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A Comparison of the Conditions in a Fire Resistance Furnace When Testing Combustible and Non-combustible Construction
Abstract
This paper reports on two experiments conducted in a fire resistance furnace to study the differences in the boundary conditions, the fire dynamics and the fuel required to run the furnace when a combustible timber specimen as opposed to a non-combustible concrete specimen is tested. In both experiments measurements were taken in the furnace to evaluate the difference in the environments of the furnace and the response of the elements being tested. These include non-control plate thermometers distributed throughout the furnace; O2, CO2 and CO gas measurements taken at different distances from the specimen surface and in the furnace exhaust; instrumentation of one of the bricks comprising the furnace lining with thermocouples at different depths from the exposed surface; and mass loss of the combustible timber specimen. Thermal exposure of elements in a furnace is discussed, as well as the impact of the different materials on the similarity of thermal exposure. This is done through analysis and discussion of the different measurements taken and the apparent influence of the specimen being tested on the boundary condition of the heat diffusion equation. We conclude that; (1) the fire dynamics in a furnace are dependent on the specimen being tested; (2) that the test with the combustible specimen requires less fuel flow to the burners such that the control plate thermometers follow the ISO 834 temperature–time curve compared to the non-combustible specimen, however that this is not only a result of the combustibility of the specimen but is also a consequence of the different thermal inertia of the two materials; (3) that the boundary condition for heat transfer to a test object in furnace tests is dependent on the properties of the specimen being tested; and (4) that the timber when placed on the furnace experiences smouldering combustion after the char layer has formed. A fire resistance test of combustible construction of a given period represents a significantly less onerous test in terms of energy absorbed or fuel made available than one of a non-combustible construction, implying that the existing fire resistance framework may not be appropriate for timber structures and that an alternative approach may be required.
... More recently, the questions about the use of the standard fire resistance framework has been directed towards its application to timber members [6,7]. This is due to timber's combustible nature which provides additional heating fuel in the furnace, which consequently affects the actual applied fuel needed to control the time-temperature curve (see Figure 1). ...
... In that year, BS 476 was created which laid down the test procedure for assessing structural elements by means of a standard test, which adopted the time temperature heating curve from ASTM [41]. It would not be until BS 476 was adopted in the 1930s, which largely mirrored the ASTM fire standard from that time in its initial conceptions but deviates today in test control 6 . BS 476 would later evolve into ISO 834. ...
... The discussion spoken of today [6,7] regarding the time-temperature curve's usage on combustible construction is not new, but we do have better measurement tools to quantify it and investigate its implications [6,7]. The temperatures given off by timber during a standard fire resistance test are not fully understood, nor are all building materials when real fires are considered as the field of fire dynamics is still evolving. ...
This review aims to provide additional context to the historical narrative of the development of the standard temperature–time heating curve used for the determination of the fire resistance of structural elements. While historical narratives of the development of the standard temperature–time heating curve exist, there are portions of the timeline with missing contributions and contributions deserving of additional examination. Herein, additional newly available contributions (owing to recent digitization efforts) from the original standard development cycle not distinctly covered by existing historical narratives are introduced and reviewed. Though some engineers have long been recognized for their contributions to the curve’s development, lesser-recognized influences are re-examined. These include contributions to fire resistance testing from Sylvanus Reed, that are acknowledged for the first time in a contemporary light. Practitioners will find discussion from the temperature–time heating curve’s development period that is useful for current philosophical discussions pertaining to the curve’s use for combustible material testing. This study identifies that no currently available historical literature can support the definition of the temperature points which describe the standard temperature–time heating curve. This reinforces contemporary discussion that the heating curve lacks scientific basis in its representation of a real fire.
... This gives an indication of how much energy exposed CLT contributes to a standard furnace test. A similar detailed comparison between the fire dynamics in a furnace with combustible versus noncombustible elements subjected to the standard temperature curve was researched by Lange et al. 2020 [126]. As shown in [126], the difference between exposed timber in a furnace test and concrete is partly due to the extra fuel from the timber, but also partly from the lower conductivity of wood compared to concrete. ...
... A similar detailed comparison between the fire dynamics in a furnace with combustible versus noncombustible elements subjected to the standard temperature curve was researched by Lange et al. 2020 [126]. As shown in [126], the difference between exposed timber in a furnace test and concrete is partly due to the extra fuel from the timber, but also partly from the lower conductivity of wood compared to concrete. A concrete sample will absorb much more energy, therefore requiring more energy input to the furnace to meet the same temperature curve. ...
Fire safety in wooden buildings remains topical.
Since the previous publication of the report "Fire Safety in Timber Buildings
A review of existing knowledge" (2020) much research in this area has been carried internationally. As there is more knowledge available that can be important to know for those working with fire protection in timber buildings, this report has been updated.
... In turn, this may result in fire spread outside the compartment of origin and potentially structural failure (Law and Hadden, 2020). Despite the significant body of literature that now exists highlighting the potential for inadequate fire performance of mass timber where the sole design mode is furnace testing to a traditional standard fire exposure (Drysdale, 2011b, Lange et al., 2020, Brandon et al., 2021, test standards globally commonly address structural adequacy of mass timber members by prescribing a constant char rate based on traditional standard fire furnace test data (Buchanan and Abu, 2017), with no consideration of the impact of fire dynamics in a real building fire. The reliance on traditional standard fire exposure for mass timber elements to derive constant charring rates is "deeply flawed" (Drysdale, 2011b). ...
... Research undertaken by Butler (Butler, 1971) on slabs of wood in an oxygenated environment found that at an incident black-body radiant heat flux of 200 kW/m ² , which is comparable with typical compartment temperature in the order of ~1,100 °C, corresponding char rates were recorded in the order of 4.4 mm/min. For a natural fire, thermal exposure within the compartment may be significantly more than that under standard fire exposure resulting in higher burning rates and a faster reduction in load-bearing capacity compared to the furnace environment, (Li et al., 2015, Lange et al., 2020. That is to say that the reliance upon a constant charring rate in the order of 0.6 mm/minute as derived from furnace testing (e.g. ...
