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Influence of substrate on fire performance of wall lining materials
Construction and Building Materials 23 (2009) 3258–3263
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Influence of substrate on fire performance of wall lining materials Kuang-Chung Tsai Department of Safety, Health and Environmental Engineering, National Kaohsiung First University of Science and Technology, Kaohsiung 811, Taiwan
a r t i c l e
i n f o
Article history: Received 17 February 2009 Received in revised form 20 April 2009 Accepted 21 May 2009 Available online 21 June 2009 Keywords: Wall lining material Substrate Reaction to fire test
a b s t r a c t This study assessed the fire risk of attaching a qualified surface wall lining to an unqualified combustible substrate. Experimental materials were gypsum, magnesium oxide, calcium silicate board and fire-retardant plywood, which were attached to a non-fire-retardant plywood panel. The CNS 6532 Surface Test and the ISO 5660 Cone Calorimeter Test were applied. The former simulates the heating environment in the early fire stage and the latter simulates a fully developed fire. Experimental data show that when a qualified surface material was attached to a non-qualified substrate, the temperature rise in the Surface Test decreased. The substrates consequently enhance fire safety performance in the early stage of fire growth mainly due to crake prevention and a decrease in the amount of heat stored in surface materials for subsequent ignition. Additionally, the heat release rate in the Cone Calorimeter Test increased or decreased when a qualified surface material was attached to a non-qualified substrate. Therefore, the existence of substrates enhances or reduces a material’s combustibility rank when a fire is fully developed. The key mechanism is the crake or flame penetration of surface wall lining, which can lead to substrate ignition. The change of combustibility rank depends on the time at which a crake develops or flames penetrate a substrate. Ó 2009 Elsevier Ltd. All rights reserved.
1. Introduction Wall lining materials are typically used on exposed interior surfaces in a building for decoration, acoustical correction, surface insulation, or structural fire resistance. However, in a fire, these materials provide fuel and surfaces that allow a fire to spread. Heat, smoke and toxic gases are then transported to other parts of a compartment or other compartments, thereby endangering the safety of people and property. Therefore, the fire performance of such materials must be evaluated. Several test standards, such as the ISO 9705 room corner test [1], single burning item (SBI) test [2], Steiner Tunnel Test [3], ISO 5660 Cone Calorimeter Test [4] and Surface Test (JIS 1321 and Chinese National Standard CNS 6532) [5], have been developed for evaluating the combustibility of wall and/or ceiling materials exposed to specific fire conditions. According to those test standards, the specimen is the actual material used. However, interior designers often use commercial finishes that pass national combustibility regulations but attach a backing panel (substrate) to increase wall or ceiling thickness for such purposes as sound insulation. The Association of European Manufacturers of Expanded Polystyrene (EUMEPS) conducted a test program [6] to evaluate the effects of mounting and fixing conditions for expanded polystyrene (EPS) in the SBI [2] test. The main objective
E-mail address: [email protected] 0950-0618/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.conbuildmat.2009.05.010
was to precisely define these conditions to achieve a robust and reliable set of regulations for Europe. The test specimen was a 60-mm-thick fire-retardant (FR) EPS board and a substrate, either a calcium silicate board (12.5 mm thick with a density of 800 kg/m3), gypsum plaster board (12.5 mm thick with a density of 730 kg/m3), fiber cement board A (12.3 mm thick with a density of 1060 kg/m3), fiber cement board B (6 mm thick with a density of 1800 kg/m3) or wooden panel (12 mm thick with a density of 700 kg/m3). The fiber cement board performed best in terms of the amount of heat and smoke produced, whereas the burning wooden panel was extinguished manually after only 5 min due to too severe heat release. The effects of applying different substrates to a surface material were noted. Avoiding the likelihood that a material is attached to many different substrates that vary in thickness, density, thermal conductivity and combustibility characteristics is extremely difficult. To enhance the flexibility of using a material applied to an unknown substrate, the ISO 14697 (Fire tests—Guidance on the choice of substrates for building products) [7] provides guidance for selecting and using substrates onto which a sample building product is fixed for reaction-to-fire testing. Five rules are provided. Rule 1 states that end-use substrates are preferred in all cases. Rule 2 indicates that as an alternative to non-combustible substrates or substrates with limited combustibility, six reference substrates—fiber cement board, calcium silicate board, gypsum plasterboard, mineral wool rock slab, steel sheet and aluminium sheet—can be used to represent the end-use substrates that have a density equal
K.-C. Tsai / Construction and Building Materials 23 (2009) 3258–3263
to or more than the nominal density of the reference substrate. Rule 2 emphasizes that reference substrates must contribute little to the fire itself in terms of combustibility. Additionally, Rule 3 notes that reference substrates can be used to assess surface coatings but where a product in its end-use form provides a multilayer end-use substrates and methods of attachment must be used. Rule 4 specifies that where the substrates used in practice are combustible, the material should preferably be tested together with its end-use substrates and method of attachment. Rule 5 stipulates that where a standardized combustible substrate is required, the recommended reference substrate (particle board without FR treatment) can be used to represent end-use substrates that have a density equal to or more than the density of the reference substrate. Rules 2 and 5 address substrate selection directly. The EN 13238 (‘‘Reaction to fire tests for building products—Conditioning procedures and general rules for selection of substrates”) [8] employs similar rules. The following seven different standard substrates can be used: fiber cement board; calcium silicate board; rock fiber mineral wool slab; steel sheet; aluminium sheet; paper-faced plasterboard and non-FR-treated particle board. Similarly, standard substrates can be employed to represent end-use substrates that have a density equal to or exceeding the nominal density of the standard substrate.
