Vytenis Babrauskas

Heat release rate: The single most important variable in fire hazard☆

Abstract Heat release rate measurements are sometimes seen by manufacturers and product users as just another piece of data to gather. It is the purpose of this paper to explain why heat release rate is, in fact, the single most important variable in characterizing the ‘flammability’ of products and their consequent fire hazard. Examples of typical fire histories are given which illustrate that even though fire deaths are primarily caused by toxic gases, the heat release rate is the best predictor of fire hazard. Conversely, the relative toxicity of the combustion gases plays a smaller role. The delays in ignition time, as measured by various Bunsen burner type tests, also have only a minor effect on the development of fire hazard.

Estimating large pool fire burning rates

Data for estimating the burning rate and heat output of large pool fires (diameter ≳ 0.2 m) are compiled and computational equations presented. Since a large scatter in the reported data is noted, attention is also focused on areas where further research is most needed in order to improve predictability.

Ignition of Wood: A Review of the State of the Art

This review encompasses the available practical and experimental data on the ignition of solid wood. Only solid, natural wood is considered, not sawdust, chips, or products that have been treated with fire retardants or other substances, nor is the ignition of living trees. Panel products such as plywood or particleboard have ignition properties very similar to solid wood, so the solid-wood results will generally be applicable to them. Wood may ignite by flaming directly, or it may ignite in a glowing mode, which may or may not be followed by flaming. It is shown that the ignition temperature is around 250oC for wood exposed to the minimum heat flux possible for ignition, and that it invariably ignites, at least initially, in a glowing mode under these conditions. The ignition temperature rises rapidly as the heat flux is increased. Piloted ignition at heat fluxes sufficient to cause a direct-flaming ignition normally occurs at surface temperatures of 300 – 365oC. Autoignition temperatures at fluxes higher than minimum are essentially unknown. No theory is available which encompasses the possibility of glowing, glowing followed by flaming, or direct-flaming ignition modes. Most published studies have dealt with radiant or radiant+convective heating, and knowledge is extremely poor for ignition from direct contact by hot bodies or by flames. A speciesindependent correlation is derived for the radiant, piloted ignition of thermally-thick wood, but the fit is only fair. The minimum flux for ignition is 4.3 kW m -2 , based on a single study; most reported tests have been much too brief to produce useful data on this point.

Estimating room flashover potential

Flashover is the ultimate event in a room fire signaling the final untenability for room occupants and greatly increased hazard to other building spaces. Despite this importance, hazard evaluations of furnishings and other common fuel loads have normally not been based on estimates of flashover potential. This paper considers a simple combustion model and examines available experimental data.

UPHOLSTERED FURNITURE ROOM FIRES—MEASUREMENTS, COMPARISON WITH FURNITURE CALORIMETER DATA, AND FLASHOVER PREDICTIONS

This paper describes a series of room fire tests using upholstered furniture items for comparison with their open burning rates, previously determined in a furniture calorimeter. For the four tests conducted good agreement was seen in all periods of the room fires, including post-flashover, noting that only fuel- controlled room fires were considered. Difficulties in making accurate mass and heat flow measurements in the rooms window opening were found, and it is sug gested that with present day instrumentation only exhaust stack measurements are reliable. Finally, a number of simplified rules or theories for predicting room flashover based on room physical properties and open-burning heat release values were examined and compared. Broad agreement was generally found, with recommended ones selected on the basis of well-controlled asymptotic behavior.

Defining flashover for fire hazard calculations

As the use of performance-based methods for evaluating the fire behavior of materials and systems becomes more widespread, objective criteria to judge fire behavior become more important. This paper reviews techniques for predicting the most common of these criteria, the onset of flashover. The experimental basis for working definitions of flashover is reviewed. Comparisons of available calculational procedures ranging from simple correlations to computer-based fire models that can be used to estimate flashover are presented. Although the techniques range in complexity and results, the various predictions give estimates commensurate with the precision of available experimental data.

A methodology for obtaining and using toxic potency data for fire hazard analysis

A comprehensive methodology has been developed for obtaining and using smoke toxicity data for fire hazard analysis. This description of the methodology comprises (1) determination that the post-flashover fire is the proper focus of smoke inhalation deaths; criteria for a useful bench-scale toxic potency (LC50) measurement method; (2) a method which meets these criteria, especially validation against real-scale fires; (3) a computational procedure for correcting the results from the bench-scale test for the CO levels observed in real-scale post-flashover fires; (4) procedures for reducing the usage of animals and broadening the applicability of data by interpreting gas measurement data using the N-Gas Model; and (5) a procedure for identifying whether a product produces smoke within the ordinary range of toxic potency for postflashover fires.

Toxic potency measurement for fire hazard analysis

SummaryThis report is the principal product of a long-term research program to provide a technically sound methodology for obtaining and using smoke toxicity data for hazard analysis. It establishes:(a)an improved bench-scale toxic potency1 measurement, one which represents the important combustion conditions of real fires; and(b)a design and analysis framework which will allow the toxic potency data to be used in a rational, consistent, appropriate, and adequate way. This establishment of proper bench-scale test conditions, validation of the output against real-scale fire measurements, and development of a consistent framework for the inclusion of toxic potency in fire hazard2 analysis is unique and represents a successful, usable implementation of the state of the art.This method focuses on post-flashover fires. The U.S. fire statistics show that 69% of all fire deaths are associated with post-flashover fires, with the preponderance of deaths due to smoke inhalation and occurring outside the room of fire origin. These fires are characterized by:• primarily radiant heating, with heat fluxes from about 20 to 150 kW/m2 throughout the room;• many items simultaneously on fire; and• vitiated combustion air for some, but not all, burning items.

The historical basis of fire resistance testing — Part I

This review summarizes the history of fire resistance testing and its impact on the formulation of the present standard. It focuses on studies from the 1880s to 1918.

Defining flashover for fire hazard calculations: Part II

Abstract Comparison of available correlations and predictive models used to predict the minimum heat release rate (HRR) necessary to cause flashover show consistent trends for a range of empirical data. Nonetheless, available experimental data for HRR at flashover in compartments of similar geometry and venting show substantial scatter. Both the experimental data and theoretical predictions based on computer modeling indicate that a significant portion of the variability can be accounted for by the time period involved in the flashover. Although typically ignored in the available correlations, qualitatively a clear trend emerges—shorter exposure times increase the needed minimum HRR at flashover, due at least in part to the effects of heat transfer to the compartment surfaces. Additional measurement needs are suggested to facilitate better understanding of conditions leading to flashover.