

In individual evacuation, the mean evacuation speed of female participants was 16.4% lower than that of male participants under normal visibility, 14.5% lower under the 18% visibility condition, and 16.1% lower under the 6% visibility condition. These results indicate that, although reduced visibility leads to an overall decrease in evacuation speed, the magnitude of the speed difference between genders does not change substantially. In other words, regardless of visibility level, the evacuation speed of females in individual evacuation remains lower than that of males, with the difference consistently maintained within a range of approximately 14.0–17.0%. For a two-person group evacuation, under normal visibility conditions, the male–male (MM) group exhibited the highest mean speed, while the female–female (FF) group showed the lowest, with the mixed-gender (MF) group exhibiting an intermediate mean speed that was closer to that of the FF group. As visibility decreased, the mean speed of the MF group was 12.3%, 13.1%, and 13.7% lower than that of the MM group under the three visibility conditions, respectively. Meanwhile, the mean speed of the FF group was 10.6%, 9.8%, and 8.9% lower than that of the MF group, respectively. These results indicate that, under low-visibility conditions, gender-related differences in evacuation speed persist in two-person groups, with inter-group speed differences remaining within a relatively stable range of approximately 8.0–14.0%. In three-person group evacuation, under normal visibility, the male–male–male (MMM) group exhibited the highest mean speed, whereas the female–female–female (FFF) group exhibited the lowest. The mixed groups showed intermediate performance, with the male–male–female (MMF) group slightly faster than the male–female–female (MFF) group. As visibility decreased, the mean speed of the MMF group was 11.0%, 11.1%, and 10.5% lower than that of the MMM group under the three visibility conditions, respectively. The mean speed of the MFF group was 6.2%, 7.3%, and 8.1% lower than that of the MMF group, while the mean speed of the FFF group was 10.5%, 10.4%, and 10.2% lower than that of the MFF group, respectively. This indicates that speed differences among three-person groups also remain stable across different visibility conditions, with variations generally within a range of approximately 6.0–11.0%. Taken together, the experimental results for individual, two-person, and three-person groups demonstrate that gender proportion exerts a significant influence on evacuation speed, with groups containing a higher proportion of males exhibiting a more pronounced evacuation advantage. Moreover, regardless of visibility level, speed differences among different group configurations remain within relatively stable ranges. At the same time, as group size increases, the speed differences among different groups under each visibility condition tend to gradually decrease.

In multi-person group evacuation, the speed variation patterns of male and female participants differ markedly from those observed in individual evacuation. The mean evacuation speeds of all-male groups (MM and MMM) are higher than those of individual males (M), and the magnitude of this improvement becomes more pronounced as visibility decreases. By contrast, the mean evacuation speeds of all-female groups (FF and FFF) are lower than those of individual females (F), indicating that, under low-visibility conditions, male participation in team-based evacuation is more conducive to improving evacuation efficiency. Specifically, under normal visibility, the mean evacuation speeds of the MM and MMM groups were 1.8% and 1.4% higher than those of the M group, respectively. When participants wore eye masks with 18% light transmittance, the corresponding increases rose to 3.4% and 6.4%, respectively. Under extremely low-visibility conditions (6% light transmittance), the improvements further increased to 4.6% and 9.5%, respectively. These results indicate that, as visibility decreases, cooperative interactions among male participants increasingly enhance evacuation efficiency. This effect may be attributed to generally greater physical capacity and strength among male participants, which, in multi-person coordination, facilitates mutual assistance and support, thereby accelerating overall evacuation speed. In contrast, for all-female groups, under normal visibility conditions, the mean evacuation speeds of the FF and FFF groups were 3.8% and 9.2% lower than that of the F group, respectively. When participants wore eye masks with 18% light transmittance, the corresponding reductions were 5.3% and 8.1%, respectively. Under the 6% light transmittance condition, the reductions decreased to 1.9% and 3.5%, respectively. This pattern may be associated with higher psychological stress and anxiety experienced by female groups in emergency scenarios with reduced environmental visibility, leading to a greater tendency toward discussion and negotiation to coordinate movement and decision-making, which in turn reduces overall evacuation speed. These findings provide important empirical evidence for understanding evacuation patterns of groups with different gender proportions under different visibility conditions. They also suggest that, in the organization of emergency evacuation groups, careful consideration should be given to gender proportion and its potential influence on group evacuation speed, in order to develop more effective and scientifically grounded evacuation strategies.

