The Experts below are selected from a list of 1350 Experts worldwide ranked by ideXlab platform
Bogdan Z. Dlugogorski - One of the best experts on this subject based on the ideXlab platform.
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a review of cfc and Halon treatment technologies the nature and role of catalysts
Catalysis Surveys From Asia, 2006Co-Authors: Eric M. Kennedy, Adesoji A Adesina, Bogdan Z. DlugogorskiAbstract:The purpose of this review article is to provide readers with an account of CFC and Halon treatment technologies as depicted in the patent and open literature. Destruction technologies, in which Halons and CFCs are converted into species such as CO2, HX or X2 (X = Br, Cl, F), are treated less extensively. Emphasis has been placed on conversion processes, which aim at transforming (rather than destroying) CFC or Halon into environmentally benign and useful products. It has been found that catalytic hydrodehalogenation over transition metal based catalysts, Pd in particular, has great potential for conversion of CFCs and Halons to hydrofluorocarbons. In this regard, the focus of this review is on catalytic hydrodehalogenation, including an assessment of reaction mechanisms, catalytic activity, selectivity and durability.
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Experimental and computational studies of the gas-phase reaction of Halon 1211 with hydrogen.
Environmental Science & Technology, 2005Co-Authors: Hai Yu, M. D. Azhar Uddin, S.p. Sullivan, Eric M. Kennedy, Bogdan Z. DlugogorskiAbstract:The gas-phase reaction of Halon 1211 (CBrClF2) with hydrogen has been studied experimentally at atmospheric pressure in a plug flow, isothermal reactor over the temperature range of 673 to 973 K, at residence times ranging from 0.5 to 2.5 s with an input ratio of N2:H2:Halon 1211 of 19:10:1. The major carbon containing products include CHClF2, CHBrF2, CH2F2, and CH4. Gas-phase reactions of CHClF2, CCl2F2, and CH 2F2 with hydrogen are also investigated under the conditions similar to those for Halon 1211 hydrodehalogenation, and the results are used to assist in understanding the mechanism of the reaction of Halon 1211 with hydrogen. A kinetic reaction scheme involving 90 species and 430 reaction steps is developed and used to model the Halon 1211 hydrodehalogenation reaction. Generally, satisfactory agreement between experimental and computational results is obtained for the production of major species. Using the software package AURORA, the reaction pathways leading to the formation of major products are elucidated. It has been found that the reaction steps involving CF2 are responsible for the formation of CH4.
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experimental and computational studies of the thermal decomposition of Halon 1211
International Journal of Chemical Kinetics, 2005Co-Authors: Eric M. Kennedy, S.p. Sullivan, Azhar Uddin, Bogdan Z. DlugogorskiAbstract:Thermal pyrolysis of Halon 1211 (CBrClF2). diluted in nitrogen, in a tubular alumina reactor, has been studied over the temperature range of 773-1073 K at residence times from 0.3 to 2 s. At temperatures below 973 K, the major products were CCl2F2, CBr2F2, C2Cl2F4, C2BrClF4, C 2F4, and C2Br2F4. Further increasing temperature resulted in the formation of CBrF3, CCLF 3, and many other species whose formation necessitated the rupture of C - F bonds. Coke formation was also observed on the surface of the reactor at high temperatures. A kinetic reaction scheme involving 16 species and 25 reaction steps was developed and applied to model the thermal pyrolysis of Halon 1211 over the temperature range of 773 - 973 K. Sensitivity analysis suggests that the reaction CBrClF2 + CClF2 → CCl 2F2 +CBrF2 constitutes the major pathway for the decomposition of Halon 1211 under the conditions investigated.
