Ignition Probability
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2021 ◽  
Author(s):  
Jun Hu ◽  
Xueming Shu ◽  
Shifei Shen ◽  
Jun Yan ◽  
Fengshi Tian ◽  
...  

2021 ◽  
Vol 7 ◽  
Author(s):  
Derek Bean ◽  
David L. Blunck

The increasing occurrence of severe wildfires, coupled with the expansion of the wildland urban interface has increased the number of structures in danger of being destroyed by wildfires. Ignition by firebrands is a significant avenue for fire spread and structure loss; thus, understanding processes and parameters that control the ignition of fuel beds by firebrands is important for reducing these losses. In this study the effect of fuel bed characteristics (i.e., particle size and porous or solid fuel bed) on ignition behavior was considered. Modelling and analysis was conducted to better understand parameters that are dominant in controlling ignition. The fuel beds, made from Douglas-fir shavings, Douglas-fir plates, or cardboard plates, were heated with a cartridge heater (i.e., surrogate firebrand) to observe ignition. Smaller particles were observed to ignite more readily in porous beds than larger particles when heat transfer from the heater is primarily through conduction. This occurs in large part due to differences in contact area between the fuel bed and the heater coupled with thermal properties of the fuel bed. As particle sizes increased, ignition was more likely to occur at extended times (>100 s) due to the increased importance of radiation heat transfer. Douglas-fir plates were primarily observed to ignite at times where conduction was the dominant mode of heat transfer (<10 s). Heat flux delivered to the fuel bed was observed to be a more accurate predictor of ignition likelihood and ignition time than heater temperatures. The characteristic ratio of transport and chemical timescales can be used, in conjunction with the measured heat flux and thermal diffusivity of the fuel beds, as a first approximation to predict ignition for the porous fuel beds. This suggests that future work focusing on these parameters may produce a general characterization of fuel bed ignition probability across fuel beds materials and morphologies.


2021 ◽  
pp. 073490412110301
Author(s):  
Yawei Wang ◽  
Gaowan Zou ◽  
Conglin Liu ◽  
Y Gao

The Halon 1301 fixed gas fire extinguishing system used in ship engine rooms has been banned from production all over the world, because halon destroys the ozone layer. Therefore, it is necessary to find an environmentally friendly, compatible and efficient alternative firefighting system. In this study, we performed fire extinguishing tests in an ISO9705 standard room for four alternative fire extinguishing agents, as well as Halon 1301. The fire extinguishing efficiency of each agent was determined based on its cooling effect, dilution effect of oxygen concentration, the extinguishing time of the oil pool fire and the re-ignition probability of the wood stack. The test results provide data support for the selection of alternatives of Halon 1301 from the aspect of fire extinguishing efficiency. Among these results, Novec 1230 had the best ability to put out the oil pool fire, and HFC-227ea suppressed the wood stack fire the best. The difference between the cooling ability of each fire extinguishing agent was small, and the inert gas (IG-541) displayed the best ability to dilute oxygen. Hot aerosol required the longest time to extinguish fire. Consequently, under the existing design standards, HFC-227ea had the better firefighting efficiency, more suitable to replace Halon 1301.


2021 ◽  
Author(s):  
Roberto Ciardiello ◽  
Rohit Singh Pathania ◽  
Patton Allison ◽  
Pedro M. de Oliveira ◽  
Epaminondas Mastorakos

2021 ◽  
Vol 13 (14) ◽  
pp. 2737
Author(s):  
Artan Hysa ◽  
Velibor Spalevic ◽  
Branislav Dudic ◽  
Sanda Roșca ◽  
Alban Kuriqi ◽  
...  

