Richard J. Roby

Turbulence statistics in a fire room model by large eddy simulation

Fire and smoke movement in a room is influenced by the turbulence characteristics (such as Reynolds stress, turbulent heat flux, etc.) of the flow and temperature fields. In order to accurately predict fire and smoke movement by computational fluid dynamics (CFD), it is necessary to verify these turbulence quantities. The purpose of this study is to predict the turbulence structure of the flow and temperature fields due to a fire in the compartment by large eddy simulation (LES) using detailed experimental data to verify the simulation results. The results show reasonably good agreement with experimental data for both the mean flow properties and the turbulence quantities with the exception of the region near ceiling. This study provides useful information for verifying LES technique when applied to compartment fires.

An experimental investigation of glass breakage in compartment fires

An experimental investigation has been completed which examined the breaking of window glass by fire. The experiments were carried out in a compartment designed to achieve a two-layer fire environment characteristic of normal building fires. The experi mental data was collected from two test groups: the first for windows with their edges insulated from the fire (edge-protected) as occurs in normal window installations and the second for windows uniformly heated by the fire (edge-unprotected).The results of the edge-protected window tests indicated that the glass breakage was caused by a critical temperature difference between the central heated portion of the pane and the glass edge. The experimental work showed the critical value to be approximately 90°C. After the material properties of the glass were determined, the theoretical findings of Keski-Rahkonen were used to obtain a value of 70°C; the difference attributed to radia tive heating of the glass surface thermocouple. The test results also demonstr...

Advanced fire detection using multi-signature alarm algorithms *

Abstract The objective of this work was to assess the feasibility of reducing false alarms while increasing sensitivity through the use of combined conventional smoke detectors with carbon monoxide (CO) sensors. This was accomplished through an experimental program using both real (fire) and nuisance alarm sources. A broad selection of sources was used ranging from smoldering wood and flaming fabric to cooking fumes. Individual sensor outputs and various signal-conditioning schemes involving multiple sensors were explored. The results show that improved fire-detection capabilities can be achieved over standard smoke detectors by combining smoke measurements with CO measurements in specific algorithms. False alarms can be reduced while increasing sensitivity (i.e., decreasing the detection time for real fires). Patented alarm criteria were established using algorithms consisting of the product of smoke obscuration and the change in CO concentration. Alarm algorithms utilizing ionization detector smoke measurements proved to be more effective than measurements from photoelectric detectors.

Carbon Monoxide Production in Compartment Fires

The development of empirical correlations for major species yields in compartment fires has become an important priority due to the inability to calculate these quantities from first principles. Studies of simplified upper layer environments have shown that major species production rates can be correlated with the equivalence ratio in what is known as the Global Equivalence Ratio concept (GER). Due to the simplification in these past experiments, it was not known if the GER concept was valid for compartment fires. Therefore, there was a need to determine if correlations existed between major species yields and the equivalence ratio for actual compartment fires.A 2.2 m3 test compartment was used to investigate the burning of four fuels (hexane, PMMA, spruce and flexible polyurethane foam) in compartment fires. The test compartment was specially designed with a two-ventilation path system which allowed the direct measurement of the plume equivalence ratio (the ratio of the fuel volatilization rate to the ai...

The role of temperature on carbon monoxide production in compartment fires

Abstract The objective of this study was to assess the effect of temperature on carbon monoxide production in compartment fires in order to resolve the difference between global equivalence ratio-yield correlations obtained in simplified upper layer environments and more realistic compartment fires. The chemical reactivity of upper layer gases was studied using a detailed chemical kinetics model. An analysis of the modeling and experimental data in the literature provided insights into the effect of temperature on carbon monoxide production. The effect of changing temperature on compartment fire upper layer composition is twofold: (1) the generation of species in the fire plume is changed; and (2) oxidation of post-flame gases in the layer is affected. Elevated compartment temperatures correlate with increased fire plume temperatures and more complete oxidation of the fuel to CO 2 and H 2 O within the plume. The layer temperature dictates post-flame oxidation in the layer. For most situations, upper layer temperatures below 800K indicate chemically unreactive layers. As such, combustion within the fire plume dictates final CO production in the compartment. Reactions in the upper layer dictate final CO levels when upper layer temperatures are about 900K and higher.

