Walter W. Jones

Verification of a model of fire and smoke transport

Abstract A set of comparison between a comprehensive room fire model and a range of real-scale fire experiments is presented. For these comparisons, a zone-based model, CFAST (‘consolidated fire and smoke transport’ model) is used. The model predicts the evolution of a fire in a room and the subsequent transport of the smoke and toxic gases which result from this fire. These comparisons serve two purposes: to determine, within limits, the accuracy of the predictions for those quantities of interest to the users of the models (usually those extensive variables related to hazard), and to highlight the strengths and weaknesses of the underlying algorithms in the models to guide future improvements in this and other models. The predicted variables selected for comparison deal with both of these purposes. Although differences between the model and the experiments were clear, they can be explained by limitations of the model and of the experiments.

The Effect of Room Openings on Fire Plume Entrainment

Abstract The mass rate of entrainment is examined for a fire plume in a room. Entrainment rates are inferred from measurements of air flow through a door or window and from room temperature data. The effect of the air flow is to tilt the flame plume, and to increase the entrainment rate over that of a vertical free standing plume. Dimensional analysis and theoretical results for a non-reacting wind blown plume model are used to correlate the flame angle and entrainment rate results.

Quantifying Fire Model Evaluation Using Functional Analysis

Comparisons of predictive fire models with each other or with experimental data have been largely qualitative. By treating these time series curves as infinite-dimensional vectors, a branch of mathematics called functional analysis defines geometrically meaningful operations on the curves. This allows lengths, angles, and distance between two arbitrary curves to be defined and quantified. An introduction to the theory and tools provided by functional analysis is presented. Examples of the application of these tools to fire model evaluation are presented.

Development and Validation of Corridor Flow Submodel for CFAST

The modeling of fire and smoke spread is an evolvingfield. As knowledge is acquired and resources become available, models are enhanced to make their predictions more accurate and/or their computations faster. This paper will discuss the Consolidated Fire and Smoke Transport (CFAST) zone fire model, developed by the National Institute of Standards and Technology (NIST), and a recent addition to that model, referred to as the Corridor Flow Submodel. The goal of this new submodel is to more accurately predict the flow of smoke down a corridor which has an impact on fire protection issues such as detection and escape time. Prior to the addition of this new submodel, CFAST assumed that smoke traveled instantly from one side of a compartment to another. Development of the submodel will be discussed and then the enhanced CFAST, Version 4.0.1 (executable dated 3/8/00), will be used to model a real-scale experiment conducted onboard the ex-USS SHADWELL, the Navys R&D Damage Control platform.

Prediction of Corridor Smoke Filling by Zone Models

Abstract Prediction of Corridor Smoke Filling by Zone Models Abstract-Several zone models which are being used to predict the growth ano spread of fires in compartments have been examined. We have benchmarked these models against a set of experiments which were designed to isolate the phenomenon of smoke filling in a room adjacent to a fire source, and connected by a variable opening. Good agreement is achieved between multi-compartment models and experiment. As an adjunct, we have implemented correlation based on a simple theory which collapses all of the data into a single graph by using dimensionless groups. These groups then contain most of the significant variables important in describing the flow of a gas from one compartment to another.

Improvement in predicting smoke movement in compartmented structures

This paper describes improvements which have been made in the CFAST model of fire growth and smoke transport for compartmented structures. In particular, we are interested in the ability to model the movement of toxic gases from the room of origin of a fire to a distant compartment. The newest phenomena in the model are vertical flow and mechanical ventilation. Finally, we have improved the radiation transport scheme which affects energy distribution, and therefore the buoyancy forces. These are very important in actual situations relevant to fire growth and smoke propagation, as is demonstrated.

MODELING SMOKE MOVEMENT THROUGH COMPARTMENTED STRUCTURES

The paper describes a model of fire growth and smoke transport for compartmented structures, with emphasis on those aspects which are important to making correct predictions of smoke movement in multicompartment structures. In particular, the authors are interested in the ability to model the movement of toxic gases from the room of origin of a fire to a distant compartment. The newest phenomena in the model are vertical flow and mechanical ventilation. Finally, they have improved the radiation transport scheme which affects energy distribution, and therefore the buoyancy forces. These are very important in actual situations relevant to fire growth and smoke propagation, as is demonstrated.

Characteristics of Fire Scenarios in Which Sublethal Effects of Smoke are Important

A number of simulations were performed using the CFAST zone fire model to predict the relative times at which smoke inhalation and heat exposure would result in incapacitation. Fires in three building types were modeled: a ranch house, a hotel, and an office building. Gas species yields and rates of heat release for these design fires were derived from a review of real-scale fire test data. The incapacitation equations were taken from draft 14 of ISO document 13571. Sublethal effects of smoke were deemed important when incapacitation from smoke inhalation occurred before harm from thermal effects occurred. Real-scale HCl yield data were incorporated as available; the modeling indicated that the yield would need to be 5 to 10 times higher for incapacitation from HCl to precede incapacitation from narcotic gases, including CO CO2, HCN and reduce O2.The results suggest that occupancies in which sublethal effects from open fires could affect escape and survival include multi-room residences, medical facilities, schools, and correctional facilities. In addition, fires originating in concealed spaces in any occupancy pose such a threat. Sublethal effects of smoke are not likely to be of prime concern for open fires in single- or two-compartment occupancies (e.g., small apartments and transportation vehicles) themselves, although sublethal effects may be important in adjacent spaces; buildings with high ceilings and large rooms (e.g., warehouses, mercantile); and occupancies in which fires will be detected promptly and from which escape or rescue will occur within a few minutes.

The Evolution of HAZARD, the Fire Hazard Assessment Methodology

The United States alone spends

Development of an Algorithm to Predict Vertical Heat Transfer Through Ceiling/Floor Conduction

700 billion a year on new and renovated construction. About 20% of this money assures safety from unwanted fires, and this portion includes the cost of insurance to families and businesses. This enormous cost could be reduced by introducing fire safe products to the building and transportation industries, both in the United States and abroad, and by introducing advanced detectors, suppression systems, and firefighting equipment to the fire protection industry. In order to show that these products and mechanisms are safe to use, industries need performance measures. Performance-based fire standards are currently being developed to augment prescriptive standards around the world.Performance-based standards are intended to provide flexibility in maintaining accepted fire safety levels among competitive products, while ensuring life safety and reducing property loss. At the same time, performance-based requirements should reduce design and construction costs, as well as the cost of maintenance and liability coverage. In order to derive these benefits, evaluation tools are needed. One such tool, HAZARD I, helps users understand the consequences of unwanted fires by making the results of recent fire research available to them. Improvements to the program will include increased applicability, improved usability, the ability to address additional building features, and more accurate treatment of fire behavior and its effects on people and their actions. Many of the improvements made already in the software documentation are based on the experience of fire protection engineers and others who have used the program. User input, combined with other planned program improvements, constitute the first step in the overall goal of a complete Fire Hazard assessment methodology.