Research Journal of Recent Sciences ________________________________________________ ISSN 2277-2502Vol. 2(7), 43-47, July (2013) Res.J.Recent Sci. International Science Congress Association 43 Assessment of Fire Risk of Selected Agglomerated Wooden MaterialsGalla Štefan, Ivanoviová MartinaFire Research Institute of the Ministry of Interior of the Slovak Republic in Bratislava, Roavská 11, 831 04 Bratislava, SLOVAK REPUBLICAssociation of Fire Engineering, Dubská cesta 782, 02401 Kysucké Nové Mesto, SLOVAK REPUBLICAvailable online at: www.isca.in Received 12th March 2013, revised 20th April 2013, accepted 25th May 2013 AbstractIn the submitted paper, the fire risk of the oriented strand boards (OSB) and chipboards is assessed. Fire risk of these materials was assessed on the basis of heat flux density effect on the ignition time of tested materials with thickness of 12, 15 and 18 mm. The dependence of initiation time on the heat flux density was determined by the apparatus (cone heater) according to the ISO 5657:1997 through the modified testing procedure. The testing procedure modification consists of specimen heat flux exposure without any secondary initiator use. The minimal heat flux density at which ignition occurred was 43 kW / m for the OSB boards, and 40 kW / m2 for the chipboards. The obtained data show that the ignition time of assessed wooden materials decreases exponentially with increasing heat flux density. Obtained data imply also a fact that the influence of studied materials thickness on the ignition time decreases with increasing heat flux density. Measured data imply an independence of minimal heat flux density on studied materials thickness, as well. Keywords: assessment of material fire risk, heat flux density, fire propagation dynamics, ignition of material, fire technical characteristic of materials. IntroductionTo assess material fire risk, it is essential to measure the heat release rate and chemical composition of combustion products. The question of assessment of the heat release rate from materials was dealt in details, for example in Babrauskas’s work. The mass loss of selected lignocelluloses’ materials when exposed to radiant heat was determined for example by Osvaldová, Makovický, Zachar and Skrovný. The results from those cited authors’ show an exponential dependence of the mass loss on a studied materials distance from the infrared radiation source. The effect of external conditions on chemical composition of combustion products or thermal decomposition was studied e.g. by Martinka et al. and Bubeníková, Veková. From data presented by Martinka et al. it is clear that the highest yield of toxic combustion products (carbon oxide) is produced in the initiation phase of wooden materials. The time to initiation of materials depending on the heat flux density is very suitable parameter for comparison of material regarding the fire propagation dynamics. The time of initiation is a time interval from exposing material to the constant temperature or to the constant heat flux density to the material ignition. The ignition time of selected natural or synthetic polymers was studied by several authors, for example Tereová and Martinka et al.10. According to Martinka et al.10, also the parameters of the oxidation atmosphere (prevailingly the flow rate and oxygen concentration in it), except temperature or heat flux density respectively, have a significant effect on the polymers ignition time10. The minimal heat flux density for material ignition depends on material chemical composition and physical characteristics. Physical properties can be divided according to characteristics joined with material itself and on environmental parameters. Among the most significant physical characteristics of material belong its geometry (shape, dimensions, and form), volume mass (density), moisture content, surface quality, thermal conductivity, mechanical properties, and mutual orientation between exposed sample surface and radiant heat source11. Thermal conductivity and mechanical properties of materials are, however, depended on temperature; this topic is described in details by Nazmul et al.12, Kumar et al.13 and many others authors14-16. Besides material physical characteristics and chemical composition, also the presence of fire retarders has significant effect on initiation process of material. This problem is described in details by Muralidhara and Sreenivansan17. Among the most important environmental parameters that are variable under normal conditions, belong air flow rate. The air flow rate decreases minimal heat flux density down to certain limit. This effect is caused by mechanism of how the air flow rate affects the minimal heat flux. At relative small air flow rates, the increasing flow rate influence positively the decrease of minimal heat flux density due faster and more complex mixing of thermal decomposition products with air oxygen. At high air flow rates, it evokes increasing of thermal exhaust rate from reactive burning zone that is demonstrated