# Numerical Simulation of Fire Smoke Spread in a Super High-Rise Building for Different Fire Scenarios

Authors: Xin Yi; Changkui Lei; Jun Deng; Li Ma; Jing Fan; Yuanyuan Liu; Lei Bai; Chi-Min Shu
Journal: Advances in Civil Engineering
 (2019)

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## Abstract

Research on fire spread in super high-rise buildings is crucial for identifying feasible methods of fire prevention and personnel evacuation. In this study, a fire spread model was established based on the fire dynamics simulator (FDS), and fire spread results were analyzed for a fire scenario in a single room under different conditions, a fire scenario in different functional places under the same conditions, and the spread of fire outside of the room. The results revealed that the critical time required for a fire to become a safety hazard in a shop, a restaurant, or an office was approximately 200 s. The same type of fire reached the critical time required for a fire to become a safety hazard more quickly in an office than a restaurant or shop, regardless of whether the fire spread was caused by CO mass fraction or temperature. More attention should be paid to fire safety in office spaces in super high-rise buildings. Furthermore, compared with CO mass fraction and temperature, visibility was a more influential factor in determining the critical time required for fire to become a hazard, and smoke affected the adjacent open area in approximately 60 s. In the event of a fire, the temperature of the staircase and its front chamber was always lower than the threshold temperature of 60°C for human body tolerance.


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## Body

## 1. Introduction

With the rapid development of modern urban processes and the progress of architectural science and technology, numerous super high-rise buildings continue to be constructed [1–4]. Some super high-rise buildings have become prominent symbols of city modernization and urbanization, particularly those in metropolitan areas, such as the Burj Khalifa in Dubai, Shanghai Tower, and Goldin Finance 117 in Tianjin. Super high-rise buildings bring people enjoyment and optimize the land area used. However, the height and number of these buildings increases, so do the number and variety of internal combustibles. Problems associated with super high-rise buildings, such as vertical traffic problems, structural problems, and security concerns, have also become increasingly prominent [5–9].Compared with general building fires, super high-rise building fires have unique characteristics [10]: (1) fire spreads quickly, (2) super high-rise buildings have numerous fire hazards, (3) complex building structures and boundary environments cause particular fire evolution behaviors, (4) crowd evacuation in super high-rise buildings is a major safety concern, (5) fire rescue is difficult and the amount of time required to fight a fire is long, allowing the fire to readily spread, and (6) fires cause substantial loss and grave social consequences. Therefore, identifying methods for effectively preventing the occurrence, development, and spread of fire in super high-rise buildings, ensuring safe evacuation of internal personnel, and reducing casualties and property damage have become crucial concerns in the field of firefighting [11–15]. In the current research on high-rise building fires, NFPA92B is the most widely recognized and used. At the same time, researchers generally conduct research through theoretical analysis, numerical simulation, and CFD simulation methods, mainly to study the spread of smoke and evacuation of people in high-rise building fire.Zhu et al. [16] conducted research on smoke control in super high-rise building fires. Based on the CCTV North Building fire, Hou et al. [17] numerically simulated the fire spread and temperature distribution of high-rise buildings. Liu et al. [18] analyzed in detail the fire causes of high-rise building fires and proposed protective measures to facilitate evacuation. Yang et al. [19] also simulated the variation of smoke and temperature fields in a high-rise residential building in Japan by numerical simulation. Xia [20] simulated the spread of fire smoke in an elevator shaft of a high-rise building, and Cheng and Hadjisophocleous [21] produced a dynamic model of fire spread that investigated the spread of fire in both horizontal and vertical directions. Jiang et al. [22] published an independent review of the performance of Shanghai Tower in the event of a fire. Sun et al. [23] reviewed the contemporary research on the dynamics of fires in high-rise buildings. Zhang and Ren [24] used a super high-rise building in Chongqing as an example, adopting FDS and the simulation of transient evacuation and pedestrian movements to simulate the spread of smoke and evacuation in a general fire scenario and offered several suggestions for fire safety. Chen et al. [25] proposed an event-driven agent-based modeling approach to quantitatively evaluate elevator-assisted evacuation processes. Yu-ting and Zhou [26] discussed the fire safety status of the building after the 2015 fire accident in Dubai and mentioned the importance of fire protection standards and firefighting equipment. Xu et al. [27] conducted a hot smoke test in the 60 m high atrium of the Shanghai Tower and studied in detail the movement laws and smoke characteristics of fire smoke.For example, firefighting, smoke control, and personnel evacuation in super high-rise buildings are still beset by certain technical challenges [28–31]. Therefore, using scientific approaches to simulate fire scenarios to understand common modes and characteristics of fire spread is valuable for fire prevention and disaster reduction in super high-rise buildings [32, 33].This study selected an actual super high-rise building to set up specific fire scenarios, establish a FDS fire model, and analyze the direction and type of spread for a fire in different fire scenarios.


