**1. Introduction**

With the rapid development of the social economy and the advancement of modernization, urban economies have gradually developed in the direction of diversification to meet the growing needs of people for a better life. Thus, a large number of urban commercial complexes have emerged. These commercial complexes integrate entertainment, catering, fitness, shopping, offices and other functions, which greatly meet the needs of life, and bring much comfort and convenience. Indoor pedestrian streets are commonly found in various complexes and are one of their core architectural elements, found in various forms, and also in different lengths and heights. Due to the unique narrow and long building structure of the indoor pedestrian street, and the large number of combustibles in it coupled with

**Citation:** Lin, W.; Liu, Q.; Zhang, M.; Cai, B.; Wang, H.; Chen, J.; Zhou, Y. Numerical Simulation on Smoke Temperature Distribution in a Large Indoor Pedestrian Street Fire. *Fire* **2023**, *6*, 115. https://doi.org/ 10.3390/fire6030115

Academic Editor: Dahai Qi

Received: 3 February 2023 Revised: 3 March 2023 Accepted: 7 March 2023 Published: 13 March 2023

**Copyright:** © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). *fire*

the dense population and high mobility, once a fire occurs, the fire is very likely to spread to the atrium. It will spread further into the adjacent buildings through the pedestrian street walkway, causing irreparable losses. On 15 February 2004, a particularly serious fire accident occurred in Zhongbai Commercial Building in Jilin, Jilin Province. The fire was caused by the fire of a warehouse built nearby the commercial building which then spread to it. The evacuation exit was blocked, resulting in 54 deaths and more than 70 injuries. On 30 June 2012, a major fire accident occurred in the Ryde Commercial Building in Jixian, Tianjin, resulting in 10 deaths and 16 serious injuries, which was caused by electrical sparks due to overloaded air conditioning. In recent years, fire accidents in shopping malls and pedestrian streets are emerging one after another, and their serious fire risks have attracted great attention from society. Therefore, it is an obligation to research the laws of smoke spread and temperature distribution in atriums and indoor pedestrian streets, to conduct the decisive factor for personnel safety evacuation [1,2].

The spread of smoke in pedestrian streets and large atriums, the laws of temperature distribution and the effect of smoke exhaust systems have always been the focus of research of many scholars at home and abroad. Hu et al. [3] obtained the characteristics of smoke spread and the temperature distribution law of fire below the ceiling by conducting fullscale fire experiments in a long walkway. Huo [4] and others conducted fire experiments in a large-space fire experimental hall, and preliminarily studied the mechanical smoke extraction efficiency of large-space building fires. The full-scale experiment can realistically reproduce the fire scene and achieve a high degree of matching with real fire, which is very reliable. However, because of many large experimental scenes, the experiment is quite difficult, being both laborious and time-consuming. Thus, the limitations of full-scale experiments are reflected. In recent years, CFD numerical simulation technology has matured and improved, bringing not only good visualization effects, but also high fidelity, in addition to including many parameters that cannot be measured by experiments. The technology has gradually become the mainstream research method for studying large-space fires. Rho [5] and Mowrer et al. [6] used numerical simulation technology to study the smoke spread characteristics of a fire in a large-space atrium. Hadjisophocleous et al. [7] combined solid experiments and numerical simulation to analyze the smoke spread characteristics of atrium fires and the calculation method of smoke layer height. Long et al. [8] carried out full-scale fire experiments to investigate some key parameters, including the vertical and longitudinal temperature distribution, smoke layer height and smoke front arrival time under four different cases. In Jiao's work, a series of full-scale fire tests were performed to study the smoke spread characteristics and temperature distribution of indoor pedestrian street fires with different mechanical smoke exhaust modes [9]. Tian and Cai [10] used FDS to analyze and evaluate the fire hazard, effectiveness of smoke prevention measures and personnel safety of commercial complexes, and proposed performance-based design solutions. Zhao [11] studied the law of fire smoke spread and the control mode and effect of smoke in buildings through FDS numerical simulation technology, and obtained the influence of different smoke exhaust positions, fire source power, floor opening rate, smoke trapping wall height, etc., on smoke spread and the effects of smoke extraction. Jiang [12] used Fluent software to study the influence of the position of the air outlet on the smoke flow and smoke extraction effect of the atrium space of the mall, and proposed an optimization scheme.

