A guide to characterizing heat release rate measurement uncertainty for full‐scale fire tests

Accurate heat release rate measurements provide essential information to defining the fire safety characteristics of products. The size, complexity, and cost of full‐scale fire tests make achieving accurate and quantitative results a serious challenge. A detailed uncertainty analysis of a large‐scale heat release rate measurement facility is presented as a guide to the process of estimating the uncertainty of similar facilities. Quantitative heat release rate measurements of full‐scale fires up to 2.7 MW were conducted using the principle of oxygen consumption calorimetry. Uncertainty estimates were also computed for the heat input measurements from a well‐controlled natural gas burner. The measurements of heat input and heat release rate were performed independently, and the discrepancy between the two was well within the uncertainty limits. The propagation of uncertainty was performed at the level of voltage and temperature measurements, which avoided using mutually dependent measurement parameters. Reasons for the significant contribution to the combined uncertainty from the oxygen concentration and exhaust flow measurements are demonstrated. Also presented is a first‐order effort to account for the uncertainty due to factors in full‐scale fire tests such as operator error and environmental influences that are not modeled by the heat release rate equation. Published in 2008 by John Wiley & Sons, Ltd.     

Uncertainty analysis of heat release rate measurement from oxygen consumption calorimetry

Oxygen consumption calorimetry remains the most widespread method for the measurement of the heat release rate from experimental fire tests. In a first step, this paper examines by theoretical analysis the uncertainty associated with this measurement, especially when CO and soot corrections are applied. Application of theoretical equations is presented for chlorobenzene which leads to high values of CO and soot yields. It appears that the uncertainty of CO and soot corrections are high when the fuel composition is unknown. In a second step, a theoretical analysis is provided when the simplest measurement procedure is used for oxygen consumption calorimetry. The overall uncertainty can be dominated either by the uncertainty associated with the oxygen concentration, the assumed heat of combustion, the fumes mass flow rate or the assumed combustion expansion factor depending on the oxygen depletion. Copyright © 2005 John Wiley & Sons, Ltd.     

Modelling of heat release rate in upholstered furniture fire

Many fatal residential fires started from burning upholstered furniture, and so upholstered furniture fire has been studied rather extensively in developed countries. As many upholstered furniture were made in China, the hidden fire risk should be studied more. In this paper, full‐scale experiments on the burning of upholstered furniture manufactured in China were conducted and analyzed. The oxygen consumption method was used to measure the heat release rate in a room calorimeter. An ignition source of a 20‐kW gasoline pool fire of 0.2‐m diameter was used to test square foam cushions and 4‐seater sofas. A model of heat release rate predicting upholstered furniture fire in a room was developed on the basis of earlier Swedish works. Results were then used to justify the application of the Combustion Behaviour of Upholstered Furniture model to predict the heat release rate of furniture manufactured in China. The numerical values of key parameters in the model were determined. It is proposed to build up a database that can be used to model heat release rates upon burning furniture. Detailed procedures are illustrated in this paper.     

Heat release rate determination of pool fire at different pressure conditions

This research deals with the experimental determination of the heat release rate (HRR) of n‐heptane pool fire at different pressure conditions based on oxygen consumption method. The method, initially developed for open atmosphere fires, is modified for pool fires in ventilated chamber under different pressure conditions. The calculation equation of the HRR with consideration of ambient pressure is presented. The experiments are performed in the large‐scale ventilated altitude chamber of size 2 × 3 × 4.65 m under series of pressure, 24, 38, 64, and 75 to 90 kPa. Based on the experimental data, the effects of pressure on the mass burning rate and HRR are discussed; meanwhile, the calculation method of HRR is verified. The results show that the mean mass burning rate at the steady burning stage increases exponentially with pressure as , with α = 0.68. The maximum HRR increases from 27 to 63 kW as the pressure rises from 24 to 90 kPa. It is concluded that the ambient pressure has a significant effect on the fire HRR and will further influence on other fire parameters.     