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As described earlier, the reference substrates in ISO 14697 that contribute little to a fire in terms of combustibility can be used. If highly combustible substrates are used, fire performance of the composites is unknown. In this study, the Surface Test (CNS 6532 [5], equivalent to the JIS 1321) and the Cone Calorimeter Test (ISO 5660 [4]) were used to assess the combustibility of interior finish composites; the Surface Test is currently employed in Taiwan and the Cone Calorimeter Test will be the alternative in the near future. Additionally, the Surface Test simulates the heating environment typical of an early fire stage and the Cone Calorimeter Test simulates a fully developed fire period. This study presents combustibility data for materials with and without a substrate, and validates the use of existing reaction-to-fire tests for evaluating the effects of substrates. 2. Experimental In this study, the Surface Test (CNS 6532 [5]) and Cone Calorimeter Test (ISO 5660 [4]) are used to determine the combustibility of wall lining materials. Specimen size and orientation, test environment and criteria for classifying materials for the two test methods are discussed and compared. 2.1. The Surface Test and its corresponding classification system Fig. 1 schematically depicts the Surface Test apparatus, which mainly consists of a furnace, smoke accumulation chamber and optical density measurement system. A 220 220 mm specimen is placed vertically in the furnace. The furnace is heated by a propane burner with a gas flow rate of 0.35 l/min for the first 3 min. Additional heat is then supplied by two quartz lamps (total output: 1.5 kW). Total heating time for FR materials is 6 min, while that for testing non-combustible and semi-noncombustible materials is 10 min. Fig. 2 presents the average heat flux on the specimen generated by the propane burner and quartz lamps for 10 min; heat intensity is 0–13.71 kW/m2 [9]. This range for heating intensity corresponds to the periods ranging from ignition to fire in the early growth stage. Exhaust gas temperature, back surface temperature, smoke production (CA), duration of sustained flame (tl), total length of cracks (Ck) and presence of penetration over the entire thickness are determined. The time curve of exhaust temperature of a specimen is plotted versus that of a standard board to determine the time when the specimen curve exceeds that of the standard board (tc). The area between the two curves yields t dh. If these two curves do not intersect, the heat generated by the test material is less than that generated by a standard board, yielding ‘‘does no exceed” (DNE). Table 1 presents the classification system for the Surface Test. 2.2. The Cone Calorimeter Test and its corresponding classification system
Fig. 1. Schematic of the Surface Test apparatus.
The Cone Calorimeter Test provides data that characterizes how a material reacts to fire [4]. Specimen size is 100 100 mm. The specimen is located horizontally below a cone-shaped heater that generates a specific heating irradiance. An
Fig. 2. Averaged heat flux onto the specimen in the Surface Test.
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K.-C. Tsai / Construction and Building Materials 23 (2009) 3258–3263
Table 1 Classification system of the Surface Test. Class
Heating time (min.)
Criteria tc (min)
t dh (°C min)
CA (-)
Non-combustible Semi-non-combustible Fire-retardant
10
DNEa =3
0 5100 5350
<30 <60 <120
a
6
tl (s)
Ck
Crack penetration
<30
Less than one tenth of specimen thickness
No penetration over entire thickness
DNE means ‘‘does not exceed”.
Table 2 Classification system of the Cone Calorimeter Test. Class
Heating time (min)
Non-combustible Semi-non-combustible Fire-retardant
20 10 5
Criteria Total heat release (MJ/m2)
Peak HRR (kW/m2)
Penetration of crack
<8
<200
No penetration over entire thickness
electrical spark that ignites a specimen is located above the specimen. After radiant heat is applied to a specimen, ignition time is determined visually according to the appearance of a sustained flame, and burning gases are analyzed to demonstrate the history of the heat release rate (HRR) according to oxygen consumption using computer software. The data obtained by the Cone Calorimeter Test has been used in Japan to rank materials according to total heat release, peak HRR under irradiance of 50 kW/m2, and fire penetration. Table 2 presents the classification system of the Cone Calorimeter Test and a ranking of materials ranging from ‘‘non-combustible (NC),” ‘‘semi non-combustible (Semi-NC),” and ‘‘FR” to ‘‘out of class” [10]. Table 3 lists the primary differences in the designs of the Surface Test and the Cone Calorimeter Test. Specimen size, orientation and the heating environment in the two tests clearly differ. Specimen size, which is the burning area, determines the fluid mechanics mode of the flames, i.e., whether flames are turbulent or laminar [11]. The flame generated by the 220 220 mm specimen area in the Surface Test was turbulent, while that produced by the 100 100 mm specimen area in the Cone Calorimeter Test was laminar. Furthermore, heating intensity in the Surface Test increases from 0 to 13.71 kW/m2 on average, simulating a material facing a flame that evolves from ignition to growth stages. Inside the Cone Calorimeter, the heat flux (50 kW/m2) on the specimen is heating intensity of a fully developed fire [12]. This study tested four common surface materials: 9 mm thick gypsum board (symbol: GS; nominal combustibility ranking according to Chinese National Standard, CNS 6532 [5]: non-combustible), 4 mm magnesium oxide board (MO; noncombustible), 6 mm calcium silicate board (CS; non-combustible) and 12 mm FR plywood (FR-PW; out of class) and those surface materials attached onto a 10mm-thick plywood panel (PW; out of class, most common in Taiwan) using commercial resin. Table 4 lists the thickness and density of the materials. Test time was 10 min in the Surface Test and 20 min in the Cone Calorimeter Test for each specimen; all tests were conducted in triplicate.
3. Experimental data and discussion Fig. 3 shows typical time histories of exhaust temperature and HRR from the Surface Test and Cone Calorimeter Test for the 10mm-thick PW panel. Fig. 3a additionally presents the exhaust temperature curve of a standard board such that the value of t dh can be derived based on the area between the test material curve and the standard curve. Figs. 4 and 5 present exhaust temperature data and back surface temperature histories for all specimens during the Surface Tests.