in increasing of critical thermal flux density. Under fire conditions, a variability of flow rates is higher in comparison with normal conditions; in Research Journal of Recent Sciences ______ _ Vol. 2(7), 43-47, July (2013) International Science Congress Association this case the critical heat flux can also be affected by decreased oxygen concentrat ion (growth of critical thermal flux value) and increased temperature of oxidation atmosphere (decline of critical thermal flux value). The effect of external environmental parameters on burning process of wooden materials was studied in details by Ladomerský and Hroncová18. The goal of this paper is to determine the minimal thermal flux density necessary for ignition of OSB boards and chipboards with thickness of 12, 15 and 18 mm as well as determination of heat flux density effect on time to initiation. Material and Methods The time to initiation dependence of chipboards and OSB boards on heat flux density was determined on the apparatus according to ISO 5657:1997, by a modified testing procedure. The modification consisted of specimen exposure by radi heat flux, without any secondary initiator use. Before the experiment itself, the minimal heat flux was determined at which ignition of OSB boards and chipboards, without any secondary initiator use, appeared. It was found that the prolongation of ex posure time interval of OSB boards and chipboards affects a decline of minimal heat flux only within the time interval of 300 s approximately. After decreasing the critical heat flux density for 300 s time interval the ignition did not take place even at 3600 s exposure. At heat flux lower than minimal heat flux density required for ignition, the rate of thermal degradation of material did not reach a critical value necessary for reaching the flammability lower concentration limit of originated decompositio n products. Due to thermal flux from the heater, the material was subjected to thermal decomposition but it did not ignite. Specimens of OSB boards and chipboards were thermally exposed by prescribed minimal heat flux for 300 s time interval. Minimal heat flux density needed for ignition was 43 for OSB boards and 40 kW / m for chipboards. Ignition times Studied OSB board and chipboard specimens _ ________________________________ ______________ International Science Congress Association this case the critical heat flux can also be affected by decreased ion (growth of critical thermal flux value) and increased temperature of oxidation atmosphere (decline of The effect of external environmental parameters on burning process of wooden materials was studied in details by The goal of this paper is to determine the minimal thermal flux density necessary for ignition of OSB boards and chipboards 18 mm as well as determination of The time to initiation dependence of chipboards and OSB boards on heat flux density was determined on the apparatus according to ISO 5657:1997, by a modified testing procedure. The modification consisted of specimen exposure by radi ant heat flux, without any secondary initiator use. Before the experiment itself, the minimal heat flux was determined at which ignition of OSB boards and chipboards, without any secondary initiator use, appeared. It was found that posure time interval of OSB boards and chipboards affects a decline of minimal heat flux only within the time interval of 300 s approximately. After decreasing the critical heat flux density for 300 s time interval the ignition did s exposure. At heat flux lower than minimal heat flux density required for ignition, the rate of thermal degradation of material did not reach a critical value necessary for reaching the flammability lower concentration n products. Due to thermal flux from the heater, the material was subjected to thermal Specimens of OSB boards and chipboards were thermally exposed by prescribed minimal heat flux for 300 s time interval. flux density needed for ignition was 43 kW / m for chipboards. Ignition times of chipboards were determined at 40, 41, 42, 43, 44, 45, 46, 47, 48, 49 a 50 kW / m heat flux values for chipboards and 43, 44, 45, 46, 47, 48, 49 a 50 kW / m heat flux values for OSB boards. Each measurement was repeated five times minimally. Recorded extreme values were excluded from data set and replaced by values gained from repeate Specimen dimensions and configurations met the ISO 5657:1997 requirements, flat dimension was 165 x 165 mm. Thickness of studied materials was 12, 15 and moisture content of used boards was 6 % volume. Density of OSB boards was from 560 up to 580 kg / m chipboards was from 660 up to 680 kg / m Studied specimens are shown on the Results and Discussion Minimal heat flux density necessary for ignition of OSB boards was determined at 43 kW / m ; and / m2 while tested board thicknesses did not affect the minimal heat flux density. This fact, however, might be caused by narrow interval of tested chipboard and OSB board thicknesses. Determined values of minimal heat flux dens of tested materials