Fire Configuration Research Articles

N-M interaction curves for timber members’ cross-section under ambient and high temperature

Widely used for structural calculation, axial force (N) - bending moment (M) interaction curves are suitable instruments for evaluating the structural elements’ cross-section capacity, relating the ultimate values of bending moment and axial force. Also known as resistance curves in ambient temperature and fire situation, the N-M curves become strongly dependent on the temperature field because of the physical and mechanical changes that occur in the material under elevated temperatures. Therefore, the present study aims to obtain the interaction curves of timber structural elements’ cross-section of commonly used members in civil construction, subjected to the action of thermal conditions (ambient and high temperatures), using a generalized numerical strategy based on the strain compatibility method (SCM) and Newton-Raphson method coupling. The adopted strategy is validated through the construction of N-M curves for timber cross-sections, subject to ambient temperature and different fire configurations and temperature distribution. The results obtained are compared with answers available in the literature.

Detailed radiation modeling of two flames relevant to fire simulation using Photon Monte Carlo — Line by Line radiation model

This work reports benchmark data sets for radiative heat transfer in two distinct fire configurations obtained from the Measurement and Computation of Fire Phenomena (MaCFP) working group database. The cases include a 19.2 kW non-sooting turbulent methanol pool fire and a 15 kW sooting ethylene flame (referred to as the FM burner). The base configurations were simulated with large eddy simulation (LES) approaches using two different codes, namely FireFOAM and Fire Dynamics Simulator, respectively. Multiple frozen snapshots from these LES runs were radiatively evaluated using a photon Monte Carlo radiation solver and a line-by-line spectral model. The results were presented at three levels: Firstly, the radiative fields, including radiative emission, reabsorption, and heat flux contours, were shown. Secondly, the global radiative contributions from molecular gas species, soot, and wall boundaries were compared. Thirdly, a detailed spectral analysis of radiative fields for different components within five distinct spectral bands was presented. In the case of the non-sooting methanol pool fire, the radiative emission from CO2 predominates. However, for the radiation reaching the boundaries, both CO2 and H2O contribute almost equally. Conversely, for the sooty FM burner configuration, radiative emission from soot, CO2, and H2O all contribute similarly. In terms of radiation reaching the boundary, soot is the primary contributor in FM Burner. In the methanol pool fire, the pool surface receives a comparable contribution from CO2, H2O, and burner rim radiation, whereas, for the FM burner, the burner inlet surface primarily receives radiation from soot.

Relationships between wood properties and fire performance of glulam columns made from six wood species commonly used in China

Glued laminated timber stands as an increasingly favored engineered wood product in low-rise modern timber structures due to its commendable structural performance and carbon sequestration potential. Chinese standards presently fail to differentiate the effects of distinct wood species on the fire resistance of glulam. This study examined the charring rate and residual bearing capacity of glulam columns made from six commonly used wood species in China: poplar, Chinese fir, Douglas fir, hemlock, larch, and spruce. These materials exhibited densities ranging between 390 and 645 kg·m−³. ISO standard fire tests were conducted employing one- and two-adjacent-side fire exposures. Notably, the findings unveiled that high-density glulam columns demonstrated lower charring rates and slower rates of heat penetration. The two-adjacent-side fire configuration induced a corner effect, consequently amplifying the effective charring depth. The results showed a linear relationship between the ratio of diagonal to horizontal charring rate of the columns exposed to the two-adjacent-side fire and wood density. To enhance practical application, a formula was developed, employing the residual section method, to calculate the column's residual bearing capacity post two-adjacent-side fire exposure. This formula incorporates an adjustment depth to accommodate the corner effect, effectively mitigating the reduced wood strength within the pyrolysis zone.

The study of self-organised behaviours and movement pattern of pedestrians during fire evacuations: virtual experiments and survey

