A numerical study of gypsum plasterboard behaviour under standard and natural fire conditions

Gypsum plasterboards are the most widely used passive fire protection for timber structures, especially in the case of light timber frame construction. Understanding the complex thermo‐physical behaviour of plasterboard at elevated temperature is vital in the performance‐based design of any structure adopting gypsum as passive fire protection (PFP). Numerous heat transfer studies have been conducted over the years where attempts have been made to simulate the fire performance of gypsum‐protected assemblies, subject to standard fire exposure. However, contradictory thermal properties for gypsum plasterboard are apparent throughout. As a result, it is unclear from a practitioner's perspective as to which studies represent reasonable properties for design purposes. In recognition of this the authors present a numerical study highlighting the consequences of adopting many of the differing property sets available in the literature, the sensitivity of temperature development resulting from deviations from the assumptions that underpin such properties, and the consequences of adopting plasterboard properties derived from standard fire tests, in natural fire situations. The study presents heat transfer simulations conducted using the finite element software TNO DIANA coupled with both laboratory and natural fire tests conducted on Structural Insulated Panels (SIPs) and Engineered Floor Joists (EFJs). It is found from this study that plasterboard properties are highly sensitive to the assumed free and chemically bound moisture contents. Minor percentage changes are shown to have a significant influence on the temperature development of SIPs exposed to standard furnace fires, while some of the most accepted plasterboard properties available in the literature are found, in some cases, to be non‐conservative when adopted in simulations of SIPs. More interestingly, it is also found that the properties of plasterboard available in the literature, largely derived from standard fire tests, are not independent of the heating rate. As a result, when such properties are applied to natural fire problems significant inaccuracies can occur. Copyright © 2011 John Wiley & Sons, Ltd.     

Effective thermal inertia in relation to normalized heat load

Normalized heart load, obtained by dividing heat absorption by thermal inertia, is a quantity useful in building design for relating fire severity in fully developed compartment fires to fire severity in standard fire resistance tests. Harmathy has shown how normalized heat load may be used for determining required fire resistance in projected buildings. The present work describes how effective values of thermal inertia can be calculated for such important materials as brick and concrete, both normal and lightweight, for which thermal properties depend strongly upon temperature.     

Modelling thermal performance of gypsum plasterboard‐lined light timber frame walls using SAFIR and TASEF

Gypsum plasterboard is commonly used as a lining material on lightweight timber or steel framing. Gypsum contains moisture, both free and chemically bound in its crystal structure. The dehydration of the gypsum and decomposition of calcium carbonate absorb heat giving gypsum plasterboard fire resistant qualities. This paper discusses the suitability of the finite element heat transfer program SAFIR for modelling plasterboard‐lined light timber frame assemblies and its limitations. The default material properties in SAFIR for gypsum plasterboard do not give good results and ‘smoothing’ of enthalpy curves has insignificant effects on the results but substantially reduces processing time. Modelling with SAFIR gives similar results to prior modelling using the program TASEF with slight differences. Both programs give better overall results for slower developing fires and furnace tests than more rapidly growing fires. Reasonable, slightly conservative results for thermal analysis of heat transfer through the walls and into timber studs can be achieved using the parameters suggested in this paper. More sophisticated and detailed models incorporating mass transfer, effect of fasteners, gaps between lining sheets and ablation are required to achieve better comparisons. Copyright © 2010 John Wiley & Sons, Ltd.     

Post‐protection effect of heat‐resistant insulations on timber‐frame members exposed to fire

In lightweight walls and floors, the load‐bearing timber members are protected by cladding on the sides to form a divider between two fire compartments or to provide appropriate fire protection to the load‐bearing members. The spaces between the timber members can be void or filled with insulation materials. Although a huge number of different insulation materials exist, the most commonly used material is mineral wool insulation. The existing design model for glass wool‐insulated timber‐frame constructions, given in European standard 1995‐1‐2, assumes collapse of the glass wool after failure of the cladding. However, a new form of glass wool insulation, suitable for use at high maximum service temperatures, is now available in the market. The charring phase after the cladding's failure is known as the post‐protection phase. The behaviour of the new heat‐resistant glass wool in the post‐protection phase is similar to that of stone wool and considerably better than that of traditional glass wool. The protective properties of stone wool have changed over the last decades. Charring is one of the main parameters needed to calculate the resistance of a structure to fire. Based on experimental investigations, this paper describes the analysis of the effect of the insulation with regard to its ability to protect timber members against charring during the post‐protection phase. Copyright © 2011 John Wiley & Sons, Ltd.     