As practitioners, we have implemented a performance-based design (PBD) framework for mass timber fire performance. We provide a literature review that articulates the need for the industry to develop a reliable PBD approach. We detail a high-level summary of this framework and a basic summary of the challenges associated with decision-making during such an assessment. This discussion is essential to normalise the assimilation of scientific research to permit practical design for industry. We conclude that: a furnace-derived char rate is often not applicable for real building fires; further research is imperative to support our understanding of timber compartment fire dynamics and to add confidence to input variable choices; and that as timber buildings get taller and more complex it is imperative that industry establishes and adopts a transparent, evidence-based and holistic approach to design the fire strategy of a mass timber building.
... Combustible materials, by their nature, will both contribute and react to a fire in ways that are not consistent with standard fire testing frameworks [5][6][7][8]. The growing interest in engineered timber and bamboo buildings is particularly relevant in this regard. ...
... Additionally, a new method for measuring temperatures in large panels was developed, wherein a cylindrical core was taken from the panel and instrumented with thermocouples inserted from the side -around the circumference of the cylinder -at different distances from the heated surface. This is an extension of the approach used by Lange et al. [6] to instrument a brick in the wall of a furnace with thermocouples running parallel to the heated surface. This technique was applied for the exposed CLT walls and ceiling, and also for a vermiculite cylinder inserted into the encapsulated rear wall. ...
In order to adequately quantify and predict the fire performance of novel construction materials and systems, their thermo-mechanical response to representative fire exposures must be defined through appropriately tailored experimentation. One of the most important components of these experiments is measurement of the in-depth temperature profile, which provides insight into the physical and chemical processes occurring within the material, and is critical in validating the output of thermal models. As a result, accurate temperature measurements are imperative. For this purpose, thermocouples of various designs have become ubiquitous in fire experimentation and thermal performance testing. However, there are errors inherent in the use of the thermocouples for solid-phase temperature measurement that, depending on the geometry and materials used, may be very significant. In particular, when a thermocouple with a relatively high thermal conductivity is embedded in a material of much lower conductivity, this can induce a disturbance in the temperature field around the thermocouple due to a ‘thermal bridging’ effect. As a result, the measured temperatures within the material may be much lower than the ‘undisturbed’ temperatures that would exist without the presence of the thermocouple.
This thesis explores the most critical error sources relevant to the measurement of in-depth temperatures in fire experimentation at different scales, in order to recommend methods for minimisation or correction of these errors. This is achieved through a series of experimental campaigns, coupled with heat-transfer modelling and parametric sensitivity analyses. The first of these campaigns involved bench-scale experiments in which samples of vermiculite insulation board – an exemplar non-combustible material – were subjected to well-defined heating conditions. In-depth temperatures were measured by thermocouples inserted either parallel or perpendicular to the heated surface. These experiments were replicated in finite element heat transfer models that were specifically tailored to the experimental conditions. The second campaign expanded on the first by introducing a charring, combustible material as the experimental sample, so that the influence of these additional complexities could be investigated. Laminated bamboo was used as the embedding material in this case, because in-depth temperature measurements are of practical relevance to the characterisation of this novel building material.
Finally, the implications of scaling were investigated through a large-scale compartment fire experiment, in which the performance of both combustible and non-combustible materials was measured. This experiment involved a ‘real’ fire in a full-scale compartment constructed from cross-laminated timber, with a combination of exposed and protected timber surfaces. Each of the walls and the ceiling were heavily instrumented with in-depth thermocouples inserted perpendicular or parallel to the heated surfaces.
In all of the experimental cases, the influence of thermocouple selection and orientation on the measured results was clearly observable. Temperatures measured by thermocouples inserted perpendicular to the heated surface were significantly lower than those from thermocouples in the parallel configuration. These results matched closely with the model predictions for the bench-scale experiments, which accurately reproduced the thermal disturbance induced by the presence of a thermocouple.
A simplified error correction methodology was proposed, which predicts the ‘undisturbed’ temperature at a particular location within the embedding material. This method ‘corrects’ the measurements from a thermocouple inserted perpendicular to the heated surface, and only requires detailed knowledge of the geometry and thermal properties of the thermocouple. The thermal boundary conditions and properties of the embedding material are incorporated in a parametric sensitivity analysis to produce a corrected temperature range that accounts for the uncertainty of these variables. This correction method was found to reduce the thermal disturbance error significantly, providing similar accuracy to measurements from thermocouples inserted parallel to the heated surface. The main challenge to this correction method is the occurrence of charring, moisture migration, and other phenomena that locally cause the heat transfer pathways to diverge from purely inert heat conduction between the thermocouple and embedding material. However, for the case of laminated bamboo heated perpendicular to the grain, it was found that the corrected measurements provided an accurate prediction of the in-depth temperatures until the point at which the char layer reached each thermocouple.
In the large-scale experiment, a novel method for inserting thermocouples parallel to the heated surface was developed. This method circumvents the practical constraints that often prevent the placement of thermocouples parallel to the exposed surface in large-scale experimentation. The effects of moisture migration and evaporation limited the applicability of error correction for the timber elements, but the presented correction method continued to work well for vermiculite insulation at this scale.
In some experimental cases it is unavoidable that a thermocouple will disturb the surrounding temperature field, and this can significantly reduce the accuracy of results from which heat transfer models, charring rates, and thermal behaviour are derived. This thesis provides recommendations for correcting this disturbance where possible, and for accurate measurement and interpretation of solid-phase temperature data in fire experimentation at different scales.
... One furnace experiment was conducted in the framework of a related study at Rise, Research Institutes of Sweden, Boras, where the results were already presented by Schmid et al. [14]. and Lange et al. [21]. ...
... Besides the temperature measurements with control plate thermometers (PTs) in the furnace compartment, further PTs close to the surface were installed to capture potential surface flaming. No differences from measurements with a non-combustible reference specimen were observed [21]. Sample gas was extracted from various positions in the furnace compartment, i.e. close to the combustible surface and away from it. ...