A study of carbon monoxide and smoke yields from compartment fires with external burning

Hexane fires were burned in a 2.2 m 3 compartment with a window-style exhaust vent to study the effects of external burning on carbon monoxide and smoke yields downstream of a fire compartment. External burning was observed to occur in several modes: 1) intermittent flashes, 2) bursts that lasted for only a few seconds and 3) sustained external burning. Results showed that the flammability of the compartment fire effluent was a function of the equivalence ratio and that distinguishable equivalence ratios exist that determined which mode of external burning can be obtained for a given compartment fire. Results also showed that the reduction of carbon monoxide and smoke only occurred in the presence of sustained external burning. At plume equivalence ratios above 1.7, sustained external burning always occurred and the downstream carbon monoxide yield was reduced to 10 to 25 percent of the upper layer yield and the downstream smoke yield was reduced to approximately 0 to 50 percent of the level observed prior to sustained external burning. For fires with no sustained external burning, carbon monoxide yields downstream of the compartment fire were the same as upper layer yields even when flashes or short bursts of external burning occurred. Beylers ignition criterion for layer burning was applied to the mixing of the hot fuel-rich, upper layer gases and ambient air outside of the fire compartment. The results suggest that the ignition index predicts the potential for external burning at equivalence ratios of 1.2 and greater. However, the occurrence of external burning is dependent on the presence of an ignition source which is dictated by the vent geometry and fire size.

The effect of sodium fluoride on the stability of cyanide in postmortem blood samples from fire victims

Assigning a level of significance to cyanide concentrations found in the blood of fire victims is often hampered by the fact that cyanide is inherently unstable in cadavers and in stored blood samples. A few researchers have proposed that sodium fluoride can be used to minimize the instability of cyanide in blood samples; however, controlled studies have not been performed to support validation of this hypothesis. To test the sodium fluoride hypothesis, both treated and control blood samples from 14 autopsied fire victims were tested over a 25-30 day period. A 2% concentration of sodium fluoride was added to the blood samples at the start of testing and the samples were refrigerated between testing intervals. Cyanide concentrations in the treated and control samples were measured between 9 and 11 days post treatment and between 25 and 30 days post treatment. A statistically significant difference was not present between blood cyanide concentrations in treated and control samples between 9 and 11 days. During this time period, although there were small statistically significant increases in both treated and untreated samples the fluctuations were minor. Since the treated and control samples did not exhibit instability between 9 and 11 days, it is not surprising that the sodium fluoride appeared to have no effect. However, a statistically significant difference between blood cyanide concentrations in treated and control samples was observed between 25 and 30 days. Those samples treated with sodium fluoride showed a reduction in blood cyanide variability with virtually no overall change, over a 25-30 day period when compared to control samples, while unconditioned samples showed a significant, average increase of 35%. Based on the findings of this study, it is recommended that 2% sodium fluoride be added to blood samples obtained from fire victims to reduce cyanide instability due to bacteriological activity.

LES-PDF Modeling of Flame Instability and Blow-out in Bluff-Body Stabilized Flames

Large Eddy Simulations (LES) were performed to predict the flame profile of bluff-body stabilized premixed flame at stable and blow-out conditions. Probability density function (PDF) based approach was used to solve the scalar transport by fully resolving the chemical source termwith 14 species, 44 step propane reduced chemical kinetic mechanism using

Influence of Turbulence-Chemistry Interaction in Blow-out Predictions of Bluff-Body Stabilized Flames

Large Eddy Simulations (LES) were performed to investigate the effect of turbulence –chemistry interaction on flame instability and flame-vortex interactions in bluff body stabilized premixed flames. A semi-global reduced kinetics mechanism and a skeletal mechanism were developed and implemented with a Laminar Chemistry (LC) model and an Eddy Dissipation Concept (EDC) model to simulate bluff-body stabilized propane-air flames using the experimental conditions of Kiel et al. (2007). Simulations were performed for reactive and non-reactive cases with coarse (0.65 million cells) and fine (2.4 million cells) grids. Simulations with fine grids were able to predict the recirculation zone thickness correctly as observed in the experiments. Simulation results also show that the near-field wake behind the bluff body was dominated by the Von-Karman vortex shedding for the non-reacting case as well as the reacting case with EDC models, while a shear layer generated vortex sheet was observed for reacting flow cases with the LC models. The simulation results demonstrate that turbulence-chemistry interactions play a major role in predicting the blow-out conditions. LES predictions with the EDC model show that the blow-out occurs at 0.6 equivalence ratio as observed experimentally at a DeZubay number of ~10.

Carbon Monoxide Levels in Structure Fires: Effects of Wood in the Upper Layer of a Post-Flashover Compartment Fire

This experimental study was performed to determine the effects of wood pyrolyzing in a high-temperature, vitiated compartment upper layer on the environment inside the compartment and an adjacent hallway. This was done by comparing species concentrations and temperature measurements from tests with and without wood in the compartment upper layer. Experiments were performed with a window-type opening and a door-type opening between the compartment and the hallway. In these tests, the wood in the compartment upper layer caused CO concentrations inside the compartment to increase, on average, to 10.1% dry, which is approximately 3 times higher than levels measured without wood in the upper layer. Down the hallway 3.6 m from the compartment with wood in the upper layer, CO concentrations were measured to be as high as 2.5% dry. The use of the global equivalence ratio concept to predict species formation in a compartment was explored for situations where wood or other fuels pyrolyze in a vitiated upper layer at a high temperature.