were approximately 50 % higher when compared with data related to wooden materials referred by Lawson and Simms19 and Merryweather and Mentioned difference was caused by the test procedure modification . Cited authors determined values of minimal heat flux density of selected wooden materials by the procedure according to the ISO 5657:1997, it means with the use of secondary initiation source. Data on minimal heat flux and ignition time dependence of tes ted materials in the submitted paper were gained, on the other hand, by modified testing procedure, without the use of any secondary initiation source. Integrated effect of OSB board thicknesses and heat flux density on the initiation time is shown on chipboard thicknesses and heat flux density on the initiation time is shown on figure 3. Figure-1 Studied OSB board and chipboard specimens ______________ _________ ISSN 2277-2502 Res. J. Recent Sci. 44 of chipboards were determined at 40, 41, 42, 43, 44, 45, 46, 47, heat flux values for chipboards and 43, 44, heat flux values for OSB boards. Each measurement was repeated five times minimally. Recorded extreme values were excluded from data set and replaced by values gained from repeate d measurements. Specimen dimensions and configurations met the ISO 5657:1997 requirements, flat dimension was 165 x 165 mm. Thickness of studied materials was 12, 15 and 18 mm. Absolute moisture content of used boards was 6 % volume. Density of was from 560 up to 580 kg / m ; and that of chipboards was from 660 up to 680 kg / m . Studied specimens are shown on the figure 1. Minimal heat flux density necessary for ignition of OSB boards ; and that for chipboards at 40 kW while tested board thicknesses did not affect the minimal heat flux density. This fact, however, might be caused by narrow interval of tested chipboard and OSB board thicknesses. Determined values of minimal heat flux dens ity causing ignition of tested materials were approximately 50 % higher when compared with data related to wooden materials referred by Merryweather and Spearpoint20. Mentioned difference was caused by the test procedure . Cited authors determined values of minimal heat flux density of selected wooden materials by the procedure according to the ISO 5657:1997, it means with the use of secondary initiation source. Data on minimal heat flux and ted materials in the submitted paper were gained, on the other hand, by modified testing procedure, without the use of any secondary initiation source. Integrated effect of OSB board thicknesses and heat flux density on the initiation time is shown on figure 2; and effect of chipboard thicknesses and heat flux density on the initiation Research Journal of Recent Sciences ______ _ Vol. 2(7), 43-47, July (2013) International Science Congress Association Ignition time dependence on OSB board thicknesses and heat Ignition time dependence on chipboard thicknesses and heat flux density From visual analysis of f igures 2 and 3 follows that effect of OSB board as well as chipboard thickness declines with growing heat flux. For the 50 kW / m heat flux density the effect of board thickness was negligible. This trend was caused by effect of heat flux density on thermal material thickness Thermally thick material is defined as a material whose surface temperature on the opposite side of exposed surface at the ignition time is coming near to the ambient environment temperature. Thermally thin material is defined as a material whose surface temperature on the opposite side of exposed surface at the ignition time is coming n ear to the exposed surface temperature. From these definitions it is clear that terms “the thermally thick material” and “the thermally thin material” are relative ones in a considerable rate. Thermal thickness relativity follows from its dependence on hea low heat flux density the transfer of heat from the material _ ________________________________ ______________ International Science Congress Association Figure-2 Ignition time dependence on OSB board thicknesses and heat flux density Figure-3 Ignition time dependence on chipboard thicknesses and heat flux density igures 2 and 3 follows that effect of OSB board as well as chipboard thickness declines with heat flux density the effect of board thickness was negligible. This trend was caused by effect of heat flux density on thermal material thickness 21. Thermally thick material is defined as a material whose surface opposite side of exposed surface at the ignition time is coming near to the ambient environment temperature. Thermally thin material is defined as a material whose surface temperature on the opposite side of exposed ear to the exposed surface temperature. From these definitions it is clear that terms “the thermally thick material” and “the thermally thin material” are relative ones in a considerable rate. Thermal thickness relativity follows from its dependence on hea t flux. At relative low heat flux density the transfer of heat from the material surface towards its inside occurs. It means that