The influence of exposed timber surfaces on compartment fires has been well documented in various studies in recent decades. Yet available design concepts still typically neglect the influence of an additional fire load from linear structural timber elements such as beams and columns. As rules for large shares of exposed timber surfaces, e.g. by panels, are rare, authorities and fire safety engineers demand often mock-up compartment fire experiments to estimate the fire safety of a particular design. Such experiments, however, are costly, time consuming, and give limited insights into the potential fire scenarios and may fail to represent properly the fundamental effects arising from exposed structural timber elements in a fire. An approach to overcome these existing limitations is presented, which is able to estimate the contributions from structural timber to a fire from its fully developed- and decay phase until burnout. The model input is developed from an experimental campaign where the relevant effects of fire exposed structural timber could be isolated and measured. It was found that the energy stored in the char layer is a key characteristic for describing the fire dynamics of compartment fires with exposed structural timber. Consequently, the proposed approach describes a framework for the Timber Charring and Heat storage, the TiCHS-model. The validation of the model is shown in this paper by means of existing compartment experiments. A current limitation is the bond line integrity of the fire exposed components as the combustion characteristics of failed char pieces on the floor are currently unknown.
... Las primeras experiencias, con materiales cuyos comportamientos ya fueron estudiados por otros autores [6], permitieron calibrar las temperaturas y adaptar la mufla eléctrica según las condiciones establecidas en la Norma IRAM 11.575, y otorgó al grupo de investigación mayor conocimiento para realizar ensayos de no combustibilidad. ...
El análisis del comportamiento ante el fuego, de los elementos constructivos, es un procedimiento que permite determinar las características que posee un material, para hacerlo más peligroso que otro ante un incendio. Esto permite establecer criterios de clasificación, para incluir a los materiales en un rango o escala que proporcione la comparación entre ellos.
En este trabajo se describe la construcción y puesta a punto de un equipo de medición, para determinar el grado de resistencia al fuego de materiales constructivos, de acuerdo a la Norma IRAM 11575.
En un principio se propuso construir un dispositivo nuevo, pero tras varios intentos fallidos y errores de diseño, se optó por adaptar una mufla eléctrica, ya existente, para realizar los ensayos. Luego de un período de puesta a prueba se realizaron las primeras mediciones.
En el presente estudio se exponen los resultados de las 3 primeras muestras ensayadas: cemento espumado de baja densidad, madera de quebracho blanco y placa de yeso cubierta de papel.
Los resultados alcanzados en esta primera etapa, son altamente promisorios y pueden utilizarse como referencia para saber si el material examinado es combustible o no, y en qué medida, por lo que se pretende continuar perfeccionando el equipo de medición y ensayar nuevos materiales biomásicos, construidos por el grupo G.I.D.E.R.
Conocer el comportamiento ante el fuego de los materiales utilizados en la edificación, permitiría disminuir los riesgos de incendio, impediría la propagación del mismo y reduciría el riego de daños a las personas y a los materiales.
... The additional energy generation from exposed combustible members is not accounted for [13]. Standard methods and calculations have been shown to potentially underpredict the loss of structural capacity [11] [14]. Moreover, calculating a Fire Resistance Level (FRL) using the existing frameworks does not allow a holistic assessment of fire safety and in no way supports the prediction of the potential for self-extinction of the combustible structural elements. ...
A holistic methodology for explicit fire safety strategies for buildings with mass timber structures has been
developed based on theoretical frameworks outlined in the literature and the current state of published research on the
fire behaviour and safety of mass timber structures. This paper presents the four main pillars of this methodology:
tenability for occupant evacuation; heating of the mass timber structure and loss of loadbearing capacity; external flaming;
and assessment of the potential for self-extinction of the mass timber structure after burnout of the movable fuel load.
The application of the methodology to three case study buildings showed the need for interdisciplinary collaboration
throughout the design and planning of mass timber buildings. Engineering and design decisions including structural
design options, the extent of exposure of the timber, façade type and construction and general building layout influence
the resultant level of fire safety to an even greater extent for buildings utilising structural mass timber elements than for
buildings with non-combustible structures. All practitioners collaborating on design projects with mass timber structural
elements require a contemporary understanding of the persisting limitations around timber fire safety strategies and
research as anyone whose work affects or limits the fire safety measures on such a project will carry a certain ethical or
legal responsibility for the outcomes and consequences of a fire
... The experimental campaign, presented in Table 1, consisted of four small-scale fire resistance tests. The use of standard fire exposure for testing wooden elements may not be representative of the most severe fire conditions in reality, particularly since the limited availability of oxygen in a standard furnace will inhibit flaming combustion or oxidation of the char layer around the joint [11], and because there is no consideration of cooling-phase heat transfer. Nevertheless, standard fire exposure can allow comparison of the fire performance of different designs, and the convective heat transfer induced is particularly relevant to the vulnerabilities created by tolerance gaps. ...
Tolerance gaps or slips in wood connections are unavoidable, for reasons of constructability and the effects of natural shrinkage in timber elements with changing moisture content. During a fire, these gaps may lead to increased heat transfer through the connection. Aluminium connectors are becoming more popular due to their high malleability and availability, but they are particularly vulnerable to elevated temperatures. Thus, the objective of this study is to investigate the effect of tolerance gaps on the fire performance of aluminium connectors in beam-to-column/wall shear connections. An experimental campaign was designed to study the temperature evolution of the aluminium connectors during standard fire exposure for 1 mm and 6 mm tolerance gaps, as well the mitigation effects of additional intumescent fire protection in a 6 mm tolerance gap connection. The results showed a clear and consistent impact of the connection gap size on the temperature evolution of the aluminium connectors. For the larger 6 mm gap, the temperature of the connector increased much faster, reaching 286 ± 36 °C after 80 minutes, at which time the connector with a 1 mm gap had only reached 97 ± 1 °C. The addition of intumescent protection in a 6 mm gap case led to lower temperatures in the connection after 40 minutes of fire exposure, in comparison to an equivalent tolerance gap without fire protection. This study shows that tolerance gaps can lead to a significant reduction in the capacity of aluminium connectors, but this may be mitigated with additional fire protection.
