Ignition Probability Research Articles

Grazing Intensity Effects on Fire Ignition Risk and Spread in Sagebrush Steppe

Wildfire activity is accelerating on many rangelands worldwide, yet the potential for grazing to be used as a fire management tool remains largely unknown. Particularly, little is known about the influence of grazing on ignition and initial spread of fire, as well as how these vary by differences in grazing management. We investigated effects of grazing intensity (light, moderate, high) on fuel characteristics, fire ignition, and initial spread during the wildfire season in a native-dominated shrub steppe in eastern Oregon. We found that differences in grazing intensity have differential effects on fuel profiles (cover, height, moisture, biomass) with resulting impacts on fire behavior, but these relationships varied across study years. In particular, grazing had a stronger effect on ignition probability in drier years. Fire behavior in lightly grazed plots were similar to ungrazed plots, while moderate grazing was similar to high-intensity grazing. Results of this study highlight that grazing can be useful as a tool for wildfire management, and grazing at moderate and high intensities can reduce the probability of fire propagation in native-dominated sagebrush ecosystems. Further, the effects of grazing are context dependent and therefore may depend on specific objectives and environmental conditions.

Theoretical Model of the Retrograde Motion of Cathode Spots of Vacuum Arc

The phenomenon of cathode spot (CS) retrograde motion has been attracting extensive research in the field of vacuum arc. Although a number of theoretical models have been proposed to explain this phenomenon, up to now, the first-principle understanding is still missing. In this work, based on the generalized Ohm’s law, it is proposed that there is a transport current in the explosive emission center when a transverse magnetic field (TMF) is applied. The investigation of the influence of the transport current on the strength of the electric field in the cathode sheath suggests that the transport current affects the ignition of new CS in the retrograde direction. In the framework of the ecton model, combined with the dynamics of explosive emission plasma, the relationship between the strength of applied TMF and the ignition probability of new CS in different directions is established, and the retrograde motion characteristics of CS are simulated using a statistical model. The simulation results show that the directionality of retrograde motion of CS is enhanced with an increase in TMF, and the retrograde motion speed of CS increases with the increase of the applied TMF. When the strength of TMF is small, the motion speed of a single CS has a linear relationship with the strength of TMF, but with the increase of the strength of TMF, the motion speed of a single CS is gradually saturated, which is consistent with experimental facts. The feasibility of the model is verified by comparing the simulation results with relevant experimental results.

Effect of Dilution on Forced Ignition of Jet-A/Air Mixtures

Consistent ignition in environments where combustion products are present is critical for the safety and reliability of some propulsion applications. Prior research has shown that residual can reduce the probability of forced ignition of mixtures by decreasing the concentration of H radicals. However, the applicability of these observations to larger hydrocarbon fuels, such as jet-A, is not known. Ignition probabilities and volumetric kernel growth rates for vaporized jet-A/air/diluent mixtures were determined from radiation intensity measurements collected using an FLIR SC6700 infrared camera. Measurements of ignition probability of jet-A/air mixtures showed no appreciable reduction in ignition probability for mixtures with similar and . Mixtures diluted with showed no statistical change in average growth rates compared to undiluted and diluted mixtures. One-dimensional reacting flow simulations were conducted to help identify why no apparent chemical sensitivity to was observed for the jet-A/air mixtures, in contrast to results reported for . A greater concentration of H radicals was predicted for jet-A/air mixtures when compared to mixtures, even when is present. Further analysis showed that different reaction pathways exist for jet-A when compared to and that these reaction pathways are affected differently in the presence of residual .