Measurement of thermophysical properties of fire‐resistive and reactive materials. Urgent problems and solutions

The ASTM Standard Test Method E2584 ‘Standard Practice for Thermal Conductivity of Materials Using a Thermal Capacitance (Slug) Calorimeter’ was developed by National Institute of Standards and Technology to measure thermal conductivity of fire‐resistive and reactive materials during monotonic heating and cooling. The heating regime adopted in ASTM E2584 is very reasonable because change of materials' composition and structure during a fire can depend on kinetic factors and thermal story of the materials. The main problem in experimental measurements of thermophysical properties is the impossibility of using standard steady‐state methods during time‐dependent processes in materials accompanied by latent heat effect. Using standard transient methods, such as hot wire or laser flash methods, is also incorrect, because the transient measurement heat process can be started only after steady‐state temperature field is established in the sample, that is, at the time when the involved physical or chemical processes could be finished. The objectives of this paper are to review and to analyze scientific problems to be taken into account in the revised version of ASTM E2584 Standard. Examples of experimental results are presented for measurement of thermophysical properties during chemical and physical processes in solid materials, powders, metals, and ceramic materials; building materials during fire; and so on. Copyright © 2016 John Wiley & Sons, Ltd.     

Experimental study on insulative properties of intumescent coating exposed to standard and nonstandard furnace curves

This paper reports the results of an experimental study on two types of intumescent coating exposed to the ISO834 standard fire and three nonstandard fire curves. The nonstandard fires were all less severe than the standard fire. A total of 72 intumescent coating protected steel specimens were tested. The expanded thickness of intumescent char was measured, and the pore feature was observed. Constant thermal conductivity for each specimen was calculated based on the measured steel plate temperature. Thermogravimetric analysis (TGA) test was carried out, and the results show that more gas is trapped within the coating due to better matching of thermal behaviour between gas evolution and polymer viscosity as the rate of heating increases. The constant effective thermal conductivities for the intumescent coating under the nonstandard fires were 65% (type‐W) and 35% (type‐S) higher than that under the standard fire, which resulted in an overestimation of the coating failure time up to 15 and 11 minutes, respectively. Therefore, it is sometimes insecure to use results from standard fire tests guiding the design of coating thickness for steel elements under nonstandard fire conditions.     

Fire losses in selected property classifications of non‐residential,commercial and residential wood buildings. Part 1: hotels/motels and care homes for aged

In an attempt to evaluate the adequacy of building code requirements for selected classifications of non‐residential, commercial and residential wood buildings, researchers at Forintek Canada Corp. have examined Canadian and American fire loss statistics and compared fire losses for the selected classifications of wood buildings with those for similar buildings of non‐combustible construction. They have also examined causal factors associated with fires in those structures, extent of flame and smoke spread, ability of sprinkler systems and building construction to minimize fire losses, and outcomes of fire events. Because of the volume of information that was analysed, the results are being reported through three separate papers. This, the first, presents the ‘big picture’ with respect to fire losses in the selected classifications of non‐residential, commercial and residential structures, and discusses in detail fire losses for hotel/motel properties and care homes for the aged. Copyright © 2006 John Wiley & Sons, Ltd.     

Uncertainties in modelling heat transfer in fire resistance tests: A case study of stone wool sandwich panels

Modelling fire performance of building fire barriers would allow optimising the design solutions before performing costly fire resistance tests and promote performance‐based fire safety engineering. Numerical heat conduction analysis is widely used for predicting the insulation capability of fire barriers. Heat conduction analysis uses material properties and boundary condition parameters as the input. The uncertainties in these input parameters result in a wide range of possible model outcomes. In this study, the output sensitivity of a heat conduction model to the uncertainties in the input parameters was investigated. The methodology was applied to stone wool core sandwich panels subjected to the ISO 834 standard fire resistance temperature/time curve. Realistic input parameter value distributions were applied based on material property measurements at site and data available in literature. A Monte Carlo approach and a functional analysis were used to analyse the results. Overall, the model is more sensitive to the boundary conditions than to the material thermal properties. Nevertheless, thermal conductivity can be identified as the most important individual input parameter.     