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conversion of Halon 1211 cbrclf2 over supported pd catalysts
Catalysis Today, 2004Co-Authors: Eric M. Kennedy, M. D. Azhar Uddin, Adesoji A Adesina, Bogdan Z. DlugogorskiAbstract:Abstract Conversion of Halon 1211 has been studied over γ-Al2O3 and supported 0.5% Pd catalysts (Pd/Al2O3, Pd/fluorinated Al2O3, Pd/AlF3, Pd/Al2O3 pretreated with CH4 and CHClF2). The experiments were performed in the temperature range of 443–523 K, in a tubular alumina reactor. The temperature of the reactor was maintained uniformly by a three zone furnace. The reaction products were quantified with a micro gas chromatograph and identified with a gas chromatograph–mass spectrometer. The catalysts were characterised with XRD diffractometry and the content of halogen on the catalysts was determined with an ion chromatograph. The measurements were presented in terms of the conversion of Halon 1211 and product selectivity, as functions of catalyst type, catalyst time on stream and composition of inlet gases. Transformation of Pd to Pd carbide is observed in the CH4 treated Pd/Al2O3, but not in the CHClF2 treated Pd/Al2O3 in which case Al2O3 was partially fluorinated. In the absence of hydrogen, the conversion of Halon 1211 over Al2O3 and Pd/Al2O3 gives a similar product profile and the reactions follow a heterogeneous halogen exchange reaction pathway, which takes place on the positively charged aluminum ions. Introduction of hydrogen has no apparent effect on either Halon 1211 conversion level or the product profile during the conversion of Halon 1211 over Al2O3. Over supported Pd catalysts, major products are hydrogenated species which include CH2F2, CH4, C2H6, C3H8, CH3Br and CHF3. The most striking feature of the hydrodehalogenation reactions is the increasing CH2F2 selectivity with time on stream, especially on Pd/Al2O3 and the CH4 treated Pd/Al2O3. The changing selectivity during the catalytic hydrodehalogenation reactions is mainly ascribed to the interaction of support with Pd.
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catalytic hydrodehalogenation of Halon 1211 cbrclf2 over γ alumina supported ni pd and pt catalysts
Catalysis Today, 2004Co-Authors: Eric M. Kennedy, Azhar Uddin, Bogdan Z. DlugogorskiAbstract:The hydrodehalogenation of Halon 1211 over Ni, Pd and Pt supported on γ-alumina was studied. The effect of reaction temperature and hydrogen/Halon 1211 input ratio was examined. Steady state catalytic activities of Pd and Pt are very similar, and much higher than that of Ni. Hydrodehalogenation over Pd favours the formation of CH2F 2, while Pt and Ni produce primarily CH4 and CH 3F, respectively. Product profiles suggest that the hydrodehalogenation of Halon 1211 over Pd and Pt follows a reaction mechanism which is similar to hydrodehalogenation of CFC-12. Over Ni catalysts, the primary hydrodehalogenation reactions are those which first remove one halogen (Cl or Br) and then remove two halogens (one F and either Br or Cl). The higher mobility of hydrogen atom on the surface of Pt is consistent with the observation that only trace amounts of C2+ hydrocarbons were detected when Pt was used compared with Pd and Ni. Increasing selectivity to CH2F2 with time on stream over Pd and Pt is mainly ascribed to the transformation of support alumina to partially fluorinated alumina.
Monique Beyer - One of the best experts on this subject based on the ideXlab platform.