... Exposed timber has also better insulative properties compared to concrete or masonry, resulting in higher heat accumulation and possibly higher fire temperatures in compartments (Bartlett et al., 2020;Lange et al., 2020;Węgrzyński et al., 2020). ...
This report is a publication of the European Network COST Action CA20139 “Holistic design of taller timber buildings – HELEN”, established with the aim to “work towards optimized holistic approaches to improve the performance of taller timber buildings and to widen their competitiveness and use across the EU and rest of the world” (https://cahelen.eu/).
The activities conducted in the first year of the Action by the Working Group (WG) 3 - Accidental load situations - are summarized in this document in the form of a state-of-the-art report (STAR) regarding design, analysis and construction methods of taller timber buildings subjected to load situations due to earthquake, fire and blast.
The report is the result of a deep review of scientific literature, international projects, national
regulations, design guidelines, as well as case studies. Particular attention has been paid to the
potential interactions with other fields of design and to the efforts made in the recent years to overcome the limitations for the progress in the construction market of timber buildings under seismic, fire and blast loads.
The information collected in this STAR document represent the starting point of discussion to identify solutions, research targets, methods and resources for the future of taller timber buildings under seismic, fire and blast loads following a holistic design approach.
Three different sub-groups (SGs) have been defined for WG3 STAR activities, namely SG1 - Seismic Loads, SG2 - Fire and SG3 - Blast. For each SG, different subtopics have been analysed and discussed.
This report is structured into three parts. Part 1 includes the review conducted by SG1 on the seismic design and seismic analysis of taller timber buildings and consist of seven documents. The review regarding the fire design situations is summarized in Part 2 through four documents. Part 3, composed of four documents, addresses the review of current knowledge on blast design of timber buildings.
... Based on this the CLT ceiling is estimated to contribute 46% of the total energy in the CLT compartments regardless of the ceiling configuration. Compared to other observations of the contribution of CLT in full scale tests, where the CLT was estimated to contribute approximately an additional 20%-40% to the internal HRR inside of a fire resistance furnace [41][42][43]. there was no CLT present in these tests. A recent review of large-scale fire tests shows that there are very few with combustible ceilings [17] and indeed the closest comparison in terms of overall behaviour may be made with the Malveira test [8]. ...
Fires in open plan compartments have been the subject of much research over the past decade. This article presents results from an experimental study conducted to explore factors that influence fire dynamics in open-plan compartments with an exposed timber ceiling.
A reduced scale testing methodology is proposed and supported by contrasting observed fire behaviour at small scale with large-scale experiments reported in the literature. The reduced-scale experiments highlight the complexity of the fire dynamics. Factors which govern the behaviour include the ignition and self-extinction of the timber; the role that the timber plays in accelerating the transition from Mode 3 (travelling) to Mode 1 (fully developed) behaviour; the ignition and self-extinction of timber which is in a downward facing orientation; the thermal inertia of the ceiling material.
Results demonstrate that: different fire modes observed in large scale compartments occur in large scale compartments with combustible timber ceilings; ceiling intrusions influence the fire; and factors that influence the response of timber in open plan compartment fires can, to a large extent, be explained by existing knowledge extracted from bench scale testing and compartment fires with non-combustible linings.
... This gives an indication of how much energy exposed CLT contributes to a standard furnace test. A similar detailed comparison between the fire dynamics in a furnace with combustible versus non-combustible elements subjected to the standard temperature curve was researched [53]. The results agree with [29] and it is concluded the fire resistance approach alone is not an appropriate benchmark to assure a level of fire safety in a timber building. ...
This report is written by Carl Pettersson fire safety engineer at Brandforsk, the Swedish Fire Research Foundation. This work has been done with the financial support of Brandforsk’s yearly funding for 2019 and 2020, and we are grateful to all the supporting organisations. A list of all the supporting organisations can be found on the back page of the report. This work has been done with the support of Birgit Östman, Mattias Delin, Robert Jönsson and Thomas Järphag. The work has also benefitted from scientific input from Alar Just, Amanda Kimball, Daniel Brandon, Luke Bisby and Robert McNamee and practical input from Martin Sparre.
... Observation and survey on longhouses found that modern longhouses design use the lowest quantity of combustible materials, lowest fire load, thus less vulnerable to fire threat. Studies on fire dynamic and a fuel requirement of combustible timber as opposed to concrete show that the wood requires less fuel flow compared to concrete [15,16]. On the other hand, the semi-modern longhouse is a mix of traditional and modern longhouse. ...
Fire hazard is a common threat in longhouses in Sarawak. Among things that are crucial in fire prevention is the evacuation route, in which highly dependent on house construction and layout. This study aims to observe the evolution of the Iban longhouse architectural design and materials used to build the longhouse. The qualitative analysis method was applied through 2D photo analysis as well as on-site visual observation and measurement. Construction materials used have been surveyed to determine its combustibility. It has been noted that longhouses have evolved over the years, from traditional to semi-traditional and modern longhouses design. The changes include the layout design and construction materials of the longhouses. Traditional and semi-traditional longhouses are often built using wooden materials that are highly flammable, while modern longhouses are made from concrete materials. The types of construction materials contribute to fire severity. It can be concluded that the longhouse architectural design, along with its construction materials, plays an essential role in the understanding of fire hazard, which will serve as fundamental on the longhouse fire reduction.
... The results from the mass loss measurements (e.g. equivalent to 37 kg/m 2 h for 100kW/m 2 and about 5 m/s) exceed known values from furnace tests in various scales of between 13 and 15 kg/m 2 h , Lange et al. 2019 Mass loss measurement were used to detect the ending of the glowing combustion. It is depending on the gas velocity and was observed between about 5 and 10 kW/m 2 . ...
