Laboratory Fire Tests Research Articles

Remote Sensing of the Light-Obscuring Smoke Properties in Real-Scale Fires Using a Photometric Measurement Method

AbstractA new photometric measurement method for the determination of temporally and spatially resolved light extinction coefficients in laboratory fire tests was recently presented. The approach relies on capturing the change in intensity of individual light sources (LEDs) due to fire smoke using a commercially available digital camera. Comparing the results for red light LEDs to measurements of the well-established MIREX system indicates the model is capable of capturing the investigated phenomena. However, a significant underestimation of this reference measurement taken in the infrared range is inconsistent with the expected increase of the extinction coefficients with lower wavelengths. In the context of new experimental investigations, this deficiency was remedied by evaluating multible colour channels of RAW image data instead of the previously used JPG files. Furthermore, extending the experimental setup by several LED strips as well as a second camera allows to verify the hypothesis of a homogeneous smoke layering. The study covers eight experiments including n-heptane fuel in style of the well documented EN 54 TF 5 testfire as well as two additional experiments with an n-heptane-toluene mixture. Considering spatial resolution as well as the high reproducibility of the results, the method appears to be a convenient tool for the validation of numerical visibility models. Nevertheless, a sensitivity analysis identified uncertainties that need to be addressed in upcoming investigations to further improve the accuracy.

Novel microencapsulated liquid fire extinguishers with a nanomodified microcapsule shell

A new process has been developed for the microencapsulation of ecologically safe and highly effective fire extinguishers, including the perfluoroketone Novec 1230 (whose Russian analog is Khladon PFK-49), which has enhanced stability for use as a basic functional component in fire-extinguishing polymer materials. When Freons are microencapsulated via common methods, an intense loss of the liquid core of the microcapsule in the course of drying and storage via diffusion through the shell occurs. The stabilization effect was attained through modification of the microcapsule shell material via addition (at the stage of shell formation) of nanoparticles of the mineral layered filler montmorillonite. The processes of thermal degradation of the resulting microcapsules have been studied and a substantial improvement in stability (reduced permeability of the shell) and, hence, the possibility of their application has been shown. Laboratory fire tests of materials were performed, and the high effectiveness of fire extinguishment by microencapsulated perfluoroketone and the fire-extinguishing polymer material has been demonstrated.

Accuracy (Trueness and Precision) of Cone Calorimeter Tests with and Without a Vitiated Air Enclosure

Over the last few years, new many laboratory fire tests have been developed. One such test is the controlled atmosphere cone calorimeter (CACC). Until now this bench-scale test has not been standardized and the device design differs from one laboratory to another. These differences can affect measurement accuracyaaAccuracy: The closeness of agreement between a test result and the accepted reference value. (truenessbbTrueness: The closeness of agreement between the average value obtained from a large series of test results and an accepted reference value. and precisionccPrecision: The closeness of agreement between independent test results obtained under stipulated conditions.) and direct comparison of literature results is difficult. No studies have been conducted to understand the effect of the design on the fire behaviour of materials and measurement accuracy in the CACC. The present publication focuses on these effects under ambient and non-ambient oxygen conditions. Several designs were investigated using Poly(methyl)methacrylate (PMMA) as the test material. Statistical analyses were performed in some cases to assess the data. The results are presented and discussed.

Angular variation of fire rate of spread

Laboratory fire tests were performed in still air, for variable inclinations (10°, 15°) and fuel bed dimensions (1.28×2.50–3.0×4.6m2), with homogeneous fuel beds of pine needles and pine wood excelsior. The fire ignition was made at a point, along a closed line with no fuel inside and along a straight edge of the fuel bed. The tests were recorded with an infrared camera and various techniques were developed to implement direct and indirect empirical methods of construction of the ‘orientation function’ of the fire in the given fuel bed and ambient conditions, showing how the rate of spread of a steady straight fire front depends on its orientation on the terrain. The direct method uses a set of straight fire fronts with various orientations whereas the indirect method uses essentially a point ignited fire front. Contrary to what is assumed in BehavePlus model, the orientation function is observed to depend significantly on the properties of the fuel bed. In all tests with closed fire fronts, the full steadiness required by the indirect method was not achieved (namely, at the head of the front), although, for slope angle of 10°, the corresponding errors induced on the orientation function were small.