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Halon 1301 further evidence of its performance as an age tracer in new zealand groundwater
Hydrology and Earth System Sciences, 2017Co-Authors: Monique Beyer, Uwe Morgenstern, Rob Van Der Raaij, Heather MartindaleAbstract:Abstract. We recently discovered a new groundwater age tracer, Halon-1301, which can be used to date groundwater recharged after the 1970s. In a previous study, we showed that Halon-1301 reliably inferred groundwater age at the majority of groundwater sites studied. At those sites, ages inferred from Halon-1301 agreed with those inferred from SF6 and tritium, two reliable widely applied groundwater age tracers. A few samples, however, showed reduced concentrations of Halon-1301, preventing meaningful age interpretation from its concentration. These reduced concentrations were likely a result of degradation or retardation of Halon-1301 in the aquifer. However, we could not provide full evidence for this due to the limited number of groundwater samples analysed (18 in total). In this study, we assess the potential of Halon-1301 as a groundwater age tracer for a larger dataset of groundwater samples under specific groundwater conditions, including highly anoxic young groundwater which can significantly degrade Halon-1301, to gain more information on the magnitude of occurrence and the causes of reduced Halon-1301 concentrations. In this study, we analysed 302 groundwater samples for Halon-1301, SF6, tritium and the CFCs CFC-11, CFC-12 and CFC-113. Comparison of age information inferred from the concentrations of these tracers allows assessment of the performance of Halon-1301 compared to other well established and widely used age tracers. The samples are taken from different groundwater environments in New Zealand and include anoxic and oxic waters with mean residence times ranging from The majority of assessed samples have reduced or elevated concentrations of CFCs, which makes it impossible to infer a reliable age using the CFCs for these samples. Halon-1301, however, reliably infers ages for CFC-contaminated waters. Three other groundwater samples were found to have elevated SF6 concentrations (contaminated). Again, at these SF6-contaminated sites, ages inferred from Halon-1301 agree with ages inferred from tritium. A few samples (14 sites) exhibit reduced concentrations of Halon-1301, which result in elevated inferred Halon-1301 ages in comparison to those inferred from SF6, tritium and/or CFC-113. Assessment of the groundwater environment at these sites gives further insight into the potential causes of Halon-1301 reduction in groundwater. Overall, Halon-1301 gives age information that matches ages inferred from SF6 and/or tritium for the majority (97 %) of the assessed groundwater sites. These findings suggest that Halon-1301 is a reasonably reliable groundwater age tracer, and is in particular significantly more reliable than the CFCs, which may have contamination and degradation problems. Halon-1301 thus has potential to become a useful groundwater age tracer where SF6 and the CFCs are compromised, and where additional independent tracers are needed to constrain complex mixing models.
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Halon-1301 – further evidence of its performance as an age tracer in New Zealand groundwater
Copernicus Publications, 2017Co-Authors: Monique Beyer, Uwe Morgenstern, Rob Van Der Raaij, Heather MartindaleAbstract:We recently discovered a new groundwater age tracer, Halon-1301, which can be used to date groundwater recharged after the 1970s. In a previous study, we showed that Halon-1301 reliably inferred groundwater age at the majority of groundwater sites studied. At those sites, ages inferred from Halon-1301 agreed with those inferred from SF6 and tritium, two reliable widely applied groundwater age tracers. A few samples, however, showed reduced concentrations of Halon-1301, preventing meaningful age interpretation from its concentration. These reduced concentrations were likely a result of degradation or retardation of Halon-1301 in the aquifer. However, we could not provide full evidence for this due to the limited number of groundwater samples analysed (18 in total). In this study, we assess the potential of Halon-1301 as a groundwater age tracer for a larger dataset of groundwater samples under specific groundwater conditions, including highly anoxic young groundwater which can significantly degrade Halon-1301, to gain more information on the magnitude of occurrence and the causes of reduced Halon-1301 concentrations. In this study, we analysed 302 groundwater samples for Halon-1301, SF6, tritium and the CFCs CFC-11, CFC-12 and CFC-113. Comparison of age information inferred from the concentrations of these tracers allows assessment of the performance of Halon-1301 compared to other well established and widely used age tracers. The samples are taken from different groundwater environments in New Zealand and include anoxic and oxic waters with mean residence times ranging from < 2 years to over 150 years (tritium-free). The majority of assessed samples have reduced or elevated concentrations of CFCs, which makes it impossible to infer a reliable age using the CFCs for these samples. Halon-1301, however, reliably infers ages for CFC-contaminated waters. Three other groundwater samples were found to have elevated SF6 concentrations (contaminated). Again, at these SF6-contaminated sites, ages inferred from Halon-1301 agree with ages inferred from tritium. A few samples (14 sites) exhibit reduced concentrations of Halon-1301, which result in elevated inferred Halon-1301 ages in comparison to those inferred from SF6, tritium and/or CFC-113. Assessment of the groundwater environment at these sites gives further insight into the potential causes of Halon-1301 reduction in groundwater. Overall, Halon-1301 gives age information that matches ages inferred from SF6 and/or tritium for the majority (97 %) of the assessed groundwater sites. These findings suggest that Halon-1301 is a reasonably reliable groundwater age tracer, and is in particular significantly more reliable than the CFCs, which may have contamination and degradation problems. Halon-1301 thus has potential to become a useful groundwater age tracer where SF6 and the CFCs are compromised, and where additional independent tracers are needed to constrain complex mixing models