## 2. Fire Scenario Settings of the Super High-Rise Building

### 2.1. Building Overview

Basically, the combustion characteristics of high-rise and super high-rise fires are the same; with that the potential spreads many ways, the speed is fast, the fire control is difficult, and the chimney effect is easy to form. The reliability of super high-rise fire facilities is low, the external rescue is difficult, and the environmental conditions are greatly affected. In the existing simulations, the influence of environmental factors on the combustion process of super high-rise buildings is less considered. For example, the boundary conditions such as air velocity and grid setting do not fully consider the characteristics of actual buildings, and there are few fire researches on super high-rise buildings. The research object of this study was the Saigao office, located in Shaanxi Province, China. The building has an approximate height of 150 m, with a total floor area of 85,532 m2, a building area of 78,836 m2 for 35 stories above ground level, and a building area of 6,696 m2 for 3 stories located underground. The building consists of a steel-reinforced concrete frame reinforcing a concrete core-tube structure. The building functions are listed in Table 1.Table 1
Summary of the super high-rise building functions.
Floor
Function
Underground 2nd and 3rd floors
Garage and equipment rooms
Underground 1st floor
Equipment and commercial space
1st floor
Office hall and commercial space
2nd to 6th floors
Commercial space
7th and 21st floors
Refuge story
8th to 20th floors
Low office
22nd to 35th floors
High office


### 2.2. Parameter Setting for Fire Scenarios

In the fire settings, the factors determining the degree and speed of fire development were mainly the heat release of the combustion material, fire growth factors, and the ambient temperature affecting the height of the neutral surface of the building. Moreover, this study combined the places for critical fire prevention to establish the fire parameters.


### 2.3. Heat Release

According to Shanghai’s “Technical specification for building smoke control DGJ 08-88-2006”, the thermal temperature released in each place varies depending on whether a sprinkler system is set up or not, as indicated in Table2.Table 2
Heat release for various sprinkler systems.
Places
Heat releaseQ (MW)
Mall with a sprinkler system
5.0
Office and room with a sprinkler system
1.5
Public place with a sprinkler system
2.5
Office and room without a sprinkler system
6.0
Public place without a sprinkler system
8.0


### 2.4. Fire Growth Factors

Rate of fire growth is a crucial indicator for measuring the risk of fire and is related to the storage of combustibles, combustion characteristics, spatial characteristics, the presence of water sprinkler systems, and ventilation devices. The relationship between fire heat release rate and duration can be expressed by(1)Qf=αt−t02,where Qf is the fire heat release rate in kW, α is the fire growth factor in kW/s2, t is the fire burning time in s, and t0 is the smoldering time of the fire in s.Because of the small effect of smoldering on the spread of fire, smoldering timet0 is usually ignored. Accordingly, equation (1) can be simplified as follows:(2)Qf=αt2.Fire growth factors for different fire types are provided in Table3. The primary functions of the super high-rise building used in this study are business and office-related activities, which feature a dense distribution of internal combustible material. Therefore, the typical fire type in such a building can be defined as a fast fire type with a fire growth factor α of 0.04689.Table 3
Fire growth factors for various fires.
Fire type
Typical combustible material
Fire growth factor (kW/s2)
Slow-spreading fire
Hardwood furniture
0.00293
Medium-spreading fire
Cotton and polyester mats
0.01172
Fast-spreading fire
Wooden shelves and foam
0.04689
Ultra-fast-spreading fire
Pool fire, fast-burning decorative furniture, and light curtains
0.18750


### 2.5. Ambient Temperature

In China, the State Council has promoted a campaign that restricts the temperature of air conditioning in public buildings, with the exception of those in certain industries; the temperature can be neither lower than 26°C in the summer nor higher than 20°C in the winter. Thus, the ambient temperature used in this study was set at 23°C.


