A Study on the Quantitative Fire Performance Evaluation Method of Building Finishing Materials with a Focus on Medical Facilities

Abstract

Buildings in modern society tend to gradually expand in size due to technological development and overcrowding, which increases the risk of fire. Therefore, continuous efforts are being made to ensure the evacuation safety of occupants by installing firefighting facilities and using flame retardant building finishing materials. This study aims to present a fire performance evaluation plan for building finishing materials using simulations and identify risks that arise from not using flame retardant building finishing materials in medical facilities with vulnerable occupants. A control group for fire performance evaluation was selected using polyurethane foam, while two types of cellulose-based building finishing materials with different flame retardants were chosen for analysis. The cellulose-based finishing materials included expanded graphite, magnesium hydroxide, montmorillonite, and ammonium polyphosphate. Fire performance was evaluated using FDS and path detector simulations based on NES 713 and ISO 5660-1. The results of the study showed that there was a difference of three people in the prediction of the number of deaths depending on the scope of analysis, and it was confirmed that the toxic gas detected was different depending on the added flame retardant. Additionally, construction finishing materials with flame retardant performance increased ASET by at least 130 s compared to polyurethane foam, and the evacuation safety exceeded 1, confirming the effectiveness of securing evacuation stability for occupants.

1. Introduction

In modern society, buildings tend to grow in size, with technological development and overcrowding leading to larger and higher floors. This increase in size brings with it fire hazards and the risk of fire damage [1,2]. From 1993 to 2020, there were an average of 2.4 million fires per year worldwide, resulting in approximately 40,000 deaths. Of these fires, 82.7% occurred in buildings [3].

Currently, due to factors such as an aging population and the occurrence of respiratory infectious diseases, medical facilities are being expanded to accommodate more hospital rooms and the need to strengthen bed spacing standards [4,5]. However, the fire safety risk in medical facilities can be exacerbated by a number of factors, including the presence of patients who are vulnerable to evacuation in the event of a fire, hazardous substances such as alcohol and radiation, and combustible substances such as mattresses [6]. Thus, safety-related laws and regulations, such as regulations on the installation of fire-fighting facilities in medical facilities, have been strengthened and applied more strictly compared to general building structures [7].

A fire at Miryang Hospital in South Korea in 2018 caused serious casualties due to the spread of flames and the release of toxic gas resulting from the use of organic finishing materials [8]. A fire at a Swedish psychiatric detention clinic resulted in increased casualties as PVC flooring was a major cause of the fire and smoke [9].

Table 1 illustrates hospital fires and casualties worldwide.

Table 1. Fires accident at global medical facilities [10,11].

Date	Casualties		Fire Location	Country
	Death	Injury
23 January 2014	32	-	Elderly care facility	Canada
28 May 2014	21	8	Jangseong nursing hospital in Jeolla-do	Korea
25 January 2015	38	6	Private nursing home	China
29 May 2016	17	5	Nursing home in Kiev	Ukraine
26 January 2018	39	151	Miryang nursing hospital in Ggyeongsang-do	Korea
31 January 2018	11	3	Elderly livelihood security beneficiary self-support facility in Sapporo	Japan
24 September 2019	2	56	Kimpo nursing hospital in Gyeonggi-do	Korea
24 March 2021	2	-	New York evergreen court home nursing home	USA

Table 1. Fires accident at global medical facilities [10,11].

Date	Casualties		Fire Location	Country
	Death	Injury
23 January 2014	32	-	Elderly care facility	Canada
28 May 2014	21	8	Jangseong nursing hospital in Jeolla-do	Korea
25 January 2015	38	6	Private nursing home	China
29 May 2016	17	5	Nursing home in Kiev	Ukraine
26 January 2018	39	151	Miryang nursing hospital in Ggyeongsang-do	Korea
31 January 2018	11	3	Elderly livelihood security beneficiary self-support facility in Sapporo	Japan
24 September 2019	2	56	Kimpo nursing hospital in Gyeonggi-do	Korea
24 March 2021	2	-	New York evergreen court home nursing home	USA

Research on the safety of medical facilities is continually ongoing due to the fact that fires in medical facilities pose a higher risk of casualties compared to fires in general buildings. Ahn et al. [11] predicted fatalities based on evacuation routes through a quantitative comparison of available safe egress time (ASET) and required safe egress time (RSET) in nursing hospitals. They discovered the importance of ramps and proper management of combustibles in medical facility evacuation routes [11].

