1. Introduction
In the event of fire in a building, the primary cause of human injury is suffocation or toxic gas, owing to increased smoke concentration, rather than the heat generated from combustible indoor materials [
1]. In case of fire in an apartment, the fire is mainly originates in the bedroom or kitchen counter. When the apartment door is opened, smoke generated from the fire flows along the corridor, which is an evacuation passage, and penetrates the safety compartment such as the evacuation stairway annex or elevator platform, thereby adversely affecting evacuation safety [
2]. Therefore, it is essential to prepare smoke control measures for the safe evacuation of occupants.
Smoke ventilation methods include natural and powered ventilation. Corridor-type apartments have no windows in the corridor and are exposed to outside air; therefore, smoke ventilation is easy in case of fire and smoke control equipment is exempted [
3]. However, since the corridor is always open, it is vulnerable to snow, rain, and wind resulting in frequent freezing and falling accidents and consequently frequent complaints from residents requesting window installation [
4]. Nevertheless, as corridor-type apartments are considered an indoor space, it is impossible to install windows under the current law because it is necessary to install fire protection equipment, such as smoke control and sprinkler system, according to fire-related laws.
In this study, a model corridor was construced to examine the smoke exhaust performance according to the opening ratio of windows installed in an apartment corridor, and a small-scale fire experiment was conducted to determine the changes in smoke concentration, thermal flow temperature, and smoke layer thickness. This is intended to be used to prepare evacuation safety design standards for occupants and develop performance-based design methods for ventilation systems in corridor-type apartments.
2. Experimental Equipments and Method
In the event of fire in a corridor-type apartment, an experiment on smoke ventilation performance according to the outdoor air opening ratio on the corridor side was conducted using the following procedure:
a) Establishing a fire scenario for corridor-type apartments
b) Evaluating the minimum opening ratio of the corridor that can secure smoke exhaust performance through fire demonstration experiments
c) Comparing smoke exhaust performance according to the presence or absence of sprinklers in households
2.1 Model fire room and corridor
As shown in
Figure 1, the model fire room comprises a living room, kitchen, and corridor, and is finished with plywood and gypsum boards on the pipe frame. The household size is 7 m (L) × 3 m (W) × 2.7 m (H), and the corridor size is 7 m (L) × 1.5 m (W) × 2.7 m (H). As for the corridor structure, the handrail height is 1.35 m from the floor as shown in
Figure 2, and the opening above the handrail is 1.35 m (H) × 7 m (L). The opening ratios of the corridor window were set to 50% and 20% to evaluate the smoke ventilation performance, with the completely open condition of no windows on the handrail set to 100%.
2.2 Fire source and combustibles
As shown in
Figure 3, the fire source and combustibles for generating smoke are composed of woodden crib and simulated furniture [
5]. First, the woodden crib weighs 2.5~3.2 kg and measures 305 mm × 305 mm × 152 mm. Each timber is 38 mm × 38 mm in size and 305 mm long, and the crib is made by stacking four alternating layers. The timber on each floor was evenly spaced, aligned with the floor below, and secured using nails. The woodden crib was installed on a 6 mm thick heptane pan, measuring 300 mm × 200 mm × 100 mm, and is located at a 50 mm distance from the wall.
Two model furniture pieces were arranged at right angles around the woodden cribs. They are composed of plywood of size 840 mm × 790 mm × 12.7 mm and polyether foam cushion measuring 810 mm × 760 mm × 76 mm with 27.2~30.4 kg/m3 density and a maximum heat release rate of (230 ± 50) kW/m2. A cushion was attached to the plywood surface maintained at (21 ± 2.8) ℃ and a relative humidity of (50 ± 10) % for at least 24 h before the experiment, and installed on a steel frame to support it in the vertical direction.