It can be seen from the research status at home and abroad that the research on smoke control theory and smoke extraction mode has been relatively detailed. Although many studies have been carried out on large-space indoor pedestrian street fires, most of them focus on the influence of different smoke exhaust locations or smoke control modes on the flow and control of fire smoke. There are few studies on the temperature distribution characteristics of fire smoke in large-space indoor pedestrian streets. Therefore, this paper aims to study and discuss the characteristics of atrium smoke spread, vertical smoke temperature distribution and horizontal smoke temperature distribution under the ceiling under different ignition heat release rates, and establish a dimensionless theoretical model of smoke temperature rise. continuous development and breakthrough, relatively mature research methods have been formed. Currently, fire numerical simulation research has been widely used in build-

**2. Numerical Simulation Parameter Setting and Experimental Verification**

aims to study and discuss the characteristics of atrium smoke spread, vertical smoke temperature distribution and horizontal smoke temperature distribution under the ceiling under different ignition heat release rates, and establish a dimensionless theoretical model

Fire numerical simulation research technology began in the 1960s. Over decades of

### **2. Numerical Simulation Parameter Setting and Experimental Verification** ing fire research, performance building fire design, personnel safety escape and evacua-

*Fire* **2023**, *6*, x FOR PEER REVIEW 3 of 19

### *2.1. Introduction of PyroSim* tion and other aspects. In this paper, PyroSim simulation software was selected to study

of smoke temperature rise.

*2.1. Introduction of PyroSim*

Fire numerical simulation research technology began in the 1960s. Over decades of continuous development and breakthrough, relatively mature research methods have been formed. Currently, fire numerical simulation research has been widely used in building fire research, performance building fire design, personnel safety escape and evacuation and other aspects. In this paper, PyroSim simulation software was selected to study the fire characteristics of indoor pedestrian streets for numerical simulation. This software is a fire dynamic simulation software based on the principle of large eddy simulation (LES), researched and developed by the National Institute of Standards and Technology (NIST). PyroSim is based on computational fluid dynamics and provides fire simulation parameters and fire model settings with a visual interface, which can accurately simulate and predict fire smoke spread, temperature, visibility, toxic and harmful gas concentration distribution and other parameter indicators [13,14]. the fire characteristics of indoor pedestrian streets for numerical simulation. This software is a fire dynamic simulation software based on the principle of large eddy simulation (LES), researched and developed by the National Institute of Standards and Technology (NIST). PyroSim is based on computational fluid dynamics and provides fire simulation parameters and fire model settings with a visual interface, which can accurately simulate and predict fire smoke spread, temperature, visibility, toxic and harmful gas concentration distribution and other parameter indicators [13,14]. *2.2. Commercial Pedestrian Street Experiment* The experimental area was located in a pedestrian street and adjacent ring corridor

### *2.2. Commercial Pedestrian Street Experiment* in a building complex in Fuzhou, as shown in Figure 1. The building has 4 floors, each

The experimental area was located in a pedestrian street and adjacent ring corridor in a building complex in Fuzhou, as shown in Figure 1. The building has 4 floors, each with a floor height of 4.5 m, and the pedestrian street is a narrow and straight, 154 m long and 17 m wide. Corridors on both sides are 4 m wide with a height of 2.8 m under the ceiling. The pedestrian street contains three atriums 1#, 2# and 3#. All three atriums are 19.8 m high. The experimental location is Atrium 2#, which is 32.4 m long and 8 m wide. The doors and windows on both sides of the ring corridor were kept closed during the experiment. The smoke exhaust system was opened according to different working conditions of the experiment, and the volume of the top smoke exhaust fan was 64,200 m3/h. with a floor height of 4.5 m, and the pedestrian street is a narrow and straight, 154 m long and 17 m wide. Corridors on both sides are 4 m wide with a height of 2.8 m under the ceiling. The pedestrian street contains three atriums 1#, 2# and 3#. All three atriums are 19.8 m high. The experimental location is Atrium 2#, which is 32.4 m long and 8 m wide. The doors and windows on both sides of the ring corridor were kept closed during the experiment. The smoke exhaust system was opened according to different working conditions of the experiment, and the volume of the top smoke exhaust fan was 64,200 m³/h.