Modified carbon‐dioxide measurement to predict the heat release rate of fire burning in a compartment based on the three‐zone model

The heat release rate (HRR) of fuels has been described as the single important variable of fuels in fire hazard, and the HRR experimental measurement remains a key issue in fire science. A modified carbon‐dioxide generation (CDG) method, applying a three‐zone smoke model, is developed to predict the HRR of gas, liquid, and solid fuel fires. The three‐zone smoke model with three layers is determined by the vertical thermal stratification, and their physical thermal properties are computed. The application of modified method on typical gas fuel, liquid fuel, and simple solid‐fuel fires is verified. The prediction accuracy is examined quantitatively by the cosine similarity comparison of predicted results with the experimental data. In addition, the ventilation effects on the predicted results are also explored. Results show that the application of three‐zone model improves the HRR prediction accuracy, because it can accurately capture the mixing behavior from the upper layer to the lower layer. The effect of ventilation on modified CDG method is positive as the ventilation enhances the smoke mixing and the smoke distribution in each layer is relatively uniform.     

Flame extension and the near field under the ceiling for travelling fires inside large compartments

Structures need to be designed to maintain their stability in the event of a fire. The travelling fire methodology (TFM) defines the thermal boundary condition for structural design of large compartments of fires that do not flashover, considering near field and far field regions. TFM assumes a near field temperature of 1200°C, where the flame is impinging on the ceiling without any extension and gives the temperature of the hot gases in the far field from Alpert correlations. This paper revisits the near field assumptions of the TFM and, for the first time, includes horizontal flame extension under the ceiling, which affects the heating exposure of the structural members thus their load-bearing capacity. It also formulates the thermal boundary condition in terms of heat flux rather than in terms of temperature as it is used in TFM, which allows for a more formal treatment of heat transfer. The Hasemi, Wakamatsu, and Lattimer models of heat flux from flame are investigated for the near field. The methodology is applied to an open-plan generic office compartment with a floor area of 960 m² and 3.60 m high with concrete and with protected and unprotected steel structural members. The near field length with flame extension (fTFM) is found to be between 1.5 and 6.5 times longer than without flame extension. The duration of the exposure to peak heat flux depends on the flame length, which is 53 min for fTFM compared with 17 min for TFM, in the case of a slow 5% floor area fire. The peak heat flux is from 112 to 236 kW/m² for the majority of fire sizes using the Wakamatsu model and from 80 to 120 kW/m² for the Hasemi and Lattimer models, compared with 215 to 228 kW/m² for TFM. The results show that for all cases, TFM results in higher structural temperatures compared with different fTFM models (600°C for concrete rebar and 800°C for protected steel beam), except for the Wakamatsu model that for small fires, leads to approximately 20% higher temperatures than TFM. These findings mitigate the uncertainty around the TFM near field model and confirm that it is conservative for calculation of the thermal load on structures. This study contributes to the creation of design tools for better structural fire engineering.     

Poly(vinyl chloride) and its fire properties

This work provides an up‐to‐date review of the fire properties of poly(vinyl chloride) (PVC) materials, both rigid (unplasticized) and flexible (plasticized). The fire properties addressed include ignitability, ease of extinction (oxygen index), flame spread (small scale and intermediate scale), heat release, smoke obscuration, smoke toxicity, hydrogen chloride emission and decay, and performance in real‐scale fires. This comprehensive review includes a wide selection of references and tables illustrating the properties of PVC materials in comparison with those of other polymeric materials, including, in many instances, wood materials. The work puts these fire properties in perspective, showing that the heat release rate (the key fire property) of rigid PVC (and that of properly flame‐retarded flexible PVC) are among the lower values found for combustible materials. This work also shows that the smoke toxicity and smoke obscuration resulting from burning PVC materials in real‐scale fires is in the same range as those of other materials.     

Thermal properties of gypsum plasterboard at high temperatures

Light timber frame wall and floor assemblies typically use gypsum‐based boards as a lining to provide fire resistance. In order to model the thermal behaviour of such assemblies, the thermo‐physical properties of gypsum plasterboard must be determined. The relevant literature and the chemistry of the two consecutive endothermic dehydration reactions that gypsum undergoes when heated are reviewed. The values determined for the thermo‐physical properties are modified to create smooth enthalpy and thermal conductivity curves suitable for input into a finite element heat transfer model. These values are calibrated within a reasonable range and then validated using furnace and fire test data. The type of plasterboard used in these tests is an engineered product similar to the North American type C board. The temperature at which the second dehydration reaction occurs is altered to be consistent with later research with little apparent affect on the comparison with test results. Values for specific heat, mass loss rates and thermal conductivity for gypsum plasterboard that are suitable for use in finite element heat transfer modelling of light timber frame wall and floor assemblies are recommended. Copyright © 2002 John Wiley & Sons, Ltd.     

