Oxygen Consumption Calorimetry Research Articles

Uncertainties in the use of oxygen consumption calorimetry for heat release measurements in lithium-ion battery fires

Accurate measurement of the heat release from a battery fire is vital for risk management, product development and construction of accurate models. Oxygen consumption calorimetry is the most common method for heat release measurements in experimental fire tests. The strength of the method is that it can be applied to unknown compositions of fuel with sufficient accuracy. Despite that this method is used to estimate heat release from battery fires, the method is subject to discussion. In this work, the method is studied in-depth, and potential errors are structured and quantified. Uncertainties associated with self-generated oxygen and internal heat generation, total gas release from the battery and impact on the heat release calculations, as well as the assumed E-factor (i.e., heat release per unit mass of oxygen consumed), are thoroughly discussed. For a Li-ion battery fire, it is concluded that oxygen consumption calorimetry will exclude internal heat generation and underestimate the total heat released from the external flaming fire by up to 10 %. In addition, high rate of combustion reactions can result in that the measured peak heat release rate is underestimated much more, up to 100 %.

Exhaust flow calibration for a large-scale calorimetry system using tracer gas dilution.

Exhaust flow measurements are a significant source of uncertainty for measurements of heat release rate in large-scale fire experiments. Irregular flow distributions are often present in the exhaust ducts making it difficult to measure flow accurately. Tracer gas dilution (TGD), a measurement method for volume flow, is not sensitive to flow distribution and has been applied to calibrate flow measurement devices at the exhaust ducts of a large-scale open calorimetry system. The in-line calibration reduced the bias in the exhaust flow measurement by as much as 6% improving the overall measurement accuracy of the heat release rate. Experimental results provide evidence that the flow calibration is an improvement over the accepted practice of developing a flow correction from the comparison of oxygen consumption calorimetry with the heat output from a gas burner. The flow calibration is valid for a wide range of flow conditions and decouples the oxygen consumption calorimetry measurement from any error in determining the heat release rate from the gas burner.

A feasible heat release rate estimation approach for fire hazard assessment in green design

New energy harvesting systems in buildings are becoming more attractive in new green buildings. However, the potential fire hazard of the combustible items used in new green building limits their wider application. Fire behaviour of combustible items in new green designs should be studied carefully. Heat release rate of burning combustible items of different materials is important in fire hazard assessment and can be estimated by oxygen consumption calorimetry. An exhaust hood with a fan-duct system was built to collect flue gas. As the burning was likely to be incomplete in building fires, carbon monoxide, carbon dioxide, water vapor and soot would be emitted. Heat release rates of combustible items were estimated by measuring the transient amount of oxygen, carbon monoxide and carbon dioxide collected by the hood. Based on mass balancing, there are at least three equations in terms of mass flow rates of oxygen, carbon monoxide and carbon dioxide in the incoming air and exhaust gas. There are always questions about using which equations because measuring gases in full-scale burning tests is difficult and expensive. These three equations are introduced and compared in this paper. Heat release rates of four selected combustible items were studied as an example case. Accuracy of the results based on the measured oxygen concentration only was similar to the values provided by commercial software. Results from the experimental data are useful in further full-scale burning tests on combustible items in energy harvest systems planning at the moment.

Upward flame spread behaviour of cladding materials on a medium-scale ventilated façade experimental setup with a single combustible wall

A parametric experimental study was performed to characterise the fire spread dynamics in a simplified ventilated façade using a medium-scale testing rig comprised of a non-combustible and a combustible cladding wall (1800 × 600 mm). Three different cavity widths and four different cladding materials were tested. Measurements of the flame height, the incident heat flux on the non-combustible cavity wall and oxygen consumption calorimetry were performed. A strong relationship between flame height and heat release rate was found for the growth phase of the fire. It has been shown that the time for encapsulation failure and subsequent cladding material core ignition decreased as the cavity width was reduced since the heat transfer to the walls was enhanced. The increase in the heat transfer to the opposite wall with all the materials could lead to external heat fluxes above the critical heat flux for ignition of a number of combustible cladding materials. This highlights the importance of considering the interaction of the products used in the façade and its geometry for the design of façade assemblies when accounting for the fire performance of the system. The results also show the need to understand the impact of the interaction between the design variables and the system performance, since the material performance observed at bench-scale may fail to capture the performance in heat transfer and flame spread scenarios observed at a system scale.