### 2.6. Fire Scenario Setting

According to the distribution of the building functional area and the process of smoke spread in different spaces, six fire places were deliberately selected and set up for simulation studies, as detailed in Table4.Table 4
Fire scenario design for this study.
Fire location
Fire scenario
Fire growth factor (kW/s2)
Sprinkler system
Smoke extraction system
Maximum heat release rate of fire (MW)
F1 shop A
A00
0.04689
Invalid
Invalid
8.0
A01
0.04689
Invalid
Valid
8.0
A10
0.04689
Valid
Invalid
5.0
A11
0.04689
Valid
Valid
5.0
F4 restaurant B
B00
0.04689
Invalid
Invalid
8.0
B01
0.04689
Invalid
Valid
8.0
B10
0.04689
Valid
Invalid
2.5
B11
0.04689
Valid
Valid
2.5
F15 an office area C
C00
0.04689
Invalid
Invalid
6.0
C01
0.04689
Invalid
Valid
6.0
C10
0.04689
Valid
Invalid
1.5
C11
0.04689
Valid
Valid
1.5
F14 an office area and staircase D
D00
0.04689
Invalid
Invalid
6.0
D01
0.04689
Invalid
Valid
6.0
D10
0.04689
Valid
Invalid
1.5
D11
0.04689
Valid
Valid
1.5
F14-15 an office area and staircase E
E00
0.04689
Invalid
Invalid
6.0
E01
0.04689
Invalid
Valid
6.0
E10
0.04689
Valid
Invalid
1.5
E11
0.04689
Valid
Valid
1.5
F14-15-16 an office area and staircase F
F00
0.04689
Invalid
Invalid
6.0
F01
0.04689
Invalid
Valid
6.0
F10
0.04689
Valid
Invalid
1.5
F11
0.04689
Valid
Valid
1.5


### 2.7. Fire Hazard Criteria

Considering that the study of fire hazard is usually to ensure the safe evacuation of personnel, it is usually taken in conjunction with the environmental limit which the human body can withstand [34, 35]. Generally, it is considered from three aspects: the smoke layer height, the clear layer temperature, and the visibility, from a position 2.0 m above the ground.(1)
In this paper, the respirable air temperature not higher than 60°C is determined as the safe temperature.(2)
The visibility in a large-space fire field should be no less than 10 m, and the visibility in a small space should be no less than 5 m.(3)
It is generally considered that the tolerance value of the human body is not higher than 500 ppm when the smoke drops to a dangerous height.


### 2.8. Building Modeling Setting

From the perspective of personnel safety, in the construction fire, the harm of smoke is greater than the casual hazard of the fire. According to statistics, 80% of the deaths in such fire are caused by smoke. The building modeling process does not consider the damage effect of fire on the internal separation structure of the building but the spread process of the smoke. Set the door connecting the aisle in the room and divide the internal room into a noncombustible wall. Generally, the indoor window is closed. The fire cannot affect the automatic opening of the window, so it is considered to be closed, and at the same time, all the walls are incombustible walls.


## 2.1. Building Overview

Basically, the combustion characteristics of high-rise and super high-rise fires are the same; with that the potential spreads many ways, the speed is fast, the fire control is difficult, and the chimney effect is easy to form. The reliability of super high-rise fire facilities is low, the external rescue is difficult, and the environmental conditions are greatly affected. In the existing simulations, the influence of environmental factors on the combustion process of super high-rise buildings is less considered. For example, the boundary conditions such as air velocity and grid setting do not fully consider the characteristics of actual buildings, and there are few fire researches on super high-rise buildings. The research object of this study was the Saigao office, located in Shaanxi Province, China. The building has an approximate height of 150 m, with a total floor area of 85,532 m2, a building area of 78,836 m2 for 35 stories above ground level, and a building area of 6,696 m2 for 3 stories located underground. The building consists of a steel-reinforced concrete frame reinforcing a concrete core-tube structure. The building functions are listed in Table 1.Table 1
Summary of the super high-rise building functions.
Floor
Function
Underground 2nd and 3rd floors
Garage and equipment rooms
Underground 1st floor
Equipment and commercial space
1st floor
Office hall and commercial space
2nd to 6th floors
Commercial space
7th and 21st floors
Refuge story
8th to 20th floors
Low office
22nd to 35th floors
High office


## 2.2. Parameter Setting for Fire Scenarios

In the fire settings, the factors determining the degree and speed of fire development were mainly the heat release of the combustion material, fire growth factors, and the ambient temperature affecting the height of the neutral surface of the building. Moreover, this study combined the places for critical fire prevention to establish the fire parameters.


## 2.3. Heat Release

According to Shanghai’s “Technical specification for building smoke control DGJ 08-88-2006”, the thermal temperature released in each place varies depending on whether a sprinkler system is set up or not, as indicated in Table2.Table 2
Heat release for various sprinkler systems.
Places
Heat releaseQ (MW)
Mall with a sprinkler system
5.0
Office and room with a sprinkler system
1.5
Public place with a sprinkler system
2.5
Office and room without a sprinkler system
6.0
Public place without a sprinkler system
8.0