For the assessment of the fire resistance of timber members, the depth of the virgin wood has been documented as crucial parameter in numerous scientific experiments in the past; results are used for the load-bearing resistance verification. An excessive number of tests with timber members have been performed with various products (e.g. beams, cross-laminated timber) in furnace environments showing a consistent charring rate of 0.65 mm/min ± 0.1 for standard fire exposure. More severe fire exposure (e.g. hydrocarbon fire) showed a moderate increase of the charring rates to about 1.1 mm/min. The interest for performance based design moved the focus away from the fully developed fire phase and included other conditions, where further parameters as the oxygen concentration and gas movement are relevant. In furnaces mainly the charring rate has been observed while in oxygen rich environments further a reduction of the char layer can be observed. This paper presents results from a charring investigation apparatus where relevant exposure levels up to 120 kW/m 2 and relevant gas velocities up to 10 m/s (heated gas) in moderately and highly turbulent conditions were investigated showing charring rates up to 2.4 mm/min caused by the consumption of the protective charcoal layer measured up to 1.6 mm/min. At multi-level exposure, the ending of the glowing combustion considering the gas velocity was measured recording the mass loss rates. For all conditions, the heat release rate was determined as input for further calculation models.
... The web PT of beam A was hotter than the web PTs of beams B and C. The PTs facing down had no systematic variation between the different beams. These differences are a common feature in fire resistance testing where thermal exposure never is 100% uniform (Lange et al., 2020). ...
Glass structures have been increasingly utilised in modern construction for decades with load-bearing walls or facades as the most common elements. However, the use of glass beams has recently been given more attention but its application as load-bearing elements has been limited by the low tensile resistance, its brittle behaviour during failure and concerns of its performance in case of fire. Parts of these aspects can be covered by using Timber-Glass composites beams, with timber flanges and a glass web. Previous research and practical application show high potential for this type of composites in ambient temperatures but its performance in fire has not yet been assessed and thus not completely understood. This study describes what to our knowledge is the first full scale fire resistance tests of Timber-Glass composites beams. These tests results are also analysed using finite-element simulations in order to understand the mechanisms of failure during the tests. It was shown that adding a timber flange to a glass web can have severe complications for the fire resistance, however, there are many possible ways to circumvent these issues.
Temperature control is a challenging task because it possesses high nonlinearity, complexity and dead time. Most of temperature process control requires a model which describes the behavior of the control system accuracy to construct a model-based controller for tracking a predefined temperature-time curve. This paper presents the identification of a gas-fired furnace to achieve a model using the experimental data. The identification model is obtained by two approaches: the bilinear model and first order plus dead time. Several experiment tests are conducted on the gas-fired industrial furnace with different steady-state inputs to reach the steady-state temperature output. The model parameters are estimated based on three experimental tests, while the other serves as the form of validation. The accuracy of identification models is validated through a comparison to the experimental tests on the gas-fired industrial furnace, with the objective of minimizing the mean square error.
Tolerance gaps in wood connections are unavoidable, for reasons of constructability and the effects of natural shrinkage in timber elements with changing moisture content. During a fire, these gaps may lead to a substantial heat transfer to the metal connectors that are considered heat protected being embedded by the wooden components of the connection. Aluminium connectors are popular due to their ease of production and assembly, but they are particularly vulnerable to elevated temperatures. This study investigates the effects of tolerance gaps on the fire performance of aluminium connectors in beam-to-column/wall shear connections. Reduced-scale experiments were designed to study the temperature evolution of aluminium connectors during standard fire exposure for 1 mm and 6 mm tolerance gaps, as well the mitigation effects of additional intumescent fire protection in a 6 mm tolerance gap connection. For the 6 mm gap, the temperature of the connector increased much faster, reaching 286 ± 36°C after 80 min, at which time the connector with a 1 mm gap had only reached 97 ± 1°C. The addition of intumescent protection in a 6 mm gap case led to lower temperatures in the connection, in comparison to an equivalent tolerance gap without protection. Subsequently, two additional loaded fire tests were performed, for 6 mm and 22 mm tolerance gaps without fire protection, to investigate the critical failure mode of the connectors. In these cases, the failure occurred in the connectors at 87 min and 32 min, respectively, when their average temperatures reached approximately 315°C. This study demonstrates the critical influence of gap size on the fire performance of aluminium-wood joints.
Das Ziel des Forschungsvorhabens ist die Schaffung von Grundlagen durch experimentelle und numerische Untersuchungen zur Fortschreibung bauaufsichtlicher Brandschutz-Regelungen im Hinblick auf eine erweiterte Anwendung des Holzbaus. Das Forschungsvorhaben wird institutsübergreifend von der Technischen Universität Braunschweig, der Hochschule Magdeburg-Stendal, dem Institut für Brand- und Katastrophenschutz Heyrothsberge und der Technischen Universität München bearbeitet.
Estimation of design fires and thermal exposure conditions is an important step in structural fire engineering procedures. Mass timber, as a combustible
material, may contribute to the fire intensity, yet there lacks methods to estimate
design fires in compartments with exposed timber. This paper summarizes available
experimental data on the contribution of exposed timber to heat release rate,
describes a simple analytical method to evaluate this contribution, and discusses the
effects on time–temperature curves and required firefighting resources based on a case
study. Results show that the total heat release rate in compartments increases with
the surface of exposed timber. This total heat release rate can be conservatively estimated using empirical relationships for ventilation-controlled burning rate and charring depth. In estimating gas temperature–time curves, both external flaming and
extended fire duration combustion models can be applied to obtain an envelope of
fire severity inside the compartment and for external spread. The proposed assessment approach provides a method to evaluate realistic design fires in timber buildings
and to estimate the water supply required to put out these fires. Accurate modeling
of the contribution of timber to fire severity is important for the design of mass timber construction as well as for the safety of firefighters.
