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Applied Chemistry and Physics
Published in Robert A. Burke, Applied Chemistry and Physics, 2020
Halogens in column 7 are nonmetals; they may be solids, liquids or gases. Fluorine and chlorine are gases at normal temperatures and pressures. Bromine is a solid up to 19.7°F and a liquid up to 136°F and produces vapor readily when above that temperature. Iodine is a solid, and astatine is a radioactive solid; however, such a small amount has ever been found that you are not likely to encounter it. Halogens are all toxic and strong oxidizers; fluorine is a much stronger oxidizer than oxygen. In fact, fluorine is the strongest oxidizer known. In the pure elemental form, halogens do not burn; however, they will accelerate combustion much like oxygen because they are oxidizers. Some halogen compounds were components of former fire extinguishing agents called halon. Halon was phased out in the United States because of the damage caused to the ozone layer.
Extinguishing Systems and Equipment
Published in Peter M. Bochnak, Fire Loss Control, 2020
Halon fire-extinguishing systems suppress fires very effectively when designed for specific fire protection uses. Halons are hydrocarbons in which one or more hydrogen atoms have been replaced by atoms from the halogen series: fluorine, chlorine, bromine, or iodine. At present, the halons used in fire suppression are Halon 1211 (bromochlorodifluoromethane), Halon 1301 (bromotrifluoromethane), and Halon 2402 (dibromotetrafluoroethane). Halon 1211 and Halon 1301 are liquified, compressed gases; Halon 2402 is a liquid. They are electrically non-conductive and have high liquid densities, which permits use of compact storage containers. They rapidly vaporize in fire and leave no corrosive or abrasive residue. The halons have been particularly effective in data-processing (computer) areas, industrial control rooms, telecommunication centers, sensitive medical diagnostic equipment, and other employee-attended occupancies housing electrical equipment (6).
General Princlpes
Published in Martin B., S.Z., of Industrial Hygiene, 2018
Organohalide compounds have halogen-substituted hydrocarbon molecules. This means that each compound has fluorine, chloride, bromine, or iodine atoms in its structure. Alkyl halides in this group include dichlo-romethane (found in paint strippers), carbon tetrachloride (refrigerants), and 1,2-dibromoethane (an insecticide). The alkenyl or olefinic organohalides include: vinyl chloride (used to produce polyvinyl chloride, PVC), a known carcinogen, trichlorethylene (used for degreasing and as a drycleaning solvent), tetrachloroethylene, and hexachlorobutadiene (used as a hydraulic fluid). Aryl halides are used in chemical synthesis and as pesticides and solvents. They are derivatives of benzene and toluene. Polychlorinated bi-phenyls (PCBs), highly toxic materials, are an example of a halogenated biphenyl. Chlorofluorocarbons (CFCs), halons, and hydrogen-containing chlorofluorocarbons are of significant importance to the environment. CFCs, once used primarily as refrigerants and aerosol propellents, are believed to have caused the breakdown of the ozone layer and have been banned from production. Halogens used in fire extinguishers as halon have also been implicated in the depletion of the ozone layer and are being phased out. Hydrogen containing chlorofluorocarbons (HFCs) are being touted as the substitute for CFCs as refrigerants and plastic foam blowing agents. Chlorinated phenyls such as pentachlorophenol, are used to treat wood against fungi and insect infestation. The byproduct of that process causes hazardous waste, which has been known to cause liver damage and dermatitis.