2.3 Sprinkler system
In corridor-type apartments built in the past, sprinklers were installed only on the 16th floor or above. In this study, a sprinkler system was additionally installed to examine its effect on smoke exhaust performance according to the opening ratio of the corridor. The sprinkler pipe is a carbon steel pipe with vertical and horizontal diameters of 32 A and 25 A, respectively. A pipe was connected to the pump to supply fire-extinguishing water, which went up to the ceiling-center along the center of the sidewall of the model corridor and was then connected to the sprinkler in the living room. A quick response flush type sprinkler, with a nominal operating temperature of 72 ℃ and flow coefficient of K50 was installed in the center of the living room and the minimum water discharge pressure was set at 0.1 MPa.
2.4 Measuring devices
As shown in
Figure 4, the measuring devices for the smoke ventilation experiment consisted of a light transmittance meter for smoke concentration measurement, a thermocouple (K-type), a data logger, and a stopwatch.
2.5 Experimental method and procedure
2.5.1 Fire scenario
a) Smoking in the living room ignites the sofa, which burns freely. The smoke generated by burning combustibles accumulates on the ceiling of the living room.
b) Smoke accumulated in the living room spreads through the corridor when a resident who recognizes a fire opens the front door for evacuation.
c) Residents move horizontally through the corridor to the stairway, open the stairway door and evacuate.
2.5.2 Experimental conditions and methods
a) The location of the fire is in the corner of the living room, where the model furniture and wood crib are installed.
b) In case of fire, the door opening time for evacuation of residents is generally based on the total evacuation delay time. Evacuation delay is the time until the occupant recognizes the occurrence of fire and starts evacuating, whereas in the fire room, it is the detection time of the fire detector. In this study, the fire room was small; therefore, the door was opened when a fire broke out.
c) The entrance door installed with an automatic closing device was completely opened.
d) The opening ratio of the corridor window is set to 100%, 50%, and 20% and the experiment is conducted.
e) The above experiment was conducted for the cases where the wet sprinkler system automatically operated and did not operate to compare the smoke exhaust performance according to the presence or absence of the sprinkler system.
-
f) During the experiment, the following items were measured at a height of 1.8 m (breathing line) from the floor, in the center of the corridor near the entrance door.
For the quantitative evaluation of smoke exhaust performance, the life safety standards set forth in "Methods and standards for performance based design of firefighting facilities" was reffered. The effects of heat, visual distance, and toxicity at a height of 1.8 m from the floor, which was the respiratory line of the evacuees, were evaluated by considering the measured values and time to reach the reference values.
3. Experiment Results and Consideration
3.1 Smoke concentration
In this study, smoke concentration was calculated based on light transmittance measured using a light transmittance meter. That is, since the light transmittance is 100% when there is no smoke and 0% at the maximum smoke concentration, it was displayed as smoke concentration (%) = 100 - light transmittance (%).
By measuring the smoke concentration according to the corridor opening rate at the breathing line height in the center of the corridor during a fire, it was possible to secure visibility during evacuation because the smoke concentration did not appear at the breathing line height regardless of whether the sprinkler was operating when the opening rate of the corridor was 50% or more. However, as shown in
Figure 5 and
Table 1, if the sprinkler does not operate (W/O Sprinkler) when the aperture ratio is 20%, the smoke concentration begins to be measured in the breathing line 1 min 40 s after ignition, 30% at 2 min 20 s, and 50% at 2 min 44 s. and reached its highest concentration of 66% at 3 min 40 s. However, when the sprinkler was operated (W/ Sprinkler) for the same opening ratio, the maximum smoke concentration was 18% at 2 min 50 s, which was reduced to less than 1/3.
3.2 Thermal flow temperature
Measuring the thermal flow temperature generated in the same experiment, its maximum was 27 ℃ on the breathing line when the opening rate of the corridor was 100% as shown in
Figure 6, but it rose to 62 ℃ % and 107 ℃ at 50% and 20%, respectively, in case of free combustion without sprinkler operation. Therefore, if the upper temperature limit of 60 ℃ of the life safety standard mentioned in the previous section is applied, continuous evacuation is possible when the opening ratio of the corridor is 100%, but at 50%, the evacuation time is 3 min 31 s and at 20% it is reduced to 2 min 24 s. Therefore, the risk of evacuation increases gradually when the corridor opening is blocked.