Development of the cone calorimeter—A bench-scale heat release rate apparatus based on oxygen consumption

A new bench-scale rate of heat release calorimeter utilizing the oxygen consumption principle has been developed for use in fire testing and research. Specimens may be of uniform or composite construction and may be tested in a horizontal, face-up orientation, or, for those which do not melt, in a vertical orientation. An external irradiance of zero to over 100 kW m^?2 may be imposed by means of a temperature-controlled radiant heater. The rate of heat release is determined by measuring combustion product gas flow and oxygen depletion, while the mass loss is also recorded simultaneously. The instrument has been designed to be capable of higher accuracy than existing instruments and yet to be simple to operate and moderate in construction cost. The instrument is thermed a ‘cone calorimeter’ because of the geometric arrangement of the electric heater.     

Steady heat release rate by the moment–area method

A simple mathematical procedure is described for computing temporal averages of heat release rate (HRR) data from the moments and area of the history. The moment–area method was used to calculate average HRRs for over 200 specimens having a wide range of chemical composition and sample thickness tested on a bench‐scale fire calorimeter at various external heat fluxes. The average values of HRR obtained by the moment–area method are essentially independent of sample thickness and are potentially useful for ranking material flammability and determining material combustion properties. Published in 2007 by John Wiley & Sons, Ltd.     

Rate of heat release by oxygen consumption in an open test arrangement

Equipment has been developed for measuring the rate of heat release from building materials in an open test arrangement. The method is based on an oxygen consumption technique. A vertical sample is placed under an open hood in which the combustion gases and a certain amount of air are collected. The decrease in oxygen concentration and the mass flow of the gases are measured in the exhaust duct. The rate of heat release is then calculated. The equipment has been calibrated with good agreement between input and measured effects. The total response time for the system is 10s. The method has been used for testing building materials at radiation intensities up to 5W Cm^?2. It is able to distinguish between different board materials, and the repeatability is good, The paper describes the equipment, including the weighing of a burning sample and the selection of test condition. Smoke and gas analysis can be added when desirable. Some test results with building materials are also presented.     

An investigation on compartment fires with plywood cribs

An experimental investigation has been carried out for the burning of plywood cribs in a compartment under different ventilation conditions and two different crib patterns. A total of four experiments were conducted. Of them, three experiments were performed: the burning of regular crib pattern for 0%, 10%, and 100% compartment door opening. The fourth experiment was conducted for the staggered crib pattern with 100% door opening. Several measurements were made during experiments that include the flame temperature, ceiling temperature, total heat flux, outgoing gas temperatures, and heat release rate to investigate the burning characteristics and compartment environment. The rate of increase of heat release rate during growth period for staggered pattern crib was 11.5 kW/min, whereas for regular pattern crib, it was 8 kW/min. However, the peak heat release rate was only 15 kW higher as compared with that of the regular pattern crib. Increasing the ventilation to 10% and 100% has resulted in increase in the heat release rate by 61.6% and 77.4%, respectively. The compartment gas temperature and the total heat flux were highest for 10% door opening, whereas no significant changes were observed in flame temperatures with different ventilation conditions as well as crib pattern. Copyright © 2016 John Wiley & Sons, Ltd.     

Estimation of heat release rate based on analysis of flame spread behavior in mattresses

To investigate the fire danger of mattresses, combustion experiments were conducted with a mattress installed at different heights above the floor to better understand their combustion behavior. The installation height was varied because the height of a mattress varies depending on the bed frame, and the combustion behavior is expected to change with the installation height. Experiments with a mattress installed at 0–515 mm above the floor revealed that the fire growth was faster, and the maximum heat release rate (HRR) increased with installation height. In contrast, in a series of experiments where a mattress was installed above a water pool, the flame spread rates and HRR histories were comparable for all installation heights. This demonstrate that the combustion behavior of the mattress was affected by the combustion of the molten mattress material that dropped to the floor, and this effect was influenced by the mattress installation height. Furthermore, we analyzed the HRR per unit area of mattress construction material using cone calorimeter tests to mimic the combustion taking place on the floor. Combining these results with the relation between the length of the burning part of a mattress at the front of flame spread and the HRR, we proposed a model for predicting the HRR history of mattress for a flame ignition at the center of its longitudinal side. The derived predictive model for the HRR history of mattress combustion emphasize that it is necessary to understand factors such as the intense radiant heat from the pool fire.     