In this study, Minecraft was adopted to investigate pedestrian behaviours and evacuation processes in non-fire (normal) and fire conditions involving multiple simultaneous players. We built a PaddlePaddle-based deep learning platform for the automatic recognition of pedestrian coordinates from the Minecraft background database. To verify the virtual experiments in Minecraft, we conducted a series of experiments under identical conditions in a real (physical) room and virtual environment on the Minecraft platform. The pedestrian behaviour, flow patterns and evacuation time in the Minecraft experiments fit well with the results of the real-life experiments, indicating the potential of Minecraft for realistically simulating evacuation processes. To further demonstrate the feasibility of using Minecraft for evacuation studies, we conducted a series of virtual evacuation experiments with different fire configurations and room geometries in Minecraft. The pedestrians were found to keep higher distance towards fire and greater detour angle during the fire emergency in a square room. Furthermore, in the scenario of a fire in a corridor, in addition to the aforementioned fire avoidance behaviours, the pedestrians exhibited orderly queuing and exited the room one by one, resulting in increased walking speeds and thus a faster evacuation for most pedestrians. Finally, one post-experiment survey was designed to assess participants' perceptions of the Minecraft environment and the pedestrian behaviours and related psychological factors. The results show that the Minecraft can generate considerate realistic real-life situations, and pedestrians chose self-organised behaviours including away from fire, along the wall and detour towards fire in both survey and evacuation experiments.

Gas mixture conditions conducive to backdraft phenomenon

This work examines the influence of gas mixture compositions on backdraft phenomenon. A series of experiments were conducted in a reduced-scale enclosure subjected to various fire configurations, including a 25.0 kW and a 37.5 kW methane fire and a 16.7 kW and a 25.0 kW propane fire. Three different metrics were used to evaluate backdraft phenomenon: (1) internal conditions within the enclosure before an anticipated backdraft; (2) ignition of a local gas mixture resulting in a backdraft; and (3) intensity of resulting backdraft. The gas mixture composition within the compartment before a backdraft was determined using measurements obtained from an enhanced phi meter and gas analyzer. Ignition resulting in a backdraft was evaluated from the equivalence ratio and gas species concentration measurements surrounding a triggered spark ignitor. Backdraft intensity was analyzed by quantifying the total heat release of the exiting fireball via carbon dioxide generation calorimetry. Real-time equivalence ratio measurements showed the progressive state of the gas mixture composition within the compartment before ignition. Backdraft was observed to occur when the gas mixture surrounding the ignition soure was greater than stoichiometric conditions. The total heat release of backdrafts was found to correspond to the initial mass fraction of fuel residing within the compartment for experiments with propane fires.

Leading edge stabilisation of vertical boundary layer diffusion flames

The leading edge stability of vertical boundary layer diffusion flames established over a 3D-printed porous gas burner is revealed through Planar Laser-Induced Fluorescence imaging of the OH radical (OH-PLIF). Flame stability is studied by premixing methane and ethylene with increasing volume fractions of bromotrifluoromethane (CF3Br/Halon-1301) to increase the characteristic chemical timescale. Blow-off occurs at 15.7% and 37.3% CF3Br addition for methane and ethylene respectively, which are remarkably large limits compared to other flame configurations. As CF3Br is added, the flame stand-off distance increases and the reaction zone broadens, thereby increasing the flame length. This accelerates the buoyancy-induced flow ahead of the leading edge, promoting O2 entrainment into the flame anchor. Consequently, the radical scavenging effects on the flame anchor reactivity are dampened, resulting in the flame re-anchoring slightly downstream along the plate. Towards extinction, the flame shortens dramatically due to efficient catalytic cycling and radiative quenching at the flame tip resulting from the brominated species and excessive soot formation. This reduces the O2 mass flux into the kinetically dampened flame anchor resulting in blow-off extinction. Therefore, blow-off is controlled by both the leading edge reactivity and trailing edge length. Methane is shown to be considerably more sensitive compared to ethylene to CF3Br owing to its larger flame speed. These results demonstrate that fire-induced buoyancy greatly increases blow-off limits when using chemically active or inert agents in vertical wall fire configurations.

Evaluation of angular resolution requirements in the finite-volume-method solution of the radiative transfer equation

The performance of the finite volume method (FVM) used to solve the radiative transfer equation (RTE) is investigated in a simple benchmark configuration corresponding to a hot plate radiating towards sensors located at various separation distances. The study is performed using the Fire Dynamics Simulator (FDS). The objective of this study is to evaluate angular resolution requirements in the FVM-RTE solver to provide suitable accuracy and to avoid ray effects. The FDS-simulated radiative heat fluxes are compared to exact analytical expressions based on view factors. It is found that the numerical error has spatial and angular discretization components. The spatial discretization error is controlled by the size of computational cells and is generally small. The angular discretization error is controlled by the number of radiation angles (NRA) and becomes large in the far-field unless NRA is sufficiently large. A design criterion is proposed to select suitable values of NRA to achieve converged numerical solutions. This criterion is applied to the case of radiant emissions from a benchmark pool fire configuration; this application illustrates how the choice of NRA should be adjusted depending on the size of the region where accurate calculations of radiative heat fluxes are expected.

