Fire Suppression Substitutes and Alternatives to Halon for U.S. Navy Applications (1997) / Chapter Skim
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ASSESSMENT OF RESEARCH ON ALTERNATIVES FOR HALON
ASSESSMENT OF RESEARCH ON ALTERNATIVES FOR HALON
Pages 6-21
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From page 6... ...
Alternative agents with higher boiling points tend to be less effective overall.9 The coexistence of liquid and gas in delivery lines complicates the dynamics of distribution, and incomplete vaporization at the nozzle can greatly impede delivery of a total flooding agent to the flame source. This chapter describes fire suppression models and the complex chemical and physical processes involved in understanding fires and their extinguishment, outlines the chemistry of manufacture of alternative agents currently proposed by industrial suppliers, and indicates the relative performance of commercially available halon replacements.
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From page 7... ...
the potential for discovering an environmentally acceptable equivalent. CHEMICAL AND PHYSICAL CONSIDERATIONS IN EVALUATING ALTERNATIVE FIRE SUPPRESSION AGENTS Several large chemical manufacturing concerns have invested heavily in the search for economically viable halon replacements, although the compounds investigated tend to be related to existing commercial products or their precursors.
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From page 8... ...
From the global reaction mechanism, we need to write down a reaction mechanism based on individual reaction steps, each of which is a fundamental chemical process, a unimolecular, bimolecular, or termolecular reaction. Then we have to determine the kinetics of each fundamental reaction step and use the rate constants to solve for a global kinetic rate.
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From page 9... ...
Many of these reactions are termolecular in nature, involving an unreactive third body such as N2, the predominant gas in the atmosphere, and they increase in rate with decreasing temperature. By understanding the reaction mechanism, it should be possible to design a reagent that can interfere with the production of an important radical and hence reduce the chain length.
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From page 10... ...
Alternative agents that contain iodine tend to be readily tropodegradable; that is, they react in the lower atmosphere through photolysis or some other mechanism to produce stable compounds that will not deliver iodine radicals to the stratosphere. These compounds, while retaining the effective chemical mechanism of fire suppression common to haloes, tend to be either unstable with respect to storage and material compatibility, or toxic, or both.
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From page 11... ...
- ohs.) H-1301 CF3Br 17.6 2.9 14.7 IFC-13I1 CF3I 3.0 HCF-23 CF3H 23.0 12.6 10.4 HCFC-22 CF2HC1 21.3 11.6 9.7 HCFC-124 CF3-CHC1F 13.5 6.7 6.8 PFC-14 CF4 20.0 13.8 6.2 HFC-236fa CF3-CH2-CF3 11.1 5.6 5.5 HCFC-123 CF3CHCl2 12.9 7.5 5.4 PFC-116 CF3-CF3 12.5 7.8 4.7 HFC-125 CF3-CHF2 13.8 9 4 4 4 HFC-227ea CF3-CFH-CF3 10.3 6.3 4.0 PFC-218 CF3-CF2-CF3 9 7 6.1 3.6 HFC-134a CF3-CFH2 14.1 10.5 3.6 PFC-3- 1 - 10 CF3-CF2-CF2-CF3 7.4 5.0 2.4 Manufacturability of Commercially Available Halocarbon Fire Suppression Agents The manufacture of halon replacements is typically more complex than the manufacture of haloes themselves.
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From page 12... ...
. Table 2.2 Commercially Available Replacement Agents for Total Flooding Applications Halocarbon Number Chemical Formula Supplier Designation PFC-218 CF3-CE2- CF3 3M CEA-308_ PFC-3- 1 - 10 CF3-CF2-CF2-CF3 3M CEA-410_ HFC-23 CF3H DuPont FE-13_ HCFC-125 CF3-CHF2 DuPont FE-25_ HFC-227ea CF3-CFH-CF3 Great Lakes Chemical FM-200_ HFC-236fa CF3-CH2-CF3 DuPont FE-36_ HCFC-124 CF3-CHC1F DuPont FE-241_ HCFC Blend A, a blend of: North American Fire Guardian NAF-S-II HCFC-22 CF2HC HCFC- 123 HCFC-124 CF3CHC12 CF3CHC1F IFC-13I1 CF3I Pacific Science Triode_ Table 2.3 Commercially Available Replacement Agents for Streaming Applications Halocarbon Number Chemical Formula Supplier Designation PFC-5-1-14 CF3-(CF2~4- CF3 3M CEA-614_ HFC-227ea CF3-CFH-CF3 Great Lakes Chemical FM-200_ HFC-236fa CF3-CH2-CF3 DuPont FE-36_ HCFC-123 CF3CHCl2 DuPont FE-232_ HCFC-124 CF3CHC1F DuPont FE-241_ HCFC Blend B
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From page 13... ...
This process is typically carried out in the liquid phase utilizing a Lewis acid catalyst and hydrogen fluoride as the fluorine source.26 CHCl3 + HF CHFCI2 + HF CHF2C!
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From page 14... ...
. HCC-230fa is then treated with hydrogen fluoride in the liquid phase in the presence of a Lewis acid catalyst to give HFC236fa.
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From page 15... ...
Effectiveness of Alternative Commercially Available Fire Suppression Agents The various agents discussed above have been evaluated using a standard cup burner test with nheptane fuel.43 Table 2.4 shows the results for those agents and others, ranked in order of performance, where performance is based on the volume fraction required to extinguish the flame-the most effective agent is that which requires the lowest volume for extinguishment. Halon 1301 is included for comparison.
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From page 16... ...
EPA-sponsored Federal Advisory Committee on Acute Exposure Guidance levels,44 and more information on the effects of brief exposures will likely be available from future studies. In addition to observations for lethality, detailed clinical observations of test animals should be conducted during and after exposure.
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From page 17... ...
In the event of a positive finding, a second study, with rabbits, should be considered. The results from these studies, along with an estimate of potential exposure levels, should be considered in Staining the potential risk to pregnant women exposed to chemical fire suppressants during maintenance or other procedures and in area discharges.
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From page 18... ...
30 1, 2, Abstract 1489 (March 1996~. at acute inhalation toxicity, cardiac sensitization, potential developmental toxicity, and possibly the effects of repeat exposure, along with a limited genetics screen, should be adequate to characterize the toxicity of potential substitute flame suppressant materials.
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From page 19... ...
issued a report in 1990 whose objective was to initiate a systematic search for halon replacements.s6 This report is firmly grounded in the science and technology of combustion and current understanding of the role of halogenated compounds in ozone depletion in the stratosphere. The centerpiece of the publication is a list of 103 chemicals "covering a range of chemical and physical principles thought to affect flame suppression capability.
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From page 20... ...
Tsang, Construction of an Exploratory List of Chemicals to Initiate the Search for Halon Alternatives, NIST Technical Note 1279, U.S. Department of Commerce, Washington D.C.
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From page 21... ...
46. Acute Toxicity (Skin Irritatio~, Official Journal of ~e European Communities, English Edition, Legislation 35, L383A, December 29 (1992~.
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