CHARACTERIZATION OF THE BURNING OF ORIENTED STRAND BOARDS EXPOSED TO FLAME

Since the methods based on the interaction of a relatively low intensity flame on the lignocellulose sample surface often do not allow measuring the heat release rate (HRR), a procedure using oxygen consumption calorimetry was proposed. The method was applied to OSB samples with dimensions of 320 mm x 140 mm x 25 mm placed in a vertical position. During the measurement, in addition to the HRR, the production of smoke, which was significant after stopping the burner, was also monitored. The average net value of HRR at burner outputs of 3 kW, 4 kW and 5 kW was 2.339 kW and the smoke specific extinction area was in the range of 10.88 m2.kg-1 and 13.19 m2.kg-1.

Experimental study on the combustion characteristics of carbonate solvents under different thermal radiation by cone calorimeter

When a lithium-ion battery is thermally out of control, the internal heat is mainly coming from the mutual reaction of the internal components of the battery. It is well known that the breakdown and combustion of carbonate solvents inside lithium-ion batteries contribute a large part of the heat when thermal runaway occurs. Therefore, it is necessary to analyze the combustion characteristics of several common carbonate solvents. The cone calorimeter was used to test the combustion of four common carbonate solvents and their mixed solution under different thermal radiation conditions. The obtained heat release rate (HRR), mass loss rate (MLR) and total heat release (THR) were used to analyze its combustion characteristics. Meanwhile, the HRR of different carbonate solvent configurations was explored and compared by oxygen consumption calorimetry (OC) and thermochemical theory (TC). The results show that the HRR curve obtained by the TC method and the OC method basically coincide, which confirms the reliability of the OC method to measure the HRR of solvent combustion. The linear carbonates usually burn at an early stage in the combustion process because the evaporation rates of linear carbonates are higher than those of cyclic carbonates. The peak HRR of the solution combustion has a significant drop when the sample contains EC, whether it is under the premise of thermal radiation or without thermal radiation. The external thermal radiation is proved to have a great increasing influence on the peak HRR per unit area and MLR. These tests can be the reference of more detailed analysis of electrolyte reaction during lithium-ion battery fire, and provide a theoretical basis for preventing and restraining the thermal runaway.

Effect of lithium salts LiPF6 and LiBF4 on combustion properties of electrolyte with EC/PC/EMC under different pressures

In this paper, the combustion properties of ethylene carbonate/propylene carbonate/ethyl methyl carbonate (EC/PC/EMC) with LiPF6 or LiPF4 were studied by cone calorimeter under various environmental pressures in Hefei (100.09 kPa), Lijiang (76.11 kPa) and Lhasa (65.23 kPa), respectively. The impact of lithium salts and pressure on the significant fire parameters of electrolyte such as flame temperature, mass loss rate (MLR) and heat release rate (HRR) were analyzed to evaluate the degree of thermal hazard. The experimental results showed that with the decrease of ambient pressure, the peak HRR (pHRR) and total heat release (THR) declined, and the combustion duration increased significantly. In the steady combustion stage of electrolyte pool fire, the mean value of MLR had an exponential relationship with the external pressure. The error of HRR obtained by oxygen consumption (OC) calorimetry and stoichiometric thermochemistry (TC) theory was about 15%.

New In-Flame Flammability Testing Method Applied to Monitor Seasonal Changes in Live Fuel

Improving the accuracy of fire behavior prediction requires better understanding of live fuel, the dominant component of tree crowns, which dictates the consumption and energy release of the crown fire flame-front. Live fuel flammability is not well represented by existing evaluation methods. High-flammability live fuel, e.g., in conifers, may maintain or increase the energy release of the advancing crown fire flame-front, while low-flammability live fuel, e.g., in boreal deciduous stands, may reduce or eventually suppress flame-front energy release. To better characterize these fuel–flame-front interactions, we propose a method for quantifying flammability as the fuel’s net effect on (contribution to) the frontal flame energy release, in which the frontal flame is simulated using a methane diffusion flame. The fuel’s energy release contribution to the methane flame was measured using oxygen consumption calorimetry as the difference in energy release between the methane flame interacting with live fuel and the methane flame alone. In-flame testing resulted in fuel ignition and consumption comparable to those in wildfires. The energy release contribution of live fuel was significantly lower than its energy content measured using standard methods, suggesting better sensitivity of the proposed metric to water content- and oxygen deficiency-associated energy release reductions within the combustion zone.