Table 5 summarizes Surface Test data. The values of t dh and CA were expressed in terms of durations of 0–6 and 0–10 min for further material classification. The values of t dh remained zero for non-combustible surface materials (GS, MO and CS) after substrates were attached. For the 12-mm-thick FR-PW, the t dh values decreased. The exhaust temperature rise is due to heat released after ignition. The heat conducted on substrates decreased the amount of heat that contributes to the burning of surface materials, thereby decreasing the heat released. Additionally, the back surface temperatures clearly declined when a substrate was attached. The increase in back surface temperature is caused by heat conduction across the entire thickness of specimen. This experimental finding is consistent with the conclusion of Tsantaridis and Ostman [12], who studied the charring of wood studs in the Cone Calorimeter at a constant heat flux of 50 kW/m2. The exposed side of the wood studs was unprotected or protected with gypsum plasterboards. They demonstrated an increase in time to reach charring temperature when gypsum plasterboard was attached to the wood studs, and the time increase increased as specimen thickness increased. Thus, specimen thickening delays heat conduction across the entire specimen thickness. Furthermore, crack penetration disappeared when substrates were attached. The existence of substrates provided bases for attaching whole surface materials and absorbed some heat which would have otherwise remained in the surface materials, resulting in thermal expansion. Moreover, the amounts of smoke were similar with or without a substrate. Therefore, the fire risk with a substrate attached did not increase during the 10-min tests. Fig. 6 presents the time histories of the HRR during the Cone Calorimeter Test of all specimens; Table 6 summaries test data for durations of 5, 10 and 20 min, which are used to further use to rank materials (see Table 2). For the GB, MO and CS specimens, ignition did not occur when a PW substrate was not attached and a strong fire developed after a certain time when the PW substrate was attached. Clearly, the fire was from the substrate. The heat
Table 3 Main differences of designs of the Surface Test and Cone Calorimeter Test. Specimen size and orientation
Heating environment
The way to measure heat release
Surface Test
220 220 mm, vertical
Exhaust temperature and time curve
Cone Calorimeter Test
100 100 mm, horizontal
Varied and un-uniform heat flux distribution from 0 to 13.7 kW/m2 Constant and uniform heat flux distribution of 50 kW/m2
Oxygen concentration according to oxygen consumption principle
K.-C. Tsai / Construction and Building Materials 23 (2009) 3258–3263 Table 4 Information of specimens. Material
Symbol
Thickness (mm)
Density (kg/m3)
Gypsum board Magnesium oxide board Calcium silicate board FR plywood Plywood panel
GB MO CS FR-PW PW
9 4 6 12 10
750 1320 1380 630 620
Fig. 3. Exhaust temperature data (symbol, d) in the Surface Test (with standard curve) and HRR curve in the Cone Calorimeter Test of 10 mm thick PW panel.
generated generally decreased before ignition of the substrate, but increased suddenly after ignition. Ignition was caused by a crack through which heat was transferred onto the substrate. The ob-
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served crack is consistent with this inference. Furthermore, the rank of the qualified materials (GB, MO, CS and FR-PW) may change when a substrate was attached to them. Although a strong fire developed eventually, any change of in ranking depends on the time at which the fire was strong. The rank of GB (9 mm thick) was ‘‘semi-non-combustible,” but changed to ‘‘non-combustible” due to decreased total heat released when a substrate was attached. Conversely, the classifications of MO and CS specimens changed from ‘‘non-combustible” to ‘‘semi-non-combustible” due to increased total heat released when a substrate was attached. The FR-PW specimens had two HRR peaks due to composite material characteristics. Clearly, attaching the PW substrate delayed the second peak. The total heat released decreased after ignition when a substrate was attached. Notably, the peak HRR also declined, and crack penetration across specimen thickness disappeared when the substrate was attached. Thus, attaching a combustible substrate enhances or reduces the combustibility rank of a material. Additionally, according to different stages of fire growth in the two tests, we conclude that a substrate enhances fire safety performance of a material in the early fire growth stage and enhances or decreases the combustibility rank of a material when the fire is fully developed in a compartment [13]. Clearly, material combustibility rank may change when a substrate was attached, however, the experimental result obtained depends on which test was utilized. This finding engenders a discussion of whether fire behavior of a specimen in a small-scale apparatus mimics that in another small-scale apparatus or even an intermediate- or large-scale apparatus. In the report by EUMEPS [6], a surface material was tested using SBI when a 12-mm-thick particleboard with a density of 700 kg/m3 was attached. This substrate conformed to EN 13238 [8] and data are applicable to represent end-use wood-based substrates that have a density equal to or exceeding 700 kg/m3 [8]. This application condition suggests that fire performance is enhanced when a thick or dense substrate is attached. In this study, the 10-mm-thick PW panel with a density of 620 kg/m3, is thinner and has a lower density than the substrate used in the EUMEPS study [8]. We predict that if the substrate used in the EUMEPS study [8] were applied in this study, the combusti-
Fig. 4. Time histories of exhaust temperature of all specimens in the Surface Test ( denotes surface material only; N represents when a substrate was attached).
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K.-C. Tsai / Construction and Building Materials 23 (2009) 3258–3263
Fig. 5. Time histories of back surface temperature of all specimens in the Cone Calorimeter Tests. ( denotes surface material only; N represents when a substrate was attached).
Table 5 Summary of test data for the Surface Test. Material
GB GB + PW MO MO + PW CS CS + PW FR-PW FR-PW + PW PW a b
tc(min)
DNEa DNE DNE DNE DNE DNE 3.5 ± 0.2 3.5 ± 0.8 3.5 ± 0.6
t dh (°C min)
CA
0–6 min
0–10 min
0–6 min
0–10 min
0 0 0 0 0 0 387.33 ± 18.54 351.13 ± 34.21 395.95 ± 27.24
0 0 0 0 0 0 1244.4 ± 32.2 1216.3 ± 39.2 1241.2 ± 61.2
3 ± 0.2 3 ± 0.2 1.5 ± 0.2 3 ± 0.5 0 0 18 ± 4.7 18 ± 2.2 18 ± 9.2
5 ± 0.2 7.5 ± 0.5 7.5 ± 1.3 6 ± 0.8 0 0 30 ± 5.2 31.5 ± 4.2 61.5 ± 19.2
tl(s)
CK or PK (mm)
Class
0 0 0 0 0 0 57 ± 27 116 ± 33 184 ± 38
0.2 ± 0.2 N 0.3 ± 0.2 N 0.5 ± 0.4 N N N 180 ± 23.2
NCb NC NC NC NC NC Out of class Out of class Out of class
DNE means ‘‘does not exceed”. NC means ‘‘non-combustible”.