To improve the perceived equivalency of fire testing of combustible and non-combustible members we have proposed a simple modification in the fire resistance test procedure by introducing a lower limit of the heat release rate of the furnace. With this approach the combustion of the sample adds to the heat of the furnace, which is in contrary to current approach and does increase the severity of the test. To quantify the consequences, three wall assemblies were tested with pre-defined heat release curves and modified furnace conditions. The assemblies were timber walls built from two layers of Oriented Strain Boards (OSB, 25 mm thick) on a timber frame with an air cavity (100 mm). A reference experiment with a well-insulated wall was performed to determine the furnace’s minimum heat release rate (HRR) required to maintain the standard (ISO 834) temperature/time curve. The first wall was tested with a standard fire resistance test, and in the 2nd and 3rd wall experiment, the furnace followed the minimum HRR value determined in a reference experiment. In experiment 2, the furnace ventilation matched the air requirements of the burners, and in experiment 3, the furnace was over ventilated. Peak temperatures measured in experiments 2 and 3 exceeded the standard temperature/time relation by 420°C and 600°C, respectively. The assembly’s failure (integrity criterion) was observed after 27 min, 23 min and 14 min of experiments 1, 2 and 3, respectively. The limitations of the approach used related to reproducibility and validity are discussed.
This study presents a three-dimensional finite element model to describe the thermomechanical behaviour of flax chipboards under fire conditions. The model is based on kinetic models considering the thermal degradation during the pyrolysis phase and the evolution of the physico-mechanical properties as functions of temperature. The numerical model is integrated into Abaqus via user subroutines (Umat and Umatht) and applied to the analysis of the fire behaviour of panels made of flax chipboards. Thermogravimetric tests are performed on flax particles to serve for the identification of the kinetic parameters of the pyrolysis models. Once these kinetic parameters are determined, they are integrated into a complete numerical model to simulate the behaviour under fire of flax chipboards on small and large scales. The obtained trends in the predicted values indicate good agreements when compared to the measured values. The simulations show that the numerical model is capable of accurately modelling the thermomechanical transfers taking place within the material during exposure to fire.
Timber is an innovative and sustainable construction material, but its uptake has been hindered by concerns about its performance in a fire. Current building regulations measure the fire performance of timber using the metric of fire resistance tests. In these tests, the charring rate is measured under a series of heat exposures (design fires) and from this the structural stability is deduced. Charring rates are currently only well known for one heat exposure regime (standard fire), which restricts the use of performance-based design. This study aims to study charring rates under a range of design fires. We used a novel multiscale charring model validated at the microscale (mg-samples), mesoscale (g-samples), and macroscale (kg-samples) across different wood species exposed to different heating regimes and boundary conditions. At the macroscale, the model blindly predicts measured in-depth temperatures and char depths during standard and parametric fires with an error between 5% and 22%. Comparing simulations of charring under travelling fires, parametric fires, and the standard fire revealed two findings. Firstly, their charring behaviour differs with maximum char depths of 42 mm (travelling), 46 mm (parametric), and 59 mm (standard fire) at the end of the fire and one (standard fire) to four (travelling fire) charring stages (no charring, slow growth, fast growth, steady-state). Secondly, we observed zero-strength layers (depth between the 200 °C and 300 °C isotherm) of 7 to 12 mm from the exposed surface in travelling fires compared to 5 to 11 mm in parametric fires and 7 mm in the standard fire. Both, therefore, need to be considered in structural calculations. These results help engineers to move towards performance-based design by allowing the calculation of charring rates for a wide range of design fires. In turn, this will help engineers to build more sustainable, economical, and complex structures with timber.
Brandschutzexperten diskutieren derzeit die Gültigkeit von Brandprüfungen für Holzbauteile. Im Raum steht einerseits die allgemeine Aussage, dass brennbare Bauteile in Prüfungen einer von nicht brennbaren Bauteilen abweichenden thermischen Einwirkung ausgesetzt werden. Andererseits wird darauf hingewiesen, dass die sichere Verwendung von flächigen Holzbauteilen (Massivholzbauteile), z. B. Brettsperrholz, durch Normbrandprüfungen nicht geprüft werden kann, da diese Bauteile die Brandlast erhöhen und somit keine Aussagen im traditionellen Rahmenwerk des Feuerwiderstands getätigt werden können. Der vorliegende Beitrag zeigt Übereinstimmungen und Unterschiede zwischen nicht brennbaren und brennbaren Bauteilen in Normbrandprüfungen auf. Es wird gezeigt, dass die thermische Einwirkung für nicht brennbare und brennbare Bauteile in Normbrandprüfungen gleichwertig ist, auch wenn es sich um – wie im Falle von Brettsperrholz – großflächige Bauteile handelt. Die durch brennbare Bauteile zusätzlich im Brandraum verbrennende Brandlast kann durch Normbrandprüfungen nicht direkt ermittelt werden. Hierfür müssen, falls notwendig, andere Methoden verwendet werden, die zum Teil erst in der Entwicklung stehen. Die durch brennbare raumbildende Tragstrukturen zusätzliche Brandlast führt nicht zu höheren Temperaturen im Brandraum, sondern zu einer veränderten Brandeinwirkung an der Fassade. Diesem Umstand wird im Moment in Bauordnungen durch verschiedene Regeln Rechnung getragen.
This paper details a novel method for quantifying irradiation (incident radiant heat flux) at the exposed surface of solid elements during large-scale fire testing. Within the scope of the work presented herein, a type of Thin Skin Calorimeter (TSC) was developed intending for a practical, low cost device enabling the cost-effective mass production required for characterising the thermal boundary conditions during multiple large-scale fire tests. The technical description of the TSC design and a formulation of the proposed calibration technique are presented. This methodology allows for the quantification of irradiation by means of an a posteriori analysis based on a temperature measurement from the TSC, a temperature measurement of the gas-phase in the vicinity of the TSC and a correction factor defined during a pre-test calibration process. The proposed calibration methodology is designed to account for uncertainties inherent to the simplicity of the irradiation measurement technique, therefore not requiring precise information regarding material thermal and optical properties. This methodology is designed and presented so as to enable adaption of the technique to meet the specific requirements of other experimental setups. This is conveyed by means of an example detailing the design and calibration of a device designed for a series of large-scale experiments as part of the ‘Real Fires for the Safe Design of Tall Buildings’ project.