## 2.4. Fire Growth Factors

Rate of fire growth is a crucial indicator for measuring the risk of fire and is related to the storage of combustibles, combustion characteristics, spatial characteristics, the presence of water sprinkler systems, and ventilation devices. The relationship between fire heat release rate and duration can be expressed by(1)Qf=αt−t02,where Qf is the fire heat release rate in kW, α is the fire growth factor in kW/s2, t is the fire burning time in s, and t0 is the smoldering time of the fire in s.Because of the small effect of smoldering on the spread of fire, smoldering timet0 is usually ignored. Accordingly, equation (1) can be simplified as follows:(2)Qf=αt2.Fire growth factors for different fire types are provided in Table3. The primary functions of the super high-rise building used in this study are business and office-related activities, which feature a dense distribution of internal combustible material. Therefore, the typical fire type in such a building can be defined as a fast fire type with a fire growth factor α of 0.04689.Table 3
Fire growth factors for various fires.
Fire type
Typical combustible material
Fire growth factor (kW/s2)
Slow-spreading fire
Hardwood furniture
0.00293
Medium-spreading fire
Cotton and polyester mats
0.01172
Fast-spreading fire
Wooden shelves and foam
0.04689
Ultra-fast-spreading fire
Pool fire, fast-burning decorative furniture, and light curtains
0.18750


## 2.5. Ambient Temperature

In China, the State Council has promoted a campaign that restricts the temperature of air conditioning in public buildings, with the exception of those in certain industries; the temperature can be neither lower than 26°C in the summer nor higher than 20°C in the winter. Thus, the ambient temperature used in this study was set at 23°C.


## 2.6. Fire Scenario Setting

According to the distribution of the building functional area and the process of smoke spread in different spaces, six fire places were deliberately selected and set up for simulation studies, as detailed in Table4.Table 4
Fire scenario design for this study.
Fire location
Fire scenario
Fire growth factor (kW/s2)
Sprinkler system
Smoke extraction system
Maximum heat release rate of fire (MW)
F1 shop A
A00
0.04689
Invalid
Invalid
8.0
A01
0.04689
Invalid
Valid
8.0
A10
0.04689
Valid
Invalid
5.0
A11
0.04689
Valid
Valid
5.0
F4 restaurant B
B00
0.04689
Invalid
Invalid
8.0
B01
0.04689
Invalid
Valid
8.0
B10
0.04689
Valid
Invalid
2.5
B11
0.04689
Valid
Valid
2.5
F15 an office area C
C00
0.04689
Invalid
Invalid
6.0
C01
0.04689
Invalid
Valid
6.0
C10
0.04689
Valid
Invalid
1.5
C11
0.04689
Valid
Valid
1.5
F14 an office area and staircase D
D00
0.04689
Invalid
Invalid
6.0
D01
0.04689
Invalid
Valid
6.0
D10
0.04689
Valid
Invalid
1.5
D11
0.04689
Valid
Valid
1.5
F14-15 an office area and staircase E
E00
0.04689
Invalid
Invalid
6.0
E01
0.04689
Invalid
Valid
6.0
E10
0.04689
Valid
Invalid
1.5
E11
0.04689
Valid
Valid
1.5
F14-15-16 an office area and staircase F
F00
0.04689
Invalid
Invalid
6.0
F01
0.04689
Invalid
Valid
6.0
F10
0.04689
Valid
Invalid
1.5
F11
0.04689
Valid
Valid
1.5


## 2.7. Fire Hazard Criteria

Considering that the study of fire hazard is usually to ensure the safe evacuation of personnel, it is usually taken in conjunction with the environmental limit which the human body can withstand [34, 35]. Generally, it is considered from three aspects: the smoke layer height, the clear layer temperature, and the visibility, from a position 2.0 m above the ground.(1)
In this paper, the respirable air temperature not higher than 60°C is determined as the safe temperature.(2)
The visibility in a large-space fire field should be no less than 10 m, and the visibility in a small space should be no less than 5 m.(3)
It is generally considered that the tolerance value of the human body is not higher than 500 ppm when the smoke drops to a dangerous height.


## 2.8. Building Modeling Setting

From the perspective of personnel safety, in the construction fire, the harm of smoke is greater than the casual hazard of the fire. According to statistics, 80% of the deaths in such fire are caused by smoke. The building modeling process does not consider the damage effect of fire on the internal separation structure of the building but the spread process of the smoke. Set the door connecting the aisle in the room and divide the internal room into a noncombustible wall. Generally, the indoor window is closed. The fire cannot affect the automatic opening of the window, so it is considered to be closed, and at the same time, all the walls are incombustible walls.


