Experimental Investigation on Combustion Characteristics of Massage Chairs in Waiting Halls of High-Speed Railway Stations

Abstract

In order to provide fire-scene parameters for fire protection design and data support for fire safety management of waiting halls in high-speed railway stations, this study systematically investigated the combustion characteristics of single, two, and three massage chairs using an industrial calorimeter. The results showed the following: The change in heat release rate in the growth stage of the massage chairs’ combustion tests was consistent with the t² fast fire (with a growth coefficient of 0.04689). The maximum HRR was 1.2 MW for the single-massage-chair combustion test, 2.5 MW for the two-massage-chairs combustion test, and 3.5 MW for the three-massage-chairs combustion test. In the full-scale massage chairs combustion test, setting a 6.0 m fire isolation zone could effectively serve the functions of fire prevention and heat insulation. Considering a certain safety margin, and with a safety factor of 1.5 adopted, it is recommended that a fire isolation zone with a width of 9.0 m be used in the waiting halls of high-speed railway stations, which provides a direct, actionable design basis for engineering practice.

1. Introduction

With the rapid development of high-speed rail construction, by the beginning of 2024, China’s railway operating mileage had reached 159,000 km, of which the operating mileage of high-speed railways had reached 45,000 km, and it has become one of the main modes of transportation for peoples’ daily travel due to its convenience, comfort, and fast speed [1,2,3]. High-speed railway stations are places with large passenger flow and dense population. In order to provide comfort for waiting passengers, massage chairs are usually set up in the waiting halls of high-speed railway stations, which increases the fire load in the waiting area and poses a challenge to the fire safety of the entire building [4]. Figure 1 is the picture of the massage chairs in the waiting halls of a high-speed railway station. Therefore, it is very necessary to study the characteristics and development laws of fires in massage chairs in the waiting halls of high-speed railway stations.

Many scholars have achieved certain research results in the aspects of smoke generation characteristics and smoke toxicity of seat materials, and they have also conducted combustion characteristics tests on seats in stadiums and transportation vehicles. Xie et al. [5] carried out a series of full-scale experiments in an ISO 9705 [6] fire test room, using an upholstered chair placed at four typical locations, to investigate the effects of boundary conditions on the combustion characteristics of combustible items in a room. They [7] also changed the ignition position from the geometric center of the seat surface to the top of the backrest to investigate the effects of both boundary conditions and ignition positions on the combustion characteristics of a combustible item in a room. Regarding seats in public places, such as stadiums and theaters, Shi et al. [8] conducted a fire safety assessment on seats in Olympic venues. Lu et al. [9] conducted a small cone calorimeter test and a full-scale fire test on spectator seats in stadiums, and obtained parameters such as heat release rate (HRR), smoke generation rate, and ignition time of seats made of polypropylene. Yang et al. [10] conducted a full-scale fire test on the continuous combustion of theater seats, and obtained parameters such as heat release rate, total heat release, and flame propagation speed. It is worth noting that Ma et al. [11] studied the development process of electrical fires in seats at high-speed railway stations through numerical simulation and found that the fire growth type was between medium fire and fast fire. Yang et al. [12] used numerical simulation methods to study the development process of fires in a whole group of multifunctional seats and summarized the critical ignition distance in the fully developed stage. Gu et al. [13] conducted full-scale fire tests on single and row massage chairs. Compared with the seats in public places, such as stadiums and theaters, studied by previous researchers, these massage chairs are more complex and have richer functions. The HRR of single and two chairs when burning was obtained through experiments, and the fire growth coefficient was within the range of slow fire and medium fire. The trend of external heat-flux change is basically similar to that of HRR change. Regarding the seats of transportation vehicles, Zhu et al. [14] studied the HRR, exhaust pipe temperature, smoke production, and other parameters of double seats under different ventilation conditions for CRH1 high-speed rail seats. Yang et al. [15] conducted combustion performance tests on seats of urban short-distance passenger buses, high-speed rail first-class seats, and Airbus A380, and compared the development characteristics of the combustion process, HRR, and total heat release. Li et al. [16] conducted horizontal and vertical combustion tests on four types of automobile seat materials and obtained the flame retardancy of different seat materials during horizontal and vertical combustion and the gas toxicity of different materials during combustion. Mitrenga et al. [17] studied the initial ignition temperature of upholstered seats and the temperature of surfaces of organic upholstery and analyzed the sample (weight) smoldering time and degradation length using one-way ANOVA statistical analysis. Jang et al. [18] used eco-friendly silicone material with improved flame retardancy to develop a nonslip pad for railway seats and assembled its four different shapes into a usable chair. The optimum shape was selected by passenger comfort experiments and full-scale fire test was carried out. First, Hohenwarter [19] investigated how the fire test regulations for railway seats changed over time, then the fire behavior of the seat under different test conditions, the heat release of the seat in different periods, and the combustion behavior of the seat composed of different materials were studied by several sets of comparative experiments.