Under normal visibility conditions, in two-person mixed-gender groups, the mean evacuation speed of female participants increased by 6.9% compared with that of individual females, whereas the mean speed of male participants decreased by 10.7% relative to individual males. When participants wore eye masks with 18% light transmittance, the speed of females increased by 8.0%, while the speed of males decreased by 9.2%. Under extremely low-visibility conditions (6% light transmittance), the speed increase for females reached 9.7%, whereas the speed reduction for males was 8.7%. In these cases, the magnitude of the speed increase for females exceeded the magnitude of the speed reduction for males, indicating that male participants can effectively facilitate and motivate female participants, enabling them to complete the evacuation more rapidly. In a three-person mixed-gender group evacuation, under normal visibility conditions, the mean evacuation speed of female participants increased by 4.7% relative to individual females, while the mean speed of male participants decreased by 12.5% relative to individual males. When participants wore eye masks with 18% light transmittance, the corresponding speed increase for females was 6.6%, whereas the speed reduction for males was 8.8%. Under the 6% light transmittance condition, the speed increase for females rose substantially to 12.2%, while the speed reduction for males decreased to 5.9%. Notably, under this extremely low-visibility condition, the magnitude of the speed increase for females in three-person mixed-gender groups not only exceeded the corresponding speed reduction for males but was also more pronounced than that observed in two-person mixed-gender groups.

In summary, in practical emergency evacuation scenarios—particularly under low-visibility conditions—a mixed-gender evacuation strategy is recommended. Specifically, it is advisable for male participants, who generally exhibit relatively higher movement speeds, to be positioned at the front of the group to guide the evacuation direction. In general, males tend to possess advantages in physical capacity and movement speed; when positioned at the front of the group, they can more efficiently assess escape routes, avoid obstacles along the path, and rapidly identify safe exits, thereby setting the overall pace of group movement. Such an arrangement can effectively reduce problems commonly encountered under low-visibility conditions, including formation disorder and route hesitation caused by visual obstruction. As a result, overall evacuation efficiency can be significantly improved, enabling all occupants to leave hazardous areas more rapidly and ultimately contributing to the optimization of the emergency evacuation process.

3.3. Analysis of Physiological Indicators and Behavioral Characteristics

3.3.1. Physiological Indicators

After the experiments, the heart rate data recorded by the chest-worn heart rate sensor were exported and standardized, followed by the analysis of individual heart rate curves, group statistical analysis, and an investigation into the causes of heart rate variations. The results indicated that heart rate changes are jointly influenced by visibility, group size, and gender.

• Characteristics of Typical Individual Heart Rate Variations

Two male and two female participants were randomly selected from the valid dataset, and their heart rate data were used to generate representative curves (Figure 6). All curves exhibited a consistent three-stage variation pattern:

First is the rapid rise phase: within 0–75 s after the start of evacuation, the heart rate rose sharply from the resting baseline (65–80 bpm) to 140–160 bpm. This resulted from the combined effects of the emergency response and physical exertion, and the psychological anxiety induced by environmental uncertainty under low visibility further accelerated the heart rate rise. Second is the peak maintenance phase: during 75–150 s, the heart rate remained at the peak level (150–170 bpm) for approximately 75 s. Sustained physical activity and environmental stress kept the sympathetic nervous system in a state of high excitation. Third is the slow recovery phase: after 150 s, the heart rate decreased gradually, yet the recovery rate was significantly slower than the rise rate. It took 80–100 s for the heart rate to return to the baseline level after the cessation of movement, indicating that the physiological and psychological stress induced by emergency evacuation required a relatively long period to dissipate. Notably, the variations in the curves were closely associated with gender and visibility: the peak heart rate of female participants (160–175 bpm) was generally higher than that of male participants (150–165 bpm); under the condition of 6% light transmittance, the peak maintenance phase of all individuals was prolonged by 20–30 s compared with that under normal visibility, which reflects the persistence of the stress response under extremely low visibility.

