Richard G. Gann

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.

Sublethal Effects of Fire Smoke

Fire smoke toxicity has been a recurring theme for fire safety professionals for over four decades. There especially continue to be difficulty and controversy in assessing and addressing the contribution of the sublethal effects of smoke in hazard and risk analyses. The Fire Protection Research Foundation (FPRF), the National Institute of Standards and Technology (NIST), and NFPA have begun a private/public fire research initiative, the “International Study of the Sublethal Effects of Fire Smoke on Survival and Health” (SEFS) to provide scientific information on these effects for public policy makers. The papers in this issue of Fire Technology present results from the first phase of the project: estimates of the magnitude and impact of sublethal exposures to fire smoke on the U.S. population, the best available lethal and incapacitating toxic potency values for the smoke from commercial products, the potential for various sizes of fires to produce smoke yields that could result in sublethal health effects, and state-of-the-art information on the production of the condensed components of smoke from fires and their evolutionary changes during transport from the fire.

Estimating Data for Incapacitation of People by Fire Smoke

Fire hazard and risk analyses establish the basis for providing conditions of safety for people, including those that are more sensitive to fire smoke than others. For this purpose, this paper develops a method for estimating, from information on lethal and incapacitating exposures for rats, smoke toxic potency values for incapacitation of smoke-sensitive people. For those engineering applications where the mix of combustibles is unknown, generic values are derived of the concentration of smoke that would incapacitate smoke-sensitive people in 5 min: 6 g/m3 for a well-ventilated fire and 3 g/m3 for an underventilated (e.g., post-flashover) fire. These values are estimated with significant assumptions in their derivation, resulting in an estimated uncertainty of about a factor of two. Further, there is a wide range of smoke toxic potency values reported for various combustibles, and some of these will lead to values significantly higher or lower than these generic figures.

Next-Generation Fire Suppression Technology Program

The Next-Generation Fire Suppression Program (NGP), now on its second year, has as its goal the development by 2004 of alternative firefighting technologies to Halon 1301 that can be economically implemented in aircraft, ships, land combat vehicles, and critical mission support facilities. This paper describes the first projects and their early results.

Evaluation of Toxic Potency Values for Smoke from Products and Materials

Many devices have been used to generate data on the toxic potency of smoke from burning products and materials. This paper critically reviews those apparatus and sorts them by the combustion conditions (related to a type of fire) producing the smoke, the specimens tested, and the animal effect measured. All the usable data were derived using rats, and the toxicological effects encountered were lethality, represented by an LC50value, and incapacitation, expressed as an IC50 value. The data showed a wide range of toxic potency values for the products and materials tested. For those engineering applications where the mix of combustibles is unknown, generic values of smoke toxic potency were derived. Statistical analysis of the wealth of published data yielded a generic LC50value of 30 g/m3 ± 20 g/m3 (one standard deviation) for 30 minute exposure of rats for smoke from well-ventilated combustion. There are limited data for underventilated combustion, and a value of 15 g/m3 ± 5 g/m3 is suggested. The mean value of the ratios of IC50 values to LC50values is 0.50 ± 0.21, consistent with a prior review. Thus, for well-ventilated fires, a generic 30 minute IC50 value (for rats) would be 15 g/m3 ± 10 g/m3; for underventilated fires, the corresponding number would be 7 g/m3 ± 2 g/m3. There are some materials with appreciably lower potency values, indicating higher smoke toxicity. If materials like these are expected to comprise a large fraction of the fuel load, a lower generic value should be used.

Large-Scale Validation of Bench Scale Fire Toxicity Tests

A sizable number of bench-scale fire toxicity tests have been pro posed over the last two decades. To date, no test method has successfully passed through the standards bodies ISO, ASTM, or BSI. The reasons are varied, but a major concern has been that none of the methods were seen to adequately pre dict the behavior of real, large-scale building fires. Such validation efforts have been held back both due to a shortage of good quality data, and because agree ment had not been reached on the criteria for successful validation. NIST has now completed a pilot project to address both of these issues. In this study, sev eral criteria for validation have been put forth. An initial data set has been compared against these criteria, comprising 2 bench-scale methods, 3 test materials, and a single real-scale fire scenario. The project results indicate that the course being pursued is appropriate, and provide illustrative performance data for the two bench-scale methods. The present project was a pilot study; fur ther validation data will have to come from additional test materials and addi tional real-scale fire scenarios being examined. As a result of these studies, a factor-of-3 agreement between bench-scale and real-scale results was estab lished as both useful and practical.