all material is overheated and heat is absorbed in material. The ability of material to accumulate heat in a volume unit is ph represented by thermal inertia that can be mathematically expressed as a sum of the thermal conductivity coefficient, density and thermal capacity coefficient. During increasing of heat flux density, the surface temperature is growing rapidly fast er that temperature inside the material, thus the same material with the same dimensions and the same thermal inertia can be either thermally thin material for certain heat flux and also thermally thick material for higher heat flux. Thermal thickness of m aterial thus depends mainly on its thermal inertia, material thickness, thermal conductivity coefficient, heat flux density and moisture content. Water content in a material absorb certain heat necessary to water evaporation, but on the other hand, at hig ______________ _________ ISSN 2277-2502 Res. J. Recent Sci. 45 flux density Ignition time dependence on chipboard thicknesses and heat flux density surface towards its inside occurs. It means that all material is overheated and heat is absorbed in material. The ability of material to accumulate heat in a volume unit is ph ysically represented by thermal inertia that can be mathematically expressed as a sum of the thermal conductivity coefficient, density and thermal capacity coefficient. During increasing of heat flux density, the surface temperature is growing rapidly er that temperature inside the material, thus the same material with the same dimensions and the same thermal inertia can be either thermally thin material for certain heat flux and also thermally thick material for higher heat flux. Thermal aterial thus depends mainly on its thermal inertia, material thickness, thermal conductivity coefficient, heat flux Water content in a material absorb certain heat necessary to water evaporation, but on the other hand, at hig h heat flux Research Journal of Recent Sciences ______________________________________________________________ ISSN 2277-2502Vol. 2(7), 43-47, July (2013) Res. J. Recent Sci. International Science Congress Association 46 values it can cause extremely fast water evaporation and consequent creation of cracks enabling faster penetration of thermal degradation products. Based on determined average ignition time difference between OSB boards with thickness of 12 mm (91 s) and 18 mm (170 s), respectively, at critical heat flux density (43 kW / m), it cannot be said that 12 mm thick OSB board is a thermally thin material at critical heat flux density, because the temperature measured on unexposed side, even in this case, does not exceed 40°C, while with increasing heat flux and increasing OSB board thickness, the temperature on unexposed side decreased at the ignition time. The same conclusion is also valid for chipboards, where average ignition time at critical heat flux density (40 kW / m) was 119 s for 12 mm thickness; and 139 s for 18 mm thickness, while temperature on unexposed side did not exceeded 40 °C at the ignition time. To determine thickness influence on ignition time of OSB boards and chipboards in studied thickness interval and heat flux density interval, the one-factor variance analysis (ANOVA) was used. Based on calculated criteria for OSB boards = 2.4493 0.05 crit = 3.4668, the zero hypothesis on equality of variances of ignition times for OSB boards with different thickness was confirmed on the significant level = 0.05. Thus, from the one-factor variance analysis follows that OSB board thickness has no significant effect on ignition time thereof under studied conditions. Similarly, based on calculated criteria for chipboards = 1.4324 0.05 crit = 3.158, the zero hypothesis on equality of variances of ignition times for chipboards with different thickness was confirmed on the significant level = 0.05. Finally, from the one-factor variance analysis follows that chipboard thickness has no significant effect on time ignition thereof under studied conditions. Conclusion From data measured it is clear, that influence of thickness of chipboards and OSB boards on ignition time during exposure by radiant heat flux declines with increasing heat flux density. For OSB boards, board thickness has a negligible effect on ignition time from heat flux density value of 50 kW / m. This value represents 115% of minimal heat flux density value that caused ignition of tested OSB boards. For chipboards, board thickness has a negligible effect on ignition time, similarly like for OSB boards, from heat flux density value of 50 kW / m. This value is 125% of minimal heat flux density value that caused ignition of tested chipboards. Stated conclusion is valid, however, only for studied thicknesses (12, 15, and 18 mm). Temperature on unexposed side of OSB boards or chipboards did not reach even 40°C (at none studied thicknesses 12, 15 and 18 mm and at none studied heat flux densities 40 up to 50 kW / m). The minimal heat flux density necessary for ignition of OSB boards was 43 kW / m