Study on the heat exhaust coefficient and smoke flow characteristics under lateral smoke exhaust in tunnel fires

The heat exhaust coefficient and smoke flow characteristics under lateral smoke exhaust in tunnel fires were studied in this paper. Through the dimensional analysis, the dimensionless relationship between the heat exhaust coefficient, heat release rate, exhaust vent size, and exhaust velocity was obtained. In addition, this paper also studied the effect of the lateral exhaust vent on the smoke flow field. Results showed that the lateral smoke exhaust caused strong air entrainment on the downstream of the exhaust vent and boundary layer separation on the upstream of the exhaust vent. As the exhaust velocity increased, the degree of air entrainment gradually increased, and the smoke layer near the exhaust vent gradually became thinning and plug‐holing phenomenon occurred; meanwhile, the boundary layer separation would be suppressed or disappear, but the increase of the heat release rate would enhance the boundary layer separation. As the exhaust vent got narrower, the air entrainment downstream of the exhaust vent was reduced, and the boundary layer separation also got weaker.     

The calculation of the heat release rate by oxygen consumption in a controlled‐atmosphere cone calorimeter

The standard cone calorimeter according to ASTM E 1354 and ISO 5660 enables reaction‐to‐fire tests to be performed in ambient atmospheric conditions. A controlled‐atmosphere chamber modifies the standard apparatus in a way that allows tests to be performed in nonambient conditions as well. The enclosed chamber is placed underneath the standard exhaust hood and does not have a closed connection to the hood. With this open arrangement, the exhaust gases are diluted by excess air drawn in from the laboratory surroundings. Heat‐induced changes in the consequential dilution ratio affect the calculation of fire quantities and, when neglected, lead to deviations of up to 30% in heat release rate. The paper introduces a test protocol and equations to calculate the heat release rate taking dilution effects into account. A mathematical correction is shown that compensates for the dilution effects while avoiding extensive mechanical changes in the equipment. Copyright © 2013 John Wiley & Sons, Ltd.     

Experimental determination of fire heat release rate with OC and CDG calorimetry for ventilated compartments fire scenario

This research deals with the experimental determination of the heat release rate (HRR) of fires in mechanically ventilated compartments based on oxygen consumption (OC) and carbon dioxide generation (CDG) calorimetry. It proposes formulations for fire in force‐ventilated compartments on the same basis as the relations established for hood calorimetry in an open atmosphere but considering inertia and unsteady behavior of the fire via the time variation mass of O₂ and CO₂ in the compartment. The value of the new formulations of HRR has been tested in two series of propane gas fire experiments performed in a large‐scale facility. The first series involves a fire scenario with one compartment, and the second series, a fire scenario with three compartments connected to each other by doorways. In the first test series, the OC and CDG formulations for HRR are assessed. In the second test series, the OC and CDG formulations are presented with two approaches to definition of the control volume: approach involving three rooms and the flow rate in the ventilation network and approach involving only the fire room and the flow rate through the doorways. On the basis of the fire experiments considered, the most accurate method (accuracy to within 10%) for determining the HRR is the CDG formulation with approach for the control volume without considering the flow rates at the doorways. This analysis points out the different features of each method (OC and CDG) and thoroughly discusses their advantages and drawbacks. The overall analysis allows guidelines to be formulated for fire HRR calculation in confined and ventilated compartments. Copyright © 2013 John Wiley & Sons, Ltd.     

Temperature effects on the mass flow rate in the SBI and similar heat‐release rate test equipment

In various medium‐to‐large‐scale fire test equipments like the ISO room corner test (RC), and more recently, the single burning item test (SBI) the mass flow rate measurement of the combustion gases plays a key role in the determination of the heat‐release rate and smoke‐production rate. With the knowledge of the velocity profile and the temperature of the flow, the mass flow rate is obtained by measuring the velocity on the axis of the duct. This is done by means of a bi‐directional probe based on the pitot principle. However, due to the variation of the mean temperature and the temperature gradient in any cross section of the duct, introduced by ever changing combustion gas temperatures, the velocity nor the density profile are constant in time. This paper examines the resulting uncertainty on the mass flow rate. Copyright © 2006 John Wiley & Sons, Ltd.     