Modelling of hydrogen cyanide formation in room fires

A chemical kinetics model for calculation of the formation of hydrogen cyanide (HCN) has been made. The combustion of a mixture of methylamine and ethylene has been modelled using the stationary laminar flamelet concept. The flamelet calculations are based on several thousand elementary reaction steps including the chemical kinetics of HCN in combustion. The flamelets for both cold (293K) and hot (1000K) combustion product recycling have been calculated. The effect of strain is also included in the flamelet calculations. Scalar dissipation rates from 0.01s−1 to extinction values have been varied. Also the effect of radiation is included in the flamelet state relationships.Separate flamelet sets for various levels of radiation, from adiabatic up to 30% radiation losses, incremented by 1%, have been made. In the flow field calculation, the flamelet options may be used either as adiabatic, constant radiation or an interpolation between flamelet sets of different radiation.The chemical kinetics model, incorporated into a Reynolds-Averaging Navier–Stoke (RANS) type CFD code, has been used to simulate two laboratory fire tests of the combustion of nylon. Changing the size of the opening in the test room varied the ventilation between the two tests. Flamelet sets for a mixture of methylamine and ethylene with nitrogen content close to that of nylon were used in these simulations. The simulations were made with and without recycling the combustion products back to the fire.The calculations show that recycling of the combustion products to the fire increases the formation of HCN and CO. Similarly, a lowered ventilation rate increases the formation of these species. The calculated temperatures and main species concentrations, including HCN, agree reasonably well with the trends in the laboratory measurements.

Prediction of fire resistance of concrete filled tubular steel columns using neural networks

A functional relationship between the fire resistance of a concrete filled steel column and the parameters which cause the fire resistance is represented using an artificial neural network. Experimental data obtained from previous laboratory fire tests are used for training the neural network model. The model predicted values are compared with actual test results. The results indicate that the model can predict the fire resistance with adequate accuracy required for practical design purpose. The developed neutral network can be used to predict the fire resistance of similar columns under fire by observing various factors influencing the resistance such as: (a) structural factors, (b) material factors, and (c) loading conditions. The structural engineer is required to provide the magnitude of these influencing factors as inputs to the neural network and the network will predict the fire resistance, based on the combined effect of these factors. This system can be used by structural engineers to predict the resistance of fire in similar concrete filled steel columns without conducting costly fire tests, by using the known parameters such as column dimensions, column height, and loading conditions.

Evaluation of the fire‐retardant properties of zinc hydroxystannate and antimony trioxide in halogenated polyester resins using the Cone Calorimeter method

AbstractAn investigation of the burning behaviour of a series of halogenated polyester resin formulations has been carried out using the Cone Calorimeter technique. The data obtained clearly indicate that zinc hydroxystannate (ZHS) is more effective than antimony trioxide (Sb2O3) in reducing the average and peak rates of heat release in a chlorinated resin and in decreasing the peak rate of heat release in a brominated resin. The decreases in average heat release rate in the brominated resin are similar for ZHS and Sb2O3. Hence, at an addition level of 2 phr (parts per hundred of resin), ZHS reduces the average heat release rates of a chlorinated and a brominated resin by 41% and 26%, respectively, and the peak heat release rates of the same resins by 38% and 39%, respectively. The degree of smoke suppression exhibited by ZHS in these Cone experiments is significantly greater than that given by Sb2O3. In general, the correlation between Cone Calorimeter data and results obtained using other laboratory fire tests (UL‐94, LOI) is poor, except in the case of smoke density measurements, where the correlation with NBS Smoke Box data is remarkably good. No correlation is observed between the measured values of CO and CO2 output by different test methods, although it is now generally considered that small‐scale fire tests cannot be used to predict gaseous concentrations in real‐fire situations.

Flame‐Retarded polypropylene: A comparison of large‐ and small‐scale tests

AbstractThis paper describes work carried out on flame‐retarded polypropylene comparing results on selected small‐scale laboratory fire tests with those obtained on a larger‐scale test designed to simulate the typical real life hazard situation. In the latter test a number of important parameters such as heat build‐up, Hame spread, smoke development and gas evolution were assessed. The results indicate that there is need to use both types of tests to gain a fuller understanding prior to using new materials. An assessment based on small‐scale tests alone could be misleading and allow the use of potentially hazardous material in the particular application involved.