전선의 허용곡률반경과 턴(TURN)에 따른 발화 가능성 연구

In this paper, two tests were performed using the commonly used HFIX(1.5SQ) cable for the purpose of analyzing the impact of a cable’s Cable Bend Radius and Turn on fire risk. In each test, 14A and 16A stationary electrical currents without a functioning molded case circuit breaker (MCCB) were applied respectively for 180 seconds, and then an infrared camera was used to verify the temperature characteristics and the ignition probability. The results of the tests showed that the Cable Bend Radius, within the scope of not causing physical damage to the copper wire or the cable sheath, did not have meaningful impact upon thermal accumulation. For the Turn however, there was a linear increase in the temperature of the cable even within the range of allowable current of the cable as the number of Turn increased, verifying the risk of fire from the cable sheath. Therefore, to minimize the risk of cable fires, the cable must be correctly used at all times and constant preventive actions through maintenance including regular inspection and repairs are needed.

Experimental Study on Transient Ignition Characteristics of Acoustic Excited Methane Jet Diffusion Flames

The ignition process of fuel plays an important role in the flame development and emission characteristics, which has attracted intensive attention in the combustion field. However, the transient ignition process for jet flames under acoustic excitation is rarely reported. In the current study, the effect of external acoustic excitation with different frequencies on the ignition process of methane jet diffusion flames has been studied experimentally using high-speed color and schlieren imaging systems. The fuel nozzle used in the experiment features a concentric ring structure, with fuel in the middle and air around it. The acoustic excitation was added to the air side through the loudspeaker, and the frequency of the acoustic excitation was set as 10 Hz, 30 Hz, 50 Hz and 100 Hz, respectively, while a case without external excitation was used as the control group. It is found that the periodic vortex structure propagates downstream in the flow field after acoustic excitation is added, which leads to an uneven velocity distribution in the flow field and the appearance of a local high-speed zone. The acoustic excitation of 30 Hz and 50 Hz can reduce the probability of successful ignition, which is mainly because the acoustic wave propagates in the flow field and causes drastic velocity changes near the ignition position. For the case of 100 Hz, the acoustic perturbation is confined in a small region near the nozzle exit, while the flow field velocity is slightly higher than the case without acoustic excitation.

A hybrid stochastic Lagrangian – cellular automata framework for modelling fire propagation in inhomogeneous terrains

A stochastic model motivated by the Lagrangian transported probability density function method for turbulent reacting flows and the cellular automata approach for forest fires was put together to simulate propagation of fires in terrains with inhomogeneous composition. In contrast to the usual cellular automata models for fires where the probability of ignition is prescribed, here the ignition of cells is determined by a random walk that mimics turbulent convection and diffusion of the hot gases and firebrands from upwind and neighbouring fire fronts. Radiation is also included. The model is aimed at speed of computation while approximating the key physics through only a few terrain-related inputs and tunable parameters representing fire intensity, hot gas and ember decay timescales, cell ignition delay and local turbulence. These parameters were calibrated against controlled fire experiments and the model was then used to give reasonable predictions for fires of increasing complexity. The presented framework allows improvements for more accurate representation of the flammable material characteristics, fire-induced flow modifications, and most other phenomena present in fires, hence providing an extendable and simple yet physically-realistic novel modelling approach.

Effects of Moisture on the Ignition and Combustion Characteristics of Lignite Particles: Modeling and Experimental Study.

The influence of the moisture content on the ignition and combustion characteristics of lignite single particles was studied using an ignition model of single coal particles with moisture and experimental investigations in a visual drop tube furnace under the temperature of 1300 K. The moisture content and the lignite particle size were varied within the ranges of 0–20% and 75–250 μm, respectively. The images of the combustion process illustrated that higher moisture content caused a significant ignition delay. The probability of homogeneous ignition was greatest when the particle size was 125–150 μm and the moisture content was 5%. An ignition model was employed to explain the mechanism of the influence of moisture content on the ignition and combustion characteristics, which embedded the chemical percolation devolatilization model to increase the accuracy of predictions. The predicted results show that there was an overlap in the release of moisture and volatile matter from the lignite particle during the combustion at a high heating rate. The devolatilization rate increases with the increase of moisture, which explains the increase in the probability of homogeneous ignition and fragmentation. Both particle size and moisture content have two-sided effects on the ignition mode, which causes the complexity and irregularity of the ignition mode of particles with moisture.