Experimental comparison of Oxygen Consumption Calorimetry and Sensible Enthalpy Rise Approach for determining the heat release rate of large-scale lithium-ion battery fires

From a fire safety point of view, the burning behavior of lithium-ion batteries is of high interest. The heat release rate (HRR) is the most important fire parameter to analyze the fire hazards of burning objects, so that an accurate determination of it is crucial. In this paper, two different measurement techniques, the Oxygen Consumption Calorimetry (OCC) and the Sensible Enthalpy Rise Approach (SERA) are simultaneously performed in the same calorimeter to measure the HRR of two different types of lithium-ion batteries. HRR values as well as total energies determined by SERA are higher than measured with OCC: The total energy released is about 10–12 times (SERA) and 6–9.5 times (OCC) the electrical stored energy for both battery types, whereas the timescales of the release differ strongly between the types, resulting in maximum HRRs of 3.4 MW (SERA) and 1.5 MW (OCC) for one module of type A and 0.8 MW (SERA) and 0.6 (OCC) of type B respectively. Furthermore, a sensitive dependency of the HRR measurement with SERA on the position of the wall temperature measurement is observed.

Experimental study on combustion parameters and temperature distribution of linear fire under different oxygen concentration in tunnel

Many cables are placed in the underground utility tunnel, which are with greater fire hazards. Once fire occurs in an enclosed tunnel, thermal radiation may ignite the adjacent cables, which will cause cable fire and further expanding of fire scale, and oxygen will be consumed over time. Thus, it's important to investigate cable fire under low oxygen concentration. In this paper, a fire experiment has carried out in a reduced-scale enclosed tunnel with different heights of linear fire near the side wall. The combustion parameters, as well as transverse temperature distribution and maximum ceiling temperature rise under different oxygen concentration are investigated. Based on oxygen consumption calorimetry, the combustion efficiency and heat release rate of each fire source can be obtained. And two formulas to predict transverse temperature distribution and temperature rise under ceiling are proposed based on dimensionless analysis. Results show that different combustion parameters changing under varies oxygen concentrations, two temperature peaks exist in the cross section and the highest temperature is directly above the fire source. Conclusions are given to provide references in fire protection work in utility tunnel.

Comparison of oxygen consumption calorimetry and thermochemistry theory on quantitative analysis of electrolyte combustion characteristics

In this paper, the combustion characteristics of electrolyte containing carbonate and carboxylate solvents ethylene carbonate/dimethyl carbonate/ethyl methyl carbonate (EC/DMC/EMC) and EC/DMC/ethyl acetate (EC/DMC/EA) were studied by using the cone calorimeter. The results showed that when replacing EMC with EA, the flash point of EC/DMC/EA blend increased by 2.2 °C and the ignition temperature rose by 2.1 °C. When the external heat flux gained from 15 kW/m2 to 35 kW/m2, the difference between the peak heat release rate (pHRR) of the two samples widened from 57.3 kW to 111.1 kW, while the relative value did not change significantly, from 19.3% to 20.6%. In addition, the addition of EA increased the fire growth index (FGI) value of the electrolyte by 19.8% on average, which accelerated the fire development process. According to the results of flame temperature, after adding EA, the flame temperature decreased in the whole combustion process at 15 kW/m2, which reduced by 5.3% and 34.1%, respectively in the two steps. As the heat flux increased, the reduction amplitude declined. Thermochemistry (TC) theory was applied to verify the HRR values and change trend by calculating the theoretical heat release from normalized electrolyte molecules, and the results has been compared with those obtained from the cone calorimeter experiments based on the principle of oxygen consumption (OC) calorimetry, while HRR curves exported from the two methods were with the similar value and trend.

Application of Oxygen Sensor for Healthcare to Measure Heat Release Rate Based on Oxygen Consumption Calorimetry

In an oxygen consumption calorimeter system for measuring heat release rate, the CO/CO<sub>2</sub> analyzer and the O<sub>2</sub> analyzer for chemical species analysis of the sampling gas are the main factors that increase the construction cost of the system. In this experimental study, a low-cost device with performance similar to that of the existing high-cost device was developed. To evaluate the contribution of the CO/CO<sub>2</sub> analyzer to the measurement of the heat release rate, the performance of unsteady and steady-state conditions depending on whether CO/CO<sub>2</sub> was measured for diffusion flames with various fire growth rates was examined. As a result, it was confirmed that when only the O<sub>2</sub> concentration was considered, the heat release rate could be measured accurately. Based on these results, the measurement performance of a low-cost O<sub>2</sub> analyzer manufactured using an oxygen sensor for healthcare was verified. As a result of the verification of the low-cost O<sub>2</sub> analyzer for diffusion flames with various fire growth rates, it was confirmed that the relative error was within 10% for unsteady and steady-state fire sources and can be used to measure the heat release rate.