Experimental study on heat release rate measurement in tunnel fires

Knowledge about the heat release rate (HRR) is essential for studying tunnel fires. The standard method in ISO 9705 is widely applied to calculate the HRR of combustion by measuring the consumption of oxygen in a fire. However, the studies of HRR measurement in full‐scale tunnel fires are rare because of the complication and costs of large experiments. This paper presents a system based on the principle of oxygen consumption calorimetry for the measurement of HRR and total heat release (THR) of full‐scale fires in tunnels. A total of 22 fire experiments are performed in a large‐scale ventilated testing metro tunnel with dimension of 100.0 m × 5.5 m × 5.5 m to validate the reliability and effectiveness of this system. Firstly, four oil spray fire tests are conducted with nozzle flow of 106 L/h at (1 ± 0.1) MW HRR to calibrate the instrumentation. Then, 18 full‐scale fire tests using square diesel pools at five sizes (0.5, 1.0, 2.5, and 5.0 m²) and wood cribs as fire sources are carried out for the measurement of HRR and THR. Results provided by the comparison between the measured HRR and THR values of the fire tests and the theoretically calculated ones show that our system works effectively in the HRR measurement of full‐scale fires in tunnels.     

Investigations of the phenomenon of spontaneous heating of chloroprene cover wear‐off in fire‐resistant conveyor belts

The paper presents investigations into the phenomenon of spontaneous heating of rubber wear‐off from covers of fire‐resistant chloroprene conveyor belts. The results of thermal analysis of cover fragments, and cover wear‐off in an atmosphere of air and of nitrogen are reported. It has been found that the phenomenon of spontaneous heating of rubber wear‐off from covers of fire‐resistant chloroprene conveyor belts used in coal mines creates a hazard of fires. Copyright © 1999 John Wiley & Sons Ltd.     

Performance of a light timber‐framed compartment in natural fire subjected to lateral load

A common approach for designing buildings for lateral stability during and post‐fire in New Zealand is to ensure that a fire‐rated structure does not collapse when subjected to a nominal horizontal force. For external walls of residential buildings, which are required to resist a lateral load of 0.5 kPa, it is hypothesised that the adjacent unrated construction could provide sufficient support. A natural fire experiment has been conducted to evaluate the fire performance of a laterally loaded light timber‐framed compartment, with external dimensions of 4.33 m × 3.35 m and a stud height of 2.4 m constructed with a timber truss roof and plasterboard ceiling. During the experiment, the ceiling collapsed at 12 to 13 minutes, and the bottom chord of the roof truss failed in tension after 28 minutes which resulted in the fire‐rated wall losing its lateral stability at 28 minutes. The fire severity experienced in the compartment has been estimated to correspond to an equivalent time of 33‐minute exposure to a standard furnace time‐temperature. It is concluded that there is no need to provide nominal (additional) moment‐resisting fixity at the base of the fire‐rated wall when exposed to the standard fire for no more than 30 minutes.     

Temperature of post‐flashover compartment fires—Calculations and validation

This paper describes and validates by comparisons with tests a one‐zone model for computing temperature of fully developed compartment fires. Like other similar models, the model is based on an analysis of the energy and mass balance assuming combustion being limited by the availability of oxygen, ie, a ventilation‐controlled compartment fire. However, the mathematical solution techniques in this model have been altered. To this end, a maximum fire temperature has been defined depending on combustion efficiency and opening heights only. This temperature together with well‐defined fire compartment parameters was then used as a fictitious thermal boundary condition of the surrounding structure. The temperature of that structure could then be calculated with various numerical and analytical methods as a matter of choice, and the fire temperature could be identified as a weighted average between the maximum fire temperature and the calculated surface temperature of the surrounding structure as a function of time. It is demonstrated that the model can be used to predict fire temperatures in compartments with boundaries of semi‐infinitely thick structures as well as with boundaries of insulated and noninsulated steel sheets where the entire heat capacity of the surrounding structure is assumed to be concentrated to the steel core. With these assumptions, fire temperatures could be calculated with spreadsheet calculation methods. For more advanced problems, a general finite element solid temperature calculation code was used to calculate the temperature in the boundary structure. With this code, it is possible to analyze surrounding structures of various kinds, for example, structures comprising several materials with properties varying with temperature as well as voids. The validation experiments were accurately defined and surveyed. In all the tests, a propane diffusion burner was used as the only fire source. Temperatures were measured with thermocouples and plate thermometers at several positions.     