Wildfire Risk in the Complex Terrain of the Santa Barbara Wildland–Urban Interface during Extreme Winds

Each year, wildfires ravage the western U.S. and change the lives of millions of inhabitants. Situated in southern California, coastal Santa Barbara has witnessed devastating wildfires in the past decade, with nearly all ignitions started by humans. Therefore, estimating the risk imposed by unplanned ignitions in this fire-prone region will further increase resilience toward wildfires. Currently, a fire-risk map does not exist in this region. The main objective of this study is to provide a spatial analysis of regions at high risk of fast wildfire spread, particularly in the first two hours, considering varying scenarios of ignition locations and atmospheric conditions. To achieve this goal, multiple wildfire simulations were conducted using the FARSITE fire spread model with three ignition modeling methods and three wind scenarios. The first ignition method considers ignitions randomly distributed in 500 m buffers around previously observed ignition sites. Since these ignitions are mainly clustered around roads and trails, the second method considers a 50 m buffer around this built infrastructure, with ignition points randomly sampled from within this buffer. The third method assumes a Euclidean distance decay of ignition probability around roads and trails up to 1000 m, where the probability of selection linearly decreases further from the transportation paths. The ignition modeling methods were then employed in wildfire simulations with varying wind scenarios representing the climatological wind pattern and strong, downslope wind events. A large number of modeled ignitions were located near the major-exit highway running north–south (HWY 154), resulting in more simulated wildfires burning in that region. This could impact evacuation route planning and resource allocation under climatological wind conditions. The simulated fire areas were smaller, and the wildfires did not spread far from the ignition locations. In contrast, wildfires ignited during strong, northerly winds quickly spread into the wildland–urban interface (WUI) toward suburban and urban areas.

Grazing Effects on Fuels Vary by Community State in Wyoming Big Sagebrush Steppe

Limiting fire in Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis [Beetle & A. Young] S.L. Welsh) steppe is often a management priority as fires threatens its ecological integrity and rural economies that depend on it. However, the Wyoming big sagebrush steppe is vast and occurs in different community states from intact (sagebrush-bunchgrass dominated) to exotic annual grass dominated. Grazing has been suggested as the only tool that is likely feasible to apply across such large landscapes to manage fine fuels, but there is concern that over time grazing may induce undesirable shifts in plant community composition (e.g., increases in exotic annuals) that increase fire risk. Therefore, we evaluated the longer-term (+10 yr) effects of contemporary, moderate grazing by cattle compared with grazing exclusion on fuel characteristics in three community states: intact, degraded, and exotic annual grass states. We accomplished this by measuring fuel characteristics in five grazed and ungrazed areas in each community state in 2020 and 2021. Grazing generally decreased fine fuel continuity and biomass and increased the live-to-dead ratio. These fuel alterations are consistent with decreasing the probability of fire ignition and, if ignited, producing a slower spreading fire with shorter flame lengths. The response of several fine fuel characteristics to grazing varied by community state. Fine fuel characteristics also commonly varied among community states and between years. These results suggest that fuel management plans need to recognize that grazing effects will vary by community state and be flexible because fuel characteristics vary spatially and temporally. Overall, our results suggest that contemporary grazing in the Wyoming big sagebrush steppe reduces the probability of wildfire and likely increases the effectiveness and safety of fire suppression. Consequently, grazing exclusion in these communities increases the probability of frequent, large wildfires that are difficult and dangerous to suppress.

Comprehensive ignition characterization of a non-toxic hypergolic hybrid rocket propellant