Numerical analysis of the performance of a PID-controlled air curtain for fire-induced smoke confinement in a tunnel configuration

In order to effectively meet the requirements of smoke confinement in different fire scenarios, this paper proposes an adaptive intelligent smoke control method combining PID (Proportional Integral Derivative) system with a traditional air curtain. By taking a tunnel fire configuration as an example, the feasibility of PID-controlled air curtains is explored and the calculation method of PID control parameters is clarified. The stability and reliability of the PID-controlled air curtain in realizing the smoke control effect in different complex fire scenarios are studied. The method of determining optimal PID coefficients is first proposed. Then, the robustness of the PID-controlled air curtain has been assessed by discussing the sensitivity of these parameters with different fire scenarios. The results show that the PID-controlled air curtains can effectively meet the requirements of smoke control in different complex fire scenarios. The impact of different fire scenarios on the PID-controlled air curtain system lies in the pre-control period, such as the system features of delay time, response time, overshoot, etc.

Experimental investigation of the effects of a sidewall and cable arrangement on a horizontal cable tray fire in an open atmosphere

AbstractThe work deals with the influence of a sidewall and cable arrangement on the behavior of a fire involving horizontal cable trays in the framework of fire safety assessments in nuclear installations. The analysis is based on large‐scale fire tests performed in the open atmosphere in the frame of the OECD Nuclear Energy Agency (NEA) PRISME 3 project and on the corresponding simulations applying the FLASHCAT model for predicting the fire heat release rate. The fire configuration consists of five horizontal trays filled with PVC‐insulated power cables. The parameters investigated are the presence or absence of a sidewall and the cable arrangement (loose or tight bundles). The results show that the presence of a sidewall increases the fire HRR in comparison to a scenario without a sidewall. This effect is due to the increase of the flame spread velocity on the lower trays. Regarding cable arrangement, a tight configuration in bundles reduces the fire HRR in comparison to a scenario with a loose arrangement. This result is due to the reduction of the fire heat release rate per unit of area (HRRPUA) as well as the flame spread velocity. The performance of the FLASHCAT model in predicting the effects of the sidewall and the cable arrangement was also assessed on the basis of the fire tests and satisfactory agreements are reported. The presented analysis demonstrates that the fire scenario with horizontal cable trays against a sidewall and with a loose cable arrangement represents a conservative scenario for fire risk assessment. In addition, on the basis of these experiments, the effect of cable arrangement is more substantial than the sidewall effect.

Flame downwash behavior in horizontal jet fires with crossflow: Experiment and physical model

A flame downwash phenomenon was investigated for horizontal jet fire with crossflow perpendicular to the fuel discharge direction. Such a jet fire configuration involves complex flow and air-fuel mixing interactions due to relatively different directions of the fuel jet, buoyant flow, and cross-flow, for which a systematic data does not exist yet. Experiments were conducted with various nozzle diameters (8 ∼ 20 mm) with propane fuel and varying fuel flow rate. The crossflow air speed, generated by a wind tunnel, varied from 1.76 to 4.56 m/s. Results showed that the length of flame downwash first increased and then decreased with the increase in the fuel supply flow rate. The flame downwash length became smaller with the increase in the crossflow air speed at relatively small fuel flow rate and became larger with the increase in the crossflow air speed at relatively large fuel flow rate. A dimensional analysis was performed on flame downwash behavior of the horizontal jet fires based on the analysis of controlling mechanisms, from which three characteristic parameters were identified. First, the dimensionless mass flow rate (Sm˙f/ρ∞)/[Uc×(Uc2/G)2] represents the fuel flow rate normalized by the characteristic air entrainment, which influences the total flame length. Second, the momentum flux ratio of jet to crossflow R represents the relative drag force of negative pressure zone in the leeward side, which determines the amount of fuel or total flame length trapped along the leeward side to produce the downwash flame. Third, the competition of the jet momentum to flame buoyancy flux (m˙fUj/ρ∞)3/4/(m˙fG/ρ∞)1/2 represents the characteristic length in the jet discharged direction where the flame motion turns from horizontal (jet momentum controlled) to vertical (buoyancy controlled) direction. The measured length of flame downwash considering the nozzle diameter, fuel flow rate, and crossflow air speed was satisfactorily correlated by the proposed mechanisms/parameters.