In summary, existing studies have mainly focused on ordinary seats in stadiums, transportation, and other occasions, and there are few studies on the combustion characteristics of massage chairs in high-speed railway station waiting halls. Since the functions of massage chairs in high-speed railway station waiting halls are relatively complex, the electrical components, material types, and usage scenarios of the chairs are different from those of ordinary seats. Therefore, this study uses an industrial calorimeter to analyze the combustion characteristics of single, two, and three massage chairs, providing fire-scene parameters for the fire protection design of high-speed railway station waiting halls, and offering data reference for the fire safety management of high-speed railway station waiting halls.

2. Experimental Design

2.1. Experimental Method

Industrial calorimeter tests were carried out according to relevant standards [20,21,22]. A 5 MW industrial calorimeter was used to carry out the full-scale multifunctional massage chairs’ combustion characteristic test to measure the HRR during the combustion process, and thermocouples and heat-flux meters were placed according to the specific test scene to measure the temperature and heat flux at different points [23,24]. Massage chairs commonly found in high-speed railway station waiting halls were selected as the test subjects. The chairs were placed in the center of the test site, and the collecting hood was 8.0 m × 6.0 m long and wide. The test site is shown in Figure 2. The chair samples used in the test are mainly composed of leather, plastic, fabric, and other materials as well as some electronic components, as detailed below: the surface of the massage chairs is made of leather, the remote control casing is made of plastic, the seat cushion is fabric, and the electronic components—including power switches and control panels, etc.—are mainly located on the bottom of the chair back and inside the chairs. Their dimensions are 1300 mm long, 680 mm wide, and 950 mm high. The net weight of the product is about 45 kg.

2.2. Experimental Scenarios

A total of three groups of full-scale massage chair combustion tests were conducted, including three scenarios: single, two, and three massage chairs (SMC, TWMC, and THMC) combustion test. The test chairs were placed individually or side by side in the center of the venue. For the SMC combustion test, a heat-flux meter was placed at 1 m, 1.5 m, 2.0 m, 2.5 m, and 6.0 m in front of the test chair, 3.0 m and 6.0 m behind the chair, and 1.5 m to the right of the chair. The heat-flux meter was 1.0 m above the ground. A thermocouple tree was arranged directly in front of the test chair at 2.5 m, 6.0 m, and on the right side of the test chair. For the TWMC combustion test, place another chair 1.5 m behind and 1.5 m to the left of the test chairs. A heat-flux meter was placed at 1.5 m, 2.0 m, 2.5 m, 3.0 m, and 9.0 m in front of the test chairs, 1.5 m and 3.0 m behind the test chairs, and 1.5 m to the right of the test chairs, and the heat-flux meter was 1.0 m above the ground. A thermocouple tree was placed 9.0 m in front of the test chairs, 1.5 m behind the test chairs, close to the left sides of the test chairs, and between two test chairs. For the THMC combustion test, a heat-flux meter was placed at 1.5 m, 2.0 m, 2.5 m, 3.0 m, and 9.0 m in front of the test chairs, 1.5 m and 3.0 m behind the test chairs, and 1.5 m to the right of the test chairs, and the heat-flux meter was 1.0 m above the ground. A thermocouple tree was placed 9.0 m in front of the test chairs, close to the back of the chairs, and close to the left and right sides of the chairs. The specific layout plan is shown in Figure 3.

At the initiation of the experiment, a torch soaked with a small volume of alcohol (ca. 10 mL) was used to ignite the massage chair at the designated ignition point. The torch was promptly removed from the test area and extinguished to avoid any potential interference of its HRR with the experimental measurements.