bility rank of a surface material when the substrate was attached would be enhanced further to, say, at least ‘‘semi-non-combustible” in the Surface Test and Cone Calorimeter Test. However, the particleboard test was stopped at 5 min due to too severe heat damage. Clearly, the effect of a substrate depends on the test used. Conclusively, the fire risk after attaching a combustible substrate behind a surface material was high in an intermediate-scale apparatus and low in small-scale apparatuses; thus, fire risk depends on the apparatus used. The experimental result obtained with the small-scale apparatuses may underestimate the fire risk of a composite specimen. However, costs increase when an intermediate- or large-scale test is utilized. Further research is needed to harmonize data from different tests simulating different fire scenarios. 4. Conclusions This study assessed the fire risk associated with attaching a material to a combustible substrate by conducting an experimental program based on use of the Surface Test and Cone Calorimeter Test. The materials tested were 9-mm-thick GS board (non-com-
bustible, according to Chinese National Standard, CNS 6532 [5]), 4-mm-thick MO board (non-combustible), 6-mm-thick CS board (non-combustible) and 12-mm-thick FR-PW (out of class) fixed on a 10-mm-thick plywood panel (most common in Taiwan; out of class) using a commercial resin. Experimental data obtained in the Surface Test show that the heat which conducted to substrates decreased the heat contribution to the burning surface materials, thereby reducing the amount of heat released. The amounts of smoke produced were similar with or without a substrate. Furthermore, a crack disappeared when a specimen was attached to a substrate. In the Cone Calorimeter Test, material combustibility rank was enhanced or decreased depending on crake development or flame penetration. Therefore, the effect of attaching a substrate depends on the apparatus used to test material combustibility. That is, different apparatuses simulate different stages of fire growth. Thus, we conclude that a substrate enhances material fire safety in the early stage of fire growth and may enhance or decrease the fire safety of a material when the fire is fully developed in a compartment. Results of this study demonstrate that the fire risk after attaching a combustible substrate behind a surface material is high in an
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Fig. 6. Time histories of HRR of all specimens in the Cone Calorimeter Tests.
Table 6 Summary of test data for the Cone Calorimeter Test. Material
GB GB + PW MO MO + PW CS CS + PW FR-PW FR-PW + PW PW a b c
tig(s)
NIa NI NI NI NI 934 ± 18 23 ± 5 28 ± 4 27 ± 3
Total heat release (MJ/m2)
Peak HRR (kW/m2)
0–5 min
0–10 min
0–20 min
0–5 min
0–10 min
0–20 min
1.87 ± 0.29 2.30 ± 0.24 0.55 ± 0.21 0.57 ± 0.12 2.63 ± 0.14 0.80 ± 0.19 25.80 ± 2.91 23.41 ± 1.23 29.30 ± 3.02
4.93 ± 1.23 2.48 ± 0.84 2.50 ± 0.42 3.17 ± 0.33 4.55 ± 0.32 3.21 ± 0.22 64.90 ± 9.22 43.55 ± 4.20 69.37 ± 5.57
13.21 ± 2.20 4.25 ± 0.65 4.39 ± 0.62 17.05 ± 0.67 7.93 ± 0.28 21.69 ± 2.42 87.86 ± 12.24 87.24 ± 8.11 105.70 ± 10.25
17.4 ± 1.6 39.0 ± 6.2 6.5 ± 1.2 5.5 ± 1.4 12.8 ± 3.2 9.0 ± 2.2 187.3 ± 19.7 130.1 ± 20.6 138.0 ± 18.2
17.4 ± 1.6 39.0 ± 6.2 9.3 ± 2.7 16.7 ± 4.2 12.8 ± 3.2 12.3 ± 3.2 214.9 ± 22.8 130.1 ± 20.6 181.8 ± 21.2
17.4 ± 1.6 39.0 ± 6.2 9.3 ± 2.9 59.8 ± 4.6 12.8 ± 3.2 82.0 ± 13.2 214.9 ± 22.8 130.1 ± 20.6 181.8 ± 21.2
PR
Class
N N N N N N Y N Y
Semi-cNC NCb NC Semi-NC NC Semi-NC Out of class Out of class Out of class
NI means ‘‘no ignition”. NC means ‘‘non-combustible”. Semi-NC means ‘‘semi-non-combustible”.
intermediate apparatus, but low in a small-scale apparatus. Smallscaled apparatuses underestimate the fire hazard of a composite. Further research is needed to harmonize data obtained from different tests simulating different fire scenarios. Acknowledgements The author express the deepest thanks to Architecture and Building Research Institute (ABRI) for financial support and Mr. Shin-Chuan Huang for carrying out experimental data. References [1] ISO 9705: 1993(E). Fire tests – full-scale room test for surface products. International Standards Organization, Geneva, Switzerland; 1996. [2] EN 13823: 2001(E). Reaction to fire tests for building products – building products excluding floorings exposed to the thermal attack by a single burning item. European Committee for Standardization, Brussels; 2001. [3] ASTM E 84-05. Standard test method for surface burning characteristics of building materials. ASTM; 2005.
[4] ISO 5660: 2002(E). Reaction-to-fire tests – heat release, smoke production and mass loss rate – Part 1: Heat release rate. International Standards Organization, Geneva, Switzerland; 2002. [5] CNS 6532: 1994(E). Method of test for incombustibility of interior finish materials for buildings. Chinese National Standard, Taipei, Taiwan; 1994. [6] Allanic X. Reaction to fire behavior – SBI testing program – mounting and fixing conditions for EPS boards. The Association of European Manufactures of Expanded Polystyrene (EUMEPS); 2004. [7] ISO 14697. Fire tests – guidance on the choice of substrates for building products. International Standards Organization, Geneva, Switzerland; 1997. [8] EN 13238. Reaction to fire tests for building products – conditioning procedures and general rules for selection of substrates. European Standard; 2001. [9] Chen CH, Jang LS, Lei MY, Chou S. A comparative study of combustibility and surface combustibility of building materials. Fire Mater 1997;21:271–6. [10] Regulatory proposal and regulatory assessment, ire hazard properties of building materials and assemblies, Proposal to amend the building code of Australia. Australian Building Codes Board; 2002. [11] Tsai KC, Drysdale D. Flame height correlation and upward flame spread modeling. Fire Mater 2002;26:279–87. [12] Tsantaridis L, Ostman B. Charring of protected wood studs. Fire Mater 1998;22:55–60. [13] Drysdale D. An introduction to fire dynamics. Willy; 1998.