The plate thermometer is a device used mainly to measure temperatures in fire resistance tests according to ISO 834-1 and EN 1363-1 and to measure the so-called adiabatic surface temperature. However, it can also be used to measure incident radiant heat flux (q·″inc) as a simpler, more robust and less-expensive alternative to water-cooled heat flux meters. The accuracy of the measured q·″inc is subject to simplifications in the heat transfer analysis model and uncertainties of parameters such as convective heat transfer coefficients, emissivities and ambient gas temperatures. This study investigates the accuracy of the model itself, isolated from the uncertainties of the physical surrounding, by comparing a simple one-dimensional model to the results of finite element modelling. The so-obtained model includes a heat transfer coefficient due to heat losses of the plate thermometer, found to be KPT = 8 W/m2 K and a heat storage lumped heat capacity CPT = 4200 J/m2 K for an ISO/EN standard plate thermometer. The model is also compared to real field experiments.
This paper shows that the plate thermometer as described in the fire resistance test standards ISO 834-1 and EN 1363-1 can be used for measuring incident radiant flux under ambient conditions as an alternative to water cooled total flux heat metres (HFMs). Measurements with a plate thermometer mounted in the cone calorimeter and exposed to different heat flux levels were analysed as well as simultaneous measurements with total HFMs and plate thermometers in large scale tests. It is shown how the incident radiant flux to a target can be derived from measurements with total HFMs and plate thermometers, respectively, and how well these two methods match. The plate thermometer is therefore deemed to be a practical alternative for measuring thermal conditions including incident radiant heat flux particularly under field conditions. It is, however, recommended that the plate thermometer should be modified when used under ambient conditions to reduce errors.
The measured fire resistance of a structure tested in different furnaces in accordance with ISO 834 may differ considerably. Similarly, the fire resistance of that same structure may be 25% longer when tested in accordance with ISO than it is when tested in accordance with ASTM. These anomalies complicate the evaluation of test results and must be eliminated to reach harmonized international testing.
The heat transfer to a test specimen in a test furnace at high temperature depends primarily on radiant flux rather than convection. Temperature measurement devices used to control furnaces should therefore respond to this type of heating in a way similar to that in which test specimens respond. They should have a large area so that the radiant heat transfer dominates, and they must, at the same time, have a quick thermal response.
The plate thermometer is designed to have these properties. It consists of a thin steel plate, 100 mm by 100 mm and 0.7 mm thick, with an insulating fiber board on one side. A thermocouple is welded to the center of the plate. It should be placed in front of the specimen, with the insulated side facing the specimen. The exposed side will then receive the same radiant heat flux as the specimen.
This paper describes the plate thermometer and gives a basic theoretical analysis of the heat transfer conditions in furnaces. Measurements with the plate thermometer in several furnaces are also reported.
Standard fire resistance tests have been used in the design of structural building elements for more than a century. Originally developed to provide comparative measures of the level of fire safety of noncombustible products and elements, the recent resurgence in engineered timber construction raises important questions regarding the suitability of standard fire resistance tests for combustible structural elements. Three standard fire resistance floor tests (5.9 m × 3.9 m in plan), one on a concrete slab and two on cross‐laminated timber (CLT) slabs, were undertaken to explore some of the relevant issues. The fuel consumption rate within the furnace was recorded during these tests, and the energy supplied from this was determined. An external fuel supply (from natural gas supplied to the furnace) equating to approximately 3 MW was recorded throughout the concrete test, whereas this was about 1.25 MW throughout the CLT tests. The total heat release rate was calculated using carbon dioxide generation calorimetry; this yielded values of approximately 1.75 MW during the CLT tests (ie, an additional energy contribution of approximately 0.5 MW from the timber). This demonstrates that considerably more energy input (by about 1.25 MW) was needed to heat the system when the test sample was noncombustible. A further series of six large‐scale compartment fire experiments (6 m × 4 m × 2.52 m) was undertaken to further explore comparative performance of combustible versus noncombustible construction when the external fuel load is kept constant and is governed by more realistic compartment fire dynamics. For a fuel‐controlled case, the peak temperatures in the compartment with an unprotected CLT ceiling were approximately 200°C higher than in the compartments with a concrete ceiling, whereas for a ventilation‐controlled case, the compartment with a CLT slab ceiling displayed a burning duration that increased by approximately 15 minutes. Potential implications for standard fire resistance testing of combustible specimens are discussed.
The paper aims to explain the differences found in the heat release rate measurements in a large sample of standard fire tests (EN 1363-1). A total of 379 tests of vertical assemblies was investigated, all performed in furnace SPARK of the ITB Fire Testing Laboratory, in 2015-2018. The assemblies were subdivided into two groups-wall assemblies and fire-rated doors. These assemblies were also compared with the results of the test of a wall built with aerated autoclaved concrete blocks that was considered as the benchmark test. It was observed that walls built with highly insulated sandwich panels require less heat to maintain standard thermal exposure conditions (20%-30% less) than their counterparts built from gypsum plasterboard or aluminium and fire-rated glass. In case of doors, it was observed that combustible samples required significantly less heat than the benchmark case (40%-70% less), which indicates that the combustion of the sample inside of the furnace was an additional , significant source of heat release, that may skew the qualitative assessment of their performance in fire. A more in-depth discussion of the results is provided, with some ideas on the direction of further developments in fire testing.
A new more insulated and faster responding plate thermometer (PT) is introduced, which has been developed for measurements particularly in air at ambient temperature. It is a cheaper and more practical alternative to water‐cooled heat flux meters (HFMs). The theory and use of PTs measuring incident radiation heat flux and adiabatic surface temperature are presented. Comparisons of measurements with PTs and HFMs are made. Finally, it is concluded that incident radiation in ambient air can be measured with HFMs as well as with the new insulated type of PT. In hot gases and flames, however, only PTs can be recommended. At elevated gas temperatures, convection makes measurements with HFMs difficult to interpret and use for calculations. However, they can be used in standard or well‐defined configurations for comparisons.