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assessment of Halon 1301 as a groundwater age tracer
Hydrology and Earth System Sciences, 2015Co-Authors: Monique Beyer, Uwe Morgenstern, Rob Van Der Raaij, Bethanna JacksonAbstract:Groundwater dating is an important tool to assess groundwater resources in regards to their dynamics, i.e. direction and timescale of groundwater flow and recharge, contamination risks and manage remediation. To infer groundwater age information, a combination of different environmental tracers, such as tritium and SF 6 , are commonly used. However, ambiguous age interpretations are often faced, due to a limited set of available tracers and their individual restricted application ranges. For more robust groundwater dating multiple tracers need to be applied complementarily (or other characterisation methods need to be used to complement tracer information). It is important that additional, groundwater age tracers are found to ensure robust groundwater dating in future. We have recently suggested that Halon-1301, a water soluble and entirely anthropogenic gaseous substance, may be a promising candidate, but its behaviour in water and suitability as a groundwater age tracer had not yet been assessed in detail. In this study, we determined Halon-1301 and inferred age information in 17 New Zealand groundwater samples and various modern (river) water samples. The samples were simultaneously analysed for Halon-1301 and SF 6 , which allowed for identification of issues such as contamination of the water with modern air during sampling. All analysed groundwater sites had also been previously dated with tritium, CFC-12, CFC-11 and SF 6 , and exhibited mean residence times ranging from modern (close to 0 years) to over 100 years. The investigated groundwater samples ranged from oxic to highly anoxic. All samples with available CFC data were degraded and/or contaminated in one or both of CFC-11 and CFC-12. This allowed us to make a first attempt of assessing the conservativeness of Halon-1301 in water, in terms of presence of local sources and its sensitivity towards degradation, which could affect the suitability of Halon-1301 as groundwater age tracer. Overall we found Halon-1301 reliably inferred the mean residence time of groundwater recharged between 1980 and 2014. Where direct age comparison could be made 71% of mean age estimates for the studied groundwater sites were in agreement with ages inferred from tritium and SF 6 (within an uncertainty of 1 standard deviation). The remaining (anoxic) sites showed reduced concentrations of Halon-1301 along with even further reduced concentrations of CFCs. The reason(s) for this need to be further assessed, but are likely to be caused by sorption or degradation of the compounds. Despite some groundwater samples showing evidence of contamination from industrial or agricultural sources (inferred by elevated CFC concentrations), no sample showed a significantly elevated concentration of Halon-1301, which suggests no local anthropogenic or geologic sources of Halon-1301 contamination.
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potential groundwater age tracer found Halon 1301 cf3br as previously identified as cfc 13 cf3cl
Water Resources Research, 2014Co-Authors: Monique Beyer, Uwe Morgenstern, Rob Van Der Raaij, Bethanna JacksonAbstract:Groundwater dating using anthropogenic and natural tracer substances is a powerful tool for understanding groundwater dynamics for improved management of groundwater resources. Due to limitations in individual dating methods, often multiple tracers are used to reduce ambiguities. It is commonly accepted that there is a need for further complementary age tracers, in addition to current ones (e.g., tritium, SF6, and CFCs). We propose a potential new groundwater age tracer, Halon-1301 (CF3Br), which can easily be determined using gas chromatography with an attached electron capture detector (GC/ECD) developed by Busenberg and Plummer (2008). Its peak was noted by Busenberg and Plummer (2008), but they believed it to be CFC-13 (CF3Cl) at that time. We performed rigorous tests on gases containing or excluding Halon-1301 and CFC-13 and modern water samples and concluded that the two compounds have extremely similar retention times. Additionally, we found that the ECD response of CFC-13 is far too low to be detected in groundwater or air using standard volumes and sampling techniques. However, the peak areas and concentrations Busenberg and Plummer (2008) reported are in line with what would be expected for Halon-1301. Thus, we are confident that the peak formerly identified as CFC-13 is actually Halon-1301. Busenberg agrees with our findings. We further suggest that Halon-1301 has potential as a (complementary) age tracer, due to its established atmospheric history, and could hypothetically be used to date groundwater recharged in the 1970s or onward. We discuss known relevant properties, such as solubility and stability of Halon-1301 in the context of how these effect its potential application as a groundwater age tracer. Some open questions remain concerning how conservative Halon-1301 is—is it subject to degradation, retardation, and/or local contamination in groundwater. We are confident that Halon-1301 possesses important tracer relevant properties, but further work is required to fully assess its applicability and reliability as a groundwater age tracer in different groundwater environments.
