**1. Introduction**

In recent years, an increasing number of urban commercial complexes have emerged, not only bringing great convenience to people's lives, but also causing greater fire hazards. The mall atrium is a large space which integrates shopping, entertainment, leisure and other functions. Usually, there are dense personnel and numerous combustibles in the mall atrium, which brings a high fire risk. Once a fire occurs, it is likely to spread to the buildings next to the atrium, which causes serious economic losses and casualties; moreover, smoke is the most critical factor that threatens the safety of people in fires. Therefore, it is of great significance to study the law of smoke spreading and smoke extraction efficiency

**Citation:** Liu, Q.; Xiao, J.; Cai, B.; Guo, X.; Wang, H.; Chen, J.; Zhang, M.; Qiu, H.; Zheng, C.; Zhou, Y. Numerical Simulation on the Effect of Fire Shutter Descending Height on Smoke Extraction Efficiency in a Large Atrium. *Fire* **2022**, *5*, 101. https://doi.org/10.3390/fire5040101 4.0/). *fire*

Academic Editors: Chuangang Fan and Dahai Qi

Received: 14 June 2022 Accepted: 15 July 2022 Published: 17 July 2022

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in the atrium and indoor pedestrian street, which is the key passage for personnel safety evacuation [1–3].

The research on the spread and control of fire smoke in large-space buildings started in the 1970s. Many scholars have studied the factors affecting the fire plume and smoke spread characteristics, and given many mathematical relationships through experiments, such as Thomas et al. [4], McCaffery [5,6], Zukoski et al. [7,8], Heskestad [9,10] and Tanaka et al. [11]. In addition, they established some theoretical models of axisymmetric fire plumes, which laid the theoretical foundation for the study of fire smoke development in large spaces. Since then, their results have been widely used in the prediction and control of fire smoke. With the increase of research by domestic and foreign scholars, the understanding of the fire smoke spread characteristics has gradually increased and a relatively complete system has been formed. In the 1990s, with the development of computational technology, the advantages of numerical simulation technology have gradually been highlighted, which has good visualization effects and simple operation methods. Nowadays, it has become the mainstre am method of studying indoor large-space fire [12–16].

Fires generate a great deal of heat and smoke, which threaten people's lives. On the one hand, fire and smoke separations are required to hinder the further spread of fire and smoke; on the other hand, heat and smoke also need to be exhausted from the atrium by smoke vents. Therefore, the efficiency of smoke extraction is closely linked to the safe evacuation of people. Different smoke exhaust systems will cause different smoke flowing and temperature distribution laws. As a rule, mechanical smoke exhaust systems are more responsive and reliable than natural smoke exhaust systems, which are now widely used for fire and smoke extraction in large spaces. Many scholars have carried out exhaustive research on large space atrium fires. For example, Klote et al. [17,18] found the law and calculation method of smoke flow in atrium fire. Hadjisophocleous et al. [19–22] combined experiments and numerical simulation to analyze the smoke spread and filling characteristics of atrium fires, the calculation method of smoke layer height and the smoke extraction efficiency of the mechanical smoke exhaust system in the atrium. Rho and Ryou [23] studied the characteristics of smoke flow in a large space atrium by numerical simulation. Chow et al. [24–26] investigated the fire development form and the smoke flow characteristics of the atrium through numerical simulation and small-scale experiments. Wong [27] figured out the influence of the distance between the fire shutter and the evacuation distance of the emergency exit under various circumstances. Yu and Wei [28] ensured the safe distance from combustibles to the fire shutters in the atrium. Yu [29] aimed at the safety and reliability of the fire shutter.

Long et al. [30] carried out full-scale fire experiments for several vital parameters including the vertical temperature distribution, the longitudinal temperature distribution, smoke layer height and smoke front arrival time under four different scenarios. Huang et al. [31] found the enlargement of the difference between the two heights, and the smoke spread process became slower at the constant heat release rate. Zhang et al. [32] solved the impact of the segmented smoke exhaust of the ultra-thin and tall atrium on fire prevention and control by using a full-scale hot smoke experiment method. Xu's results via the fire dynamics simulator (FDS) indicate that the temperature is changed more sharply than the visibility while the ceiling height gets higher [16].

Although scholars have studied the smoke extraction efficiency of the atrium through experiments or simulations, there is little involved in the impact of the fire shutter on it. The existence of a fire shutter has significantly changed the fire situation; this results in a research gap.

A fire shutter is a facility used for fire protection, heat insulation and smoke prevention for buildings; it also has an effect on the efficiency of smoke extraction in large spaces. The descending height of the fire shutter will affect the airflow, thus affecting the smoke extraction efficiency; besides, the smoke extraction method (including natural smoke extraction and mechanical smoke extraction) also has an effect on the smoke extraction efficiency; however, current studies have not given the influence mechanism of fire shutter

on the smoke extraction effect. Therefore, this study is expected to reveal the relationship between the two parameters by numerical simulations.