Contents lists available at ScienceDirect
Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
Influence of substrate on fire performance of wall lining materials Kuang-Chung Tsai Department of Safety, Health and Environmental Engineering, National Kaohsiung First University of Science and Technology, Kaohsiung 811, Taiwan
a r t i c l e
i n f o
Article history: Received 17 February 2009 Received in revised form 20 April 2009 Accepted 21 May 2009 Available online 21 June 2009 Keywords: Wall lining material Substrate Reaction to fire test
a b s t r a c t This study assessed the fire risk of attaching a qualified surface wall lining to an unqualified combustible substrate. Experimental materials were gypsum, magnesium oxide, calcium silicate board and fire-retardant plywood, which were attached to a non-fire-retardant plywood panel. The CNS 6532 Surface Test and the ISO 5660 Cone Calorimeter Test were applied. The former simulates the heating environment in the early fire stage and the latter simulates a fully developed fire. Experimental data show that when a qualified surface material was attached to a non-qualified substrate, the temperature rise in the Surface Test decreased. The substrates consequently enhance fire safety performance in the early stage of fire growth mainly due to crake prevention and a decrease in the amount of heat stored in surface materials for subsequent ignition. Additionally, the heat release rate in the Cone Calorimeter Test increased or decreased when a qualified surface material was attached to a non-qualified substrate. Therefore, the existence of substrates enhances or reduces a material’s combustibility rank when a fire is fully developed. The key mechanism is the crake or flame penetration of surface wall lining, which can lead to substrate ignition. The change of combustibility rank depends on the time at which a crake develops or flames penetrate a substrate. Ó 2009 Elsevier Ltd. All rights reserved.
1. Introduction Wall lining materials are typically used on exposed interior surfaces in a building for decoration, acoustical correction, surface insulation, or structural fire resistance. However, in a fire, these materials provide fuel and surfaces that allow a fire to spread. Heat, smoke and toxic gases are then transported to other parts of a compartment or other compartments, thereby endangering the safety of people and property. Therefore, the fire performance of such materials must be evaluated. Several test standards, such as the ISO 9705 room corner test [1], single burning item (SBI) test [2], Steiner Tunnel Test [3], ISO 5660 Cone Calorimeter Test [4] and Surface Test (JIS 1321 and Chinese National Standard CNS 6532) [5], have been developed for evaluating the combustibility of wall and/or ceiling materials exposed to specific fire conditions. According to those test standards, the specimen is the actual material used. However, interior designers often use commercial finishes that pass national combustibility regulations but attach a backing panel (substrate) to increase wall or ceiling thickness for such purposes as sound insulation. The Association of European Manufacturers of Expanded Polystyrene (EUMEPS) conducted a test program [6] to evaluate the effects of mounting and fixing conditions for expanded polystyrene (EPS) in the SBI [2] test. The main objective
E-mail address: [email protected] 0950-0618/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.conbuildmat.2009.05.010
was to precisely define these conditions to achieve a robust and reliable set of regulations for Europe. The test specimen was a 60-mm-thick fire-retardant (FR) EPS board and a substrate, either a calcium silicate board (12.5 mm thick with a density of 800 kg/m3), gypsum plaster board (12.5 mm thick with a density of 730 kg/m3), fiber cement board A (12.3 mm thick with a density of 1060 kg/m3), fiber cement board B (6 mm thick with a density of 1800 kg/m3) or wooden panel (12 mm thick with a density of 700 kg/m3). The fiber cement board performed best in terms of the amount of heat and smoke produced, whereas the burning wooden panel was extinguished manually after only 5 min due to too severe heat release. The effects of applying different substrates to a surface material were noted. Avoiding the likelihood that a material is attached to many different substrates that vary in thickness, density, thermal conductivity and combustibility characteristics is extremely difficult. To enhance the flexibility of using a material applied to an unknown substrate, the ISO 14697 (Fire tests—Guidance on the choice of substrates for building products) [7] provides guidance for selecting and using substrates onto which a sample building product is fixed for reaction-to-fire testing. Five rules are provided. Rule 1 states that end-use substrates are preferred in all cases. Rule 2 indicates that as an alternative to non-combustible substrates or substrates with limited combustibility, six reference substrates—fiber cement board, calcium silicate board, gypsum plasterboard, mineral wool rock slab, steel sheet and aluminium sheet—can be used to represent the end-use substrates that have a density equal
K.-C. Tsai / Construction and Building Materials 23 (2009) 3258–3263
to or more than the nominal density of the reference substrate. Rule 2 emphasizes that reference substrates must contribute little to the fire itself in terms of combustibility. Additionally, Rule 3 notes that reference substrates can be used to assess surface coatings but where a product in its end-use form provides a multilayer end-use substrates and methods of attachment must be used. Rule 4 specifies that where the substrates used in practice are combustible, the material should preferably be tested together with its end-use substrates and method of attachment. Rule 5 stipulates that where a standardized combustible substrate is required, the recommended reference substrate (particle board without FR treatment) can be used to represent end-use substrates that have a density equal to or more than the density of the reference substrate. Rules 2 and 5 address substrate selection directly. The EN 13238 (‘‘Reaction to fire tests for building products—Conditioning procedures and general rules for selection of substrates”) [8] employs similar rules. The following seven different standard substrates can be used: fiber cement board; calcium silicate board; rock fiber mineral wool slab; steel sheet; aluminium sheet; paper-faced plasterboard and non-FR-treated particle board. Similarly, standard substrates can be employed to represent end-use substrates that have a density equal to or exceeding the nominal density of the standard substrate.