and that of chipboards 40 kW / m, thus those materials can be considered to be thermally thick materials for purpose of combustion initiative parameters assessment. Obtained data also indicate independence of minimal heat flux density on material thickness. This statement was proved on for thicknesses of 12, 15 and 18 mm. To generalize it, further experiments will be necessary to carry out. Further research should be focused on determination of minimal thickness of studied materials at which these materials begin to behave as thermally thin materials at minimal heat flux density required for their ignition. It should also be focused on determination of material thermal thickness impact on amount of main fire emissions (carbon oxide and carbon dioxide) and on correlation thereof with heat release rate from wooden materials, in similarly way as was determined by Xu et al.15 for synthetic polymers. Acknowledgement Submitted paper arose on basis of data obtained in specialized laboratories of the Fire Research Institute of the Ministry of Interior of the Slovak republic (Poiarnotechnický a expertízny ústav Ministerstva vnútra Slovenskej republiky) in Bratislava. References 1.Wang Y., Hadjisophocleousb G. and Zalok E. Smoke movement in multi-storey buildings using CUsmoke, Saf. Sci., 52(1), 13-27 (2013)2.Babrauskas V., The cone calorimeter, SFPE handbook of fire protection engineering. Massachusetts: National Fire Protection Association (2002)3.Osvaldová L. and Makoviccký P., Burning of fire retarded spruce wood. Ostrava: SPBI (2004)4.Zachar M. and Skrovný R., Influence of heat on thermal degradation of spruce wood, Acta Fac. Xylologiae, 49(1), 61-68 (2007)5.Martinka J., Kaíková D., Hroncová E. and Ladomerský J., Experimental determination of the effect of temperature and oxygen concentration on the production of birch wood fire emissions, J. Therm. Anal. Calorim, 110(1), 193-198 (2012)6.Bubeníková, T. and Veková, V., Volatile products of wood degradations, Delta., 1(2), 18-20 (2007)7.Xu Q., Majlingova A., Zachar M., Jin C., Jiang Y. Correlation analysis of cone calorimetry test data assessment of the procedure with tests of different polymers, J. Therm. Anal. Calorim., 110(1), 65-70 (2012)8.Okoya S., Ignition times for a branched-chain thermal explosion chemistry with heat loss, Toxicol. Environ. Chem., 91(5), 27-29 (2008) 9.Tereová ., Hydro-isolating belts in structural members of new buildings in terms of the fire safety, Zvolen: Bratia Sabovci (2010) Research Journal of Recent Sciences ______________________________________________________________ ISSN 2277-2502Vol. 2(7), 43-47, July (2013) Res. J. Recent Sci. International Science Congress Association 47 10.Martinka J., Balog K., Chrebet T., Hroncová E. and Dibdiaková J., Effect of oxygen concentration and temperature on ignition time of polypropylene, J. Therm. Anal. Calorim., 110(1), 485-487 (2012)11.Osvald, A., Fire characteristics of wood and wooden materials, Zvolen: Technical University in Zvolen (1997)12.Nazmul A.D.M., Md. Nazrul I., Khandkar-Siddikur R. and Md. Rabiul A. Comparative study on physical and mechanical properties of plywood produced from eucalyptus (Eucalyptus camaldulensis Dehn.) and simul veneers (Bombax ceiba L.), Res. J. Recent Sci., 1(9), 54-58 (2012)13.Kumar A., Chauhan R.R. and Kumar P., Effective thermal conductivity of cucurbit as a function of temperature by thermal probe method, Res. J. Recent Sci., 1(10), 33-36 (2012)14.Gordillo-Delgado F. and Marín E., Cortés-Hernández D.M., Thermal diffusivity behavior of guadua angustifolia kunth as a function of culm zone and moisture content, Res. J. Recent Sci., 1(1), 17-23 (2012)15.Selvakumar B., Prabhu Raja V., NandhaKumar R., Senthil Kumar A.P., Vignesh M.S., VivekSharma G.R. and Karthikeyan P., Hexagonal geometrical inclusion to estimate effective thermal conductivity (ETC) of porous system and suspension system including the effect of natural convection, Res. J. Recent Sci., 1(1), 33-39 (2012)16.Senthil Kumar A.P., Karthikeyan P., Selvakumar B. Jagadheeshwaran M., Dinesh J. and Kandasamy S., Influence of density and concentration on effective thermal conductivity of two phase materials using square guarded hot plate apparatus, Res. J. Recent Sci.,1(8), 42-47(2012)17.Muralidhara K.S. and Sreenivansan S., Adaptation of Pyrolytic conduit of polyester cotton blended fabric with flame retardant chemical compositions, Res. J. Chem Sci., 2(10), 20-25 (2012)18.Ladomerský J. and Hroncová, E. 2003. Investigation of appropriate conditions of wood combustion in combustion chamber by emissions analysis., Acta Mech. Slovaca, 7(3), 595-600 (2003) 19.Lawson D. I. and Simms, D. L. The ignition of wood by radiation, Br. J. Appl. Phys., 3(2), 288-293 (1952)20.Merryweather G. and Spearpoint M. J., Ignition of New Zealand wood products in the LIFT, RIFT and ISO 5657 apparatus using the ASTM E 1321-97 protocol, J. Fire Sci., 26(1), 63-88 (2008) 21.Meister G., Vapour bubble growth and recondensation in subcooled boiling flow, Nucl. Eng. Des., 54(1), 97-114 (1979)