Robert Brady Williamson

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.

Compartment fire experiments : Comparison with models

Abstract Twenty full-scale compartment fire experiments suitable for model comparison were conducted. Ceiling jet temperatures, surface heat fluxes and heat transfer coefficients which have not been previously reported are discussed. The ceiling jet temperatures 0·10 m below the ceiling show the effects of compartment ventilation, near-field entrainment conditions and burner location on the ceiling jet. Net and radiant incident heat fluxes to the upper and lower-walls and the floor are estimated. Combined (radiation and convection) interior heat transfer coefficients for the three surfaces are reported. As compartment fire models such as CFAST and FIRST continue to develop in sophistication, it is important that they be compared to experimental data. Data at three heat release rates: 330, 630 and 980 kW, are used to evaluate these comprehensive compartment fire models and two simpler models for the upper-layer gas temperature. CFAST predicts upper-layer gas temperatures 150–260°C hotter than the measured bulk outflow gas temperatures. The increased temperatures appear to be due to insufficient heat transfer through the compartment surfaces. FIRST predicts upper-layer gas temperatures that are slightly cooler (on average, 20C) than the measured bulk outflow gas temperatures. The two simpler models are within 40°C, on average, of the measured upper-layer gas temperatures

Estimating room temperatures from fires along walls and in corners

Determination of temperatures associated with room fires provides a means of assessing an important aspect of fire hazard: the likelihood of the occurrence of flashover. Layer temperatures in excess of 600°C have been associated with the occurrence of flashover. A data correlation has previously been presented to estimate layer temperatures for fires burning in the center of rooms. For fires in corners and along walls, restricted entrainment results in higher layer temperatures than predicted by the previous correlation. Modification factors for the previous correlation are developed to extend its applicability to wall and corner burning geometries. The present analysis suggests that a fire in a corner may cause flashover with only half the heat release rate necessary for a fire burning in the center of a room.

Compartment fire near-field entrainment measurements

Abstract A widely accepted consensus on entrainment models for large fires in compartments does not yet exist. To obtain further information on such entrainment rates, 20 full-scale, near-field experiments were conducted. Near-field entrainment occurs when hot layer interface heights are beneath the burner mean flame height so that cold layer entrainment occurs only near the burner surface. A durable compartment, similar to the standard fire test compartment, was designed and used in conjunction with a 0·61 m × 1·22 m porous surface propane burner to produce compartment fires with heat release rates from 330 to 980 kW. Entrainment rates of 0·74–0·98 kg/s were calculated from temperature measurements made within the compartment and in the doorway. The entrainment rates determined here were correlated with values from the literature. This correlation led to two curve fits which modify Zukoskis far-field offset model and can be used to estimate near-field entrainment rates. An offset for the near-field model of Thomas was also developed. The fire plume model of Baum and McCaffrey was found to compare favorably with the entrainment rates determined here.

Modeling of fire spread through probabilistic networks

Abstract The postflashover fire spread from room to room is treated in a stochastic analysis beginning with the development of a probabilistic network, and followed by a method of solving the network for discrete probability distributions. The first step in this analysis is the construction of a graph representing a space in which the rooms are nodes, and the walls and other fire barriers are links between the nodes. The space network graph is then transformed into a probabilistic network by introducing one node for representing the preflashover state and another node for representing the postflashover state of each room with the link between them representing the probability of flashover and the time characteristic to flashover. Each link between a flashed-over room and an adjacent space has a probability of the barrier being breached and a characteristic time of fire resistance. The probabilistic network is then solved by creating an “equivalent network” which has multiple links between the nodes to represent the uncertainty intrinsic to fire spread. For instance, a door may be open or closed. This would be represented by two links, one with the probability of the door being open with a characteristic time of zero, and the other with the probability of the door being closed with the time associated with the fire resistance of the door. The analysis of the possible flow through equivalent networks is discussed and the probability of a source node connecting with the sink node as well as the expected shortest travel time are calculated. Finally a numerical example is solved in which the source node is the room of origin of a fire, and the sink node is a section of the corridor which is critical to the escape of the occupants in nearby rooms Two cases are developed, one with “5-minute” doors and the other with “20-minute” doors and automatic closures. A different fire scenario is shown to be represented by each path through the equivalent network, and the probability and characteristic time for each of these scenarios is also calculated. The consequence of the changing to a 20-minute door is presented in quantitative terms and the probability of the door being open is used as a sensitivity parameter.

Methods to characterize heat release rate data

Methods to characterize experimentally measured heat release rate data are developed. Exponential and t-squared representations are considered in detail; algorithms for these two representations are presented. These characterizations require the selection of two representative data pairs from a measured heat release rate history and evaluation of the peak heat release rate and the total cumulative heat released by a product. A superposition method is developed for the evaluation of composite products. Comparisons with measured heat release rate data are presented for a number of products. The selection of characterization parameters based on basic material properties remains for the future.

The effect of ignition source exposure and specimen configuration on the fire growth characteristics of a combustible interior finish material

Abstract The potential fire hazard presented by plastic based combustible interior finish materials is discussed. Compartment fire experimental methods and apparatus based on Uniform Building Code Standard No. 42-2 were used to study the effect of ignition source exposure and specimen configuration on the actual fire growth characteristics of polyvinyl chloride (PVC) foam wall covering. The results obtained are qualitative in nature, clearly demonstrating two important characteristics of the fire behavior of PVC foam: (i) the PVC foam has a ‘critical’ ignition source strenght of 64–75 kW; (ii) preheating the PVC foam greatly increases its peak net rate of heat release.

Advances in assessment methods for fire safety

Abstract In this paper, the term ‘assessment method’ implies a broad class of standardized experiments which are used in the process of evaluating the fire safety of materials, products or systems. A subset of methods exists which has traditionally been referred to as ‘fire tests’. A brief history of full-scale and bench-scale fire tests is presented. A framework for evaluating the fire performance of building elements, assemblies, contents or materials is described and used to discuss the recent advances in fire tests. The role of fire scenarios is discussed in the context of assessment methods. The continuing theme throughout the paper is the impact of the oxygen depletion method of measuring the rate of heat release, one of the most important advances in the assessment of fire safety during the past 15 years. Corner tests of wall coverings including the effects of changing ‘stand off’ distance between ignition source and the wall of a corner test are discussed. Representative data from a series of different experiments are given to illustrate the use of corner tests. A concept of the critical ignition energy to cause propagation is introduced.

Temperature measurement in fire test furnaces

A study of errors associated with temperature measurement in fire endurance test furnaces has shown that conventionally used thermocouples are subject to large time constant errors in the first 20 minutes of a standard test.

Fire protection of flammable work stations in the clean room environment of a microelectronic fabrication facility

An applied engineering program is described which investigates the fire safety of combustible wet stations used within microelectronic clean room fabrication facilities. The main concern involves the impact of a wet bench fire on the clean room environment of the fabrication facility. The effectiveness of the installed fire detection and suppression systems are discussed as well as the additional steps which should be taken in order to insure early detection and suppression of fires within wet benches.