This paper describes a comprehensive characterization of ignition properties of a metal-hydride based non-toxic hypergolic hybrid rocket propellant. The propellant consists of Rocket Grade Hydrogen Peroxide (RGHP) as oxidizer, high-density Polyethylene (HDPE) as fuel and sodium borohydride (NaBH4) as the additive, embedded in the HDPE matrix. Ignition quality was characterized as ignition delay, ignition probability and flame spread. In a drop-test setup, ignition characteristics were determined as a function of seven parameters: RGHP concentration, additive loading, oxidizer droplet impact velocity, oxidizer droplet volume, pressure, diluent gas, and environmental exposure. The parameters encompass thermo-chemical, fluid/droplet dynamics and environmental factors affecting ignition. Ignition delays as low as 3 ms were observed, one of the lowest using non-toxic hypergolic hybrid propellants in open-air. An overwhelming majority of conditions tested yielded <10 ms ignition delays and 100% ignition success. All conditions tested affected ignition to varying degrees with RGHP concentration, NaBH4 loading and drop impact velocity significantly affecting ignition. Further, contrary to expectations, exposing sanded fuel samples to humidity for a few h enhanced ignition instead of hampering it and exposure for 24 h did not lead to ignition degradation. Tests with diluent gases other than air (at atmospheric and elevated pressures) revealed that atmospheric oxygen played a negligible role in the reaction process. This proved that oxygen for the initial ignition event was obtained from RGHP decomposition, with atmospheric oxygen playing no role in ignition performance. Aside from demonstrating excellent ignition characteristics, our results further show a need to go beyond thermo-chemical properties and to consider aspects of ignition other than ignition delay in hypergolic propellant research to enable a complete understanding of the ignition processes. The comprehensive ignition characterization demonstrates the chosen propellant's ability to overcome ignition challenges in hybrid rockets and serves as a proof of concept for its further development.

Effect of particle size polydispersity on the minimum ignition temperature of PMMA dust clouds

For minimum ignition temperature (MIT) values, the variation is not significant for blends with the same median particle size (D 50 ) but varying polydispersity (σ D ) However, the contribution of small particles to the ignition sensitivity in a G-G furnace should not be discarded due to small changes in MIT values. The ignition delay times and ignition probability are additional parameters that can be obtained by MIT testing. These are useful for further exploring the effect of polydisperse powders on explosion taking place in a G-G furnace. When studying the ignitability of dust clouds from a risk assessment perspective, the kurtosis and σ D should not be considered primary parameters for describing the particle size distribution of polydisperse dust. Compared to σ D and kurtosis, skewness (Sk g ) and Sauter mean diameter (D 3,2 ) provide a more accurate description of polydisperse dust particle size distributions because they are more correlated with the ignition delay time and ignition probability. • The MIT parameter is not very sensitive to polydisperse dust clouds with the same D 50. • Ignition delay times and the ignition probability are additional parameters that can be obtained by MIT testing. • The ignition probability escalation interval of PMMA is given (50–60 °C). • D 3,2 and skewness have a high potential for application in the field of dust explosions.

Combining community observations and remote sensing to examine the effects of roads on wildfires in the East Siberian boreal forest

The paper is aimed at assessing the associations between the road networks geography and dynamics of wildfire events in the East Siberian boreal forest. We examined the relationship between the function of roads, their use, and management and the wildfire ignition, propagation, and termination during the catastrophic fire season of 2016 in the Irkutsk Region of Russia. Document analysis and interviews were utilized to identify main forest users and road infrastructure functional types and examine wildfire management practices. We combined community observations and satellite remotely sensed data to assess relationships between the location, extent, and timing of wildfires and different types of roads as fire sources, barriers, and suppression access points. Our study confirms a strong spatial relationship between the wildfire ignition points and roads differentiated by their types with the highest probability of fire ignition near forestry roads and the lowest near subsistence roads. Roads also play an important role in wildfire suppression, working as both physical barriers and access points for firefighters. Our research illustrates the importance of local and Indigenous observations along the roads for monitoring and understanding wildfires, including “zombie fires”. It also has practical implications for fire management collectively developed by authorities and local communities.