2.

Statistical Verification of Heart Rate at the Group Level

Statistical analysis was conducted on the heart rate data of the 72 participants, with the key indicators presented in

Table 11. Statistical Indicators of Heart Rate at the Group Level (Mean ± SD).

Group Size	Visibility Condition	Resting Heart Rate (bpm)	Peak Heart Rate (bpm)	Heart Rate Amplitude (%)	Recovery Time (s)
Individual (M)	Normal visibility	72.3 ± 4.1	156.8 ± 5.2	116.9	82.5 ± 10.3
	Wearing eye masks with 18% light transmittance	71.8 ± 3.9	160.5 ± 4.8	123.5	91.7 ± 11.2
	Wearing eye masks with 6% light transmittance	72.1 ± 4.3	164.2 ± 5.5	127.7	105.3 ± 12.1
Individual (F)	Normal visibility	74.5 ± 3.8	167.2 ± 4.9	124.4	88.6 ± 9.7
	Wearing eye masks with 18% light transmittance	73.9 ± 4.2	169.8 ± 5.3	129.8	98.4 ± 10.5
	Wearing eye masks with 6% light transmittance	74.2 ± 3.7	172.5 ± 5.1	132.3	112.7 ± 11.8
Two-person group (MM/MF/FF)	Normal visibility	72.6 ± 3.5	152.4 ± 4.6	109.9	79.3 ± 9.2
	Wearing eye masks with 18% light transmittance	72.1 ± 3.8	157.6 ± 4.3	118.6	87.5 ± 10.1
	Wearing eye masks with 6% light transmittance	72.4 ± 4.0	161.3 ± 4.9	122.8	99.6 ± 10.7
Three-person group (MMM/MMF/MFF/FFF)	Normal visibility	71.9 ± 3.6	151.7 ± 4.5	109.6	78.7 ± 8.9
	Wearing eye masks with 18% light transmittance	72.3 ± 3.9	156.8 ± 4.7	116.3	86.2 ± 9.8
	Wearing eye masks with 6% light transmittance	71.7 ± 3.4	160.5 ± 5.0	123.9	97.8 ± 11.3

:

The statistical results indicated the following: ① The group-level indicators were consistent with the characteristics of the typical individual curves, where the peak heart rate increased with decreasing visibility and the recovery time was prolonged accordingly; ② Under the same visibility conditions, the peak heart rate of multi-person groups was 2–16 bpm lower than that of individuals, with the recovery time shortened by 4–15 s, which verified the stress buffering effect of group evacuation; ③ Under all visibility conditions, the heart rate amplitude of individual female groups (124.4–132.3%) was higher than that of individual male groups (116.9–127.7%), reflecting gender differences in physiological stress responses.

3.

Analysis of Causes for Heart Rate Variations

By integrating individual heart rate curves and group-level statistical results, the drivers of heart rate changes during evacuation are inferred as follows. First, heart rate elevation stems from the combined effects of physical exertion and psychological stress: physical exertion raises oxygen demand, while environmental uncertainty triggers anxiety—both activating the sympathetic nervous system. Second, the lower peak heart rate and shorter recovery time observed in multi-person groups compared to individual groups reflect the group buffering effect: mutual assistance and information sharing among members during group evacuation reduce environmental uncertainty and inhibit excessive activation of the sympathetic nervous system. Third, gender-related differences stem from both physiological and psychological traits: females have lower cardiac output and hemoglobin concentration, requiring a higher heart rate to meet oxygen demand during the same level of physical activity; additionally, females are more risk-sensitive and tend to rely on external support to regulate their state, resulting in greater heart rate amplitude and longer recovery time. These gender-specific characteristics in heart rate responses further corroborate the influence of physiological differences between males and females on adaptability to emergency evacuation. They also provide physiological evidence supporting the consideration of gender-related factors in the development of evacuation strategies.