Eric M. Kennedy - One of the best experts on this subject based on the ideXlab platform.
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a review of cfc and Halon treatment technologies the nature and role of catalysts
Catalysis Surveys From Asia, 2006Co-Authors: Eric M. Kennedy, Adesoji A Adesina, Bogdan Z. DlugogorskiAbstract:The purpose of this review article is to provide readers with an account of CFC and Halon treatment technologies as depicted in the patent and open literature. Destruction technologies, in which Halons and CFCs are converted into species such as CO2, HX or X2 (X = Br, Cl, F), are treated less extensively. Emphasis has been placed on conversion processes, which aim at transforming (rather than destroying) CFC or Halon into environmentally benign and useful products. It has been found that catalytic hydrodehalogenation over transition metal based catalysts, Pd in particular, has great potential for conversion of CFCs and Halons to hydrofluorocarbons. In this regard, the focus of this review is on catalytic hydrodehalogenation, including an assessment of reaction mechanisms, catalytic activity, selectivity and durability.
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Experimental and computational studies of the gas-phase reaction of Halon 1211 with hydrogen.
Environmental Science & Technology, 2005Co-Authors: Hai Yu, M. D. Azhar Uddin, S.p. Sullivan, Eric M. Kennedy, Bogdan Z. DlugogorskiAbstract:The gas-phase reaction of Halon 1211 (CBrClF2) with hydrogen has been studied experimentally at atmospheric pressure in a plug flow, isothermal reactor over the temperature range of 673 to 973 K, at residence times ranging from 0.5 to 2.5 s with an input ratio of N2:H2:Halon 1211 of 19:10:1. The major carbon containing products include CHClF2, CHBrF2, CH2F2, and CH4. Gas-phase reactions of CHClF2, CCl2F2, and CH 2F2 with hydrogen are also investigated under the conditions similar to those for Halon 1211 hydrodehalogenation, and the results are used to assist in understanding the mechanism of the reaction of Halon 1211 with hydrogen. A kinetic reaction scheme involving 90 species and 430 reaction steps is developed and used to model the Halon 1211 hydrodehalogenation reaction. Generally, satisfactory agreement between experimental and computational results is obtained for the production of major species. Using the software package AURORA, the reaction pathways leading to the formation of major products are elucidated. It has been found that the reaction steps involving CF2 are responsible for the formation of CH4.
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experimental and computational studies of the thermal decomposition of Halon 1211
International Journal of Chemical Kinetics, 2005Co-Authors: Eric M. Kennedy, S.p. Sullivan, Azhar Uddin, Bogdan Z. DlugogorskiAbstract:Thermal pyrolysis of Halon 1211 (CBrClF2). diluted in nitrogen, in a tubular alumina reactor, has been studied over the temperature range of 773-1073 K at residence times from 0.3 to 2 s. At temperatures below 973 K, the major products were CCl2F2, CBr2F2, C2Cl2F4, C2BrClF4, C 2F4, and C2Br2F4. Further increasing temperature resulted in the formation of CBrF3, CCLF 3, and many other species whose formation necessitated the rupture of C - F bonds. Coke formation was also observed on the surface of the reactor at high temperatures. A kinetic reaction scheme involving 16 species and 25 reaction steps was developed and applied to model the thermal pyrolysis of Halon 1211 over the temperature range of 773 - 973 K. Sensitivity analysis suggests that the reaction CBrClF2 + CClF2 → CCl 2F2 +CBrF2 constitutes the major pathway for the decomposition of Halon 1211 under the conditions investigated.
