Analysis of CF₃Br Flame Suppression Activity Using Quantitative Laser-Induced Fluorescence Measurements of the Hydroxyl Radical

Abstract

The recent ban on the production of CF₃Br (Halon 1301) because of its deleterious effect on the global ozone layer has intensified the search for new fire suppressants with comparable properties. The present study focuses on further understanding the relatively established mechanism by which CF₃Br operates as an effective fire suppressant so as to help guide the search for alternative suppressants. Laser-induced fluorescence (LIF) was used to measure quantitatively the concentration of hydroxyl in opposed CH₄/air di ffusion flames as a function of the amount of CF₃Br added to the air steam. Experimental profiles of OH concentration in undoped and CF₃Br-doped flames were obtained and compared with those predicted from kinetic modeling. Good agreement was found at lower percentages of CF3Br, but at higher percentages nearer extinction, the reduction in OH concentration was overpredicted by the kinetic model.

Quantitative reaction path (QRP) and sensitivity analyses were performed so as to improve our understanding of the controlling CF₃Br chemical kinetics. The QRP analysis verified that scavenging of H by CF₃Br and HBr constitutes the primary inhibitory mechanism. As expected, the H radical was found to be more sensitive than the OH radical to changes in the CF3Br kinetics. Based on both QRP and sensitivity studies, the pre-exponential factor for CF₃Br + H -> CF₃ +HBr required reduction by nearly an order of magnitude to provide good agreement with the measured peak OH concentrations. The extent of this reduction implies that further work is required on the chemical mechanism describing inhibition by CF₃Br.

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NORMAND M. LAURENDEAU

Corresponding author: Normand M. Laurendeau Telephone: [phone] Fax: [phone] E-mail: [email protected]