## 3. Simulation Analysis of Smoke in a Super High-Rise Building

According to the setting of the fire scenario presented in Table4, typical scenarios were selected for use in the analysis of the simulation results. The building structure model in the FDS is displayed in Figure 1.Figure 1
The super high-rise building structure model used in FDS.Whether the fire develops in accordance with the heat release rate of the fire depends on the ratioD∗/δ∗ of the feature size of the fire source to the cell size of the grid where the source is located:(3)D∗=Qfρ∞cpT∞g2/5,where D∗ is the feature size of the fire, ρ∞ is the gas density at ambient temperature in kg/m3, cp is specific heat at constant pressure of the gas in kJ/(kg⋅K), T∞ is ambient temperature in K, and g is gravitational acceleration in m/s2.Considering the increase in the heat release rate of the fire source and performance of the computer, the FDS User Manual suggests that theD∗/δ∗ value is most reasonable within the range of 4 to 16. Thus, D∗/δ∗ was calculated according to the cell size of the grid where the fire source was located (δ∗ = 0.2 m), as detailed in Table 5.Table 5
Q vs. D∗ and D∗/δ∗ values.
Q (kW)
8
6
5
2.5
1.5
D
∗
2.18
1.95
1.81
1.37
1.12
D
∗
/
δ
∗
10.90
9.75
9.05
6.85
5.60As evident in Table5, we demonstrated that the grid size was reasonable and that the established fire model was accurate and credible. Furthermore, by employing the adaptive test, we discovered that, to a certain extent, the results did not change significantly (approximately 0.1%) when the number of meshes increased, which further illustrated the reliability of the established fire model.


### 3.1. Fire Conditions of a Single Room in Different States

The thresholds for fire hazard for the three functional rooms are listed in Table6. The black areas in Figures 2–4 denote the range in which the room reached the critical threshold. The larger the value, the greater the visibility and the lower the risk. Table 6 specifies the critical time required for fire to become a hazard in three scenarios: Catering area B > shop area A > office area C.Table 6
Critical time required for fire to become a hazard for the three functional rooms.
Fire location
Fire scenario
Critical time required for fire to become a hazard (s)
F1 shop area A
A00
184
A01
196
A10
191
A11
212
F4 catering area B
B00
190
B01
196
B10
194
B11
214
F15 an office area C
C00
119
C01
121
C10
124
C11
133Figure 2
Critical time of fire hazard for scenario A. (a) A00, (b) A01, (c) A10, and (d) A11.
(a)
(b)
(c)
(d)Figure 3
Critical time of fire hazard for scenario B. (a) B00, (b) B01, (c) B10, and (d) B11.
(a)
(b)
(c)
(d)Figure 4
Critical time of fire hazard for scenario C. (a) C00, (b) C01, (c) C10, and (d) C11.
(a)
(b)
(c)
(d)The analytical results revealed that the critical time required for fire to become a hazard in the shop area did not vary significantly under various failure conditions for the automatic sprinkler system and smoke extraction system. Smoke in all scenarios gathered from the corner. In fire scenarios in which the automatic sprinkler system or smoke extraction system experienced a single failure, critical time required for fire to become a hazard was similar, with a difference ≤5 s. The critical time of fire hazard was approximately 200 s in all the aforementioned fire scenarios, but the maximum straight-line distance from any point in the room to the evacuation gate was 20 m for high-rise buildings with first-rate and second-rate fire-resistance. Therefore, this length of time is sufficient to ensure that people can escape from a single room.


### 3.2. Fire Conditions of Different Functional Places in the Same State

Scenarios A10, B10, and C10 were selected for comparative analysis in which the fire type was a fire controlled by a sprinkler system.As can be clearly seen from Figures5 and 6, the CO mass fraction did not reach the critical value at 600 s, and the entire space of the three different functional sites all reached a dangerous temperature. Therefore, the criterion of CO mass fraction did not play a role in the parameters affecting evacuation time and reduced the critical time required for temperature to become a hazard. At 1800 s, the temperature at the fire source decreased and the fire became smaller, which was related to the fact that the fire scenario selected featured a dysfunctional smoke extraction system and an effective sprinkler system. The temperature and CO mass fraction growth in scenario C10 were faster than those of scenarios A10 and B10. Thus, fire prevention in the office area should be taken seriously because the office areas comprised the majority of super high-rise buildings.Figure 5
Slices of the CO mass fraction in different scenarios. (a) A10, (b) B10, and (c) C10.
(a)
(b)
(c)Figure 6
Slices of the temperature in different scenarios. (a) A10, (b) B10, and (c) C10.
(a)
(b)
(c)