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conversion of Halon 1211 cbrclf2 over supported pd catalysts
Catalysis Today, 2004Co-Authors: Eric M. Kennedy, M. D. Azhar Uddin, Adesoji A Adesina, Bogdan Z. DlugogorskiAbstract:Abstract Conversion of Halon 1211 has been studied over γ-Al2O3 and supported 0.5% Pd catalysts (Pd/Al2O3, Pd/fluorinated Al2O3, Pd/AlF3, Pd/Al2O3 pretreated with CH4 and CHClF2). The experiments were performed in the temperature range of 443–523 K, in a tubular alumina reactor. The temperature of the reactor was maintained uniformly by a three zone furnace. The reaction products were quantified with a micro gas chromatograph and identified with a gas chromatograph–mass spectrometer. The catalysts were characterised with XRD diffractometry and the content of halogen on the catalysts was determined with an ion chromatograph. The measurements were presented in terms of the conversion of Halon 1211 and product selectivity, as functions of catalyst type, catalyst time on stream and composition of inlet gases. Transformation of Pd to Pd carbide is observed in the CH4 treated Pd/Al2O3, but not in the CHClF2 treated Pd/Al2O3 in which case Al2O3 was partially fluorinated. In the absence of hydrogen, the conversion of Halon 1211 over Al2O3 and Pd/Al2O3 gives a similar product profile and the reactions follow a heterogeneous halogen exchange reaction pathway, which takes place on the positively charged aluminum ions. Introduction of hydrogen has no apparent effect on either Halon 1211 conversion level or the product profile during the conversion of Halon 1211 over Al2O3. Over supported Pd catalysts, major products are hydrogenated species which include CH2F2, CH4, C2H6, C3H8, CH3Br and CHF3. The most striking feature of the hydrodehalogenation reactions is the increasing CH2F2 selectivity with time on stream, especially on Pd/Al2O3 and the CH4 treated Pd/Al2O3. The changing selectivity during the catalytic hydrodehalogenation reactions is mainly ascribed to the interaction of support with Pd.
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catalytic hydrodehalogenation of Halon 1211 cbrclf2 over γ alumina supported ni pd and pt catalysts
Catalysis Today, 2004Co-Authors: Eric M. Kennedy, Azhar Uddin, Bogdan Z. DlugogorskiAbstract:The hydrodehalogenation of Halon 1211 over Ni, Pd and Pt supported on γ-alumina was studied. The effect of reaction temperature and hydrogen/Halon 1211 input ratio was examined. Steady state catalytic activities of Pd and Pt are very similar, and much higher than that of Ni. Hydrodehalogenation over Pd favours the formation of CH2F 2, while Pt and Ni produce primarily CH4 and CH 3F, respectively. Product profiles suggest that the hydrodehalogenation of Halon 1211 over Pd and Pt follows a reaction mechanism which is similar to hydrodehalogenation of CFC-12. Over Ni catalysts, the primary hydrodehalogenation reactions are those which first remove one halogen (Cl or Br) and then remove two halogens (one F and either Br or Cl). The higher mobility of hydrogen atom on the surface of Pt is consistent with the observation that only trace amounts of C2+ hydrocarbons were detected when Pt was used compared with Pd and Ni. Increasing selectivity to CH2F2 with time on stream over Pd and Pt is mainly ascribed to the transformation of support alumina to partially fluorinated alumina.
Allen Vinegar - One of the best experts on this subject based on the ideXlab platform.