Chien et al. [12] provided a recovery process for equipment damaged in post-fire situations at the National Taiwan University Hospital and subsequently established emergency response management procedures [12].

Bish et al. [13] introduced a Hospital Evacuation Transportation Model (HETM) designed for the transfer of patients from hospitals to appropriate alternative care facilities in the event of an emergency and applied it to case studies involving hospitals in Virginia [13].

Jahangiri et al. [14] performed fire risk assessment on eight hospitals affiliated with Shiraz University of Medical Sciences using a checklist based on NFPA 101. The assessment was analyzed using the Computerized Fire Safety Evaluation System (CFSES), which revealed that measures regarding exits, such as an increase in the number of emergency exits, were necessary to enhance evacuation capacity [14].

Ebekozien et al. [15] investigated fire safety measures at Nigerian hospital facilities through case studies and questionnaires and identified electrical defects and flammable substances as common causes of fires. They also offered basic guidelines for a fire safety management plan [15].

Over the past decade, combustible wall cladding materials have caused catastrophic damage worldwide, leading to changes in building regulations concerning materials [16]. However, the characteristics of indoor finishing materials that are currently used can increase the risk to occupants through fire growth and increased combustion products [17]. Therefore, it is crucial to ensure excellent flame retardant performance and use materials that minimize harmful gas emissions during combustion.

In light of this, research on the fire performance and flame retardancy of building finishing materials continues. For instance, Rie et al. developed a risk assessment plan based on combustion toxicity by conducting a gas hazard test on the thickness of a urethane sample used as a core material for a sandwich panel [17].

Konstantinova et al. analyzed the impact of paint and varnish coatings on the thermal flow rate of polymer-based building materials to evaluate their flammability across a range of densities [18].

Son produced ultralight inorganic insulation by mixing glass bubbles with cement-based materials and determined the appropriate amount of glass bubbles through experiments on the compressive strength, insulation performance, and flame retardant properties of the resulting materials [19].

Vojta et al. analyzed the types and content of flame retardants used in building materials and found that the amount of flame retardants in most building materials was insufficient to ensure effective flame retardancy [20].

Guo developed a flame retardant polystyrene composite plate by mixing magnesium hydroxide and sodium dodecylbenzene sulfonate (SDBS) with polystyrene [21].

Medical facilities continue to make efforts to secure the safety of residents through the installation of firefighting facilities such as sprinklers based on performance-oriented design [22,23]. However, in the case of failure or poor management of these facilities, occupants will be exposed to the risk of fire. Therefore, fundamental prevention is essential through the use of building finishing materials with flame retardant performance.

Previous research efforts have primarily focused on developing and manufacturing flame retardant building finishing materials, and there is insufficient evaluation of the fire risk associated with the use of indoor finishing materials.

Despite its low thermal stability and mechanical strength, polyurethane foam is a commonly used insulation finishing material in construction due to its insulation and buffering properties. However, being composed of organic compounds, there is a risk of toxic gas leakage during combustion [17,24,25].

In contrast, cellulose is an eco-friendly material that can minimize the production of harmful substances. It can be used as a building finishing material with the added advantage of securing escape time for occupants [26].

This study evaluated the fire performance of cellulose-based building finishing materials by selecting two types of materials with different types of flame retardants and the lowest total heat release (THR) value for 10 min based on the ISO 5660-1 test [27]. To facilitate clear comparisons with the fire characteristics of building finishing materials, polyurethane foam was used as a control. The fire performance evaluation quantitatively confirmed the suitability of the application of these building finishing materials using fire simulations on medical facilities where vulnerable evacuation groups reside. FDS, NIST’s CFD-based fire analysis program, was used to analyze available safe egress time (ASET), while Pathfinder from Thunderhead Engineering Consultants, Inc. (Manhattan, KS, USA) was used to analyze required safe egress time (RSET). Figure 1 shows the research flowchart.

The physical characteristics of the building finishing material to be used in the simulation were measured through the cone calorimeter and LFA 1000 experiments. Subsequently, the basic toxicity index was detected in the NES 713 experiment [28]. Additionally, ASET and RSET were measured using FDS and Pathfinder simulations, and the evacuation stability evaluation of the building finishing material was conducted for quantitative comparison.

The purpose of this study is to demonstrate the necessity of sustainably evaluating the fire risk of building finishing materials using this methodology.

2. Experimental

2.1. Flame Retardant Additive

2.1.1. Expandable Graphite

Expandable graphite is a flame retardant produced by acid treatment of natural graphite and heat treatment of a layered compound. It offers advantages such as excellent carbon formation ability, expansion efficiency, and low cost [29,30]. Moreover, it is effective in suppressing the diffusion of flames as it expands into a “worm” form by heat, creating dense char layers with low thermal conductivity that suppress heat transfer [31].