### 3.3. Fire Spread

As the fire occurred in a room in the building, smoke, heat radiation, and temperature promptly augmented the space, and the smoke spread along various gaps to other areas. During the process of evacuating personnel to the staircase, the accommodation space in the front chamber was limited. Therefore, staff would require a certain space in the aisle.Scenario D10 was selected for simulation and analysis of the situation in which the automatic sprinkler system was effective but the smoke extraction system was faulty. In the simulation, changes in fire temperature were evaluated by setting thermocouple points, as displayed in Figure7. The thermocouples were arranged in the key area of the F14 room, and its connected staircase at a height of 2 m from the roof to detect temperature changes, as displayed in Figure 8.Figure 7
Temperature vs. time inside the room in fire scenario D10.Figure 8
Thermocouple arrangements of F14. (a) 2D thermocouple arrangements; (b) 3D thermocouple arrangements.
(a)
(b)F14-1 and F14-3 were the thermocouples in the front chamber of the staircase, and F14-2 and F14-4 were the thermocouples in the staircase. F14-aisle 1, F14-aisle 2, F14-aisle 3, and F14-aisle 4 were the thermocouples in the aisle, and F14-aisle 1 was located 5 m beneath the fire point. The distance between two adjacent thermocouples was 5 m, and because the area was relatively symmetrical, thermocouples were arranged on the left side only. F14-door 1 and F14-door 2 were thermocouples at the door of the room, and the distance from the fire source was 17 and 4 m, respectively. F14-room 1, F14-room 2, and F14-room 3 were thermocouples in the room with distances from the red fire source of 5, 10, and 15 m, respectively.According to the simulation results, as displayed in Figure9, the CO mass fraction at 1800 s was at most 3 × 10−4, which did not exceed the maximum tolerance limit of 5 × 10−4. Therefore, CO does not generally affect the safety evacuation.Figure 9
Slice of the CO mass fraction at 1800 s.In practice, visibility is a parameter closely related to smoke, as indicated in Figure10, where black is the critical line of visibility for people, with a value of 5 m. The rate of smoke spreading and lowering was exceptionally high, with an adjacent open area being affected almost every 60 s. At 101 s, the top of the room began to gather smoke. At 162 s, the smoke had filled the entire room and spread to the top of the outside aisle, whereas visibility in the room exceeded the visual distance of a person. At 221 s, smoke continued to sink lower in the aisle, spread to the front of the stairs, and then began to gather at the top of the front chamber. At 292 s, the smoke spread to the staircase and gathered at the top of the staircase, further threatening safety evacuation of personnel. At 508 s, the smoke filled the entire space, and all areas were invisible, which seriously affected the normal actions of the personnel.Figure 10
Visibility slice of fire scenario D10.According to the temperature detected by thermocouples, as presented in Figure11, the temperature inside the room was higher than 60°C, which exceeded the temperature range bearable to the human body. In the room, the temperature was higher at greater distances from the fire source; after 200 s, the temperature detection point tended to remain stable, with Troom1 > Troom2 > Troom3, Tdoor2 > Tdoor1 > 60°C. Tdoor1 had the lowest average temperature, which remained stable at 65°C after 200 s. The distance between door 2 and the fire source was 4 m, but heat was exchanged inside and outside the room and reduced the temperature of door 2 because the door was open and the temperature outside the room was lower than the temperature inside the room. Accordingly, Troom2 > Tdoor2, as presented in Figure 7.Figure 11
Temperature slice of fire scenario D10.Compared with the temperature inside the room, the temperature outside the room (Figure12) was generally much lower. The maximum temperature did not exceed 52°C, which was lower than the 60°C threshold for tolerability by the human body. After 200 s, the temperature remained steady, with Taisle > Tstairroom > Tfore-room > 28°C and Taisle4 > Taisle3 > Taisle2 > Taisle1 > 42°C.Figure 12
Temperature vs. time outside the room of fire scenario D10.A comparison of the three fire criteria (CO mass fraction, visibility, and temperature) revealed that the dominant factor with the most significant effect on safety evacuation time was visibility. Relevant studies have demonstrated that smoke is the primary cause of death during fires [36–38]. Therefore, the first step during evacuation is to leave the fire room quickly and avoid remaining in a corner, which can effectively prevent harm caused by smoke.Fire scenario E is displayed in Figure13; the grid is the fire simulation area in which the temperature condition of the upper floor was the same as that of the lower floor when the fire occurred. The thermocouple arrangement in F14 was the same as in fire scenario D, and the measuring points were arranged in the walkway on the 15th floor, the staircase, and its front chamber, the same as in F14.Figure 13
Structure of fire scenario E.Fire scenario F is displayed in Figure14, and the thermocouple arrangement in F14 was the same as scenario D. The thermocouples of F15 and F16 were arranged in the walkway in the same manner as in F14, as were the staircase and its front chamber.Figure 14
Structure of fire scenario F.According to the simulation results of fire scenarios E and F detected by the thermocouples, the temperature of the staircase and its front chamber in the two scenarios were always lower than the threshold temperature of 60°C for tolerance by the human body. From the perspective of temperature, when a fire occurred in scenarios E and F, the staircase and its front chamber were relatively safer areas that could be used to temporarily protect personnel.