3. Results and Analysis

3.1. Combustion Characteristics of Massage Chair Fire

For the SMC combustion test, Figure 4 shows its process. The ignition moment was used as the zero moment of data collection, and the combustion process was divided into four stages according to the fire HRR curve. The first stage was the incipient stage, starting from the ignition of the massage chair. After the massage chair was ignited, the combustion started 2 s, and obvious flames appeared at the ignited chair; when the combustion reached 42 s, visible black smoke was produced, and the flames began to spread to the backrest and cushion area, and the fire gradually increased. At 65 s, it entered the second stage, the growth stage, at which time the flames spread to the backrest and cushion, and the chair armrests were in a smoldering state; at 70 s, for the first time, a combustion fragment was captured falling off the chair surface. Next, it entered the third stage, the fully developed stage at 110 s, at which time the chair cushion and backrest were burned through, and obvious flames could be seen at the bottom of the chair; at 300 s, the chair burned violently, and a large amount of leather, plastic, and other materials melted due to the heat, and a large amount of combustion fragment fell around the chair. At 440 s, the combustion entered the fourth stage, the decay stage, at which time the seat structure had been completely destroyed; at 520 s, as the combustibles were burned out, the flames gradually weakened, and only the metal frame of the chair remained.

For the TWMC combustion test, Figure 5 shows its process. The ignition time was used as the zero time of data collection, and the combustion process was divided into four stages according to the fire HRR curve. The first stage was the incipient stage, starting from the ignition of the massage chair. After the massage chair was ignited, the combustion started at 2 s, and obvious flames appeared at the ignited chair; when the combustion reached 54 s, the flame spread to the backrest, cushion, and left armrest, and for the first time, a combustion fragment fell off the seat surface. At 104 s, it entered the second stage, the growth stage. At this time, the cushion and backrest of the chair that was ignited first, were burned through, and obvious flames could be seen at the bottom of the chair; at 130 s the fire of the chair that was ignited first intensified, and the flame spread from the top of the chair to the adjacent chair. At 165 s it entered the third stage, the fully developed stage, at which time the adjacent chair backrest had been completely ignited; at 350 s the two chairs burned violently, a large amount of leather, plastic, and other materials melted due to the heat, and a large amount of combustion fragments dripped around the chair. At 440 s, the fourth stage, the decay stage, was entered. At this time, the chair that was ignited first was burned first, and the metal frame could be clearly seen. The chair that was ignited later was still burning. At 590 s, as the combustibles burned out, the flames gradually weakened, and only the metal frame remained.

For the THMC combustion test, Figure 6 shows its process. The ignition time was used as the zero time of data collection, and the combustion process is divided into four stages according to the fire HRR curve. The incipient stage is from the ignition of the massage chair. After the massage chair was ignited, the combustion started at 2 s, and obvious flames appeared on the ignited chair; when the combustion reached 68 s, the flame spread to the backrest and cushion, producing visible black smoke, and the fire gradually increased. At 110 s, the fire entered the growth stage, at which time the flames spread to the top of the massage chair that was ignited first; at 160 s, the fire intensified, and the flame spread from the top and the left and right armrests of the chair, that was ignited first, to the chairs on both sides, respectively. At 165 s, the combustion entered the fully developed stage, at which time the backrests of the two adjacent chairs had been completely ignited, and the cushion and backrest of the chair that was ignited first were burned through, and obvious flames could be seen at the bottom of the chair; at 337 s, the fire reached its maximum, and the three chairs burned violently, a large amount of leather, plastic, and other materials melted due to the heat, and a large amount of combustion fragments fell around the chairs. At 500 s, the fire entered the decay stage. At this time, the chair in the middle was burned first, and the metal frame could be clearly seen. The chairs on both sides were still burning. At 600 s, as the combustibles were burned out, the flames gradually weakened, and only the metal frames of the chairs remained.

Figure 7 shows the HRR curves of massage chair combustion tests in different scenarios, slow fire and fast fire curves, as well as the results of previous studies. It could be seen that, in the incipient stage of the SMC combustion test, the flame combustion intensity was small, the amount of smoke produced was small, and the HRR was relatively small. When the combustion process lasted for 65 to 110 s, the chair began to burn violently and produced a large amount of hot smoke. During this stage, the HRR increased rapidly and entered the fully developed stage, and the HRR reached the first peak of 1136 kW. In the fully developed stage, the HRR reached a maximum value of 1206 kW. After a certain period of stable combustion, the HRR gradually decreased as the combustibles were consumed, and the HRR gradually decays until the flame was extinguished. Similarly, the HRR change trend of the TWMC and THMC combustion tests also showed a trend of rapid growth first and then gradual decay. Due to the presence of more combustibles, the maximum HRR of the TWMC and THMC combustion tests reached 2515 kW and 3453 kW, respectively.