Soot Volume Fraction Measurements by Auto-Compensating Laser-Induced Incandescence in Diffusion Flames Generated by Ethylene Pool Fire

The main characteristics of pool fire flames are flame height, air entrainment, pulsation of the flame, formation and properties of soot particles, mass burning rate, radiation feedback to the pool surface, and the amount of pollutants including soot released to the environment. In this type of buoyancy controlled flames, the soot content produced and their subsequent thermal radiation feedback to the pool surface are key to determine the self-sustainability of the flame, their mass burning rate and the heat release rate. The accurate characterization of these flames is an involved task, specially for modelers due to the difficulty of imposing adequate boundary conditions. For this reason, efforts are being made to design experimental campaigns with well-controlled conditions for their reliable repeatability, reproducibility and replicability. In this work, we characterized the production of soot in a surrogate pool fire. This is emulated by a bench-scale porous burner fueled with pure ethylene burning in still air. The flame stability was characterized with high temporal and spatial resolution by using a CMOS camera and a fast photodiode. The results show that the flame exhibit a time-varying propagation behavior with a periodic separation of the reactive zone. Soot volume fraction distributions were measured at nine locations along the flame centerline from 20 to 100 mm above the burner exit using the auto-compensating laser-induced incandescence (AC-LII) technique. The mean, standard deviation and probability density function of soot volume fraction were determined. Soot volume fraction presents an increasing tendency with the height above the burner, in spite of a local decrease at 90 mm which is approximately the position separating the lower and attached portion of the flame from the higher more intermittent one. The results of this work provide a valuable data set for validating soot production models in pool fire configurations.

Evaluation of OpenFOAM’s discretization schemes used for the convective terms in the context of fire simulations

The influence of the numerical schemes used for discretization of the convective terms in the momentum equations and in the transport equations for scalars is investigated. To this purpose, a set of problems with exact solutions, the Taylor–Green vortex problem, an isotropic decaying turbulence problem, along with two well-known fire configurations, namely the Sandia’s helium plume and McCaffrey’s fire plume experiments, are considered for evaluation purposes. Overall, the influence of the employed numerical schemes in both equations is shown to be significant on computational meshes that are typically employed in the context of fire simulations. As expected, the discretization errors diminish when sufficiently fine grid resolutions are considered. The native schemes of OpenFOAM, filteredLinear2 and limitedLinear, are found to be relatively accurate, when compared to other numerical schemes in the literature: while maintaining boundedness of the solution, they introduce only small amounts of numerical dissipation.

Study on the role of soot and heat fluxes in upward flame spread using a wall-resolved large eddy simulation approach

The present study aims to obtain further understandings of vertical flame spreading phenomena by analysing the influences of soot and individual heat flux components on PMMA walls using large eddy simulation. Total heat flux consists of convective and radiative components, but it is not clear which one has a significant role in fire spread. The computational code used is an in-house version of FireFOAM 2.2.x, which has recently undergone specific development and validation for flame spread studies by the authors. The present study has conducted numerical simulations for flame spread and full wall fire configurations. By scale-up of the PMMA size from 0.4 to 1.0 m, the convective heat flux decreased by 41.4% at the location of the pyrolysis front, radiative heat flux increased by 86.9%, and radiative heat flux due to soot grew by 215.2%. As the pyrolysis height increases from 0.3 to 1.0 m, the convective heat flux decreased by 26.8% at the location of the pyrolysis front. The radiative heat flux increased by 96.8%, and its components of combustion of the gaseous fuel and soot grew by 55.9% and 233.3%, respectively. Moreover, the ratio of radiative heat flux to total heat flux increased by 66.5%, and that of soot to radiative heat flux grew by 73.9%. The contribution of soot to radiative heat flux almost linearly increased against the pyrolysis height and that was higher at a higher pyrolysis height.