Machine learning on the ignition threshold for inertial confinement fusion

In inertial confinement fusion, the ignition threshold factor (ITF), defined as the ratio of the available shell kinetic energy to the minimum ignition energy, is an important metric for quantifying how far an implosion is from its performance cliff. Traditional ITF research is based on analytical theories with explicit scaling laws and parameters obtained by numerically fitting simulation data. This present study uses machine learning (ML) methods to train implicit but more reliable ITF expressions. One-dimensional numerical simulations are used to develop a dataset with 20 000 targets, in which alpha particle heating magnifies the fusion yield by a factor of 6.5. These targets are defined as marginal ignition targets whose ITF equals unity. ML models such as neural networks, support vector machines, and Gaussian processes are trained to connect the minimum ignition velocity vigt with other implosion parameters, yielding an ML-based ITF of (vimp/vigt)7.5, where vimp represents the implosion velocity. Then, these ML models are used to obtain curves of the ignition probability vs the ITF and improved ignition cliffs that show considerably better accuracy than traditional scaling laws, which are observed. The results demonstrate that ML methods have promising application prospects for quantifying ignition margins and can be useful in optimizing ignition target designs and practical implosion experiments.

Spatial Predictions of Human and Natural-Caused Wildfire Likelihood across Montana (USA)

Spatial wildfire ignition predictions are needed to ensure efficient and effective wildfire response, and robust methods for modeling new wildfire occurrences are ever-emerging. Here, ignition locations of natural and human-caused wildfires across the state of Montana (USA) from 1992 to 2017 were intersected with static, 30 m resolution spatial data that captured topography, fuel availability, and human transport infrastructure. Once combined, the data were used to train several simple and multiple logistic generalized linear models (GLMs) and generalized additive models (GAMs) to predict the spatial likelihood of natural and human-caused ignitions. Increasingly more complex models that included spatial smoothing terms were better at distinguishing locations with and without natural and human-caused ignitions, achieving area under the receiver operating characteristic curves (AUCs) of 0.84 and 0.89, respectively. Whilst both ignition types were more likely to occur at intermediate fuel loads, as characterized by the local maximum Normalized Difference Vegetation Index (NDVI), naturally-ignited wildfires were more locally influenced by slope, while human-caused wildfires were more locally influenced by distance to roads. Static maps of ignition likelihood were verified by demonstrating that mean annual ignition densities (# yr−1 km−1) were higher within areas of higher predicted probabilities. Although the spatial models developed herein only address the static component of wildfire hazard, they provide a foundation upon which dynamic data can be superimposed to forecast and map wildfire ignition probabilities statewide on a timely basis.

On pulse energy and energy distribution for ignition of flowing mixtures

The effects of energy distribution on ignition during a burst of nanosecond-pulsed high-frequency discharges (NPHFD) are investigated in methane-air mixtures at a nominal flow velocity of 5.7 m/s, equivalence ratio of 0.61 and inter-electrode gap distance of 2 mm. These effects were considered in the context of three pulse-coupling regimes, occurring at different inter-pulse time (IPT) conditions: fully-coupled (short IPT, high PI), partially-coupled (intermediate IPT, low PI), and decoupled (long IPT, variable PI). High-speed schlieren imaging was used to analyze ignition probabilities (PI) and kernel growth characteristics. Two approaches were utilized to explore the effects of energy distribution. First, four nominal levels of energy per pulse (Epp) were explored across a wide range of IPTs using a fixed number of pulses. In the fully-coupled regime, Epp did not show any influence over PI or kernel growth rate. Outside of the fully-coupled regime, PI drops to 0 for the lowest level of Epp, whereas the highest level of Epp has PI of 1 for the entire range of IPTs. For intermediate levels of Epp, a partially-coupled regime characterized by significant drops in PI is observed, with recovering PI in the decoupled regime at longer IPT. Second, the energy per pulse (Epp), inter-pulse time (IPT), and the number of pulses are varied such that their individual effects could be isolated while maintaining constant total deposited energy or total discharge duration. In this exploration, IPT is found to be the driving parameter determining the inter-pulse coupling regimes and PI. Lastly, single kernel analysis clarifies the effect of destructive kernel interactions in the partially-coupled regime, which, against intuition, results in increasing minimum ignition power for higher Epp. In conclusion, high-frequency, low-energy discharge pulses can be the optimal ignition method for NPHFD ignition with high PI and optimal energy efficiency.