Fabrics for testing the ignition propensity of cigarettes

This paper reports an analysis of data from a study conducted by the cigarette industry to determine whether the fabrics used in a measurement method for cigarette ignition propensity reasonably represent the ignition behaviour of actual upholstery fabrics. A ‘consistency score’ is defined to evaluate objectively the relative agreement of ignition test results on various test fabrics compared with the cotton duck fabrics used in the measurement method. Particular attention is paid to those cases where the cigarettes show statistically significant di⁄erences by the chi-squared test. This analysis finds that the aggregated set of 79 industry fabrics ranks the four test cigarettes in the same order as do the three cotton duck fabrics in the measurement method. Thus, to the extent that the industry set is representative of those fabrics used in upholstery, it would be proper to use the three test fabrics as surrogates for the purpose of determining the relative ignition propensity of a cigarette. The analysis does identify six to ten fabrics that would be expected to show persistent reversals compared to the aggregate ordering; however, three-fourths of the fabrics rank the cigarettes consistently with the cotton duck fabrics. ( 1997 John Wiley & Sons, Ltd.

Mechanism of cellulose smoldering retardance by sulfur

The addition of elemental sulfur is effective in preventing cotton smoldering, a process which leads to a major fraction of fire loss. The objective of this work is to determine the mechanism of the observed retardance. Double thickness samples of cotton terrycloth approximately 18 mm by 100 mm, were smoldered in a pyrex cylinder. The samples contained 0, 5, 8 and 10 percent sulfur by weight. The air velocity over the face of the sample was about 10 cm/s. Ten percent treated samples self-extinguished or smoldered with difficulty. The smoldering velocities and peak temperatures of the other samples were determined using embedded thermocouples; both decreased with increasing sulfur concentration. Calculations and experiments indicate that the sulfur does not simply act as a heat sink as has been suggested for many flame retardants. Electron paramagnetic resonance data showed that a reduction in the number of free radicals in the char by a factor of two resulted from the addition of five percent sulfur. X-ray fluoresence measurements showed that the concentration of bound sulfur in the char was comparable to that of eliminated free radicals. Mass spectrometric studies indicated that the major vapor phase products of sulfur oxidation Mass spectrometric studies indicated that the major vapor phase products of sulfur oxidation were SO 2 and COS, but these were present in much lower concentration than O 2 and CO 2 . This result eliminates the possibility of oxygen depletion by reaction with sulfur as an important contribution to the retardancy. Rather, the sulfur vaporizes and reacts with the radical sites in the char. In the absence of sulfur, these sites would oxidize exothermically and regenerate to continue the smoldering. As a result of some radical sites being poisoned, less heat is released, and the resulting pyrolysis of further fuel is retarded. Thus the critical properties of sulfur are vaporization at the correct temperature, reactivity with the char, and stability of the resulting adduct.

Investigation of Surrogate Smoldering Ignition Sources for Testing Soft Furnishings

The introduction of cigarette ignition propensity standards has led to a reduction in the availability of high ignition propensity commercial cigarettes. Since high ignition propensity cigarettes are needed for soft furnishing flammability tests, a standard reference cigarette, SRM 1196, was developed. The current supply of SRM 1196 cigarettes is limited, and so the feasibility of a surrogate ignition source was examined. The surrogate ignition source should be repeatable, sustainable, relatively inexpensive, and should have a similar ignition propensity to the SRM 1196 cigarette on a broad range of substrates. A literature review identified several potential surrogate ignition sources including cartridge heaters, hot slugs, and materials that can smolder, such as charcoal, cotton plugs, and cotton rope. Experiments quantified the heat transfer characteristics and ignition propensity of the SRM 1196 cigarette as a baseline for evaluating candidate ignition sources. In particular, thermocouples were used to measure the temperatures at the interface of the cigarette and the substrate for both reactive and inert substrates. Screening experiments were performed to estimate the ignition propensities of the candidate surrogate sources. Analysis of and experiments with these sources found that cartridge heaters are impractical for routine testing and that commercial versions of the combustible materials do not show appropriate or repeatable values of ignition propensity. The use of hot slugs would require additional testing in which the materials, dimensions, shape, and mass were all systematically varied. Extensive testing to identify fabrics which, when supported on a foam slab, would lead to some, but not 100 % ignitions did not find enough fabrics to demonstrate equivalence to the SRM 1196 cigarette. Because of the unlikelihood of success, it is recommended that these tests not be performed and that the National Institute of Standards and Technology (NIST) order another supply of SRM 1196 cigarettes.