Large eddy simulation of the unstable flame structure and gas-to-liquid thermal feedback in a medium-scale methanol pool fire

The objective of the present study is to perform fine-grained Large Eddy Simulations (LES) of a canonical 30-cm-diameter methanol pool fire configuration in order to evaluate the ability of current fire models to predict the flame structure and the rate of heat transfer to the liquid fuel surface. The simulations are performed using an LES solver called FireFOAM, a prescribed fuel evaporation rate, and a “wall-resolved” approach; the simulations also include a description of the fuel pan lip. Great attention is paid to the design of the computational grid and to the control of spatial resolution. Less attention is paid to the LES model formulation: except for the treatment of radiation for which we consider both a simplified model using a prescribed global radiant fraction and a more advanced model based on the Weighted-Sum-of-Gray-Gases approach, the simulations use baseline FireFOAM treatments to describe subgrid-scale turbulence and combustion. Results suggest that grid-converged solutions are achieved at a spatial resolution of 2 mm in the near-pool-surface region and 5 mm in the bulk of the flame region. Consistent with experimental observations, the simulated flames feature a strong instability characterized by the cyclic formation of thin boundary layer flames at the liquid pool surface and vortex rings at the burner rim that grow into large puffs and determine the structure of the entire flame. Predictions of the mean and root-mean-square temperature and velocity are found to be in good agreement with measurements taken from the literature. Equally encouraging results are obtained for the mean radiative and convective heat fluxes near the pool surface; quantitatively, simulations are found to overestimate the intensity of the thermal feedback by 25%. These results suggest that provided that the computational grid is fine enough, current fire models can be used to predict the gas-to-fuel thermal feedback.

Flame geometry of downward buoyant turbulent jet fires under cross flows: Experiments, dimensional analysis and an integral model

This study investigates the flame geometry of vertically downward facing buoyant turbulent jet fires issuing from a nozzle subject to cross flows, which deflect the jet flow by interacting with downward momentum issuing from the source and the upward buoyant forces owing to the flames. The flames turn eventually upwards as the buoyant forces dominate. The objective of this work is to understand the physics and develop non-dimensional correlations and modeling for the flame geometry of this jet fire configuration never investigated before. For this purpose, experiments are conducted having 4 circular nozzles (diameter at 3, 4, 5 and 7 mm) with propane employed as fuel under various heat release rates. The cross flows are generated by a wind tunnel having a uniform cross flow air speed varying from 0.31 m/s to 2.08 m/s. The horizontal and downward distance from the nozzle to the lowest point of the jet flame, the vertical thickness of the flame at the lowest point, the flame vertical height from lowest point to the flame tip, the flame tip horizontal projection distance are measured. Three characteristic length scales developed by dimensional analysis considering initial downward momentum M0, flame buoyancy g′, inertial cross flow force ua2 together with the normalized air required for complete combustion Sm˙f/ρaua×(ua2/g′)2, are found to represent well the aforementioned properties of the flame geometry. An integral model, considering the mass and momentum conservations, is developed to predict the trajectory and geometric properties of the downward jet flame under cross flow showing good agreement with the experimental results.

Radiative transfer calculations in fire simulations: An assessment of different gray gas models using the software FDS

The accuracy of the gray gas (GG) assumption for modeling the radiative transfer in fire simulations is studied for a closed compartment, an open environment, and a compartment with an opening. The liquid fuels used for each case are ethanol, heptane and methanol, respectively. Three different GG formulations, implemented on the solver Fire Dynamics Simulator (FDS), are tested and compared to experimental data. Transient, large eddy simulations (LES) are carried out in FDS, where the radiative transfer is solved coupled to the fluid flow and combustion processes. For each fire configuration, the GG formulations are compared to each other and to experimental data. The mean radiative heat flux computed in the simulations showed a good correspondence to measurements, especially for the ethanol and heptane flames, with average deviations ranging between 7% and 21%, which indicates that the GG assumption is adequate even for these weakly-sooting fuels. Among the GG models tested, the default formulation employed by FDS and the one based on a weighted-sum-of-gray-gases estimation of the medium emittance performed similarly, both providing in general more accurate results than the approach using the Planck-mean absorption coefficient.

On the Use of Semi-empirical Flame Models for Spreading Chaparral Crown Fire

Flame geometry plays a key role in shaping fire behavior as it can influence flame spread, radiative heat transfer and fire intensity. For wildland fire, a thorough understanding of relationships between flame geometry including flame length, flame height and flame tilt can help advance the derivation of comprehensive models of wildfire behavior. Within the fire community, a classical flame modeling approach has been the development of semi-empirical models. Many of these models have been derived for surface fuels or for pool fire configurations. However, few have sought to model flame behavior in chaparral crown fires. Thus, the objective of this study was to assess the applicability of existing semi-empirical models on observed chaparral crown fire geometry. Semi-empirical models of flame tilt, flame height and flame length were considered. Comparison with experimental observation of crown fuel layer flame height showed good agreement between two-fifths power law that relates flame height to heat release rate. Predictions of flame tilt were obtained from application of semi-empirical power-law correlations relating flame tilt angle to Froude number. Observed flame tilt values exhibited low correlation with predicted values. Thus, two new power-law correlations were proposed. Coefficients for new models were obtained from regression analysis.

