Research Journal of Recent Sciences _________________________________________________ ISSN 2277-2502 Vol. 3(11), 85-87, November (2014) Res.J.Recent Sci. International Science Congress Association 85 Fire Safety Properties of Heat Treated WoodMüllerová Jana Department of Fire Engineering, Faculty of Special Engineering, University of Zilina, 1. mája 32, 010 08 ilina, SLOVAKIAAvailable online at: www.isca.in , www.isca.me Received 12th November 2013, revised 26th February 2014, accepted 25th April 2014Abstract Thermal modification of spruce and pine wood has positive impact on its both indoor and outdoor use.Many tests had been done to measure fire safety properties. Heat treated spruce samples reduce the smoke released comparing to untreated sample. Heat treated pine shows opposite effect. Heat treated soft wood has decreased ignition time and heat release when burning. Slightly decreased heat conductivity was measured. Keywords: Fire safety, heat treatment,thermowood, pine, spruce, ignition, smoke. IntroductionSmoke is the major cause of fire deaths according global fire statistics. Not direct contact with fire but the smoke is the fatal for victims of fire. Gormsen states that soot in the respiratory tract was found in about 90% of consequent 169 cases of fire deaths. Decreasing the smoke emission is therefore key for fire safety increasing. Wood constructions, floorings and furniture, generally, release less smoke comparing to common plastic and other materials. Heat treated wood timbers and board properties differ from normally dried wood also in sense of fire safety. Wood thermal characteristicWood combustion is defined as a process of Thermic decomposition of basic components bounds, when the chemical content is being changed and much volatile matters as well as much solid matters are released. Wood is characterized by main three components. Typically, Hemicelluloses, Celluloses and Lignin represent 90 97% of wood structure. The rest are organic and inorganic matters – the most flammable substances. Their content is up to 10% of wood volume. Table 1 shows approximate temperatures of wood component degradation. Hemicelluloses are the less heat radiation resistant components of wood. They are pyrolised by temperature of 170240 °C. Celluloses degrade by 250-300 °C. Highest stability belongs to lignin. It is decomposed in two stages. Firstly, alkyl bounds then active lignin pyrolysis starts by 350 °C. Behaviour of heated lignin is well described in details by Kaíková. However, first of all some organic and inorganic substances are pyrolised by wood warmed over 100 C for a longer time. These matters can include water, oily substances, wax etc. Therefore they can cause esthetical problems on the surface, when stains and spots are unwanted. Thermal conductivity and mechanical properties of wooden materials are, however, depended on temperature; this topic is described in details by Nazmul et al, Kumar et al Table-1 Temperature interval for wood compound pyrolysis Temperature Interval (°C) Wood Component 100 Organic and inorganic matters 150 170 Hemicelluloses 240 250 Celluloses 300 320 Lignin alkyl bounds 350 350 Lignin active pyrolysis 390 Wood heat treatment process The sense of thermal modification is to decrease the volume of flammable substances present in wood. The volatile and vapor substances sublimes by the higher temperature. The procedure has to be very careful in order not to degrade the wood unwanted way. The tests showed up that thermo modification is more progressive in inert environment rather than in oxidizing environment7,8 The procedure is made in gas (air or nitrogen) or liquid (vegetable oil) environment. The wood can be heated for over 180°C for several hours. All the three factors (environment, temperature, duration) have certain impact on results. Thermal modification of the wooden materials as boards and timbers during the manufacturing is an extra step before their final use. The mostly used wood species for Thermo Wood production are spruce (47%) and pine (47%). Other minor species are Aspen, Birch and others. But totaly less then 7% of official production in 2012Patented Thermo Wood® has been produced since 2000 in Finland, Sweden, Japan and another countries having licensed Research Journal of Recent Sciences ______________________________________________________________ ISSN 2277-2502Vol. 3(11), 85-87, November (2014) Res. J. Recent Sci. International Science Congress Association 86 partners in Scandinavian countries and other European, American and Asian countries. The production programs of thermo-wood vary in temperature, time and environment. Wood is treated in three phases. First phase, temperature increase rapidly over 100°C then steadily to 130°C. The moisture content drops to almost zero. This phase is processed in the steam atmosphere. During the second phase the wood is heated up to 185 ºC- 215ºC. The duration of this phase depends on the final use requirements. Controlled cooling and moisturizing is the next phase. ThermoWood Association uses water spray system to reach 4 -7 %.8 The same effect can be reached after 2 days in normal atmosphere. Fire resistance tests Fire resistance test were done by VTV, Finland.Fire resistance properties of ThermoWood were tested on spruce and pine samples according to ISO 5660 using Cone Calorimetric method. The samples were heat treated for 5, 8 or 10 hours at temperatures of for the Cone Calorimetric tests. The heat of 50 kW/m2 was applied on pine sample, 25 kW/m2 was