Experimental thermal hazard investigation on carbonate electrolytes using a cone calorimeter

During the thermal runaway (TR) processing of lithium-ion batteries (LIBs), electrolyte would release most of the heat as the main component. Thus, study on the fire risk of electrolyte is conductive to quantitatively evaluate the safety of LIBs. In this work, the combustion characteristics of three kinds of carbonate mixture electrolytes and the composition of residue were investigated. The significant parameters from the cone calorimeter tests reflecting the thermal hazards such as heat release rate (HRR), mass loss rate (MLR) and open cup flash point were measured. The HRR curves at the radiant power of 15 and 25 kW/m2 were more gradual than those at 35 kW/m2 which had one or two apparent peaks. The addition of diethyl carbonate (DEC) increased the HRRs significantly. The applicability of thermal chemistry (TC) theory used to calculate HRR in previous works was studied. The results of TC technique had a disparity with those from the cone calorimeter called oxygen consumption (OC) calorimetry especially for the electrolyte containing DEC, which was proved by thermogravimetry-Fourier transform infrared spectroscopy (TG-FTIR) experimental results, while it is different from the conclusion reported in previous study. The constituent of carbonate electrolytes residue was analyzed by the X-ray Fluorescence (XRF). Element fluorine (F) accounted for over 90% of the residue. The open cup flash point and ignition temperature were determined by the open cup flash point apparatus. The results showed that the fire point was very close to the open cup flash point, and the difference was within 0.1 K.

Thermal Decomposition and Fire Behavior of Carbon Fiber/Nomex Honeycomb Composite

The thermal decomposition and fire behavior of a Carbon fiber/Nomex honeycomb sandwich, used as partition material in aircrafts, was studied using thermogravimetric analysis (TGA) and oxygen consumption calorimetry (Cone Calorimeter). TGA results indicated that the thermal decomposition of the exposed material is conducted in two main stages. The identification of the most probable reaction mechanism, based on TGA tests performed at different heating rates of 5, 10, and 20 °C/min, was conducted for the white decorative skin layer. The Ozawa-Flynn-Wall and the Kissinger-Akahira-Sunose methods and their corresponding iterative techniques were used for the estimation of the kinetic parameters, including activation energy, E (kJ/mol−1), and pre-exponential factor, A (m−1). Both methods as well as the iterative techniques gave similar results. Cone calorimeter tests at several incident heat fluxes between 30 to 70 kW/m2, provided information on the reaction to fire characteristics of the material, including Heat Release Rate, mass loss, CO, CO2, and smoke production. At low heat fluxes, material burning proceeded in one stage while at higher fluxes combustion was carried out in two stages, with higher mass loss. The corresponding two stages observed in the CO production curves indicated incomplete combustion during the first stage and smoldering combustion in the second, which intensified close to and after flameout. Cone Calorimeter results and observations were coupled with thermogravimetric analysis to evaluate and analyze the overall thermal behavior of the material.

Improving the State-of-the-Art in Flow Measurements for Large-Scale Oxygen Consumption Calorimetry.

The accuracy of the exhaust flow measurement contributes significantly to the uncertainty of calorimetry measurements for large fire testing. Less than ideal flow characteristics such as skewed velocity distributions are typical of these large-scale flows and make it difficult to achieve the desired measurement accuracy. Consensus standards for fire testing recommend either bi-directional probes or orifice plates to determine exhaust flow. Both have limited accuracy in the presence of less than ideal flow conditions. Averaging pitot probes are an off-the-shelf technology widely used to monitor flows for industrial processes. They have been utilized in a system of large fire calorimeters to demonstrate differences of less than 5% between heat release rate measurements by oxygen consumption calorimetry and the theoretical heat output from a gas burner. Differences exceeded 5% for a small set of conditions but were still less than 10%. Both levels of agreement are within the confirmation requirements of the consensus standards and were achieved without a system calibration as recommended by the standards. Including this technology as an alternate method to measure exhaust flow would be an improvement to relevant fire testing standards and to the overall accuracy of calorimetry measurements for large fire testing.

The characteristics of a 1 m methanol pool fire

A series of measurements was made to characterize the structure of a 1 m diameter methanol (CH3OH) pool fire steadily burning with a constant lip height in a quiescent environment. Time-averaged local measurements of gas-phase temperature were conducted using 50 μm diameter, Type S, bare wire, thermocouples with a bead that was approximately spherical with a diameter of about 150 μm. The thermocouple signals were corrected for radiative loss and thermal inertia effects. The mass burning rate was measured by monitoring the mass loss in the methanol reservoir feeding the liquid pool. The heat release rate was measured using oxygen consumption calorimetry. The heat flux was measured in the radial and vertical directions and the radiative fraction was estimated, which correspond to previous results.