High and Low Air Temperatures and Natural Wildfire Ignitions in the Sierra Nevada Region

The Sierra Nevada region has experienced substantial wildfire impacts. Uncertainty pertaining to fire risk may be reduced by better understanding how air temperature (Ta: °C) influences wildfire ignitions independently of other factors. We linked lightning-ignited wildfires to Ta patterns across the region from 1992 to 2015 and compared monthly high- and low-air-temperature patterns between ignition and non-ignition locations at local scales (4 km). Regionally, more ignitions occurred in springs with a greater number of high-Ta months and fewer cool Ta months (analyzed separately) and in summers with fewer cool Ta months. Locally, summer ignition locations experienced warmer summer months on a normalized scale than non-ignition locations. The probability of a wildfire ignition was positively associated with a greater number of high-Ta months during and prior to fire seasons. Regionally, springs with a greater number of high-Ta months had more wildfire ignitions. Locally, as individual locations in the region experienced a greater number of high-Ta months preceding and including the fire season, they exhibited substantial increases in spring (+1446%), summer (+365%), and fall (+248%) ignitions. Thus, the frequent occurrence of high-Ta months is positively associated with lightning-ignited wildfires in the Sierra Nevada region.

Confronting double-detonation sub-Chandrasekhar models with the low-luminosity suppression of Type Ia supernovae

ABSTRACT Type Ia supernovae (SNe Ia) are likely the thermonuclear explosions of carbon–oxygen (CO) white-dwarf (WD) stars, but their progenitor systems remain elusive. Recently, Sharon &amp; Kushnir used The Zwicky Transient Facility Bright Transient Survey to construct a synthesized 56Ni mass, MNi56, distribution of SNe Ia. They found that the rate of low-luminosity ($M_\text{Ni56}\approx 0.15\, \mathrm{M}_{\odot }$) SNe Ia is lower by a factor of ∼10 than the more common $M_\text{Ni56}\approx 0.7\, \mathrm{M}_{\odot }$ events. We here show that in order for the double-detonation model (DDM, in which a propagating thermonuclear detonation wave, TNDW, within a thin helium shell surrounding a sub-Chandrasekhar mass CO core triggers a TNDW within the core) to explain this low-luminosity suppression, the probability of a low-mass ($\approx 0.85\, \mathrm{M}_{\odot }$) WD explosion should be ∼100-fold lower than that of a high-mass ($\approx 1.05\, \mathrm{M}_{\odot }$) WD. One possible explanation is that the ignition of low-mass CO cores is somehow suppressed. We use accurate one-dimensional numerical simulations to show that if a TNDW is able to propagate within the helium shell, then the ignition within the CO core is guaranteed (resolved here for the first time in a full-star simulation), even for $0.7\, \mathrm{M}_{\odot }$ WDs, providing no natural explanation for the low-luminosity suppression. DDM could explain the low-luminosity suppression if the mass distribution of primary WDs in close binaries is dramatically different from the field distribution; if the Helium shell ignition probability is suppressed for low-mass WDs; or if multidimensional perturbations significantly change our results.

Особенности анализа риска возникновения пожара в электрических распределительных щитах

In Russia, a third of all fires annually occur from the electrical equipment. One of the first places in the fire statistics is occupied by the switchboards and their components. For the purpose to optimize the use of fire protection measures, it becomes quite obvious and appropriate to use the requirements of the technical regulations of the Eurasian Economic Union on a risk-oriented approach when developing methods for assessing and ensuring fire safety of the electrical products. For solving this problem, the publications of the International Electrotechnical Commission are focused on a qualitative analysis of the risk of a fire emergence, while in Russia a quantitative risk assessment in the electrical products is used by determining the likelihood of a fire emergence, and for an object — and damage from it. It is shown that for the switchboards it is advisable to combine qualitative and quantitative fire risk analyzes. For this, it is proposed, on the basis of a qualitative risk analysis, the provisions of which are presented in DS/IEC TR 63054:2017, to establish connections between the events that contribute to the fire emergence in the switchboards according to the electrical circuit, and taking into account the failure rates of the component elements in accordance with GOST 12.1.004—91 determine the probabilities of failure and ignition of the elements, as well as the resulting probability of a fire emergence from the switchboard. An example of the use of qualitative analysis for risk assessment is an experimental assessment of the possibility of emergence and propagation of combustion in a two-section switchboard, based on the results of which the practical recommendations are given. Practical implementation of the provisions set forth in the article will allow to justify the need for additional fire protection measures (modification of the product) or their sufficiency, and thereby reduce the number of fires from the switchgears.

