No abstract is provided for this article.
This contribution reports an approximate analytical model to predict transient mass flux and ignition time of translucent fuel, black poly(methyl methacrylate) (PMMA), subjected to a time-dependent incident heat flux, atb , where t is time and a and b are constants. The model can be easily extended to other non-charring translucent solids. The model takes into account in-depth absorption of thermal radiation in the condensed phase, which is typically ignored in the analytical formulations. Both critical temperature and critical mass flux were employed as the ignition criteria to examine their effects on the predictions. The model was validated using exact numerical solutions and experimental data, and compared with earlier analytical models based on the assumption of surface absorption. Linear and quadratic heat fluxes were considered for validation and discussion. The results show that surface absorption accelerates the pyrolysis process and leads to higher mass flux and shorter ignition time with respect to the in-depth absorption case. The discrepancy between the predicted transient mass fluxes of these two absorption modes increases with increasing a. The ignition heat flux increases with increasing a and decreases with increasing b for both surface and in-depth absorption cases. However, the critical energy is independent of heat flux in in-depth absorption scenario. Furthermore, parametric studies of in-depth absorption coefficient and critical mass flux were conducted to investigate their effects on the quality of the model predictions. Also, the equivalent ignition temperature was calculated and compared with the experimental values. It is expected that the developed model will find its use in performance-based design applications.
Methane explosion in underground coal mine is one of the most deadly hazards to the miners and the surrounding environment. An improved analytical hierarchy process (IAHP) was developed to investigate the influencing factors of methane explosion quantitatively. IAHP was validated by statistical data, showing its advantages in reducing bias. Both IAHP results and statistical data indicated that electrical spark, blasting and friction spark were the leading ignition sources. Blasting operation, digging process, explosive charge and gas detect procedure showed the highest influencing weights to methane explosion. A case/example was provided to determine the safety level of an underground coal mine. Implementations were provided to avoid methane explosion in underground coal mines, such as avoiding high methane concentration (10–15vol.%), taking care of rocks with more than 30% quartz and larger than 70μm particle size, and using high melting point tool/equipment, and limiting coal pick speed within 1.5m/s.
No abstract is provided for this article.
No abstract is provided for this article.
Toxic gases are significant in fire risk evaluation. Previous studies have focused on their characteristics by piloted ignition. Spontaneous ignition is a complex phenomenon that combustible materials are ignited by internal heating, without the spark plug. Comparing with piloted ignition, process of spontaneous ignition is much closer to the development of real fire. Therefore, carbon monoxide (CO) of six species of wood samples under external heat flux by spontaneous ignition in a cone calorimeter was investigated. Results showed that influence of thickness to peak CO release rate can be ignored, but time to peak is postponed with a higher thickness. Peak CO release rate decreases with a higher external heat flux, but the decrease is not obvious when heat flux increases from 50 to 75kW/m2. The flame also has influences to the CO release rate. A sharp decrease of CO release rate happens shortly after ignition and a second peak is near the end of the experiment. Moisture reduces CO release rate and postpones time to peak CO release rate. An empirical model of CO yield of wood samples under different external heat flux and moisture content by spontaneous ignition was developed. This empirical model can be used not only for fire risk evaluation, but also for modeling input and validation.
Timber is one of the most frequently adopted combustible materials in the built environment. The thermal properties are the determining factors for assessing the fire risk in a building. The main thermal properties of timber and their char are reviewed, especially those temperature-dependent and moisture-dependent properties, including kinetic properties, ignition properties, thermal conductivity, specific heat capacity, effective heat of combustion and thermal diffusivity. The study has collected and summarized various thermal properties data and empirical models of hardwood and softwood with different mass percentages in cellulose, hemicellulose and lignin, as temperature increases. The average ignition temperature and effective heat of combustion of softwood are about 12.9% and 9.5% higher than those of hardwood, respectively. From most of the previous models, the thermal conductivity of timber char increases as temperature rises. Cellulose with a high density shows a higher thermal conductivity, but its impacts on the specific heat capacity are limited. Models to predict the main thermal properties of the hardwood, softwood and char are recommended. The collected data, together with those empirical models, can provide useful data resources and tools for the related fire risk assessments.
Fire in a sealed ship engine room is different from open fires, while its suppression is critically important to the emergency rescue and structure safety for a ship. This study focused on the vertical distribution of temperature rise during a sealed engine room fire. A series of experiments were carried out to investigate fire behaviors in a reduced-scale sealed ship engine room with a dimension of 3 m (length) × 3 m (width) × 3.5 m (height). The results suggested that there are vertical temperature gradients of smoke layer, showing a little lower than those of open fires. The experimental results demonstrated that the time to reach the maximum temperature is different for smoke layers at various heights, while a lower height showed a relatively long delay time. The vertical gradient of temperature rise was found increasing with pool diameter where the gradient of temperature rise of a 30 cm pool fire is about 9 times of that of a 10 cm pool fire. Furthermore, an empirical model was developed to predict the vertical temperature rise distribution along the height at the time of the maximum temperature for sealed engine room fires.
Preparing porous geopolymer for an insulation material was performed by a protein-assisted foaming and non-sintering method. Samples was produced by fly ash, sodium water glass, water and foam as original material, and the protein is used as foaming agent. The influences caused by the dosage (ratio of foam, water glass and water), and curing temperature on the properties were investigated to achieve the optimal performance. Porosity, bulk density, thermal conductivity, mechanical property and thermal evolution behaviors of the produced samples in this study were analyzed accordingly. It was known based on the experimental results that the optimal performance is achieved with a ratio of 35:35:5 for foam, sodium water glass and water under curing temperature of 55 °C, showing a porosity of 90.87%, bulk density of 235.5 kg/m3, thermal conductivity of 0.0564 W m−1 K−1 and compressive strength of 0.51 MPa. The obtained research outcomes from this study not only solve the problem of reutilizing waste materials, but also address a new strategy for obtaining non-flammability insulating materials.
The prediction of fire detector activation time is essential to ship fire safety design. In this study, a model was developed to predict heat detector activation time under ship fires in a long-narrow space. Firstly, smoke transport time of fires in a long-narrow space was determined by the time of smoke spreading from fire resource to the target location (i.e. the location of heat detector in this study) on the ceiling. Theoretical calculation method concerning smoke transport time under steady fires was then proposed based on the correlations of temperature and velocity developed in previous studies. Series of experiments were conducted in a reduced-scale test rig for validation. Using the proposed method, a dimensionless model of transport time under steady fires was theoretically derived. Secondly, following the temperature rise equation of heat detector and considering the influence of smoke transport time lag, analytic solution was obtained by integrating for steady or quasi-steady fires. And a time-varying spreadsheet template combining with Improved Euler's Method was proposed to predict the activation time for unsteady fires. Case study results showed the proposed model is applicable for long-narrow spaces, which breaks its usage limits of DETACT-T2.