Recently, standard fire resistance testing has been questioned for combustible products. A part of the comments address the thermal boundary conditions and the different thermal exposure of combustible products in comparison to incombustibles. These comments are evaluated in this technical note.
To compare heat flux measurements of combustibles and incombustible products when tested in a furnace, furnace tests were performed. The furnace was controlled by plate thermometers to follow the EN 1363/ISO 834 standard temperature-time curve. It could be proven that (a) the heat flux measurements at the specimens surface behind the plate thermometer (PT) are not higher than in front of the PT. The reason for this is most likely that no flaming combustion is possible near the surface due to the low oxygen content typically for a furnace. It could be further shown (b) that the heat flux measurements when combustibles are tested follow the trend reported in literature for incombustibles. Further, (c) that the lower burner fuel used in furnaces is due to the contribution of the specimen (ca. 30% in the presented tests) and due to the lower thermal inertia (ca. 20% in the presented tests). Finally it can be concluded that the thermal exposure of combustibles and incombustibles is equivalent in furnaces simulating a ventilation controlled fire development for a pre-defined duration.
The critical mass loss rate and critical heat flux for self-extinction of flaming combustion during steady-state burning of timber was measured in this study for a range of timber species. A vertical mass loss calorimeter was used to provide the external heat flux and to measure the mass loss of the timber samples. The results showed that the critical mass loss rate was dependent upon the timber species but did not show a clear dependency with the timber density. Critical mass loss rates and heat fluxes for self-extinction exist for each of the timber species tested for both the solid timber and cross laminated timber (CLT). Debonding of both the char layer and the individual lamella of the CLT caused increased mass loss rates, re-ignition after self-extinction and increased flame lengths. Both char and ply fall-off were observed.
Protective structures are designed explicitly to fulfil a function that in many cases is an extreme event; therefore, an explicit design has to properly and precisely account for the nature of the solicitation imposed by the extreme event. Extreme events such as explosions or earthquakes are reduced to design criteria on the basis of either empirical or historical data. To determine the design criteria, the physical data has to be translated into physical variables (amplitudes, pressures, frequencies, etc.) that are then imposed to the protective structure. While there is debate on the precision and comprehensive nature of this translation, years of research have provided strong physical arguments in supporting these methods. Performance is then quantified on the basis of the structure’s capability to perform its required function. Classified solicitations may then be used to translate performance into prescribed requirements that provide an implicitly high confidence that the structure performs its function. When addressing fire, performance has been traditionally determined by imposing standardized requirements that necessarily attempt to bear a strong relationship with the reality of potential events – the fire performance of a protective structure is thus defined as a fire resistance period. This paper addresses the concept of fire resistance and its relevance to the design of protective structures. The mathematical description of the thermal boundary conditions for a fire is of extreme complexity, therefore simplified approaches, that include the Fire Resistance concept, are currently used. By using classical heat transfer and structural engineering arguments, the work described herein demonstrates that an adequate level of complexity and precision for the thermal boundary conditions and input parameter is fundamental to correctly describe the response of a structure during a fire event. Simple criteria are presented to qualify the relevance of current approaches and to highlight important issues to be considered.
A review is presented of fire studies beginning with the work of Ingberg at the National Bureau of Standards, who attempted to relate the severity of a fire endurance test in the laboratory to the conditions existing during actual building fires. He showed the importance of weight of combustibles per unit floor area as a major factor. He recognized the importance of ventilation in controlling fire behavior but did not specify it as a separate variable. Fujita in Japan is credited with emphasizing the importance of ventilation. His work has been followed and enlarged by others around the world. Ventilation parameters, compartment geometry, and fuel arrangement have been shown to exert a powerful influence. The radiance from a burning building is dependent to a large extent on the nature of the ventilating openings. Fire severity is not well defined, since it depends on the interaction of the temperature-time curve developed during a fire and the thermophysical properties of the materials exposed. There is a great need for further research on the influence of fuel arrangement, building geometry, and ventilation on fires in buildings.
During the latter part of 1966, the author visited 42 organizations in 11 nations of Europe and Asia. These organizations
are engaged in all phases of the fire problem. Here, he summarizes his findings and discusses the strengths and weaknesses
of the fire effort abroad.
Information concerning the power or fuel input into fire test furnaces or other furnaces operating under variable state conditions has been developed. The power or fuel consumption of fire test furnaces depends considerably on the thermal properties of the test specimen, as is indicated by data reported here. L'auteur expose les données existantes sur l'apport de combustible ou la puissance fournie aux fours d'essais ou à d'autres fours fonctionnant dans des conditions variables. Il montre que la consommation d'énergie ou de combustible des fours d'essais dépend fortement des propriétés thermiques de l'échantillon essayé. RES
"Drysdale's book is by far the most comprehensive - everyone in the office has a copy...now including me. It holds just about everything you need to know about fire science." (Review of AnIntroduction to Fire Dynamics, 2nd Edition). After 25 years as a bestseller, Dougal Drysdale's classic introduction has been brought up-to-date and expanded to incorporate the latest research and experimental data. Essential reading for all involved in the field from undergraduate and postgraduate students to practising fire safety engineers and fire prevention officers, An Introduction to Fire Dynamics is unique in that it addresses the fundamentals of fire science and fire dynamics, thus providing the scientific background necessary for the development of fire safety engineering as a professional discipline. An Introduction to Fire Dynamics. Includes experimental data relevant to the understanding of fire behaviour of materials; Features numerical problems with answers illustrating the quantitative applications of the concepts presented; Extensively course-tested at Worcester Polytechnic Institute and the University of Edinburgh, and widely adopted throughout the world; Will appeal to all those working in fire safety engineering and related disciplines.
Calibration of fire resistance furnaces with plate thermometers. Commission of the European Communities, BCR Information
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10. EN 1363-1; Fire resistance tests. General requirements
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