We bring a practical and comprehensive GIS-based framework to utilize freely available remotely sensed datasets to assess wildfire ignition probability and spreading capacities of vegetated landscapes. The study area consists of the country-level scale of the Romanian territory, characterized by a diversity of vegetated landscapes threatened by climate change. We utilize the Wildfire Ignition Probability/Wildfire Spreading Capacity Index (WIPI/WSCI). WIPI/WSCI models rely on a multi-criteria data mining procedure assessing the study area’s social, environmental, geophysical, and fuel properties based on open access remotely sensed data. We utilized the Receiver Operating Characteristic (ROC) analysis to weigh each indexing criterion’s impact factor and assess the model’s overall sensitivity. Introducing ROC analysis at an earlier stage of the workflow elevated the final Area Under the Curve (AUC) of WIPI from 0.705 to 0.778 and WSCI from 0.586 to 0.802. The modeling results enable discussion on the vulnerability of protected areas and the exposure of man-made structures to wildfire risk. Our study shows that within the wildland–urban interface of Bucharest’s metropolitan area, there is a remarkable building stock of healthcare, residential and educational functions, which are significantly exposed and vulnerable to wildfire spreading risk.


Author(s):  
Lorenzo Palanti ◽  
Antonio Andreini ◽  
Bruno Facchini

The optimization of the igniter position is a critical issue in modern aviation gas turbines since it can help to minimize the amount of energy required for ignition and to guarantee a fast relight in case of flameout. From a numerical perspective, several spark discharges should be simulated for each spark position, to account for different realizations due to time-dependent turbulent motions. Unfortunately, standard simulations are impractical to use for this purpose, due to the need of carrying out several unsteady simulations, leading to a huge associated computational effort. This is why low-order models have been developed, providing an affordable estimation of the local ignition probability, by sacrificing the accuracy and the physical consistency of the prediction. In the present work, a previously developed low-order design model has been implemented in ANSYS Fluent 2019R1® and used to investigate the ignition performance of a single-sector, confined spray flame, where data from laser ignition experiments are available. A non-reactive Large Eddy Simulation, which is validated against experimental data, provides the base flow needed to feed the model. If the tuning parameters of the ignition model are well calibrated, it provides quite good results. In the test case here investigated, it is shown that ignition is possible in the outer recirculation zone and very unlikely elsewhere. Later, a discussion about the effect of the most relevant tuning parameters is carried out. It is shown that the model mostly succeed to identify the area of possible ignition, even if the lack of calibration could lead to a poorer agreement with the experimental data.


FLORESTA ◽  
2021 ◽  
Vol 51 (3) ◽  
pp. 696
Author(s):  
Benjamin Leonardo Alves White ◽  
Maria Flaviane Almeida Silva

The measurement of the fine dead fuel moisture content (FDFMC) is extremely important for forest fire prevention and suppression activities, as it has a great influence on the ignition probability and fire behavior. The Fine Fuel Moisture Code (FFMC) from the Fire Weather Index (FWI), is one of the most used models to estimate the FDFMC. Nevertheless, studies that assess the efficiency of this model in Brazil or in low latitude regions are rare. The present study aimed to evaluate the efficiency of the FFMC in an equatorial climate area and to develop a new model capable of estimating the FDFMC with greater precision. For this purpose, 861 random samples of fine dead fuel had their moisture content determined through oven drying. The obtained values were compared with those estimated by the FFMC and correlated with meteorological parameters to build a regression model. The results obtained show that the FDFMC was overestimated by the FFMC. The independent variables with the greatest influence on the FDFMC were, in decreasing order of significance: air relative humidity, air temperature, amount of rainfall in the last 24 hours and number of days without rainfall. The developed model presented good statistical parameters (r2 = 0.86; p <0.0001; RMSE = 0.22) and can be used, in areas with similar characteristics of the study area, to estimate the daily fire risk and to determine ideal conditions for prescribed burns.