Experimental study of the burning behavior of n‐heptane pool fires at high altitude

The same configured calorimeters were built in Hefei (99.8 kPa) and Lhasa (66.5 kPa), respectively. Four sizes of round pans with diameters of 10, 15, 20, and 25 cm were adopted to study the effect of high altitude on the burning behavior of liquid pool fires. Analysis on the burning rate obtained in this study and in the literature at different altitudes indicates that pressure fire modeling performs better than radiation fire modeling in correlating the burning intensity (burning rate per unit area) with pressure and pool diameter for cases under low ambient pressure. The study also shows that heat release rate and combustion efficiency decrease at higher altitude. For medium pool fires, the burning intensity and heat release rate are proportional to D^5/2, thus the combustion efficiency being independent on pool sizes but decreases at higher altitude by a factor approximate to the pressure ratio. Copyright © 2014 John Wiley & Sons, Ltd.     

Effects of passenger blockage on smoke flow properties in longitudinally ventilated tunnel fires

This paper investigates the effects of passenger blockage on smoke flow properties in longitudinally ventilated tunnel fires. A series of numerical simulations were conducted in a 1/5 small-scale tunnel with the different heat release rates (50-100 kW), longitudinal ventilation velocities (0.5-1 m/s), passenger blockage lengths (2-6 m), and ratios (0.17-0.267). The typical smoke flow properties in different tunnel fire scenarios are analyzed, and the results show that under the same heat release rate and longitudinal ventilation velocity, the smoke back-layering length, maximum smoke temperature, and downstream smoke layer height decrease with increasing passenger blockage length or ratio. The Li correlations can well predict the smoke back-layering length and maximum smoke temperature in tunnel fire scenarios without the passenger blockage. When the passenger blockage exists, the modified local ventilation velocity that takes the blockage length and ratio into account has been proposed to correct the Li correlations. The smoke back-layering length and maximum smoke temperature with the different blockage lengths and ratios can be predicted by the modified correlations, which are shown to well reproduce the simulation results.     

Flame retardants and heat release: review of data on individual polymers

This is part of a project considering whether flame retardants affect polymer heat release, a critical issue to assess whether adding flame retardants decreases fire hazard. The work investigated the following. (1) Fire properties affecting fire hazard, confirming that heat release rate is the key fire property most strongly influencing fire hazard. (2) Ways to assess heat release and whether full‐scale fire heat release rate can be predicted from small‐scale test results, confirming that cone calorimeter and Ohio State University data are adequate to predict full‐scale heat release. (3) Analysis of key 1988 NBS/NIST study comparing the fire hazard of flame retarded products versus non‐flame retarded products for the same application. This confirmed that the study demonstrated that flame retardants lower fire hazard and that the levels of additives in the flame retarded products used were not excessive. (4) Review of studies investigating effects of flame retardants on various polymeric systems. The overall conclusion is that flame retardants does indeed improve fire safety (when used appropriately) primarily because they decrease heat release. Part 2 of the project (separately) considers the key polymers that need to be potentially flame retarded and reviews recent studies on effects of flame retardants on heat released by such polymers. Copyright © 2014 John Wiley & Sons, Ltd.     

多因素影响下的煤低温氧化特性试验研究

为研究氧浓度、粒度和挥发分对采空区遗煤低温氧化过程的影响,利用油浴式程序升温试验装置设计了煤低温氧化试验,研究了不同影响因素条件下煤的耗氧速率和放热强度,验证了氧浓度、粒度和挥发分等对煤低温氧化特性的影响,通过对试验数据分析,得到了煤低温氧化特性受各因素影响的变化规律。试验结果表明:在一定范围内,氧浓度的增加会加快煤的耗氧速率,提高反应的放热强度,促进煤的氧化,但不会改变氧化反应的趋势;粒度较大的煤耗氧速率低,反应释放的热量小,氧化过程缓慢且强度较低;煤的挥发分降低后,耗氧速率和反应的放热强度也随之减小,其自燃临界温度将显著提高。     