3.3.2. Behavioral Analysis

• Individual Evacuation Experiment

The evacuation process of individual participants was examined through detailed observation, with frame-by-frame analysis of video recordings. The results indicate that, under normal visibility conditions, most participants tended to select the central region of the stairway as their primary movement path during evacuation in order to reach a safe area more rapidly. This route effectively reduces interference from surrounding environmental elements or other individuals, thereby improving movement efficiency. Clear gender-related differences were observed in evacuation behavior. Male participants were more likely to adopt direct and time-efficient descending strategies, such as skipping steps or traversing two to three steps in a single stride, with a stronger emphasis on completing evacuation in the shortest possible time. In contrast, female participants placed greater emphasis on stability and safety during movement, more frequently choosing a steady, step-by-step descent with a consistent pace and prioritizing the avoidance of risks such as slipping or falling.

As visibility decreased, the area of the stairway adjacent to the handrail became the preferred movement space for participants. Under such conditions, the time required for stair descent generally increased. Participants tended to move more cautiously in order to avoid falls or other accidents, thereby requiring more time to complete the same evacuation task. This adverse effect on evacuation behavior was particularly pronounced when participants wore eye masks with 6% light transmittance. In this extremely low-visibility condition, individual participants exhibited heightened caution: not only did their movement speed decrease markedly, but a series of exploratory behaviors were also observed, such as extending their hands to probe the surroundings, closely holding the handrail, and using the wall for additional support, all aimed at ensuring personal safety. Furthermore, an examination of the causes underlying evacuation impediments among participants with relatively low evacuation speeds revealed that two female participants were wearing skirts and footwear unsuitable for physical activity. It can therefore be inferred that such inappropriate clothing may restrict limb movement, thereby hindering their ability to complete evacuation smoothly. Overall, these findings suggest that individual differences in evacuation speed are often influenced by a combination of factors, including physical fitness, relevant movement experience, and clothing comfort.

2.

Multi-person Group Experiment

Observation of the evacuation processes across different groups revealed that cooperative behaviors such as mutual assistance and waiting for companions frequently occurred within multi-person groups. In two-person groups, particularly under low-visibility conditions, participants tended to form a mutually supportive configuration, exhibiting strong cooperative behavior. Faster-moving participants often assisted slower companions, maintaining balance and orientation through close coordination, thereby increasing the movement speed of the slowest group member. Three-person groups, by contrast, were more inclined to maintain a compact formation. Through timely communication and mutual support, group cohesion was preserved, effectively reducing the risk of falls. Under reduced visibility conditions, participants relied more heavily on handrails or walls to assist stair descent in order to ensure movement safety. At the same time, pronounced following behavior was observed during evacuation, whereby individuals at the rear followed the movements of those ahead. Most groups also exhibited longitudinal queuing behavior, with faster participants positioned at the front to guide the evacuation direction. In addition, lateral pulling behaviors were observed among group members, such as holding hands or grasping a companion’s clothing, to prevent individuals from becoming separated from the group. Overall, these observations indicate that, in environments with poor visibility, evacuees are able to form effective cooperative interactions. The multi-person group evacuation mode contributes positively to improving evacuation efficiency and safety, demonstrating a beneficial role in the overall evacuation process.

To further analyze handrail usage characteristics among male and female participants during stair descent in both individual and group evacuations, the handrail dependence level under different visibility conditions was compared. Data were extracted through video observation and standardized manual coding to ensure the accuracy and consistency of behavioral identification. First, the video footage captured by cameras covering all floors of the stairwell was integrated and synchronized on a unified timeline. Second, a set of unified coding rules was formulated, with handrail usage explicitly defined as active manual contact with the handrail for a duration of no less than 0.5 s, and non-stable contact behaviors such as accidental brushing were excluded. Subsequently, three trained independent coders reviewed the video footage separately and annotated frame by frame the start and end time of each participant’s handrail contact, contact position and other relevant information. Finally, the Kappa coefficient was calculated to verify the coding consistency (a Kappa value of ≥0.85 was deemed acceptable). Discrepant annotations were collectively reviewed and calibrated, and the handrail dependence level (total duration of handrail contact/total duration of stair descent) was calculated based on the calibrated annotation data. Figure 7 intuitively presents the handrail dependence of the participants under different visibility conditions.