However, the “worm” form of expandable graphite has a disadvantage in that its cohesive power is low, which may result in degraded performance when exposed to flames from below or strong convection [32].

2.1.2. Magnesium Hydroxide

Magnesium hydroxide is an inorganic flame retardant widely used in various fields due to its ability to exhibit flame retardant effects at high temperatures [33]. When exposed to fire, it undergoes endothermic decomposition at around 300–330 °C and absorbs oxygen to produce water, thus effectively retarding the spread of flames [34]. Therefore, magnesium hydroxide has the advantages of being environmentally friendly, inexpensive, and able to exhibit effective flame retardant effects at high temperatures. However, its flame retardant efficiency is relatively low [35].

2.1.3. Ammonium Polyphosphate

Ammonium polyphosphate (APP) has a high phosphorus content of 30% and is characterized by lowering of the peripheral oxygen concentration by the expansion effect of a noncombustible gas along with the reaction of phosphorus by thermal decomposition reaction [36,37]. Furthermore, it acts as a flame retardant through surface coating, dilution of decomposition products, and reduction of melting viscosity, making it a nontoxic flame retardant material suitable for use in polymer resins, paper, wood, and paint [38].

2.1.4. Montmorillonite

Montmorillonite is a mineral clay belonging to the smectite group with high plasticity, mechanical strength, thermal stability, and expandability [39]. Moreover, montmorillonite is known to improve the flame retardant performance by forming a barrier on the surface during combustion, thereby blocking the external supply of oxygen and heat [40]. Recently, it has been studied as a nanocomposite material for polymers to enhance their mechanical, physical, chemical, heat resistance, and flame retardant properties [41].

2.2. Building Finishing Material Properties

The flame retardant performance of the building finishing material was evaluated using an ISO 5660-1 cone calorimeter, and two materials with a total heat release (THR) value of less than 8 MJ for 10 min were selected [27,42,43].

This study included polyurethane foam as the control group, and two building finishing materials based on cellulose were selected for testing. Material 1 contained a mixture of expanded graphite and magnesium hydroxide as flame retardant additives, and material 2 contained a mixture of expanded graphite, montmorillonite, and ammonium polyphosphate as flame retardant additives.

Table 2. Composition ratio of flame retardant building finishing materials.

Properties	Cellulose	Expandable Graphite	Magnesium Hydroxide	Montmorillonite	Ammonium Polyphosphate
Material 1	56 wt%	17 wt%	28 wt%	-	-
Material 2	32 wt%	10 wt%	-	29 wt%	29 wt%

shows the addition ratio of cellulose-based building finishing materials.

The physical properties of the materials were measured using a cone calorimeter (FESTEC Co., Seoul, Republic of Korea) and LFA 1000 (LINSEIS, Selb, Germany) experiment, while the FDS data value was used for the control group polyurethane foam.

Table 3. Properties of construction finishing materials.

Properties	Polyurethane Foam	Finishing Material 1	Finishing Material 2
Density (kg/m3)	40.0	409.0	466.7
Specific heat (kJ/kg∙K)	1.0	5.39	2.77
Conductivity (W/m∙K)	0.05	0.415	0.47
Heat of Combustion (kJ/kg)	30,000.0	5223.3	823.3
CO yield (kg/kg)	0.0310	0.1144	0.0128

presents the physical properties of the materials used in the simulation, and Figure 2 illustrates the cone calorimeter and LFA 1000 equipment used to measure the physical characteristics of the building finishing materials.

2.3. Toxicity Assessment Method

The Naval Engineering Standard 713 (NES 713) identifies a total of 13 types of gas components, including those classified as toxic, and their emission amounts in the combustion generated by fires: carbon dioxide, carbon monoxide, hydrogen sulfide, ammonia, formaldehyde, hydrogen chloride, acrylonitrile, sulfur dioxide, nitrogen oxides, phenol, hydrogen cyanide, hydrogen bromide, and hydrogen fluoride [28,44].

In this study, three types of test specimens for polyurethane foam, which is commonly used in building interiors, and two building finishing materials that met the flame retardant performance standards of ISO 5660-1 were used. Each specimen was prepared according to NES 713 with a weight of 1 ± 0.3 g.

Table 4. Specimen characteristics.