A review of fire growth and fully developed fires in railcars

A literature review was performed to assess the state of knowledge of the effects of railcar interior finish materials on fire growth and fully developed fires from railcars. An overview is provided on standards and requirements currently used to regulate interior finish materials. Following this review, an overview of experimental and computational research is provided on railcar interior finish flammability and its impact on fire growth. A survey of the research on fully developed fires and the potential heat release rates of railcars is then presented. This includes scaling laws, experimental research, and model development. Future research recommendations are then presented.     

Hazards of combustion products: Toxicity,opacity, corrosivity,and heat release: The experts' views on capability and issues

The science of understanding how fires burn and how heat smoke and gases are generated and affect people has progressed substantially in the last half century. The principles of facility design for life safety in fires have reached a degree of maturity. Standards and code provisions for fire detection, suppression and control have become the norm. Real‐scale (or nearly real‐scale) test methods for the flammability of furnishings and interior finish have been established. In addition, some tests have been developed that measure the results of the burning of a small sample from the finished product. Yet, while there have been numerous small‐scale apparatuses developed for assessing the generation of heat, toxic gases, and visible or corrosive smoke, these facets of life and property safety have not found widespread inclusion in building and fire codes. There has been an invigorated effort in ISO TC92 SC3, Fire Threat to People and the Environment, to develop a coherent and comprehensive set of fire safety standards and guidance documents for life safety. Smaller efforts are ongoing within some national and regional standards bodies. In November 2008, experts in this field gathered at The Royal Society in London to hear papers that captured the state of the art and to discuss where we might go from here. This paper summarizes the papers and the discussion from that meeting. Copyright © 2010 John Wiley & Sons, Ltd.     

Heat release rates of modern residential furnishings during combustion in a room calorimeter

Results are presented from a number of fire experiments that were conducted in a room environment to study the fire characteristics of typical residential furnishings and assist in the design of a subsequent phase of a project involving fully furnished room fire experiments. The experiments were conducted in a 16‐m² test room (with dimensions 3.8 m wide × 4.2 m long × 2.4 m high), which had a 1.5 × 1.5‐m window opening. The furnishings tested included mattresses, bed clothes, bed assemblies, upholstered seating furniture, clothing arrangements, books, plastic audio/video media and storage cases, toys, shoes, and a computer workstation setup. The smoke (gaseous products of combustion) from the room was collected using a hood system in order to measure the heat release rate (HRR) and optical density of the smoke. The test room was instrumented with load cells, heat flux gauges, thermocouples and velocity probes in order to take the following measurements: mass loss, total heat flux on gauge‐installed flush with the internal surfaces (floor, walls, and ceiling), temperatures at numerous locations, and gas velocities in the window opening. Twin‐size mattresses produced peak HRRs of approximately 3800 kW, and the maximum room temperature was approximately 980°C. The HRRs of bed assemblies of various sizes and configurations ranged from 1800 kW for a twin‐size bed to 6250 kW for a bunk bed. The maximum temperature and heat flux recorded in the experiments were 1071°C and 221 kW/m², respectively. Upholstered chairs and sofas had HRRs ranging from 630 kW for an ottoman to 3360 kW for a two‐seat sofa. In tests with clothing, toys, shoes, books, a computer workstation, and CD/DVD media, the peak HRRs ranged from 440 kW for a bookcase to 2045 kW for toys. Furnishings containing a large proportion of rigid thermoplastic plastics, such as shoes and media cases, produced very dense smoke even at low HRRs. The effect of parameters such as bed clothes, mattress type, foundation type, bed assembly and chair size, material composition, and fuel package arrangement was evident in the results. Because the room dimensions and wall lining materials remained constant, temperatures were linearly proportional to the peak HRR (and exposure time) until the ventilation limit (approximately 4100 kW) was reached. Copyright © 2014 John Wiley & Sons, Ltd.