A Kinetic Mechanism for CF3I Inhibition of Methane–Air Flames
Published in Combustion Science and Technology, 2022
V.I. Babushok, D.R. Burgess, G.T. Linteris
Halon 1301, CF3Br, is a highly effective flame inhibitor but has a very high Ozone Depletion Potential (ODP) and hence has been banned for terrestrial applications.1Official contribution of NIST, not subject to copyright in the United States. Certain commercial equipment, instruments, and materials are identified in this paper to adequately specify procedure. Such identification does not imply recommendation or endorsement by the National Institute of Standards and Technology. Iodotrifluoromethane, CF3I, is also an effective flame inhibitor (Babushok and Tsang 2000; Moore et al. 1994; Su and Kim 2002; Tapscott, Skaggs, Dierdorf 1995; Westbrook 1982) but is reactive in the troposphere and hence has a negligible ODP. Recently, because of an improved outlook regarding its toxicity, CF3I has gained increased consideration as replacement for CF3Br in aircraft fire suppression, for which CF3Br is still being used. In addition, CF3I is being considered as a component of refrigerant blends (Bell and Mclinden 2020; Lv et al. 2021), since it has both favorable thermodynamic properties and can reduce the flammability of new, low Global Warming Potential (GWP) hydrofluorocarbon HFC refrigerant blends, which become more flammable as their GWP decreases.
Experimental study on the effects of different ratios of inert gas and hexafluoropropane (HFC-236fa) on coal combustion
Published in Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2020
Binbin He, Baiwei Lei, Chenguang Zhao, Bing Wu
Once a fire breaks out, proper selection and utilization of the extinguishing agent are significantly important for the effective suppression of the flame combustion. The commonly used extinguishing agents that are used nowadays include water, dry powder, gas, and foam (Guo, Zhang, and Zhu 2020; Jeong 2019; Weckman 2017; Xu et al. 2012). The current halon alternatives fall into two main categories: halogenated hydrocarbons (i.e., HFC-227ea, HFC-236fa, and HFC-23) and non-halogenated hydrocarbons (i.e., carbon dioxide, IG541, and inert gases) (Jiang, Chow, and Li 2007; Li et al. 2000). The productions of HFC-227ea and HFC-23 extinguishing agents have been localized in China. The HFC-236fa-extinguishing agent exhibits an excellent extinguishing performance; however, its use is limited to hand-held fire extinguishers. Moreover, there are few researches on the flame action of HFC-236fa and its combustion products in the fire field (Markaryants 2019; Zegers et al. 2000).
Combustion of C1 and C2 PFAS: Kinetic modeling and experiments
Published in Journal of the Air & Waste Management Association, 2022
Jonathan D. Krug, Paul M. Lemieux, Chun-Wai Lee, Jeffrey V. Ryan, Peter H. Kariher, Erin P. Shields, Lindsay C. Wickersham, Martin K. Denison, Kevin A. Davis, David A. Swensen, R. Preston Burnette, Jost O.L. Wendt, William P. Linak
In the early 1990s, the National Institute of Standards and Technology (NIST) launched an effort to identify potential replacements for Halon 1301 (CF3Br) for the U.S. Army, Navy, Air Force, and Federal Aviation Administration. While Halon 1301 is an extremely effective flame inhibiting agent, it was also identified as a potent ozone depleting substance (ODS). The NIST research included both experimental and modeling components, with the major objective of the modeling “to develop a chemical mechanism based on elementary reactions steps for their destruction, their participation in and influence on hydrocarbon flame chemistry, as well as for prediction of potential by-products of incomplete combustion.” Results of these kinetic mechanism studies are available in numerous publications (Babushok et al. 1994, 1995; Grosshandler et al. 1994, 1995; Daniel et al. 1994; Linteris and Truett 1995; Westmoreland et al. 1993, 1994) and summarized in a seminal review paper (Burgess et al. 1996). Interestingly, the four candidate compounds specifically being considered as replacements for Halon 1301, CH2F2, CF3-CH2F, CF3-CHF2, and CF3-CF3, all meet the definition of PFAS. Hexafluoroethane is also one of the three species examined here. The NIST authors reasoned that when these species decompose in flames, they generate a pool of fluorinated hydrocarbon stable species and radicals and the formation of many other fluoromethanes and fluoroethanes. To capture the behavior of the candidate replacement compounds, they needed to adequately describe the chemistry of all the intermediates and products that are created.