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As described earlier, the reference substrates in ISO 14697 that contribute little to a fire in terms of combustibility can be used. If highly combustible substrates are used, fire performance of the composites is unknown. In this study, the Surface Test (CNS 6532 [5], equivalent to the JIS 1321) and the Cone Calorimeter Test (ISO 5660 [4]) were used to assess the combustibility of interior finish composites; the Surface Test is currently employed in Taiwan and the Cone Calorimeter Test will be the alternative in the near future. Additionally, the Surface Test simulates the heating environment typical of an early fire stage and the Cone Calorimeter Test simulates a fully developed fire period. This study presents combustibility data for materials with and without a substrate, and validates the use of existing reaction-to-fire tests for evaluating the effects of substrates. 2. Experimental In this study, the Surface Test (CNS 6532 [5]) and Cone Calorimeter Test (ISO 5660 [4]) are used to determine the combustibility of wall lining materials. Specimen size and orientation, test environment and criteria for classifying materials for the two test methods are discussed and compared. 2.1. The Surface Test and its corresponding classification system Fig. 1 schematically depicts the Surface Test apparatus, which mainly consists of a furnace, smoke accumulation chamber and optical density measurement system. A 220 220 mm specimen is placed vertically in the furnace. The furnace is heated by a propane burner with a gas flow rate of 0.35 l/min for the first 3 min. Additional heat is then supplied by two quartz lamps (total output: 1.5 kW). Total heating time for FR materials is 6 min, while that for testing non-combustible and semi-noncombustible materials is 10 min. Fig. 2 presents the average heat flux on the specimen generated by the propane burner and quartz lamps for 10 min; heat intensity is 0–13.71 kW/m2 [9]. This range for heating intensity corresponds to the periods ranging from ignition to fire in the early growth stage. Exhaust gas temperature, back surface temperature, smoke production (CA), duration of sustained flame (tl), total length of cracks (Ck) and presence of penetration over the entire thickness are determined. The time curve of exhaust temperature of a specimen is plotted versus that of a standard board to determine the time when the specimen curve exceeds that of the standard board (tc). The area between the two curves yields t dh. If these two curves do not intersect, the heat generated by the test material is less than that generated by a standard board, yielding ‘‘does no exceed” (DNE). Table 1 presents the classification system for the Surface Test. 2.2. The Cone Calorimeter Test and its corresponding classification system
Fig. 1. Schematic of the Surface Test apparatus.
The Cone Calorimeter Test provides data that characterizes how a material reacts to fire [4]. Specimen size is 100 100 mm. The specimen is located horizontally below a cone-shaped heater that generates a specific heating irradiance. An
Fig. 2. Averaged heat flux onto the specimen in the Surface Test.
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Table 1 Classification system of the Surface Test. Class
Heating time (min.)
Criteria tc (min)
t dh (°C min)
CA (-)
Non-combustible Semi-non-combustible Fire-retardant
10
DNEa =3
0 5100 5350
<30 <60 <120
a
6
tl (s)
Ck
Crack penetration
<30
Less than one tenth of specimen thickness
No penetration over entire thickness
DNE means ‘‘does not exceed”.
Table 2 Classification system of the Cone Calorimeter Test. Class
Heating time (min)
Non-combustible Semi-non-combustible Fire-retardant
20 10 5
Criteria Total heat release (MJ/m2)
Peak HRR (kW/m2)
Penetration of crack
<8
<200
No penetration over entire thickness
electrical spark that ignites a specimen is located above the specimen. After radiant heat is applied to a specimen, ignition time is determined visually according to the appearance of a sustained flame, and burning gases are analyzed to demonstrate the history of the heat release rate (HRR) according to oxygen consumption using computer software. The data obtained by the Cone Calorimeter Test has been used in Japan to rank materials according to total heat release, peak HRR under irradiance of 50 kW/m2, and fire penetration. Table 2 presents the classification system of the Cone Calorimeter Test and a ranking of materials ranging from ‘‘non-combustible (NC),” ‘‘semi non-combustible (Semi-NC),” and ‘‘FR” to ‘‘out of class” [10]. Table 3 lists the primary differences in the designs of the Surface Test and the Cone Calorimeter Test. Specimen size, orientation and the heating environment in the two tests clearly differ. Specimen size, which is the burning area, determines the fluid mechanics mode of the flames, i.e., whether flames are turbulent or laminar [11]. The flame generated by the 220 220 mm specimen area in the Surface Test was turbulent, while that produced by the 100 100 mm specimen area in the Cone Calorimeter Test was laminar. Furthermore, heating intensity in the Surface Test increases from 0 to 13.71 kW/m2 on average, simulating a material facing a flame that evolves from ignition to growth stages. Inside the Cone Calorimeter, the heat flux (50 kW/m2) on the specimen is heating intensity of a fully developed fire [12]. This study tested four common surface materials: 9 mm thick gypsum board (symbol: GS; nominal combustibility ranking according to Chinese National Standard, CNS 6532 [5]: non-combustible), 4 mm magnesium oxide board (MO; noncombustible), 6 mm calcium silicate board (CS; non-combustible) and 12 mm FR plywood (FR-PW; out of class) and those surface materials attached onto a 10mm-thick plywood panel (PW; out of class, most common in Taiwan) using commercial resin. Table 4 lists the thickness and density of the materials. Test time was 10 min in the Surface Test and 20 min in the Cone Calorimeter Test for each specimen; all tests were conducted in triplicate.
3. Experimental data and discussion Fig. 3 shows typical time histories of exhaust temperature and HRR from the Surface Test and Cone Calorimeter Test for the 10mm-thick PW panel. Fig. 3a additionally presents the exhaust temperature curve of a standard board such that the value of t dh can be derived based on the area between the test material curve and the standard curve. Figs. 4 and 5 present exhaust temperature data and back surface temperature histories for all specimens during the Surface Tests.