Under normal visibility, the handrail dependence level was 12.9% for male participants and 24.8% for female participants. When participants wore eye masks with 18% and 6% light transmittance, the handrail dependence level among males increased to 36.8% and 48.6%, respectively, while the corresponding values for females rose to 57.3% and 73.5%. These results indicate that, under visibility-restricted conditions, females consistently exhibited a higher handrail dependence level than males. Moreover, regardless of whether evacuation was conducted individually or in groups, handrail dependence during stair descent increased markedly as visibility decreased. Notably, at the interfaces between stair flights and landing platforms, handrail dependence level increased substantially for both male and female participants. This phenomenon may be attributed to the need for heightened caution against falls at these locations, as well as the role of handrails in assisting rapid changes in movement direction. Overall, although gender-related differences in handrail dependence were observed, both male and female participants demonstrated a significantly increased reliance on handrails during emergency evacuation under limited visibility conditions.

4. Conclusions

This study takes a super high-rise building located in Xinyang, Henan Province, China, as the research object. Through a series of emergency evacuation experiments conducted under different visibility conditions, the evacuation characteristics and influencing factors of both individual evacuees and multi-person groups within stairwells were systematically investigated. The main findings are summarized as follows:

• Synergistic effects of visibility and group size:

Visibility and group size are critical factors influencing evacuation efficiency, and a significant synergistic interaction exists between them. Under normal visibility conditions, group behavior leads to a marked reduction in evacuation speed. In contrast, under low-visibility conditions, evacuation speed increases with increasing group size. The mutually reinforcing cooperative interactions formed within multi-person groups can effectively mitigate the adverse effects of reduced visibility, thereby enhancing overall evacuation efficiency.

2.

Role of gender proportion in group evacuation:

Different gender proportions significantly affect evacuation speed, with groups having a higher proportion of males demonstrating a more pronounced evacuation advantage. Under low-visibility conditions represented by wearing eye masks with 6% light transmittance, the increase in mean evacuation speed of females in multi-person groups relative to individual females exceeds the corresponding reduction in mean speed observed for males under the same conditions. Based on these findings, a mixed-gender group evacuation strategy is recommended for low-visibility environments, whereby cooperative interactions between genders are utilized to optimize overall evacuation performance.

3.

Characteristics of physiological indicators and supportive behaviors:

Heart rate responses during evacuation are jointly influenced by visibility level and group size. Under identical visibility conditions, multi-person group evacuation exhibits a pronounced psychological stress-buffering effect, with participants’ heart rates generally lower than those observed during individual evacuation. In contrast, low-visibility environments are prone to inducing panic, resulting in significantly higher heart rates for participants within the same group compared with those under normal visibility conditions. Moreover, female participants exhibit overall higher heart rate levels and greater heart rate variability during evacuation, along with a significantly higher reliance on handrails than male participants. In addition, under low-visibility conditions, multi-person groups exhibit stronger cooperative behaviors and form more compact movement formations.

In this study, the researchers simulated the variation in visibility under fire smoke conditions using eye masks, and the analysis focused on the relative differences in heart rate responses under emergency conditions rather than the absolute stress levels. However, real fire disaster scenarios are far more complex, where multiple intricate factors, including smoke toxicity and concentration, high temperatures, noise, and unknown hazards, act synergistically to induce a more intense stress response in evacuees. Therefore, future research could incorporate a broader range of complex variables by integrating smoke simulation, temperature stimulation, and other relevant factors, so as to further investigate evacuation patterns under conditions that better align with real-world fire disaster scenarios. Overall, this study not only fills existing research gaps in the related field but also provides important theoretical insights and empirical data to support the development of scientifically sound evacuation plans for super high-rise buildings. The findings contribute to improving the effectiveness and safety of emergency response strategies.