Inversion for Fire Heat-Release Rate Using Heat Flux Measurements

Abstract In fire hazard calculations, knowledge of the heat-release rate (HRR) of a burning item is imperative. Typically, room-scale calorimetry is conducted to determine the HRRs of common combustible items. However, this process can be prohibitively expensive. In this work, a method is proposed to invert for the HRR of a single item burning in a room using transient heat flux measurements at the walls and ceiling near the item. The primary device used to measure heat flux is the directional flame thermometer (DFT). The utility of the inverse method is explored on both synthetically generated and experimental data using two so-called forward models in the inversion algorithm: fire dynamics simulator (FDS) and the consolidated model of fire and smoke transport (CFAST). The fires in this work have peak HRRs ranging from 200 kW to 400 kW. It was found that FDS outperformed CFAST as a forward model at the expense of increased computational cost and that the error in the inverse reconstruction of a 400 kW steady fire was on par with room-scale oxygen consumption calorimetry.

Comparative Room Burn Study of Furnished Rooms from the United Kingdom, France and the United States

The wide variety in country specific fire codes can dramatically affect the fire safety of home furnishings resulting in more or less escape time from structure fires. This study uses three replicates of identical rooms for each of the countries tested (France, United Kingdom, US) to increase reliability of data for a more reliable comparison. France and the US rely on smolder only furniture flammability standards while the United Kingdom relies on a combination of smolder and open flame ignition test. Each test room contained a 3 cushion couch, chair and flat panel television of identical models/manufacturers purchased from the respective countries. Additionally, each room was fitted with an identical coffee table, end table, curtain, and bookcase obtained from Walmart in the United States and 12 kg of books. All rooms were meticulously set-up to ensure comparability of results. Flat panel televisions were purchased from electronic stores in the three countries, all were 1.4 m (55 inch) Samsung FPD LED models of as similar design as possible in the markets purchased. The couches and chairs were the same Ektorp furniture line of identical color purchased from Ikea. All FPD TVs and furniture appeared to be identical. All room burns were conducted in a standard ISO 9705 room. Heat release was measured by oxygen consumption calorimetry and smoke development by light dispersion in the ventilation duct. Acute toxicity measurements were made using FTIR at two collection points, the door way and at crawling height in the center of the room. Other smoke constituents were measured for concentration of PAH, VOC, SVOCs and chlorinated and brominated dioxins and furans. Two separate collection events were performed, before and after white smoke transitioned to black smoke. The time to transition from white to black smoke for the British furnishings was five times as long as that observed for the French and US models. The same is true of the time to flashover. The average pHHR for the British rooms was 200 KW less than the US and 400 KW less than the French rooms. All rooms had pHHR between 2.5 MW and 3.3 MW. Total smoke produced for the British rooms was half that of the French and US and the Peak Smoke was delayed for the British rooms by approximately 12 min. This study illustrated that the UK standard does provide a significantly better performance for an identical size and shaped couch based on time to pHHR, pHHR, time to peak smoke, and total smoke. In addition, the chemical composition of the smoke generated in the room burns featuring UK furniture were less acutely toxic based on HCN and CO emission. The time to toxic levels for these gases was delayed 15 min. The French and US rooms reached 1200 and 1600 ppm for HCN at the doorway in 6 min. The chronic toxicity of the UK rooms also appears to be less based on the lower molecular weight and lower concentration of PAH produced. These results directly contradict results published by Stec and Hull. The condition of the test do affect the results. It is critical to test under realistic conditions to be able to predict the performance of materials in home fires.

Detailed Derivations of Formulas for Heat Release Rate Calculations Revisited: A Pedagogical and Systematic Approach.

The derivations of the formulas for heat release rate calculations are revisited based on the oxygen consumption principle. A systematic, structured, and pedagogical approach to formulate the problem and derive the generalized formulas with fewer assumptions is used. The operation of oxygen consumption calorimetry is treated as a chemical flow process, the problem is formulated in matrix notation, and the associated material balances using the tie component concept commonly used in chemical engineering practices are solved. The derivation procedure described is intuitive and easy to follow. Inclusion of other chemical species in the measurements and calculations can be easily implemented using the generalized framework developed here.

Experimental study on heat release rate measurement in tunnel fires

SummaryKnowledge 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.