Analysis of extinction and sustained ignition

The limiting conditions for sustained burning of materials are studied experimentally using gas burners. Small pool fire configurations are examined to determine the mass flux for a sustained surface diffusion flame (fire point) and the subsequent extinction limit of that flame. The burner results are compared to material data for sustained ignition, and are found to be lower. Material reported values of a critical mass flux are disparate, and burner data show that the critical mass flux can range from about 1 to 50 g/m2s. Previous studies have indicated the results depend on the convective heat transfer coefficient and the heat of combustion of the gases, but until this work no study has been presented to systematically show these dependencies. Three porous gas burners of diameters 25, 50 and 100 mm were used with fuel gases including methane, propane, isobutene, and ethylene mixed with nitrogen to precisely change the mixture heat of combustion. Diffusion flame theory based on a critical flame temperature at extinction is used to explain and correlate data for both limits. It was found that there is no statistical difference between the sustained ignition and extinction limits. A correlation for the critical mass flux is produced with heat of combustion and fuel diameter as sole dependent variables for all the fuels except methane. The results show that no burning is possible below a heat of combustion of 3–4 kJ/g. This is consistent with the European classification system for non-combustibility where the corresponding limit is set at 2 kJ/g.

Complexity of brain activity and connectivity in functional neuroimaging.

Understanding the complexity of human brain dynamics and brain connectivity across the repertoire of functional neuroimaging and various conditions, is of paramount importance. Novel measures should be designed tailored to the input focusing on multichannel activity and dynamic functional brain connectivity (DFBC). Here, we defined a novel complexity index (CI) from the field of symbolic dynamics that quantifies patterns of different words up to a length from a symbolic sequence. The CI characterizes the complexity of the brain activity. We analysed DFBC by adopting the sliding window approach using imaginary part of phase locking value (iPLV) for EEG/ECoG/MEG and wavelet coherence (WC) for fMRI. Both intra and cross-frequency couplings (CFC) namely phase-to-amplitude were estimated using iPLV/WC at every snapshot of the DFBC. Using proper surrogate analysis, we defined the dominant intrinsic coupling mode (DICM) per pair of regions-of-interest (ROI). The spatiotemporal probability distribution of DICM were reported to reveal the most prominent coupling modes per condition and modality. Finally, a novel flexibility index is defined that quantifies the transition of DICM per pair of ROIs between consecutive time windows. The whole methodology was demonstrated using four neuroimaging datasets (EEG/ECoG/MEG/fMRI). Finally, we succeeded to totally discriminate healthy controls from schizophrenic using FI and dynamic reconfiguration of DICM. Anaesthesia independently of the drug caused a global decreased of complexity in all frequency bands with the exception in δ and alters the dynamic reconfiguration of DICM. CI and DICM of MEG/fMRI resting-state recordings in two spatial scales were high reliable.

Early Triassic development of a foreland basin in the Canadian high Arctic: Implications for a Pangean Rim of Fire

Following the amalgamation of Laurasia and Gondwana to form Pangea, some Triassic tectonic models show an encircling arc system called the “Pangean Rim of Fire”. Here we show that the stratigraphy and Early Triassic detrital zircon provenance of the Sverdrup Basin in the Canadian Arctic is most consistent with deposition in a retro-arc foreland basin. Late Permian and Early Triassic volcanism was accompanied by relatively high rates of subsidence leading to a starved basin with volcanic input from a magmatic arc to the northwest. The mostly starved basin persisted through the Middle and Late Triassic with nearly continuous input of volcanic ash recorded as bentonites on the northwestern edge of the basin. In the latest Triassic it is interpreted that decreasing subsidence and a significant influx of sand-grade sediment when the arc was exhumed led to filling of the basin at the end of an orogenic cycle. Combined with other hints of Early Triassic arc activity along the western margin of Laurentia we propose that the Pangean Rim of Fire configuration spanned the entire Triassic. This proposed configuration represents the ring of external subduction zones that some models suggest are necessary for the breakup of supercontinents such as Pangea.