## 3.1. Fire Conditions of a Single Room in Different States

The thresholds for fire hazard for the three functional rooms are listed in Table6. The black areas in Figures 2–4 denote the range in which the room reached the critical threshold. The larger the value, the greater the visibility and the lower the risk. Table 6 specifies the critical time required for fire to become a hazard in three scenarios: Catering area B > shop area A > office area C.Table 6
Critical time required for fire to become a hazard for the three functional rooms.
Fire location
Fire scenario
Critical time required for fire to become a hazard (s)
F1 shop area A
A00
184
A01
196
A10
191
A11
212
F4 catering area B
B00
190
B01
196
B10
194
B11
214
F15 an office area C
C00
119
C01
121
C10
124
C11
133Figure 2
Critical time of fire hazard for scenario A. (a) A00, (b) A01, (c) A10, and (d) A11.
(a)
(b)
(c)
(d)Figure 3
Critical time of fire hazard for scenario B. (a) B00, (b) B01, (c) B10, and (d) B11.
(a)
(b)
(c)
(d)Figure 4
Critical time of fire hazard for scenario C. (a) C00, (b) C01, (c) C10, and (d) C11.
(a)
(b)
(c)
(d)The analytical results revealed that the critical time required for fire to become a hazard in the shop area did not vary significantly under various failure conditions for the automatic sprinkler system and smoke extraction system. Smoke in all scenarios gathered from the corner. In fire scenarios in which the automatic sprinkler system or smoke extraction system experienced a single failure, critical time required for fire to become a hazard was similar, with a difference ≤5 s. The critical time of fire hazard was approximately 200 s in all the aforementioned fire scenarios, but the maximum straight-line distance from any point in the room to the evacuation gate was 20 m for high-rise buildings with first-rate and second-rate fire-resistance. Therefore, this length of time is sufficient to ensure that people can escape from a single room.


## 3.2. Fire Conditions of Different Functional Places in the Same State

Scenarios A10, B10, and C10 were selected for comparative analysis in which the fire type was a fire controlled by a sprinkler system.As can be clearly seen from Figures5 and 6, the CO mass fraction did not reach the critical value at 600 s, and the entire space of the three different functional sites all reached a dangerous temperature. Therefore, the criterion of CO mass fraction did not play a role in the parameters affecting evacuation time and reduced the critical time required for temperature to become a hazard. At 1800 s, the temperature at the fire source decreased and the fire became smaller, which was related to the fact that the fire scenario selected featured a dysfunctional smoke extraction system and an effective sprinkler system. The temperature and CO mass fraction growth in scenario C10 were faster than those of scenarios A10 and B10. Thus, fire prevention in the office area should be taken seriously because the office areas comprised the majority of super high-rise buildings.Figure 5
Slices of the CO mass fraction in different scenarios. (a) A10, (b) B10, and (c) C10.
(a)
(b)
(c)Figure 6
Slices of the temperature in different scenarios. (a) A10, (b) B10, and (c) C10.
(a)
(b)
(c)