However, as shown in
Figure 7, when the opening rate of the corridor was 100%, the thermal flow temperature on the breathing line did not show a significant difference regardless of sprinkler activation, but the highest temperature occurred approximately 1 min earlier when the sprinkler was activated. It is assumed that the thermal flow is promoted when the fire-extinguishing water is discharged and turbulence is formed, resulting in a slight increase in the descending speed. When the corridor opening rate was 20%, the thermal flow temperature on the breathing line according to sprinkler activation rose up to 30 ℃ similarly before the sprinkler activation time (1 min 55 s) as shown in
Figure 8, but the difference greatly widens after that. That is, during free combustion without sprinklers, the thermal flow temperature on the breathing line increased to a maximum of 107 ℃, but when the sprinkler operated, the maximum temperature decreased to 36 ℃. In the absence of sprinklers, the evacuation time was 2 min 24 s. The experimental results according to sprinkler presence are summarized in
Table 2.
3.3 Smoke layer thickness
In the experiment, when the opening ratio was 100% the maximum smoke layer thickness on the corridor ceiling was 0.7 m, and as the opening ratio decreased, it increased to 1.2 m when the opening ratio was 20%. That is, as the opening ratio began to fall below 50%, the lower limit of the smoke layer invaded the breathing line of 1.8 m and descended.
Additionally, under the 20% opening ratio condition, the thickness of the smoke layer increased to 1.2 m even when the sprinklers were operating, as in the case of free combustion. Therefore, if windows are installed in the corridor and the opening ratio is less than 20%, even if the sprinkler operates and the heat effect is significantly reduced, the reduction in visibility due to smoke generation remains a dangerous factor. The experimental results are summarized in
Table 3.
4. Conclusions
In this study, an empirical experiment was conducted to determine the smoke exhaust performance when opening and closing windows are intentionally installed to block outside snow, wind, and rain in corridor-type apartments. The smoke concentration, thermal flow temperature, and smoke layer thickness at the breathing line height of the corridor were measured and comparatively analyzed according to the corridor opening ratio. Additionally, by examining smoke ventilation performance according to the presence or absence of a sprinkler system under the same conditions, the following conclusions were drawn:
1) When household fire breaks out in a corridor-type apartment without sprinklers, the smoke concentration at the breathing line height, which affects the corridor distance visibility (the evacuation route), significantly increases when the opening ratio is 20% or less, which significantly reduces the visibility by more than 50% at 2 min 40 s after ignition.
2) In case of no sprinkler, the maximum thermal flow temperature on the breathing line was 30 ℃ or less when the opening ratio was 100%. But when the opening ratio was 50%, the time to reach 60 ℃, that is the evacuation time limit was 3 min 31 s, which was reduced to 2 min 24 s at 20% opening ratio. Consequently, as the opening rate decreased, the evacuation time decreased and the risk gradually increased.
3) When the corridor opening rate was 20%, the maximum temperature on the breathing line rose to 107 ℃ with no sprinkler, while the maximum temperature decreased to 36 ℃ with sprinkler operation. Therefore, the effect by heat was greatly reduced, but the smoke layer thickness developed to 1.2 m in the same way as in the case of no sprinkler. Therefore, decreased visibility due to this still remains a dangerous factor.
4) In case of fire, the smoke layer thickness in the corridor developed below the breathing line height when the opening rate was 50% or less, which can affect safe evacuation.
5) Considering the smoke concentration, smoke layer thickness, and thermal flow temperature comprehensively, it was determined that it is desirable to secure a 100% opening rate of the corridor on the 15th floor and below without sprinklers in corridor-type apartments exempt from smoke control equipment, in accordance with the related standards. In addition, it is considered that openings of more than a certain ratio should always be secured, even on the floor where the sprinklers are installed in corridor-type apartments.