Gu et al. [13] also conducted related tests on the combustion of single and two massage chairs. Compared with Gu’s experiment, the massage chairs selected in this study are larger in size and differ in the ignition position: Gu’s experiment adopted ignition at the bottom of the chair, whereas this study uses the surface of the chair cushion as the ignition position. From a conservative perspective, the massage chairs in this study exhibit a faster combustion rate and, consequently, a faster fire spread rate.

As could be seen in Figure 7, the HRR curve of the chair combustion in Gu’s study was consistent with the slow fire curve, while the HRR curve measured in this test was closer to fast fire, which was related to the samples used in the test.

Based on the fire development trend of t² fires, this study conducted a correlation fitting analysis between Q and t² for three groups of working conditions, as shown in Figure 8. The R² values of the fitting results are all greater than 0.9, indicating that the test data in this study well conform to the relevant regularity. The fire growth coefficient for the SMC combustion test is 0.0454, that for the TWMC combustion test is 0.0431, and that for the THMC combustion test is 0.0461. The fire growth coefficient of the fast fire is 0.04689, and the fire growth coefficients of the three groups of working conditions are quite similar to it. It is suggested that the fast fire should be used to simulate the fire development trend of massage chairs in practical engineering applications.

3.2. Distribution of Temperature Field

The temperature distribution of the thermocouple trees at different positions in the SMC combustion test is shown in Figure 9. After the chair was ignited, the flame temperature rose rapidly, and the fire plume temperature could reach about 810 °C; when the backrest attachment fell off, the flame height decreased, and the temperature of thermocouples 6 and 7 located at a higher position decreased; as the combustion continued to develop, the HRR increased, the fire plume temperature increased, and the fire plume temperature went through an upward stage, and then the flame temperature continued to maintain a high level. Finally, as the combustibles were burned out, the flame height decreased, and the temperature dropped significantly.

The temperature change in front of test chair 2.5 m was consistent with the temperature change trend at the fire source. After the chair was ignited, the temperature began to rise rapidly, reaching a peak around 370 s, with a maximum temperature of about 21 °C. After 400 s, as the combustion entered the decay stage, the temperature also decreased, and the final temperature dropped to 12 °C. The temperature change trend at a distance of 6.0 m was consistent, but the temperature peak was only 11.5 °C, which was within 5 °C of the ambient temperature.

The temperature distribution of the thermocouple trees at different positions when the two chairs were burning is shown in Figure 10. For the TWMC combustion test, after the ignition started, the flame temperature of the thermocouple tree (thermocouples 41–47) set between the two test massage chairs rose rapidly, and the fire plume temperature would reach about 978 °C, which was the same as the change trend of the single seat test. Around 450 s, the first chair was burned out and the adjacent chairs were ignited, and the burning area gradually increased. The temperature of thermocouples 41–43 closest to the fire source remained at about 800 °C, and the temperature of the other higher thermocouples was in a rapid decrease stage due to the decrease in flame height. Finally, as the combustibles were burned out, the temperature dropped sharply.

The thermocouple tree (thermocouples 25–31) close to the right sides of test chairs had the same temperature change trend as the thermocouple tree between two test chairs. After the ignition began, the flame temperature rose rapidly, and the fire plume temperature could reach about 910 °C. Since the fire plume of the adjacent chair could not act on the thermocouple tree, the temperature dropped sharply after the first chair burned out around 450 s.

The temperature change behind test chairs, 1.5 m, was consistent with the temperature change trend at the fire source. The temperature change was small in the early stage of the combustion. After 200 s of burning, the temperature began to rise rapidly and reached a peak around 570 s, with a maximum temperature of about 70 °C. After 600 s, as the combustion entered the decay stage, the temperature also decreased. The temperature change trend in front of test chairs, 9.0 m, was consistent, but the peak temperature was only 13.5 °C, which was within 5 °C of the ambient temperature.

The temperature distribution of thermocouple trees at different positions when three chairs were burning is shown in Figure 11.