Author(s):  
Pedro M de Oliveira ◽  
Michael P Sitte ◽  
Marco Zedda ◽  
Andrea Giusti ◽  
Epaminondas Mastorakos

A physics-based, low-order ignition model is used to assess the ignition performance of a kerosene-fueled gas-turbine combustor under high-altitude relight conditions. The ignition model used in this study is based on the motion of virtual flame particles and their extinction according to a Karlovitz number criterion, and a stochastic procedure is used to account for the effects of spray polydispersity on the flame’s extinction behavior. The effects of large droplets arising from poor fuel atomization at sub-idle conditions are then investigated in the context of the model parameters and the combustor’s ignition behavior. For that, a Reynolds-averaged Navier-Stokes simulation of the cold flow in the combustor was performed and used as an input for the ignition model. Ignition was possible with a Sauter mean diameter (SMD) of 50 μm, and was enhanced by increasing the spark volume. Although doubling the spark volume at larger SMDs (75 and 100 μm) resulted in the suppression of short-mode failure events, ignition was not achieved due to a reduction of the effective flammable volume in the combustor. Overall, a lower ignition probability is obtained when using the stochastic procedure for the spray, which is to be expected due to the additional detrimental effects associated with poor spray atomisation and high polydispersity.


2021 ◽  
Vol 9 ◽  
Author(s):  
Rob Klinger ◽  
Emma C. Underwood ◽  
Randy McKinley ◽  
Matthew L. Brooks

The extent and frequency of fire has increased in many arid systems over the last century, with a large proportion of area in some regions undergoing transitions to novel conditions. Portions of the Mojave Desert in southwestern North America have undergone such transitions, most often from woody to herbaceous-dominated systems. These transitions have often been attributed to the proliferation of invasive annual grasses that promote more frequent fire, but recent evidence indicates that transitions can also occur independent of fire frequency if burn severity is high. In addition, high probability of ignition (i.e., potentially high fire frequency) and high burn severity may not always be geographically related. Therefore, our goals were to: (1) map potential burn severity, fire frequency, and probability of ignition across the Mojave; and, (2) evaluate spatial association among predicted burn severity, fire frequency and probability of ignition. We first mapped perimeters of 250 wildfires &gt; 405 ha that occurred from 1972 to 2010, then extracted data on fire frequency (number of times burned from 1972 to 2010), burn severity (the difference Normalized Burn Ratio), and 15 predictor variables representing physiography, climate, ignition, and vegetation. Maximum entropy was used to predict probability of ignition and Random Forest models were used to predict dNBR and fire frequency. Areas with high burn severity and high ignition probability had opposite spatial trends; areas with high burn severity were predicted to predominantly be in the northwest part of the region whereas areas with high ignition probability were predicted to be in the northeast. The models indicate the existence of a number of spatially structured but temporally dynamic fire regimes throughout the Mojave Desert. Two prevalent and ecologically significant regimes include one with frequent fires of low to moderate severity and another with infrequent fire of high severity. Areas with high fire frequency are currently limited in extent (&lt;1% total area). However, cover of invasive grasses can remain high decades after a burn of high or moderate severity, so grass-fire cycles could develop in areas where there may be expectations of infrequent fire as well as those with relatively high fire frequency.


Author(s):  
Guang Yang ◽  
Jibin Ning ◽  
Lifu Shu ◽  
Jili Zhang ◽  
Hongzhou Yu ◽  
...  

AbstractSpot fire increase the difficulty of fire-fighting and threaten public safety, and therefore it is important to study ignition probabilities of fuel bed by different firebrands, in order to understand ignition mechanisms and analyze the formation of spot fires. This will provide an important basis for further study to improve the fire-fighting efficiency and reduce casualties. In this study, the ignition probabilities of larch (Larix gmelinii) fuel beds with different moisture levels and packing ratios by diffreent firebrands, including cones and twigs of different sizes, was investigated. Ignition experiments were conducted at different wind speeds generated by fans. The results show that, regardless of moisture content and packing ratio, ignition probability is zero when there is no wind. Both moisture content and wind speed significantly influence ignition probability, while packing ratio has almost no effect. The maximum moisture content at which firebrand ignition occurred was 50%, and ignition probability increased with wind speed and decreased with moisture content. Cones have the highest ignition probability, followed by large twigs and by small twigs. Ignition probability is also affected by firebrand shapes and sizes that determine their potential heat and contact area to the fuel bed. Two empirical models were established to link ignition probability with fuel properties and wind speed. This study will help clarify the mechanism of spot ignition and reduce corresponding losses.


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