It is believed that the results of this study can contribute to performance based design of smoke ventilation systems in corridor-type apartments.
Acknowledgments
This work was supported by the National Fire Agency R&D program (Grant number: 20016433).
Figure 1.
Schematic of the model fire room and corridor.
Figure 2.
Schematic of windows and handrail in the corridor.
Figure 3.
Fire source and combustibles for generating smoke (Unit : mm).
Figure 4.
Model corridor and measuring devices for the smoke ventilation experiment.
Figure 5.
Smoke concentration variation at the corridor opening rate 20%.
Figure 6.
Thermal flow temperature according to corridor opening rate without sprinkler (At 1.8 m).
Figure 7.
Thermal flow temperature according to sprinkler presence at 1.8 m (opening rate 100%).
Figure 8.
Thermal flow temperature according to sprinkler presence at 1.8 m (opening rate 20%).
Table 1.
Smoke Concentration According to the Opening Rate in the Corridor (At 1.8 m)
|
Item |
Opening Rate (%) |
Elapsed Time
|
Maximum Concentration (%) |
|
Arrived at 30% |
Arrived at 50% |
|
W/O Sprinkler |
100 |
N/A |
N/A |
N/A |
|
50 |
N/A |
N/A |
N/A |
|
20 |
2 min 20 s |
2 min 44 s |
66 (3 min 44 s) |
|
W/ Sprinkler |
100 |
N/A |
N/A |
N/A |
|
20 |
N/A |
N/A |
18 (2 min 50 s) |
Table 2.
Thermal Flow Temperature According to the Corridor Opening Rate (At 1.8 m)
|
Item |
Opening Rate (%) |
Elapsed Time
|
Maximum Temperature (℃) |
Sprinkler Activation Time |
|
Arrived at 30 ℃ |
Arrived at 60 ℃ |
|
W/O Sprinkler |
100 |
N/A |
N/A |
27 ℃ (3 min 34s) |
N/A |
|
50 |
1 min 58 s |
3 min 31s |
62 ℃ (3 min 33s) |
N/A |
|
20 |
1 min 54 s |
2 min 24 s |
107 ℃ (3 min 31s) |
N/A |
|
W/ Sprinkler |
100 |
N/A |
N/A |
28 ℃ (2 min 36s) |
2 min 19 s |
|
20 |
1 min 45 s |
N/A |
36 ℃ (2 min 13s) |
1 min 55 s |
Table 3.
Smoke Layer Thickness According to the Corridor Opening Rate
|
Item |
Opening Rate (%) |
Smoke Layer Thickness (m) |
Height from the Bottom (m) |
|
W/O Sprinkler |
100 |
0.7 |
2.0 |
|
50 |
0.9 |
1.8 |
|
20 |
1.2 |
1.5 |
|
W/ Sprinkler |
100 |
0.5 |
2.2 |
|
20 |
1.2 |
1.5 |
References
1. J. G. Quintiere, “Principles of Fire Behavior”, 2nd ed., Taylor & Francis, LLC (2016).
2. B. J. Kim, Y. Yang and W. G. Shin, “Numerical Study on Air Egress Velocity of Ancillary Room Pressurization Systems in Apartment Fires”, Fire Science and Engineering, Vol. 34, No. 4, pp. 78-86 (2020),
https://doi.org/10.7731/KIFSE.d7bcc7bb.
3. National Fire Agency, "Enforcement Decree Of the Act on the Installation and Management of Firefighting Facilities", Attached Table 4 (2023).
4. Joongboo Newspaper, "LH Corporation, Which is Called the National Position... Residents of Rental Apartments Are Sorrowful" (2020).
5. ISO 6182-10, "Fire Protection - Automatic Sprinkler Systems - Part 10: Requirements and Test Methods for Domestic Sprinklers", ISO (2014).
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