## 3.3. Fire Spread

As the fire occurred in a room in the building, smoke, heat radiation, and temperature promptly augmented the space, and the smoke spread along various gaps to other areas. During the process of evacuating personnel to the staircase, the accommodation space in the front chamber was limited. Therefore, staff would require a certain space in the aisle.Scenario D10 was selected for simulation and analysis of the situation in which the automatic sprinkler system was effective but the smoke extraction system was faulty. In the simulation, changes in fire temperature were evaluated by setting thermocouple points, as displayed in Figure7. The thermocouples were arranged in the key area of the F14 room, and its connected staircase at a height of 2 m from the roof to detect temperature changes, as displayed in Figure 8.Figure 7
Temperature vs. time inside the room in fire scenario D10.Figure 8
Thermocouple arrangements of F14. (a) 2D thermocouple arrangements; (b) 3D thermocouple arrangements.
(a)
(b)F14-1 and F14-3 were the thermocouples in the front chamber of the staircase, and F14-2 and F14-4 were the thermocouples in the staircase. F14-aisle 1, F14-aisle 2, F14-aisle 3, and F14-aisle 4 were the thermocouples in the aisle, and F14-aisle 1 was located 5 m beneath the fire point. The distance between two adjacent thermocouples was 5 m, and because the area was relatively symmetrical, thermocouples were arranged on the left side only. F14-door 1 and F14-door 2 were thermocouples at the door of the room, and the distance from the fire source was 17 and 4 m, respectively. F14-room 1, F14-room 2, and F14-room 3 were thermocouples in the room with distances from the red fire source of 5, 10, and 15 m, respectively.According to the simulation results, as displayed in Figure9, the CO mass fraction at 1800 s was at most 3 × 10−4, which did not exceed the maximum tolerance limit of 5 × 10−4. Therefore, CO does not generally affect the safety evacuation.Figure 9
Slice of the CO mass fraction at 1800 s.In practice, visibility is a parameter closely related to smoke, as indicated in Figure10, where black is the critical line of visibility for people, with a value of 5 m. The rate of smoke spreading and lowering was exceptionally high, with an adjacent open area being affected almost every 60 s. At 101 s, the top of the room began to gather smoke. At 162 s, the smoke had filled the entire room and spread to the top of the outside aisle, whereas visibility in the room exceeded the visual distance of a person. At 221 s, smoke continued to sink lower in the aisle, spread to the front of the stairs, and then began to gather at the top of the front chamber. At 292 s, the smoke spread to the staircase and gathered at the top of the staircase, further threatening safety evacuation of personnel. At 508 s, the smoke filled the entire space, and all areas were invisible, which seriously affected the normal actions of the personnel.Figure 10
Visibility slice of fire scenario D10.According to the temperature detected by thermocouples, as presented in Figure11, the temperature inside the room was higher than 60°C, which exceeded the temperature range bearable to the human body. In the room, the temperature was higher at greater distances from the fire source; after 200 s, the temperature detection point tended to remain stable, with Troom1 > Troom2 > Troom3, Tdoor2 > Tdoor1 > 60°C. Tdoor1 had the lowest average temperature, which remained stable at 65°C after 200 s. The distance between door 2 and the fire source was 4 m, but heat was exchanged inside and outside the room and reduced the temperature of door 2 because the door was open and the temperature outside the room was lower than the temperature inside the room. Accordingly, Troom2 > Tdoor2, as presented in Figure 7.Figure 11
Temperature slice of fire scenario D10.Compared with the temperature inside the room, the temperature outside the room (Figure12) was generally much lower. The maximum temperature did not exceed 52°C, which was lower than the 60°C threshold for tolerability by the human body. After 200 s, the temperature remained steady, with Taisle > Tstairroom > Tfore-room > 28°C and Taisle4 > Taisle3 > Taisle2 > Taisle1 > 42°C.Figure 12
Temperature vs. time outside the room of fire scenario D10.A comparison of the three fire criteria (CO mass fraction, visibility, and temperature) revealed that the dominant factor with the most significant effect on safety evacuation time was visibility. Relevant studies have demonstrated that smoke is the primary cause of death during fires [36–38]. Therefore, the first step during evacuation is to leave the fire room quickly and avoid remaining in a corner, which can effectively prevent harm caused by smoke.Fire scenario E is displayed in Figure13; the grid is the fire simulation area in which the temperature condition of the upper floor was the same as that of the lower floor when the fire occurred. The thermocouple arrangement in F14 was the same as in fire scenario D, and the measuring points were arranged in the walkway on the 15th floor, the staircase, and its front chamber, the same as in F14.Figure 13
Structure of fire scenario E.Fire scenario F is displayed in Figure14, and the thermocouple arrangement in F14 was the same as scenario D. The thermocouples of F15 and F16 were arranged in the walkway in the same manner as in F14, as were the staircase and its front chamber.Figure 14
Structure of fire scenario F.According to the simulation results of fire scenarios E and F detected by the thermocouples, the temperature of the staircase and its front chamber in the two scenarios were always lower than the threshold temperature of 60°C for tolerance by the human body. From the perspective of temperature, when a fire occurred in scenarios E and F, the staircase and its front chamber were relatively safer areas that could be used to temporarily protect personnel.


## 4. Conclusions

To acquire a comprehensive understanding of the laws of fire spread in super high-rise buildings, a FDS simulation was performed on the Saigao office in Shaanxi Province, China. The conclusions of the simulation are as follows:(1)
The critical time required for the same type of fire to become a hazard in a shop, a restaurant, or an office was slightly more than 200 s, with the critical time being shortest in the office area, indicating that protecting and monitoring the office area for fire safety should be a priority.(2)
Compared with temperature and CO mass fraction, visibility was closely related to smoke because it had the most significant effect on the critical time required for fire to become a hazard. The critical time required for fire to become a hazard determined in terms of visibility was significantly shorter than temperature or CO mass fraction.(3)
The speed at which smoke spread and lowered was extremely fast, and smoke always began to accumulate and spread from the corner and the ceiling. From the perspective of visibility, smoke would affect an adjacent open area in almost every 60 s.



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*Source: 1659325-2019-05-14.xml*