Classification	Polyurethane Foam	Finishing Material 1	Finishing Material 2
Specimen
Mass (g)	1 ± 0.3	1 ± 0.1	1 ± 0.1

shows the specimen characteristics, and

Table 5. NES 713 sampling conditions.

Classification	Dimensions
Burner	- Flame height: 100–120 mm - Gas: methane 2 L/min, air 15 L/min - Flame temperature: 1150 ± 25 °C
Time (s)	- Burning time: 60 + α - String time: 30
Measurement gas	HF, HCl, HBr, C6H5OH, SO2, H2S, HCN, CH2CHCN, HCHO, CO, CO2, NOx, and NH3

shows the sampling conditions.

The volume of the NES 713 chamber used in the test was 0.6 m³, and the flame of the burner in the chamber was generated by a mixed gas consisting of 2 L/min of methane gas and 15 L/min of air. The experiment was conducted by adjusting the flame height to be maintained at about 100 mm and adjusting the flow rate so that the maximum temperature of the flame was maintained at 1150 ± 25°C.

After completing the sampling condition according to NES 713, the specimen was completely burned in a sealed chamber. After 1 min of combustion, the mixing fan was operated for 30 s to uniformly distribute the combustion gas in the chamber. Gas sampling was then performed using a gas detector tube to measure a total of 13 gases in the following order: HF, HCl, HBr, C₆H₅OH, SO₂, H₂S, HCN, CH₂CHCN, HCHO, CO, CO₂, NO_x, and NH₃. Lastly, after measuring the gas emissions, the volume of the chamber and the weight of the material used were used to calculate the amount of gas emitted when burning a 100 g test piece.

The amount of gas released when burning a 100 g test piece was calculated by measuring the gas generated after complete combustion of the specimen and applying the volume of the chamber and the weight of the material used [28,44].

Equation (1) shows the equation for calculating the gas generation concentration.

$${\mathrm{C}}_{\mathsf{\theta }}=\left({\mathrm{C}}_{\mathrm{i}}\times 100\times \mathrm{V}\right)/\mathrm{m}$$

(1)

where, ${\mathrm{C}}_{\mathrm{i}}$ represents the gas concentration (ppm) measured through the combustion result detection tube of the test piece, m represents the mass (g) of the test piece, and V represents the volume (m³) of the chamber.

In addition, the toxicity index for the gas generation concentration of the test specimen was calculated using Equation (2):

$$\mathrm{Toxicity} \mathrm{Index}\left(\mathrm{TI}\right)=\frac{{\mathrm{C}}_{\mathsf{\theta }1}}{{\mathrm{C}}_{\mathrm{f}1}}+\frac{{\mathrm{C}}_{\mathsf{\theta }2}}{{\mathrm{C}}_{\mathrm{f}2}}+\dots +\frac{{\mathrm{C}}_{\mathsf{\theta }\mathrm{n}}}{{\mathrm{C}}_{\mathrm{fn}}}$$

(2)

where, ${\mathrm{C}}_{\mathrm{f}}$ means the lethal dose (ppm) when a person is exposed to the gas for 30 min.

The criteria for the harmfulness of combustion gases are specified in NES 713.

Table 6. Fatal toxicity concentration by combustion gas [39].

Gas	Critical Limit (ppm)
Carbon dioxide (CO2)	100,000
Carbon monoxide (CO)	4000
Hydrogen sulfide (H2S)	750
Ammonia (NH3)	750
Formaldehyde (HCHO)	500
Hydrogen chloride (HCl)	500
Sulfur dioxide (SO2)	400
Acrylonitrile (CH2CHCN)	400
Nitrogen oxides (NOX)	250
Phenol (C6H5OH)	250
Hydrogen cyanide (HCN)	150
Hydrogen bromide (HBr)	150
Hydrogen fluoride (HF)	100

shows the mortality risk concentration [28] and the results of the toxicity test when exposed for 30 min as specified in NES 713.

2.4. Fire Risk Assessment

2.4.1. Fire Scenario and Modeling

The FDS(version 5.5.3) used in this study to obtain ASET was a computational fluid dynamics (CFD) software that is commonly and widely employed by researchers for predicting fire phenomena. Furthermore, the field model of FDS analyzes turbulence by utilizing large eddy simulation (LES) and numerically assesses the impact of fire based on the Navier–Stokes equations [45,46,47,48,49].