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modeling cardiac sensitization potential of humans exposed to Halon 1301 or Halon 1211 aboard aircraft
Aviation Space and Environmental Medicine, 2001Co-Authors: Allen VinegarAbstract:VINEGAR A. Modeling cardiac sensitization potential of humans exposed to Halon 1301 or Halon 1211 aboard aircraft. Aviat Space Environ Med 2001; 72928-36. Background: Halon 1301 and Halon 121 1 are being replaced because they contribute to the depletion of ozone. Many of the potential candidate chemicals for replacing them are, like them, halogenated hydrocarbons. These chemicals have the potential to cause cardiac sensitization at high enough exposure concentrations. Methods: A physiologically based pharmacokinetic model, which mathematically describes the uptake, distribution, metabolism, and elimination of chemicals, was used to relate exposure to these chemicals with arterial blood concentrations resulting from the exposure. This information was then used to evaluate the potential for the occurrence of a cardiac-sensitizing event. The model was used to analyze the exposures to Halon 1301 and Halon 1211 in three aircraft (Navy E-28, Cessna-4218, and Cessna21 OC). Results: Halon 1301 exposures were shown to be safe, but Halon 12 1 1 resulted in arterial concentrations in exposed individuals that reached levels that could potentially cause cardiac sensitization. Conclusions: Use of the model for evaluating the risk from exposure to Halon 1301 and Halon 121 1 is a moot point since both chemicals are being replaced. However, demonstration of the validity of the approach provides a tool for the evaluation of the health safety of replacement candidates. The National Fire Protection Association has approved use of this model for assessing times for safe egress from situations where agents are used to flood an area to extinguish a fire.
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setting safe acute exposure limits for Halon replacement chemicals using physiologically based pharmacokinetic modeling
Inhalation Toxicology, 2000Co-Authors: Allen Vinegar, Gary W Jepson, Mark Cisneros, Reva Rubenstein, William J BrockAbstract:Most proposed replacements for Halon 1301 as a fire suppressant are halogenated hydrocarbons. The acute toxic endpoint of concern for these agents is cardiac sensitization. An approach is described that links the cardiac endpoint as assessed in dogs to a target arterial concentration in humans. Linkage was made using a physiologically based pharmacokinetic (PBPK) model. Monte Carlo simulations, which account for population variability, were used to establish safe exposure times at different exposure concentrations for Halon 1301 (bromotrifluoromethane), CF3I (trifluoroiodomethane), HFC-125 (pentafluoroethane), HFC-227ea (1,1,1,2,3,3,3-heptafluoropropane), and HFC-236fa (1,1,1,3,3,3- hexafluoropropane). Application of the modeling technique described here not only
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cardiac sensitization testing of the Halon replacement candidates trifluoroiodomethane cf3i and 1 1 2 2 3 3 3 heptafluoro 1 iodopropane c3f7i
Drug and Chemical Toxicology, 1998Co-Authors: Darol E Dodd, Allen VinegarAbstract:ABSTRACTTrifluoroiodomethane (CF3I) and 1,1,2,2,3,3,3-heptafluoro-1-iodopropane (C3F7I) have been considered as replacement candidates for Halon fire suppressants due to their excellent fire extinguishant capabilities and low ozone depletion potential compared to Halon fire extinguishants in use currently. As part of the process to develop environmental and health effects criteria for Halon substitutes, a cardiac sensitization test was conducted in beagle dogs. Cardiac sensitization to adrenaline is a phenomenon associated with the inhalation of a number of unsubstituted and halogenated hydrocarbons. Adrenaline was administered by intravenous injection before and during inhalation of the test substance. CF3I was administered to dogs at concentrations in air of 0.1, 0.2, 0.4 or 1% v/v. At each of 0.4 and 1.0% CF3I, the first dog exposed developed fatal ventricular fibrillation, and no further dogs were exposed at these concentrations. There was no cardiac sensitization at 0.1 or 0.2% CF3I. For the C3F7I ex...