Table 5 summarizes Surface Test data. The values of t dh and CA were expressed in terms of durations of 0–6 and 0–10 min for further material classification. The values of t dh remained zero for non-combustible surface materials (GS, MO and CS) after substrates were attached. For the 12-mm-thick FR-PW, the t dh values decreased. The exhaust temperature rise is due to heat released after ignition. The heat conducted on substrates decreased the amount of heat that contributes to the burning of surface materials, thereby decreasing the heat released. Additionally, the back surface temperatures clearly declined when a substrate was attached. The increase in back surface temperature is caused by heat conduction across the entire thickness of specimen. This experimental finding is consistent with the conclusion of Tsantaridis and Ostman [12], who studied the charring of wood studs in the Cone Calorimeter at a constant heat flux of 50 kW/m2. The exposed side of the wood studs was unprotected or protected with gypsum plasterboards. They demonstrated an increase in time to reach charring temperature when gypsum plasterboard was attached to the wood studs, and the time increase increased as specimen thickness increased. Thus, specimen thickening delays heat conduction across the entire specimen thickness. Furthermore, crack penetration disappeared when substrates were attached. The existence of substrates provided bases for attaching whole surface materials and absorbed some heat which would have otherwise remained in the surface materials, resulting in thermal expansion. Moreover, the amounts of smoke were similar with or without a substrate. Therefore, the fire risk with a substrate attached did not increase during the 10-min tests. Fig. 6 presents the time histories of the HRR during the Cone Calorimeter Test of all specimens; Table 6 summaries test data for durations of 5, 10 and 20 min, which are used to further use to rank materials (see Table 2). For the GB, MO and CS specimens, ignition did not occur when a PW substrate was not attached and a strong fire developed after a certain time when the PW substrate was attached. Clearly, the fire was from the substrate. The heat
Table 3 Main differences of designs of the Surface Test and Cone Calorimeter Test. Specimen size and orientation
Heating environment
The way to measure heat release
Surface Test
220 220 mm, vertical
Exhaust temperature and time curve
Cone Calorimeter Test
100 100 mm, horizontal
Varied and un-uniform heat flux distribution from 0 to 13.7 kW/m2 Constant and uniform heat flux distribution of 50 kW/m2
Oxygen concentration according to oxygen consumption principle
K.-C. Tsai / Construction and Building Materials 23 (2009) 3258–3263 Table 4 Information of specimens. Material
Symbol
Thickness (mm)
Density (kg/m3)
Gypsum board Magnesium oxide board Calcium silicate board FR plywood Plywood panel
GB MO CS FR-PW PW
9 4 6 12 10
750 1320 1380 630 620
Fig. 3. Exhaust temperature data (symbol, d) in the Surface Test (with standard curve) and HRR curve in the Cone Calorimeter Test of 10 mm thick PW panel.
generated generally decreased before ignition of the substrate, but increased suddenly after ignition. Ignition was caused by a crack through which heat was transferred onto the substrate. The ob-
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served crack is consistent with this inference. Furthermore, the rank of the qualified materials (GB, MO, CS and FR-PW) may change when a substrate was attached to them. Although a strong fire developed eventually, any change of in ranking depends on the time at which the fire was strong. The rank of GB (9 mm thick) was ‘‘semi-non-combustible,” but changed to ‘‘non-combustible” due to decreased total heat released when a substrate was attached. Conversely, the classifications of MO and CS specimens changed from ‘‘non-combustible” to ‘‘semi-non-combustible” due to increased total heat released when a substrate was attached. The FR-PW specimens had two HRR peaks due to composite material characteristics. Clearly, attaching the PW substrate delayed the second peak. The total heat released decreased after ignition when a substrate was attached. Notably, the peak HRR also declined, and crack penetration across specimen thickness disappeared when the substrate was attached. Thus, attaching a combustible substrate enhances or reduces the combustibility rank of a material. Additionally, according to different stages of fire growth in the two tests, we conclude that a substrate enhances fire safety performance of a material in the early fire growth stage and enhances or decreases the combustibility rank of a material when the fire is fully developed in a compartment [13]. Clearly, material combustibility rank may change when a substrate was attached, however, the experimental result obtained depends on which test was utilized. This finding engenders a discussion of whether fire behavior of a specimen in a small-scale apparatus mimics that in another small-scale apparatus or even an intermediate- or large-scale apparatus. In the report by EUMEPS [6], a surface material was tested using SBI when a 12-mm-thick particleboard with a density of 700 kg/m3 was attached. This substrate conformed to EN 13238 [8] and data are applicable to represent end-use wood-based substrates that have a density equal to or exceeding 700 kg/m3 [8]. This application condition suggests that fire performance is enhanced when a thick or dense substrate is attached. In this study, the 10-mm-thick PW panel with a density of 620 kg/m3, is thinner and has a lower density than the substrate used in the EUMEPS study [8]. We predict that if the substrate used in the EUMEPS study [8] were applied in this study, the combusti-
Fig. 4. Time histories of exhaust temperature of all specimens in the Surface Test ( denotes surface material only; N represents when a substrate was attached).
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Fig. 5. Time histories of back surface temperature of all specimens in the Cone Calorimeter Tests. ( denotes surface material only; N represents when a substrate was attached).
Table 5 Summary of test data for the Surface Test. Material
GB GB + PW MO MO + PW CS CS + PW FR-PW FR-PW + PW PW a b
tc(min)
DNEa DNE DNE DNE DNE DNE 3.5 ± 0.2 3.5 ± 0.8 3.5 ± 0.6
t dh (°C min)
CA
0–6 min
0–10 min
0–6 min
0–10 min
0 0 0 0 0 0 387.33 ± 18.54 351.13 ± 34.21 395.95 ± 27.24
0 0 0 0 0 0 1244.4 ± 32.2 1216.3 ± 39.2 1241.2 ± 61.2
3 ± 0.2 3 ± 0.2 1.5 ± 0.2 3 ± 0.5 0 0 18 ± 4.7 18 ± 2.2 18 ± 9.2
5 ± 0.2 7.5 ± 0.5 7.5 ± 1.3 6 ± 0.8 0 0 30 ± 5.2 31.5 ± 4.2 61.5 ± 19.2
tl(s)
CK or PK (mm)
Class
0 0 0 0 0 0 57 ± 27 116 ± 33 184 ± 38
0.2 ± 0.2 N 0.3 ± 0.2 N 0.5 ± 0.4 N N N 180 ± 23.2
NCb NC NC NC NC NC Out of class Out of class Out of class
DNE means ‘‘does not exceed”. NC means ‘‘non-combustible”.