The medical facility selected for the fire scenario was a 13-story building with a floor area of 2131.2 m². To determine the general evacuation time for patients in medical facilities, the fifth floor, which consisted only of hospital rooms without hazardous materials such as radiation and without operating rooms, medical rooms, and conference rooms, was selected as the fire floor. The hospital rooms on this floor consisted of 8 single-person rooms, 10 double-person rooms, and 8 four-person rooms. All room doors were assumed to be open, and windows were assumed to be closed. Firefighting facilities were set to their worst condition in which they did not operate. Figure 3 illustrates the fire simulation model and the location of the fire source as expressed in FDS.

The ignition source for the fire in this study was set as a bed mattress, and the maximum heating value of the bed mattress from 250 to 300 s was selected as 1778.95 kW [50]. Figure 4 shows the HRR value curve of the bed mattress.

Table 7. Boundary conditions for fire simulation.

Properties		Condition
Simulation time		900 s
Air temperature		20 °C
Fire source (Mattress)	Size (W × D × H)	2.0 m × 0.2 m × 1.1 m
	Weight	21.40 kg
	Maximum HRR	1778.95 kW
Room size		89.4 m × 24.6 m × 3.0 m
Grid number		1,071,510
Sensor and firefighting equipment		Not working

shows the fire boundary conditions of FDS, and

Table 8. Performance criteria for life safety [22].

Properties	Limit
Respiratory limit line	1.8 m
Fractional effective dose (FED)	<0.3
Temperature	<60 °C
Visibility	>5 m
O2	>15%
CO	<1400 ppm
CO2	<5%

shows the life safety standards in NFSC 203.

The calculation accuracy is strongly dependent on the FDS mesh size. The size of the analysis grid can be determined by the characteristic fire diameter using Equation (3) in the fire plume analysis:

$${\mathrm{D}}^{*}={\left(\frac{\dot{\mathrm{Q}}}{{\mathsf{\rho }}_{\infty }{\mathrm{C}}_{\mathrm{p}}{\mathrm{T}}_{\infty }\sqrt{\mathrm{g}}}\right)}^{2/5},$$

(3)

where ${\mathrm{D}}^{*}$ is the characteristic fire diameter, $\dot{\mathrm{Q}}$ is the THR rate (kW), ${\mathsf{\rho }}_{\infty }$ is the outside air density (kg/m³), ${\mathrm{C}}_{\mathrm{p}}$ is the specific heat (kJ/kg·K), ${\mathrm{T}}_{\infty }$ is the outside air temperature (K), $\mathrm{g}$ is the acceleration of gravity (m/s²), and ${\mathsf{\delta }}_{\mathsf{\chi }}$ is the nominal size of a mesh cell.

The ${\mathrm{D}}^{*}/{\mathsf{\delta }}_{\mathsf{\chi }}$ parameter would only be valid if the value falls between 4 and 16 [51]. The ${\mathrm{D}}^{*}$ value applied to this analysis was 1.212 m, and ${\mathrm{D}}^{*}/{\mathsf{\delta }}_{\mathsf{\chi }}$ had a value of 4.04. Therefore, the mesh size used in the studies satisfied the convergence condition.

2.4.2. Evacuation Simulation

The Pathfinder program is commonly used by researchers to simulate and analyze data in areas with high occupant density [52,53,54]. In this study, the RSET analysis evaluated the evacuation time from the fire site to the safe zone using Pathfinder.

The occupancy density on the fifth floor was set according to the proportion of occupants in real medical facilities based on the occupant load factor of the International Building Code 2003 (IBC 2003) [55], namely, 80 hospitalized patients, 16 medical personnel, and 96 total occupants. Figure 5 shows the Pathfinder model applied in the same way as the ASET analysis drawing.

The inpatients were classified into severe, moderate, and mild categories based on their severity level. Severe patients were further classified as bed patients with two assistants and wheelchair patients with one assistant. Moderate patients were classified as wheelchair patients without assistants, while mild patients were able to walk.

Table 9 presents the occupancy density and walking speed according to occupant classification, while

Table 10. Size of wheelchair and mattress.

Vehicle	Size (L × W × H)
Mattress	2 m × 1 m × 1 m
Wheelchair	1.004 m × 0.7 m × 0.875 m

shows the specifications of the assistive devices used for patient movement.

Table 9. Load condition and moving speed of occupants [56].

Group Classification			Limit	Moving Speed (m/s)
Nondisabled (doctor, nurse, etc.)			16	1.5
Inpatient	Walkable		53	0.87
	Wheelchair	Self	15	0.83
		Aid	8	0.91
	Bedridden		4	1.0
Total			96	-

Table 9. Load condition and moving speed of occupants [56].

