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286 FIRE RESEARCH AU-purpose (alcohol) foams must be employed for extinction of water-miscible fuels (polar solvents). Foams must be applied at optimum rates of two to four times the "critical" rate (i e , that rate at which its fire destruction is balanced bj ' its mput volume per umt time) Critical rates vary from about 0 02 gpm per sq. f t to 0 05 gmp per sq. f t , dependent on the type of fuel Sub-surface apphed (mjected) foam promotes cold fuel circulation in tanks and can be equally efficient as surface apphed foam A low expansion foam must be used for this process and fuel pick-up durmg transit must not exceed 10% of the volume of liqmd in the foam layer. Fortified foams (fluoroprotein) are more tolerant of these factors and operate more successfully. "Light Water" foams perform more efficiently than other foams by factors of 2X to 4X (depending on the fuel used) and improve in performance with expansion. (An expansion of 20 is 2 X more efficient than an expansion of 4 ) They may be used on both water-miscible and immiscible fuels "Light Water" foams will not resist "burn-back" of extinguished fuels as well as pro tern type foams but will seal and close small fuel areas more leadily Medium hjgh expansion foams (50 X to 500 X ) are best for extinction of flammable hqmd fires, particularly for outdoor use. High expansion foams (500X to 1200X) are suitable for fires in compart- ments and their "critical apphcation rates" may be measured m terms of minimum rate of increase m depth to extmguish the fire These foams require special methods of distribution and where high level flames are encountered in high storage compartments the critical rates will be mcreased by at least a factor of five. H. Chemical Aspects of Fires Woolley, W. D. and Wrist, F. N. (Joint Fu:e Research Organization, Boreham Wood, England) "Coupled Gas ChromatographyâMass Spectrometry and Its Application to the Thermal Decomposition Products of Cellulose," Joint Fire Research Organization Fire Research Note No. 870 (April 1971) Section: H Subjects: Cellulose pyrolysis, Gas chromatography; mass spectrometry; Pyrolysis study Authors' Summary An analytical system, consistmg of a coupled gas chromatographâmass spec- trometer umt hnked to an on-hne decomposition furnace has been constructed for studies of the thermal decomposition products of orgamc materials The system has been evaluated by a quantitative study of the decomposition products of