**Figure 1.** Plan of a building complex in Fuzhou. **Figure 1.** Plan of a building complex in Fuzhou.

1.

The experimental working conditions include natural filling, natural smoke exhaust The experimental working conditions include natural filling, natural smoke exhaust and atrium mechanical smoke exhaust. Specific working conditions are detailed in Table 1.

and atrium mechanical smoke exhaust. Specific working conditions are detailed in Table


**Case Heat Release Rates Fire Location Smoke Exhaust Mode**

Case 2 1.5 MW Atrium 2# natural smoke exhaust Case 3 0.7 MW Atrium 2# natural filling

Case 4 0.34 MW Atrium 2# natural smoke exhaust Case 5 0.34 MW Atrium 2# mechanical smoke exhaust

During the experiment, the fire source was arranged in the center of atrium 2#, as shown in Figure 2 in accordance with the requirements of the standard hot smoke test method [15] specified in the 'Field Verification Method for the Performance of the Antismoke System' (GA/T 999-2012). The designed heat release rates are 1.5 MW, 0.7 MW and

16 L was injected for each test. Cooling water was injected into the water-bearing plate to

Case 1 1.5 MW Atrium 2# natural filling

*Fire* **2023**, *6*, x FOR PEER REVIEW 4 of 19

**Table 1.** Experiments' conditions. The basic components of the whole set of devices include the combustion plate placed

0.34 MW.

**Table 1.** Experiments' conditions.

During the experiment, the fire source was arranged in the center of atrium 2#, as shown in Figure 2 in accordance with the requirements of the standard hot smoke test method [15] specified in the 'Field Verification Method for the Performance of the Antismoke System' (GA/T 999-2012). The designed heat release rates are 1.5 MW, 0.7 MW and 0.34 MW. ensure the test safety, and the combustion plate will not float. Ammonium chloride smoke cake was selected as the smoke generating material for the test. The smoke generated by combustion was guided to the top of the fire source through an independent smoke generator. The tracer smoke was neutral, white, and basically free of residue.

**Figure 2.** Schematic diagram of fire source layout of different heat release rates (1.5 MW, 0.7 MW, 0.34 MW, from left to right). **Figure 2.** Schematic diagram of fire source layout of different heat release rates (1.5 MW, 0.7 MW, 0.34 MW, from left to right).

Five thermocouples were arranged directly above the fire source. The bottom thermocouple was 0.9 m away from the fire source, and the next ones were arranged every next 0.35 m upward, numbering 1~5 in order. The top thermocouple was 2.3 m away from the fire. From the No. 5 thermocouple, they then diverged to the south, east, north and west directions, and along that axis, 2 thermocouples were arranged in each direction at intervals of 0.35 m, numbered 6~13 in turn. There were 13 thermocouples in total. A thermocouple was arranged every 1 m at 2.3 m from the fire source. The highest point was 17.3 m, and they were numbered V1~V16 from top to bottom, to a total of 16 thermocouples. 7 thermocouples were arranged along the center line from west to east at The basic components of the whole set of devices include the combustion plate placed in the water tray and the smoke generating device close to the combustion plate. The heat generated by the combustion of the fire source drives the tracer smoke movement to simulate the smoke spread behavior under the real fire. The combustion disc in the hot smoke test device was welded from 1.6 mm thick steel plate, and the internal dimensions were 841 mm <sup>×</sup> 595 mm <sup>×</sup> 130 mm. The plate area was 0.5 m<sup>2</sup> , 95% ethanol was selected as fuel, 16 L was injected for each test. Cooling water was injected into the water-bearing plate to ensure the test safety, and the combustion plate will not float. Ammonium chloride smoke cake was selected as the smoke generating material for the test. The smoke generated by combustion was guided to the top of the fire source through an independent smoke generator. The tracer smoke was neutral, white, and basically free of residue.