applied on spruce. Average density of pine and spruce samples was 500 kg/m3 and 425 kg/m10 Control samples of spruce and pine were normal kiln dried softwood samples (up to 65°C). Single Burning Item test (EN 13823) was taken at VTV9 to measure the heat resistance of thermo wood. Rate of Heat Release (RTR) was measured. The sample wings had following dimensions: height 1.5 m, width 0.5 (1.0) m, thickness 21(25) for untreated (heat treated) sample. Gas burner released heat of max.40 kW/m2 on the sample tested. The emissions were measured according to the KET 3300495 test method. They were measured from heat-treated pine boards (50 x 150mm) in VTT chemical labs. Four hour heat treatment was applied. The tests had been made several weeks after production of heat treated samples10Results and Discussion The topic of heat treated wood fire assessment is well described by Martinka et al.12 Generally, many measurements are required to find out the exact properties of samples tested.Heat treated pine sample RTR level is 10 kW greater comparing to untreated sample. The ignition time of pine heat treated sample was 30% shorter. Spruce sample test shows that heat treatment decreases its ignition time for more than half comparing the untreated samples. Table 2 includes untreated samples of spruce and pine wood (0h). Spruce samples were heat radiated 50 kW/m and pine samples by 25 kW/m2 in Cone Calorimeter. Spruce sample treated for 8 hours had an ignition time of 97s. Ignition time of untreated spruce sample of the same size (50x150mm) was 193s. Similarly, with pine samples it took around 50% time comparing to untreated pine samples. Table-2 ThermWood association - Cone Calorimeter measurements (average values) Sample treated (230 °C) Ignition time (s) RHR (60s) (kW/m2)Smoke (m/kg) Spruce (0h) 193 113 72 Spruce (8h) 97 112 21 Pine (0h) 22 150 – 200 25 –100 Pine (5h) 12 137 180 Pine (8h) 13 136 147 Pine (10h) 16 160 120 Smoke release by treated spruce sample was 21 comparing to 72 /kg of untreated sample. It is at 71% lower smoke emission. Pine samples show different results. Heat treated pine samples have significantly increased values of smoke release comparing to untreated pine samples. Wood typically contains 3 – 10 % of organic and inorganic matters. Volatile organic compounds (VOC) emissions measured by VTT team are represented by table-3. Total amount of VOC (TVOC) rapidly decreased from 1486 to 235 µg/mh by heat treatment. It dropped by 84% from original amount of TVOC. Almost all the identified VOC compounds volatalize by heat treatment. Camphene, hexanal, limonene decrease to zero, and alpha-pinene almost zero. The presence of furfural causes the typical smoked-like smell of Thermowood. Acetic acid volume increased rapidly by heat treatment procedure from 5 to 110 µg/mh. VOC in table-3 present 50% of Total VOC volume. The rest of compounds remain unidentified. Thermal conductivity reduction up to 25% was proofed by VTT tests. ConclusionProper Thermic modification of the wooden material changes the natural properties of the wood. It improves biologic resistance and also esthetic properties. On the other hand it decreases the flexibility of the material and other mechanical properties. The main disadvantage is connected to worse mechanical properties of themal modified wood as fortress, impact strength and hardness. This effect might be unwanted by manufacturers when flexibility of board is required for some reasons. Assorted properties of heat-treated wood are shown in table-4. Research Journal of Recent Sciences ______________________________________________________________ ISSN 2277-2502Vol. 3(11), 85-87, November (2014) Res. J. Recent Sci. International Science Congress Association 87 Table-3 VTT- Volatile organic compounds emission from pine sample Emissions VOC (µg/mh) Acetic acid Alphapinene Camphene Furfural Hexanal Limonene TVOC Untreated sample 5 674 232 2 43 191 1486 Heat treated (180 °C) 78 312 32 29 8 153 828 Heat treated (230 °C) 110 24 0 10 0 1 235 Table-4 Properties of heat modified wood comparing to normal wood + - Reduced smoke emission (spruce) Ignition time decreased Reduced hygroscopy Impact strength reduced Improved durability Bending strength reduced Improved dimensional stability Splitting strength reduced Decay resistance Fortress Reduced Resin removed Biologic degradation resistance Improved accoustic properties Consistent colour Positives are on the left side, negatives on the right side of the table.. From fire protection point of view reduced smoke emission is probably the most wanted property of heat treated wood (ThermoWood®). Cone calorimetric test showed that heat treated spruce sample had significantly lower smoke release comparing to untreated sample. On the other hand, heat treated pine sample had the opposite effect. Much decreased ignition time is also unwanted effect as well as greater RTR. Heat treated wood has many important properties different to normal wood. Extra measurements focused on smoke release and emissions need to be done to enable accurate fire risk assessment. References 1.Gormsen H, Jeppesen N and Lund A., The causes of death in fire victims, Forensic Sci Int., 24(2), 107-111, (1984) 2.Osvald A. and Osvaldová L., Retardácia horenia smrekového dreva, Zvolen: TU Zvolen, (2003) 3.Buko J. and Osvald A., Rozklad dreva teplom a ohom, Zvolen: TU Zvolen (1998) 4.Kaíková D., Kaík F., Vplyv termického pôsobenia na zmeny lignínusmrekového dreva. Acta Fac. 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