Group Classification			Limit	Moving Speed (m/s)
Nondisabled (doctor, nurse, etc.)			16	1.5
Inpatient	Walkable		53	0.87
	Wheelchair	Self	15	0.83
		Aid	8	0.91
	Bedridden		4	1.0
Total			96	-

The evacuation method for the occupants was determined as follows. However, for point ⓐ and point ⓒ, the presence or absence of an elevator was considered as a variable to evaluate the difference in evacuation methods for the occupants.

-

Point ⓐ: one stair and one elevator for passengers

-

Point ⓑ: two elevators for passengers and two elevators for bed

-

Point ⓒ: one stair only

3. Results and Discussions

3.1. Analysis Results

3.1.1. Analysis Results of Toxic gases

The results showed that all test specimens were completely burnt within 1 min. Among the toxic gas components detected in the test specimens, CO₂, CO, H₂S, HCHO, CH₂CHCN, and HCN were detected in the polyurethane foam; CO₂, CO, HCHO, and NO_X were detected in material 1; and CO₂, CO, H₂S, CH₂CHCN, and NO_X were detected in material 2.

Table 11. NES 713 toxicity test results by material.

Gas	NES 713 Toxicity Test Results
	Polyurethane Foam (ppm)	Finishing Material 1 (ppm)	Finishing Material 2 (ppm)
Carbon dioxide (CO2)	5000+	5000	2500
Carbon monoxide (CO)	50	20	20
Hydrogen sulfide (H2S)	2.0	-	0.75
Ammonia (NH3)	-	-	-
Formaldehyde (HCHO)	0.5	0.3	-
Hydrogen chloride (HCl)	-	-	-
Sulfur dioxide (SO2)	-	-	-
Acrylonitrile (CH2CHCN)	2	-	0.5
Nitrogen oxides (NOX)	-	0.75	0.5
Phenol (C6H5OH)	-	-	-
Hydrogen cyanide (HCN)	2.5	-	-
Hydrogen bromide (HBr)	-	-	-
Hydrogen fluoride (HF)	-	-	-

displays the results of the NES 713 toxicity test, and Figure 6 illustrates the results of the toxicity index.

According to the results of the toxicity index calculation, polyurethane foam showed the highest toxicity index at 5.27, followed by material 1 with 3.52 and material 2 with 2.06. In the case of polyurethane foam, CO₂, HCN, and CO were the main contributors to the toxicity index, while CO₂ was identified as the main cause of the toxicity index for the cellulose-based building finishing material.

A low CO₂/CO ratio indicates incomplete combustion [57]. Although the addition of flame retardants reduces the heat release rate (HRR) and total heat release (THR) to improve flame retardant performance, it can result in incomplete combustion and toxic gas leakage [58]. The CO₂/CO ratio of the cellulose-based building finishing material was lower than that of material 1. Therefore, it can be inferred that material 2, which had a higher flame retardant addition ratio, led to incomplete combustion due to an increase in flame retardant performance.

3.1.2. Analysis Results of ASET

The ASET measurement through fire risk evaluation was based on the time exceeding the life safety standard for each element during the fire layer escape. The fire risk assessment included parameters such as fractional effective dose (FED), visibility, temperature, oxygen, carbon monoxide, and carbon dioxide and was based on a respiratory limit of 1.8 m to ensure human safety.

Figure 7 shows the ASET by life safety standard according to the measurement location of the applied finishing material.

After conducting the simulation, it was found that the polyurethane foam exceeded all safety standards during the test period. Furthermore, it had the lowest visibility with an average of 161.11 s, indicating that smoke generated during combustion is the most significant variable for securing ASET in polyurethane foam.

As for the flame retardants with building finishing materials added, material 1 exceeded safety standards for FED, CO₂, and CO. Among them, the measurement results for CO were the worst, which was identified as a major factor affecting escape time.

On the other hand, material 2 was found to satisfy all safety standards during the simulation operation time.

ASET is a factor that directly affects the evacuation of occupants and needs to be compared with RSET based on the worst outcome among the various criteria detected. Therefore, the final ASET values for polyurethane foam and material 1 were selected based on the visibility measurement and the CO measurement, respectively.

Table 12. The value of ASET by measurement location.

Materials	Time (s)
	Location ⓐ	Location ⓑ	Location ⓒ	Average
Polyurethane foam	149.40	162.02	171.91	161.11
Material 1	283.54	369.04	410.41	354.33
Material 2	>900.00	>900.00	>900.00	>900.00

shows the ASET values for each finishing material obtained through simulation.