the height of 9.3 m, 13.8 m and 18.3 m. The horizontal distance interval was 1 m. thermocouples were numbered Z3F1~Z3F7, Z4F1~Z4F7, ZTH1~ZTH7 from west to east in order, to a total of 21. A total of 37 thermocouples were used in this experiment. See Figure 3 for thermocouple layout. Five thermocouples were arranged directly above the fire source. The bottom thermocouple was 0.9 m away from the fire source, and the next ones were arranged every next 0.35 m upward, numbering 1~5 in order. The top thermocouple was 2.3 m away from the fire. From the No. 5 thermocouple, they then diverged to the south, east, north and west directions, and along that axis, 2 thermocouples were arranged in each direction at intervals of 0.35 m, numbered 6~13 in turn. There were 13 thermocouples in total.

A thermocouple was arranged every 1 m at 2.3 m from the fire source. The highest point was 17.3 m, and they were numbered V1~V16 from top to bottom, to a total of 16 thermocouples. 7 thermocouples were arranged along the center line from west to east at the height of 9.3 m, 13.8 m and 18.3 m. The horizontal distance interval was 1 m. thermocouples were numbered Z3F1~Z3F7, Z4F1~Z4F7, ZTH1~ZTH7 from west to east in order, to a total of 21. A total of 37 thermocouples were used in this experiment. See Figure 3 for thermocouple layout.

**Figure 3.** Thermocouple layout. **Figure 3.** Thermocouple layout.

### *2.3. Model Parameter Setting 2.3. Model Parameter Setting*

According to the building entity, a numerical model was established according to the size of 1:1. The wall material is made of concrete material and glass curtain wall, and all details of the model are consistent with the actual situation. The corresponding measurement points were set at each place of the thermocouples determined in the laboratory, and the temperature slices are placed in the X and Y directions at the center point of the fire source. The design heat release rates are 1.5 MW, 0.7 MW and 0.34 MW. The fire model is a t² fast fire. The simulated initial temperature was 20 °C. The simulation time was consistent with the experimental time, and all doors and windows were kept closed. According to the building entity, a numerical model was established according to the size of 1:1. The wall material is made of concrete material and glass curtain wall, and all details of the model are consistent with the actual situation. The corresponding measurement points were set at each place of the thermocouples determined in the laboratory, and the temperature slices are placed in the X and Y directions at the center point of the fire source. The design heat release rates are 1.5 MW, 0.7 MW and 0.34 MW. The fire model is a t<sup>2</sup> fast fire. The simulated initial temperature was 20 ◦C. The simulation time was consistent with the experimental time, and all doors and windows were kept closed.

The smoke exhaust vents were set in the smoke storage bin on the roof of the building and consisted of 52 vents. A total of 20 natural smoke exhaust vents with lengths of 1.5 m and heights of 0.4 m were set on the east and west sides. Furthermore, 6 mechanical smoke exhaust vents with lengths of 1.2 m and heights of 0.4 m were set on the north and south The smoke exhaust vents were set in the smoke storage bin on the roof of the building and consisted of 52 vents. A total of 20 natural smoke exhaust vents with lengths of 1.5 m and heights of 0.4 m were set on the east and west sides. Furthermore, 6 mechanical smoke exhaust vents with lengths of 1.2 m and heights of 0.4 m were set on the north and south sides.

sides. During the series of tests, the start-up time of the mechanical smoke exhaust system was 30 s after ignition, and the ambient temperature was always maintained at about 20 °C. The next group of tests were conducted after the environmental conditions recovered During the series of tests, the start-up time of the mechanical smoke exhaust system was 30 s after ignition, and the ambient temperature was always maintained at about 20 ◦C. The next group of tests were conducted after the environmental conditions recovered to the initial state.

to the initial state. The schematic diagram of numerical model of this complex is shown in Figure 4. The schematic diagram of numerical model of this complex is shown in Figure 4.