bility rank of a surface material when the substrate was attached would be enhanced further to, say, at least ‘‘semi-non-combustible” in the Surface Test and Cone Calorimeter Test. However, the particleboard test was stopped at 5 min due to too severe heat damage. Clearly, the effect of a substrate depends on the test used. Conclusively, the fire risk after attaching a combustible substrate behind a surface material was high in an intermediate-scale apparatus and low in small-scale apparatuses; thus, fire risk depends on the apparatus used. The experimental result obtained with the small-scale apparatuses may underestimate the fire risk of a composite specimen. However, costs increase when an intermediate- or large-scale test is utilized. Further research is needed to harmonize data from different tests simulating different fire scenarios. 4. Conclusions This study assessed the fire risk associated with attaching a material to a combustible substrate by conducting an experimental program based on use of the Surface Test and Cone Calorimeter Test. The materials tested were 9-mm-thick GS board (non-com-
bustible, according to Chinese National Standard, CNS 6532 [5]), 4-mm-thick MO board (non-combustible), 6-mm-thick CS board (non-combustible) and 12-mm-thick FR-PW (out of class) fixed on a 10-mm-thick plywood panel (most common in Taiwan; out of class) using a commercial resin. Experimental data obtained in the Surface Test show that the heat which conducted to substrates decreased the heat contribution to the burning surface materials, thereby reducing the amount of heat released. The amounts of smoke produced were similar with or without a substrate. Furthermore, a crack disappeared when a specimen was attached to a substrate. In the Cone Calorimeter Test, material combustibility rank was enhanced or decreased depending on crake development or flame penetration. Therefore, the effect of attaching a substrate depends on the apparatus used to test material combustibility. That is, different apparatuses simulate different stages of fire growth. Thus, we conclude that a substrate enhances material fire safety in the early stage of fire growth and may enhance or decrease the fire safety of a material when the fire is fully developed in a compartment. Results of this study demonstrate that the fire risk after attaching a combustible substrate behind a surface material is high in an
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Fig. 6. Time histories of HRR of all specimens in the Cone Calorimeter Tests.
Table 6 Summary of test data for the Cone Calorimeter Test. Material
GB GB + PW MO MO + PW CS CS + PW FR-PW FR-PW + PW PW a b c
tig(s)
NIa NI NI NI NI 934 ± 18 23 ± 5 28 ± 4 27 ± 3
Total heat release (MJ/m2)
Peak HRR (kW/m2)
0–5 min
0–10 min
0–20 min
0–5 min
0–10 min
0–20 min
1.87 ± 0.29 2.30 ± 0.24 0.55 ± 0.21 0.57 ± 0.12 2.63 ± 0.14 0.80 ± 0.19 25.80 ± 2.91 23.41 ± 1.23 29.30 ± 3.02
4.93 ± 1.23 2.48 ± 0.84 2.50 ± 0.42 3.17 ± 0.33 4.55 ± 0.32 3.21 ± 0.22 64.90 ± 9.22 43.55 ± 4.20 69.37 ± 5.57
13.21 ± 2.20 4.25 ± 0.65 4.39 ± 0.62 17.05 ± 0.67 7.93 ± 0.28 21.69 ± 2.42 87.86 ± 12.24 87.24 ± 8.11 105.70 ± 10.25
17.4 ± 1.6 39.0 ± 6.2 6.5 ± 1.2 5.5 ± 1.4 12.8 ± 3.2 9.0 ± 2.2 187.3 ± 19.7 130.1 ± 20.6 138.0 ± 18.2
17.4 ± 1.6 39.0 ± 6.2 9.3 ± 2.7 16.7 ± 4.2 12.8 ± 3.2 12.3 ± 3.2 214.9 ± 22.8 130.1 ± 20.6 181.8 ± 21.2
17.4 ± 1.6 39.0 ± 6.2 9.3 ± 2.9 59.8 ± 4.6 12.8 ± 3.2 82.0 ± 13.2 214.9 ± 22.8 130.1 ± 20.6 181.8 ± 21.2
PR
Class
N N N N N N Y N Y
Semi-cNC NCb NC Semi-NC NC Semi-NC Out of class Out of class Out of class
NI means ‘‘no ignition”. NC means ‘‘non-combustible”. Semi-NC means ‘‘semi-non-combustible”.
intermediate apparatus, but low in a small-scale apparatus. Smallscaled apparatuses underestimate the fire hazard of a composite. Further research is needed to harmonize data obtained from different tests simulating different fire scenarios. Acknowledgements The author express the deepest thanks to Architecture and Building Research Institute (ABRI) for financial support and Mr. Shin-Chuan Huang for carrying out experimental data. References [1] ISO 9705: 1993(E). Fire tests – full-scale room test for surface products. International Standards Organization, Geneva, Switzerland; 1996. [2] EN 13823: 2001(E). Reaction to fire tests for building products – building products excluding floorings exposed to the thermal attack by a single burning item. European Committee for Standardization, Brussels; 2001. [3] ASTM E 84-05. Standard test method for surface burning characteristics of building materials. ASTM; 2005.
[4] ISO 5660: 2002(E). Reaction-to-fire tests – heat release, smoke production and mass loss rate – Part 1: Heat release rate. International Standards Organization, Geneva, Switzerland; 2002. [5] CNS 6532: 1994(E). Method of test for incombustibility of interior finish materials for buildings. Chinese National Standard, Taipei, Taiwan; 1994. [6] Allanic X. Reaction to fire behavior – SBI testing program – mounting and fixing conditions for EPS boards. The Association of European Manufactures of Expanded Polystyrene (EUMEPS); 2004. [7] ISO 14697. Fire tests – guidance on the choice of substrates for building products. International Standards Organization, Geneva, Switzerland; 1997. [8] EN 13238. Reaction to fire tests for building products – conditioning procedures and general rules for selection of substrates. European Standard; 2001. [9] Chen CH, Jang LS, Lei MY, Chou S. A comparative study of combustibility and surface combustibility of building materials. Fire Mater 1997;21:271–6. [10] Regulatory proposal and regulatory assessment, ire hazard properties of building materials and assemblies, Proposal to amend the building code of Australia. Australian Building Codes Board; 2002. [11] Tsai KC, Drysdale D. Flame height correlation and upward flame spread modeling. Fire Mater 2002;26:279–87. [12] Tsantaridis L, Ostman B. Charring of protected wood studs. Fire Mater 1998;22:55–60. [13] Drysdale D. An introduction to fire dynamics. Willy; 1998.