Predicting the fire resistance of timber members loaded in tension

The paper presents a numerical model for predicting the fire resistance of timber members. Fire resistance is evaluated in a two‐step process implemented in the Abaqus finite element code: first, a time‐dependent thermal analysis of the member exposed to fire and then a structural analysis under a constant load are performed. The structural analysis considers the reduction in mechanical properties (modulus of elasticity and strength) of timber with temperature. The analysis terminates when the member can no longer redistribute stresses from the hottest to the coldest parts, leading to structural failure. The model was used to simulate fire tests carried out on specimens made from laminated veneer lumber loaded in tension. Experimental data in terms of temperature, charring depth, displacement and failure time were compared with the numerical results obtained by assuming the thermal properties and degradation of mechanical properties with temperature as suggested by Eurocode 5, showing an overall acceptable approximation. The fire resistance of the timber member was then predicted depending upon the applied tensile loads using the numerical model and analytical formulas. The proposed finite element model can be used to predict the fire resistance of timber structures as an alternative to expensive and complicated experimental tests. Copyright © 2012 John Wiley & Sons, Ltd.     

Small-scale assessment method for the fire resistance of historic plaster system and timber structures

The primary protection against the charring of timber is ensured by protection materials. Today, there are only a limited number of materials given in design codes as fire protection materials for timber. Historic surface finish materials such as plasters have rarely been studied with respect to fire; no design values exist in the current fire part of Eurocode 5. Full-scale fire testing is costly to assess the fire performance of material combinations, thus this study presents a useful tool that is specifically tailored to evaluate the fire protection ability of materials in small-scale. A review of conducted tests demonstrate that the cone heater of a cone calorimeter is a dependable device to estimate the charring performance of protected timber specimens as the test results approximate the ones obtained from furnace tests. This work contributes to the assessment of fire resistance performance of various combinations and types of plaster systems found in existing timber buildings that often require an individual approach for an adequate fire risk analysis and design decisions to meet current fire safety regulations with respect to the load-bearing capacity and compartmentation of building structures. Increased knowledge on the fire protection performance of traditional plasters is believed to facilitate their wider use in timber buildings, primarily to preserve their significance as part of the cultural built heritage.     

The effect of fire‐retardant additives and a surface insulative fabric on fire performance and mechanical property retention of polyester composites

This study investigates the simultaneous use of conventional fire‐retardant additives and an insulative intumescent thermal barrier/mat to improve the fire performance and mechanical property retention of glass‐fibre‐reinforced polyester (GRP) composites. Significant reductions in the peak heat release rate (PHRR) and total heat release (THR) were observed from measured cone calorimetric data following the addition of nitrogen, phosphorous, halogen containing and hydroxylated fire‐retardant additives. Some fire‐retarded glass‐fibre‐reinforced composites further protected by an intumescent mat containing silicate fibres, expandable graphite and borosilicate glass bound together by an organic matrix show further reductions in PHRR. Despite improving the fire retardancy of the composites, the presence of fire‐retardant additives alone does not improve flexural modulus retention following exposure to a heat source. However, the introduction of a ‘passive’ fire proofing insulative fabric enhances fire performance while preserving the mechanical properties of composites exposed to high heat fluxes or fires. Copyright © 2010 John Wiley & Sons, Ltd.     

Absorptivity and its dependence on heat source temperature and degree of thermal breakdown

The spectral absorptivity of 62 products has been measured in the wavelength region of 0.3–20 µm. Effective absorptivity for fire‐induced heat radiation typically lies in the range of 0.75–0.95. It was found that the effective absorptivity varies significantly with the temperature of the heat source. This has implications on the heating of a surface. The effect is more important when the absorptivity is used as input for calculations of ignition temperature and thermal inertia. It was also found that the absorptivity of radiation from fires for products exposed to irradiation in many cases decreased with increased exposure time. This is surprising since, for example, wood that is darkened when exposed to heat obviously has a higher absorptivity in the visual part of the spectrum than fresh non‐darkened wood. The reason that was identified for this is because the absorptivity in the IR drops, and measurement results are given which clearly illustrate this. Copyright © 2010 John Wiley & Sons, Ltd.