3.1.3. Analysis Results of RSET

RSET was measured as the time when occupants exited all fire layers through the escape port in Pathfinder. The measurement revealed that when using an elevator for evacuation, a bottleneck was observed due to the elevator’s allowable capacity.

The bottleneck phenomenon is a congestion phenomenon that occurs when the passage is narrowed, similar to the entrance of a bottle [59,60]. In this simulation, the main causes of the bottleneck were identified as obstacles such as wheelchairs at the entrance of the exit as well as the concentration of occupants due to waiting times in the elevator. Figure 8 shows the movement status of occupants for each evacuation route.

During the Pathfinder simulation, 28 walkable inpatients were evacuated to location ⓒ out of the total occupants. At location ⓐ, 24 walkable inpatients used the stairs for evacuation, while 11 wheelchair users and 2 assistants were evacuated using elevators. The remaining occupants, including bed patients, were evacuated through location ⓑ.

During the evacuation, occupants had to travel a distance of at least 17.7 m and up to 165.5 m, with an average distance of 52.4 m. Additionally, they experienced a waiting time of at least 0.325 s and up to 164.8 s, with an average waiting time of 34.85 s per occupant, due to the bottleneck phenomenon. The increase in RSET due to the bottleneck phenomenon was also observed on the stairs of location ⓐ. While 28 occupants were evacuated from obstacle-free location ⓒ in 71.45 s, only 24 occupants were evacuated from the stairs of location ⓐ in 113.8 s due to the bottleneck phenomenon in front of the elevator.

The evacuation time for each total occupant was found to be between a minimum of 29.9 s and a maximum of 228.9 s, with the overall RSET for the evacuation layer set to the maximum value of 228.9 s.

Table 13. RSET by evacuation route.

Classification	Time (s)
	Floor	Location ⓐ	Location ⓑ	Location ⓒ
RSET	228.90	228.90	199.98	71.45

shows the RSET for each evacuation point and the overall evacuation layer.

3.2. Discussion

ASET is a reference time for ensuring the safety of occupants, and if it exceeds RSET, it can be considered hazardous [61]. Therefore, if the escape time calculated through Pathfinder exceeds ASET, it can be presumed that residents would not survive.

Table 14. Estimated deaths by building finishing material.

Classification	Estimated Deaths
Polyurethane foam	8
Material 1	-
Material 2	-

presents the estimated death toll for each building finishing material.

After estimating deaths based on ASET across the evacuation floor, it was found that eight people (four in wheelchairs, one bedridden patient, and three assistants) would have died when using polyurethane foam as the building finishing material, whereas no deaths would have occurred when flame retardant finishing materials were used. However, the three exits had different ASET values at each measurement location due to their distance from the fire room, and the RSET was also different due to differences in evacuation routes. Figure 9 shows a comparison of the life safety standards and RSETs for each evacuation route.

After comparing the ASET and RSET for each exit, it was determined that visibility, temperature, and oxygen were the cause of death in location ⓐ, and visibility and temperature were the cause of death in location ⓑ. However, for location ⓒ, it was found that the occupants had sufficient time to escape. Additionally, it was discovered that the capacity of the elevator used for evacuation in location ⓐ was not sufficient, resulting in a significant difference between RSET and ASET.

Therefore, the estimated number of deaths by applying the ASET value for each evacuation route differed from the result for the entire evacuation layer.

Table 15. Estimated deaths due to building finishing materials by evacuation route.

Classification	Location ⓐ	Location ⓑ	Location ⓒ	Total
Polyurethane foam	6	5	-	11
Material 1	-	-	-	-
Material 2	-	-	-	-

shows the estimated number of deaths by evacuation route.

After conducting measurements, it was found that the use of polyurethane foam resulted in additional deaths at location ⓐ, bringing the total number of deaths to 11. This represents an increase of three deaths compared to the overall evacuation group comparison results.

The evaluation of occupants’ evacuation stability in a building requires a quantitative comparison. Therefore, the ASET and RSET values obtained from simulations were quantitatively analyzed using Equation (4) to assess the safety of the building finishing material and the safety of the occupants.

$$\mathrm{Evacuation} \mathrm{safety} \mathrm{levels}=1-\left(\frac{\mathrm{RSET}-\mathrm{ASET}}{\mathrm{RSET}}\right)$$

(4)

The evaluation of the occupants’ safety was determined based on securing the evacuation safety time when the evacuation safety level was greater than 1 [61].