For the THMC combustion test, after the ignition started, the flame temperature rose rapidly, and the fire plume temperature would reach about 972 °C, which was the same as the change trend of the single chair test. The temperature change curve of each thermocouple had two peaks. The second peak of thermocouples 41, 42, and 43 was greater than the first peak. The two peaks of thermocouples 44 and 47 were roughly the same. The second peak of thermocouples 45 and 46 was less than the first peak. The reason for the two peaks might be that the first peak appeared when the HRR of the middle chair reached its peak. As the HRR of the middle chair decreased, the temperature of all thermocouples decreased together. After dropping to the extreme point, the chairs on both sides were ignited and the combustion intensified. The increase in the total HRR caused the temperature to rise again.

After the ignition started, the temperature of the thermocouple tree of the massage chairs on both sides only rose slightly, until 165 s, when the chairs on both sides were completely ignited, and the temperature of the thermocouple tree began to rise rapidly, and the fire plume temperature reached about 927 °C, and the temperature change trend was similar to that in the middle of the fire source. The temperature change trend in front of the test chairs, 9.0 m, was consistent, but the peak temperature was only 16.8 °C, which was within 5 °C of the ambient temperature.

3.3. Distribution of Radiation Heat Flux

Figure 12 shows the data changes in each heat-flux meter during the TWMC and THMC combustion tests. Since the heat-flux meter equipment failed during the SMC combustion test, this section analyzes the heat flux of the fire tests of the TWMC and THMC combustion tests. In order to prevent the heat-flux meter closest to the fire source from being burned, heat-flux meter 8# was removed when it received excessive heat flux during the two tests. Thus, Figure 12 shows that the heat flux of this heat-flux meter plummets after peaking.

For the TWMC combustion test, the trend of heat flux over time was basically similar to the HRR curve. Among them, the heat flux of the heat-flux meter 1# was lower due to its distance from the fire source, which was obviously different from other measuring points. At the same time, it could be seen that the heat flux gradually decreased with the increase in the distance from the fire source. During the experiment, the highest heat flux at 1.5 m, 2.0 m, 2.5 m, and 3.0 m in front of the fire source were 13.5 kW/m², 8.4 kW/m², 5.6 kW/m², and 3.9 kW/m², respectively. The highest heat flux at 1.5 m behind the fire source was 19.8 kW/m², and the highest heat flux at 1.5 m to the side of the fire source was 9.1 kW/m².

For the THMC combustion test, the trend of heat flux over time was basically similar to the HRR curve. Among them, the heat flux of the heat-flux meter 1# was lower due to its distance from the fire source, which was obviously different from other measuring points. At the same time, it could be seen that the heat flux gradually decreased with the increase in the distance from the fire source. During the experiment, the highest heat flux at 1.5 m, 2.0 m, 2.5 m, and 3.0 m in front of the fire source were 17.4 kW/m², 11.2 kW/m², 8.1 kW/m², and 6.8 kW/m² respectively, the highest heat flux at 1.5 m behind the fire source was 34.2 kW/m², and the highest heat flux at 1.5 m to the side of the fire source was 10.9 kW/m².

4. Conclusions

This study used an industrial calorimeter to analyze the combustion characteristics of single, two, and three massage chairs. The main conclusions are as follows:

• The combustion of full-scale massage chair fires exhibited obvious stage characteristics. Among them, the temperature rise and HRR in the growth stage increased fastest. The change in HRR in the incipient and growth stages of the massage chair combustion was consistent with t² fast fire (with a growth coefficient of 0.04689). The t² fast fire could be applied to the fire protection design of high-speed railway station waiting halls.
• The maximum the HRR of the SMC combustion test was 1.2 MW, the maximum HRR of the TWMC combustion test was 2.5 MW, and the maximum HRR of the THMC combustion test was 3.5 MW.
• In the case of the TWMC combustion test, the massage chair, at a distance of 1.5 m from the fire source, was not ignited but melted.
• In the full-scale massage chair combustion tests, setting up a 6.0 m isolation zone could effectively serve the functions of fire prevention and heat insulation. Taking into account a certain safety margin, with a safety factor of 1.5 specifically adopted for the calculation, it is recommended that a fire isolation zone with a width of 9.0 m be used in the waiting halls of high-speed railway stations.

Through preliminary research, it was found that the most common arrangement of massage chairs in the waiting halls of high-speed railway stations is a side-by-side arrangement; thus, this study adopted this arrangement to conduct experiments. In the future, with additional funding support, further investigations will be carried out on the effects of other arrangements (such as cluster arrangements and arrangements with different directions) and different spacing on the experimental results.