Fuchen Jia

Simulating one of the CIB W14 round robin test cases using the SMARTFIRE fire field model

Numerical predictions produced by the SMARTFIRE fire field model are compared with experimental data. The predictions consist of gas temperatures at several locations within the compartment over a 60 min period. The test fire, produced by a burning wood crib attained a maximum heat release rate of approximately 11 MW. The fire is intended to represent a non-spreading fire (i.e. single fuel source) in a moderately sized ventilated room. The experimental data formed part of the CIB Round Robin test series. Two simulations are produced, one involving a relatively coarse mesh and the other with a finer mesh. While the SMARTFIRE simulations made use of a simple volumetric heat release rate model, both simulations were found capable of reproducing the overall qualitative results. Both simulations tended to over-predict the measured temperatures. However, the finer mesh simulation was better able to reproduce the qualitative features of the experimental data. The maximum recorded experimental temperature (1214°C after 39 min) was over-predicted in the fine mesh simulation by 12%.

The numerical simulation of the noncharring pyrolysis process and fire development within a compartment

Abstract A pyrolysis model for noncharring solid fuels is presented in this paper. Model predictions are compared with experimental data for the mass loss rates of polymethylmethacrylate (PMMA) and very good agreement is achieved. Using a three-dimensional CFD environment, the pyrolysis model is then coupled with a gas-phase combustion model and a thermal radiation model to simulate fire development within a small compartment. The numerical predictions produced by this coupled model are found to be in very good agreement with experimental data. Furthermore, numerical predictions of the relationship between the air entrained into the fire compartment and the ventilation factor produce a characteristic post-flashover linear correlation with constant of proportionality 0.38 kg/sm 5/2 . The simulation results also suggest that the model is capable of predicting the onset of “flashover” and “post-flashover” type behaviour within the fire compartment.

Coupled Fire/Evacuation Analysis of the Station Nightclub Fire

In this paper, coupled fire and evacuation simulation tools are used to simulate the Station Nightclub fire. This study differs from the analysis conducted by NIST in three key areas; (1) an enhanced flame spread model and (2) a toxicity generation model are used, (3) the evacuation is coupled to the fire simulation. Predicted early burning locations in the full-scale fire simulation are in line with photographic evidence and the predicted onset of flashover is similar to that produced by NIST. However, it is suggested that both predictions of the flashover time are approximately 15 sec earlier than actually occurred. Three evacuation scenarios are then considered, two of which are coupled with the fire simulation. The coupled fire and evacuation simulation suggests that 180 fatalities result from a building population of 460. With a 15 sec delay in the fire timeline, the evacuation simulation produces 84 fatalities which are in good agreement with actual number of fatalities. An important observation resulting from this work is that traditional fire engineering ASET/RSET calculations which do not couple the fire and evacuation simulations have the potential to be considerably over optimistic in terms of the level of safety achieved by building designs.

The Prediction Of Fire Propagation In Enclosure Fires

In this paper we present some early work concerned with the development of a simple solid fuel combustion model incorporated within a Computational Fluid Dynamics (CFD) framework. The model is intended for use in engineering applications of fire field modelling and represents an extension of this technique to situations involving the combustion of solid cellulosic hels A simple solid &el combustion model consisting of a thermal pyrolysis model, a six flux radiation model and an eddydissipation model for gaseous combustion have been developed and implemented within the CFD code CFDS-FLOW3D The model is briefly described and demonstrated through two applications involving fire spread in a compartment with a plywood lined ceiling. The two scenarios considered involve a fire in an open and closed compartment The model is shown to be able to qualitatively predict behaviours similar to flashover - in the case of the open room - and backdrafl - in the case of the initially closed room.