작물 보호제 중간체 CCTA의 화재 개연성 재고(再考)

In general, crop protection agents are of great interest in research and development to increase productivity by protecting crops from various pests. However, if a safety accident occurs during the manufacturing process of crop protection agents, serious environmental pollution can occur, and several fires and safety accidents related to crop protection agents have occurred in Korea. However, it was not effective in preventing fire as it was simply treated as spontaneous ignition or carelessness without a clear cause. Therefore, through this thesis, the probability of fire was studied by sharing and analyzing two cases of fires related to crop protection agent manufacturing sites in Ulsan. The main outcome of the study was to confirm the ignition potential and risk of CCTA, and suggested improvement plans during storage and a starting point for fire detection to prove the ignition probability of chemical safety accidents. And it was evaluated again that the example of the crop protection plant presented as a fire case in Ulsan in 2020 and 2021 cannot be classified as a fire.

Fine fuel changes due to timber harvesting and frequent prescribed burning in eucalypt forests of southeastern Australia

Forests are managed for a range of ecological and economic values. Prescribed burning and timber harvesting are two widely used and often co-occurring forest management activities. Both may alter wildfire risk by changing fuel characteristics. Prescribed burning alters the amount and arrangement of fuel, which changes the probability of ignition and rate of fire spread. Timber harvesting may influence future fuel composition, amount and structure directly via the addition of harvesting residue and indirectly by changing stand structure and fine fuel accumulation. Whilst there is reasonable understanding of how fuel changes immediately after a single prescribed burn or harvest in temperate eucalypt forests, the long-term effects of frequent prescribed burning combined with timber harvesting are poorly understood. We used a long-term (∼25 year) prescribed burning experiment conducted in ∼1000 ha of temperate eucalypt forest in southeastern New South Wales, Australia to determine the effects of a single selective timber harvest and 0–6 subsequent prescribed burns on the accumulation and composition of fine fuel (<25 mm thickness). It was found that fine fuel loads differed between harvested and unharvested stands, with 30 % less leaves and fine twigs (<6 mm) in the litter bed but 24 % more green understorey fuel up to 10 years post-burn in harvested stands. Frequent prescribed burning did not change total fine fuel load in harvested stands but did change fine fuel composition, with 4 times more leaves in the litter bed and 6 times less green understorey fuel in plots burnt at high frequencies (>4 fires in 25 years) versus low frequencies (0 fires in 25 years). Similar trends were observed in unharvested stands following frequent burning, however, there was 45% more leaves in the litter bed of frequently burnt, unharvested stands compared to frequently burnt, harvested stands. Our results suggest that irrespective of harvesting, frequent burning (>4 fires over 25 years) in temperate eucalypt forest may be a suitable strategy for lowering wildfire risk as it can reduce the amount of green understorey fuel, which may reduce flame heights and the likelihood of canopy fire. However, the decrease in green understorey fuel may be offset by the increase in leaves in the litter bed, which support fire ignition and spread. Our results highlight how the presence of timber harvesting changes the accumulation and composition of fine fuel post-fire, yet timber harvesting is currently not well integrated into many landscape fuel models, which often focus solely on time since last fire. Overlooking key attributes of disturbance history (timber harvesting, number of past fires), may jeopardise the accuracy of fuel models, and therefore the reliability of fire behaviour predictions.