Abstract
In a continuing study of flame extinguishment,1,2,3,4 we report on scaling studies for dry chemicals on larger heptane diffusion flames (0.29 m2 and 2.32 m2 pans). We demonstrate again that small particle sizes extinguish most effectively. Extinguishment is related to heat absorption by decomposing or vaporizing particles. We show that the limiting particle size for each dry chemical—that is, the maximum size which completely decomposes or vaporizes in the flame—is independent of flame size for the systems studied. We broaden and apply the concept of latent or maximum effectiveness2,3 to pan fires of all sizes. Finally, we describe and characterize an aerodynamic effect in the transport of powders, where large particles with their higher momentum entrain and drag smaller, more effective particles into the flame.
We also show that extinction curves, involving the ratio of real-to-latent extinction weight and the proportion of small to large particles, have predictable shapes and predictable quantitative levels for most dry chemicals. We have developed the real-to-latent concept along with scaling equations for agent mixtures and for a wide spectrum of agents and particle sizes.
This is a preview of subscription content, log in via an institution to check access.
Similar content being viewed by others
References
Ewing, C. T., Hughes, J. T. and Carhart, H. W.,Fire and Materials Volume 8, 1984, p. 148.
Ewing, C. T., Faith, F. R., Hughes, J. T., and Carhart, H. W., “Flame Extinguishment Properties of Dry Chemicals: Extinction Concentrations for Small Diffusion Pan Fires,”Fire Technology Volume 25, 1989, p. 134.
Ewing, C. T., Faith, F. R., Romans, J. B., Hughes, J. T., and Carhart, H. W., “Flame Extinguishment Properties of Dry Chemicals: Extinction Weights for Small Diffusion Pan Fires and Additional Evidence for Flame Extinguishment by Thermal Mechanisms,”Journal of Fire Protection Engineering Volume 4, 1992, p. 35.
Ewing, C. T., Faith, F. R., Hughes, J. T., and Carhart, H. W., “Evidence for Flame Extinguishment by Thermal Mechanisms,”Fire Technology Volume 25, 1989, p. 195.
Babrauskas, V., “Estimating Large Pool Fire Burning Rates,”Fire Technology, Volume 19, 1983, p. 251.
McCaffrey, B. J., “Fire Plume Dynamics—A Review,” Conference on Large-Scale Fire Phenomenology, National Bureau of Standards, Gaithersburg, MD, September 1980, pp. 10 to 13.
UL 711,Rating and Fire Testing of Fire Extinguishers, Third Edition, Underwriters Laboratories, Inc.
Fire Protection Equipment Directory, Underwriters Laboratories, Inc., January, 1988, p. 20–36.
Lee, T. G., and Robertson, A. F., “Effectiveness of Some Powdered Materials in Extinguishing Hydrocarbon Fires,”International Symposium on the Use of Models in Fire Research, National Academy of Sciences Publication, Volume 786, 1961, p. 93.
NFPA 12,Carbon Dioxide Extinguishing Systems, 1985; and NFPA 12A,Halon 1301 Fire Extinguishing Systems, 1987.
Ewing, C. T., Faith, F. R., Hughes, J. T., and Carhart, H. W., “The Extinguishment of Class A Fires by Dry Chemicals,” accepted for publication.
Sheinson, R. S., Penner-Hahn, J. E., and Indritz, D., “The Physical and Chemical Action of Fire Suppressants,”Fire Safety Journal Volume 15, 1989, p. 437.
Ewing, C. T., Beyler, C., Carhart, H. W., “Extinguishment of Class B Flames by Thermal Mechanisms; Principles Underlying a Comprehensive Theory; Prediction of Flame Extinguishing Effectiveness,”Journal of Fire Protection Engineering Volume 6, 1994, p. 23.
Davis, E. J.,Aerosol Science and Technology Volume 2, 1983, p. 121.
Davis, E. J., Zhang, S. H., Fulton, J. H., and Periasamy, R., “Measurement of the Aerodynamic Drag Force in Single Aerosol Particles,”Aerosol Science and Technology Volume 6, 1987, p. 273.
Leith, D., “Drag on Nonspherical Objects,”Aerosol Science and Technology, Volume 6, 1987, p. 153.
Geldart, D., “The Effect of Particle Size and Size Distribution on the Behavior of Gas-Fluidized Beds,”Powder Technology Volume 6, 1972, p. 201.
Laats, M. K. and Frishman, F. A., “Scattering of an Inert Admixture of Different Grain Sizes in a Two-Phase Axisymmetric Jet,”Heat Transfer—Soviet Research Volume 2, 1970, p. 7.
Lloyd, P. S. and Webb, P. J., “The Flooding of a Powder—The Importance of Particle Size Distribution,”Powder Technology Volume 51, 1987, p. 125.
Wesson, H. R., “Studies of the Effect of Particle Size on the Fire Characteristics of Dry Chemicals,”Powder Technology Volume 6, 1972, p. 173.
Thorne, P. F. and Tucker, D. M., “The Development of an Improved Dry Powder—Field Trials,”Fire Protection Note No. 1042, Fire Research Station, November 1975.
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Ewing, C.T., Faith, F.R., Romans, J.B. et al. Extinguishing class B fires with dry chemicals: Scaling studies. Fire Technol 31, 17–43 (1995). https://doi.org/10.1007/BF01305266
Issue Date:
DOI: https://doi.org/10.1007/BF01305266