CFD Fire Simulation of the Swissair Flight 111 in-Flight Fire - Part 1: Prediction of the Pre-Fire Air Flow Within the Cockpit and Surrounding Areas

The SMARTFIRE computational fluid dynamics (CFD) software was used to predict the ‘possible’ behaviour of airflow as well as the spread of fire and smoke within a Swissair configured McDonnell Douglas MD-11 commercial transport aircraft. This work was undertaken by the Fire Safety Engineering Group (FSEG) of the University of Greenwich as part of Transportation Safety Board (TSB) of Canada, Fire & Explosion Group’s investigation into the in-flight fire occurrence onboard Swissair Flight 111 (SR111): TSB Report Number A98H0003. The main aims of the CFD analysis were to develop a better understanding of the possible effects, or lack thereof, of numerous variables relating to the in-flight fire. This assisted investigators in assessing possible fire dynamics for cause and origin determination. In Part 1, the numerical analyses to pre-fire airflow patterns within the cockpit and its vicinity are presented. The pre-fire simulations serve two ends. One is to provide insight into the flow patterns within the cockpit and its vicinity and further supportive numerical evidence for the airflow flight test observations. The other is to provide plausible initial flow conditions for fire simulations. In this paper, some flow patterns at a number of primary locations within the cockpit and its vicinity are highlighted and the predicted flow patterns are compared with the findings from the airflow flight tests. The predicted patterns are found to be in good qualitative agreement with the experimental test findings.

Numerical investigation of fires in small rail car compartments

In this article, an enhanced flame spread model is used to simulate a rail car compartment fire test. The model was found to be able to reproduce the following experiential results: the predicted progressive burning locations are consistent with the experimental record; the predicted temperatures and heat fluxes at various locations essentially follow the measured trends; and the predicted onset of flashover is within 9% of the measured time of 180 s. The sensitivity of the predicted time to flashover is assessed using 18 fire scenarios in which the uncertainties in the measured material properties are systematically examined. The time to flashover is found to be most sensitive to changes in seat material properties. For the investigated rail car compartment, the impact of porosity of the overhead luggage rack structure on time to flashover is also examined and found to be significant for small ignition source fires. Language: en

The Numerical Simulation of Fire Spread Within a Compartment Using an Integrated Gas and Solid Phase Combustion Model

An integrated fire spread model is presented in this study including several sub-models representing different phenomena of gaseous and solid combustion. The integrated model comprises of the following sub-models: a gaseous combustion model, a thermal radiation model that includes the effects of soot, and a pyrolysis model for charring combustible solids. The interaction of the gaseous and solid phases are linked together through the boundary conditions of the governing equations for the flow domain and the solid region respectively. The integrated model is used to simulate a fire spread experiment conducted in a half-scale test compartment. Good qualitative and reasonable quantitative agreement is achieved between the experiment and numerical predictions.

Simulating smoke transport in large scale enclosure fires using a multi-particle-size model

In Computational Fluid Dynamics (CFD) based fire simulation, the particle laden smoke is usually assumed to be in a gaseous state. This is due to the assumption that most of the smoke particles have diameters less than about 2.0 µm and so their settling velocities can be ignored compared with the intensive turbulent fire gas flow. This simplification can lead to severely under-predicted smoke levels in the lower layer at remote locations from the fire source. This problem is addressed in this paper through the development of a Multi-Particle-Size model which takes into consideration the uneven mass size distributions of smoke particles. The model divides the smoke particles into three groups with various diameter ranges. The transport of smoke particles in each group is represented by a governing equation, in which the gravitational force is addressed by adding a correction into the convection term. The efficiency of the model to reproduce smoke transport is demonstrated by simulating a large scale PVC-cable fire experiment conducted in a long corridor. Compared with a conventional smoke transport model, the new model is shown to be better able of reproducing the measured experimental smoke data and the recorded visibilities.

Assessing levels of hydrogen cyanide in fire experiments using a generalized correlation

A generalized relationship between the normalized yields of carbon monoxide and hydrogen cyanide for nitrogen-containing materials has recently been derived. This correlation is used in the current study to analyze experimentally derived hydrogen cyanide data from three sets of fire tests. For a reduced-scale compartment fire test, the yields of hydrogen cyanide with varied equivalence ratios and the transient hydrogen cyanide concentrations are estimated; for a series of room-corridor sofa fire tests, the extremely high hydrogen cyanide level observed is demonstrated to be a realistic result and a hydrogen cyanide yield value of 0.047 g/g is suggested for this sofa in post-flashover fires for fire safety assessments; and finally, for a series of smoke chamber tests with polyurethane, possible causes for the failure to detect hydrogen cyanide are suggested. Language: en