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human inhalation of Halon 1301 hfc 134a and hfc 227ea for collection of pharmacokinetic data
1997Co-Authors: Allen Vinegar, Gary W Jepson, Robert S Cook, Mccafferty James D, Melanie C CaracciAbstract:Abstract : International agreement and regulatory decisions have driven activities to replace ozone depleting chemicals (ODCs) in fire suppression and refrigeration applications. In order to validate a human physiologically based pharmacokinetic model designed for use in estimating chemical biodistribution and establishing egress times, human volunteers were exposed via inhalation to a series of chemicals relevant to ODC replacement activity. Seven male volunteers ranging from 21-49 years of age were selected to inhale bromotrifluoromethane (Halon 1301 0.5%), 1,1,1,2-tetrafluoroethane (HFC-134a, 0.4%) and 1,1,1,2,3,3,3-heptafluoropropane (HFC-227ea, 0.6%). Each inhalation exposure was to a single chemical and was scheduled to last 30 minutes. Inhaled concentration and end alveolar expired concentration of chemical were continuously measured throughout the procedure using a non-rebreathing valve inhalation apparatus and a mass spectrometer. Blood samples were drawn through an indwelling cannula at times 0, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 10, 15, 20, 25 and 30 minutes during the exposure and for five minutes at one minute intervals following the inhalation. The blood was analyzed for the chemical of interest to determine the chemical time course in blood. Throughout the exposure period, human subjects were monitored via ECG, blood pressure and pulse rate measurements. All seven volunteers completed the Halon 1301 exposures without effect on ECG, blood pressure or pulse rate. Halon 1301 concentrations in blood at exposure termination ranged from 0.19-1.24 mg/L. The HFC-134a and HFC-227ea exposures were terminated for safety reasons following unexpected and uncontrollable rapid rises in pulse rate during the inhalation exposure.
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cardiac sensitization thresholds of Halon replacement chemicals predicted in humans by physiologically based pharmacokinetic modeling
Risk Analysis, 1996Co-Authors: Allen Vinegar, Gary W JepsonAbstract:Human exposure to Halons and Halon replacement chemicals is often regulated on the basis of cardiac sensitization potential. The dose-response data obtained from animal testing are used to determine the no observable adverse effect level (NOAEL) and lowest observable adverse effect level (LOAEL) values. This approach alone does not provide the information necessary to evaluate the cardiac sensitization potential for the chemical of interest under a variety of exposure concentrations and durations. In order to provide a tool for decision-makers and regulators tasked with setting exposure guidelines for Halon replacement chemicals, a quantitative approach was established which allowed exposures to be assessed in terms of the chemical concentrations in blood during the exposure. A physiologically-based pharmacokinetic (PBPK) model was used to simulate blood concentrations of Halon 1301 (bromotrifluoromethane, CF3Br), HFC-125 (pentafluoroethane, CHF2CF3), HFC-227ea (heptafluoropropane, CF3CHFCF3), HCFC-123 (dichlorotrifluoroethane, CHCl2CF3), and CF3I (trifluoroiodomethane) during inhalation exposures. This work demonstrates a quantitative approach for use in linking chemical inhalation exposures to the levels of chemical in blood achieved during the exposure.
Boris Svistunov - One of the best experts on this subject based on the ideXlab platform.
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Halon a quasiparticle featuring critical charge fractionalization
Physical Review B, 2018Co-Authors: Kun Chen, Yuan Huang, Youjin Deng, Boris SvistunovAbstract:The Halon is a special critical state of an impurity in a quantum-critical environment. The hallmark of the Halon physics is that a well-defined integer charge gets fractionalized into two parts: a microscopic core with half-integer charge and a critically large halo carrying a complementary charge of $\ifmmode\pm\else\textpm\fi{}1/2$. The Halon phenomenon emerges when the impurity-environment interaction is fine-tuned to the vicinity of a boundary quantum critical point (BQCP), at which the energies of two quasiparticle states with adjacent integer charges approach each other. The universality class of such BQCP is captured by a model of pseudospin-$1/2$ impurity coupled to the quantum-critical environment, in such a way that the rotational symmetry in the pseudospin $xy$ plane is respected, with a small local ``magnetic'' field along the pseudospin $z$ axis playing the role of control parameter driving the system away from the BQCP. On the approach to BQCP, the half-integer projection of the pseudospin on its $z$ axis gets delocalized into a halo of critically divergent radius, capturing the essence of the phenomenon of charge fractionalization. With large-scale Monte Carlo simulations, we confirm the existence of Halons---and quantify their universal features---in O(2) and O(3) quantum critical systems.