The evacuation safety levels were determined for the entire evacuation floor and for each evacuation exit. The risk associated with each building finishing material was analyzed by calculating the evacuation safety levels. However, for material 2, the ASET simulation time was used.

Table 16. Evacuation safety levels by building finishing material.

Classification	Floor	Location ⓐ	Location ⓑ	Location ⓒ
Polyurethane foam	0.70	0.65	0.81	2.41
Material 1	1.55	1.24	1.85	5.74
Material 2	3.93	3.93	4.50	12.60

displays the evacuation safety levels for each building finishing material.

After analyzing the evacuation safety levels, it was confirmed that materials 1 and 2, which had flame retardant additives, had levels of 1.55 and 3.93, respectively, compared to polyurethane foam, which had a level of 0.70. This indicated that they were effective in ensuring the safety of the occupants.

However, for polyurethane foam, safe evacuation was possible only in the case of location ⓒ, where there was sufficient separation from the fire room and little bottleneck phenomenon. The result suggests that both the flame retardant performance of the building finishing material and the bottleneck phenomenon that occurs in the escape route are important factors in ensuring the evacuation safety of the occupants.

4. Conclusions

In this study, a fire performance evaluation of building finishing materials was conducted for medical facilities, which are representative of facilities with weak evacuation capabilities. The building finishing materials selected were polyurethane foam and two types of flame retardant building finishing materials, and a quantitative comparison of toxic gases and ASET and RSET was performed to obtain the following results.

(1)

After evaluating the toxicity gas using the toxicity index according to the NES 713, polyurethane foam, material 1, and material 2 were found to have toxicity index values of 5.27, 3.52, and 2.06, respectively. These results demonstrate that building finishing materials with flame retardant performance emit fewer and less harmful gases during combustion than polyurethane foam in terms of type, quantity, and toxicity index.

(2)

Based on the ASET measurements using FDS, it was found that polyurethane foam and material 1 had the shortest excess time for visibility and CO concentration, respectively, among the life safety standards. As a result, their ASET values were confirmed to be 161.11 and 354.33 s, respectively. However, material 2 was found to have sufficient ASET as it did not exceed the life safety standards during the simulation operation time.

(3)

The main reason for the delay in evacuation due to the increase in RSET was bottlenecks, and in the case of medical facilities, bottlenecks are likely to occur due to the characteristics of the residents and evacuation routes. The results of the simulation showed an average evacuation delay time of 34.85 s occurred due to bottlenecks. Additionally, it was found that the evacuation time of walking patients increased due to the bottleneck in front of the elevator, resulting in a 2.1 s delay in the average movement speed of users of stairs in position ⓐ compared to position ⓒ. Consequently, the RSET for all residents was measured at 228.9 s.

(4)

The evacuation safety levels were evaluated to compare the safety of evacuating residents. The results showed that the evacuation safety levels for polyurethane foam and building finishing materials 1 and 2 were 0.70, 1.55, and 3.93, respectively. Therefore, it was found that the flame retardant performance of building finishing materials was effective in reducing evacuation delay time caused by bottlenecks.

(5)

The estimated number of resident deaths from the fire can be determined by comparing ASET and RSET. In this study, it was only observed when polyurethane foam was used as a finishing material, and it was found that the results differed depending on the analysis range. This suggests that analyzing each exit when predicting the death of evacuating residents is more accurate than targeting the entire fire layer.

(6)

Medical facilities can experience bottlenecks due to the characteristics of occupants and evacuation routes, resulting in differences in evacuation safety levels that must be taken into account during design. In particular, medical staff and means of transportation are added to help evacuate patients according to the ratio of severe and moderate cases, and the resulting bottleneck can also become severe. Therefore, flame retardant performance of building finishing materials is essential for controlling the spread of fire, particularly due to the presence of flammable and hazardous materials and the residence of vulnerable evacuees. However, different types of toxic gases can be produced depending on the type of flame retardant added and incomplete combustion due to flame retardant performance may occur, so careful consideration is necessary when using flame retardants.

The fire performance evaluation of a building depends on various factors, including the type of finishing material used and its tendency to spread fire, generate smoke, and emit hazardous gases. Moreover, the comparison between ASET and RSET may vary depending on the analysis of the escape route. However, the fire risk assessment of the building finishing materials used is not systematically prepared.

This study quantitatively compared the evacuation safety of residents by simulating different building finishing materials. The study results suggest a sustainable fire risk assessment plan using simulation. Therefore, it is expected that the results of this study can be practically applied in the fire hazard assessment of building finishing materials.