PAPER
Proceedings of the
1994 Halon Options Technical Working
Conference,
University of New Mexico, Albuquerque, NM, May 3-5, 1994
AbstractFor more information regarding this subject, please contact Dr. Nimitz at mailto:jnimitz@etec-nm.com
This paper describes the selection, properties, and current status of validation of trifluoromethyl iodide (CF3I) and its blends as attractive candidate Halon 1301 replacements. In an effort sponsored by the U.S. Air Force, five groups of chemicals were investigated: fluoroiodocarbons (FICs), geminal hydrodibromides (GHDBs), fluoroethers, hydrofluorocarbons (HFCs), and perfluorocarbons. Neat CF3I and selected blends of CF3I with HFCs 125, 134a, and 227ea were identified as outstanding candidate Halon 1301 replacements. These agents appear to meet all the desired criteria, including cleanliness, high firefighting effectiveness, very low toxicity and environmental impact, and acceptable stability and compatibility with engineering materials. The reasoning behind the selection of CF3I and its blends with selected HFCs, known information on these chemicals, and computer modeling of properties of blends are discussed. Information is given on physical properties, firefighting effectiveness, toxicities of the agents and combustion products, environmental properties (including ozone-depletion potential, global warming potential, and possible reactivity as volatile organic compounds), stability on storage, cost, and availability. The likely concentrations of optimal blends are presented. Properties predicted for attractive blends are discussed. Predicted optimal agents and their weighted rankings are given, with recommendations for the remaining validation work required.Introduction
Last year at the Halon Alternatives Technical Working conference a poster paper was presented entitled "The Ultimate Halon Replacements are in Sight" (Ref. 1). This paper uniquely described the class of chemicals most likely to provide outstanding long-term halon replacements for both flooding and streaming agents. This group consists of fluoroiodocarbons (FICs), chemicals containing fluorine, iodine, and carbon. FICs possess all the desirable properties of high firefighting effectiveness, negligible environmental impacts, and (in most cases) very low toxicities. The desirable properties of FICs have been described in some detail in publications during the past year. (Refs. 2-4)Observations on Groups of Chemicals Examined
Five groups of chemicals were originally investigated as potential long-term halon replacements: fluoroiodocarbons (FICs), geminal hydrodibromides (GHDBs), fluoroethers, hydrofluorocarbons (HFCs), and perfluorocarbons.FICs are extinguishants that perform similarly to halons, in both laboratory and field tests (Refs. 2-4). Results of thermal stability testing at the New Mexico Engineering Research Institute (NMERI) indicate that CF3I is stable at 180°F for at least 60 days. When released into the atmosphere, the C-I bond undergoes rapid photolysis in sunlight, and the atmospheric lifetime of CF3I has been estimated at 1.15 days (Ref. 5). Because of this short atmospheric lifetime, the fraction surviving to reach the stratosphere will be vanishingly small. For example, if a 60-day average transit time is assumed, the fraction surviving to reach the stratosphere would be e-60/1.15or about 10-23. This calculation does not account for any rapid mixing that may occur between the troposphere and stratosphere by tropical storms. It has been speculated that such mixing could conceivably raise the ODP for surface release to approximately 0.01. The author estimates that the actual ODP for tropospheric release will be somewhere between these values, perhaps somewhere between 1 X 10-5 and 1 x 10-10. In any case the effects on stratospheric ozone are likely to be negligible and the improvement over the ODPs of current halons will be many orders of magnitude. If FICs are released directly into the stratosphere (from aircraft in flight above the tropopause) the ODP will be much higher, probably comparable to that of Halon 1301. However, the quantities of halons released annually directly into the stratosphere worldwide appear to be very small, on the order of only 1,000 or 2,000 lbs.
Toxicity data on FICs are highly encouraging (Refs. 2-4). Incomplete reports in the older literature indicate low acute toxicities for CF3I and CF3CF2CF2I. Recent results from Armstrong Labs for CF3I indicate very low acute toxicity and rapid elimination from the body (Ref 6). The only FIC for which adverse toxicity data has been found is the two-carbon FIC, perfluoroethyl iodide, CF3CF2I, which is reported to be a strong cardiac sensitizer (Ref. 4). For this reason perfluoroethyl iodide has not been pursued as a streaming agent, despite attractive physical properties and extinguishment ability.
GHDBs are outstanding extinguishants (considerably superior to halons and FICs) but even the most volatile GHDBs (CHFBr2 and CF3CHBr2) are liquids and do not possess attractive physical properties for total flooding agents. In addition, because of the nonzero ODP (estimated by the author at 0.05 to 0.2), restrictions on hydrobromofluorocarbons under the Montreal Protocol, and concerns about toxicity, geminal hydrobromides are considered much less attractive than FICs.
HFCs are the most attractive group of blending agents to mix with FICs for firefighting. They have several advantages over fluoroethers and perfluorocarbons. HFCs have moderate firefighting ability, low toxicity, low cost, good stability, and good physical properties as total flooding agents. They have zero ODP and moderate GWPs. The only environmental factor of concern is the GWP, which might possibly lead to future regulations on releases of HFCs. However, if the HFCs used are the ones with shorter atmospheric lifetimes and as much as possible is trapped and recycled, their use may be acceptable. In examination of HFCs as potential blending agents, HFCs 32 and 143a were eliminated from consideration because of their flammability and scarcity, and perfluoropropane because of its high GWP. This left as the top candidates pure CF3I and blends of CF3I with HFCs 134a or 227ea. Blends of CF3I with HFC-134a or 227ea are predicted to be near-azeotropic or azeotropic. Any of these agents could also include the slightly higher-pressure agent HFC-125, which would assist as a propellant and is an effective extinguishant in it own right. In summary, the HFCs appearing most attractive for blending with CF3I are HFCs 125, 134a, and 227ea.
Because of their very limited availability, unexceptional extinguishing ability, relatively high GWPs, and, in some cases, thermal instabilities, fluoroethers appear to hold no advantages over HFCs and were ruled out as attractive components of firefighting agents at this time.
Although perfluorocarbons are very attractive from the standpoints of low toxicity, high firefighting effectiveness, and current availability in bulk at reasonable cost, their high GWPs make them less attractive than HFCs.
Table 1 shows that, on all bases of measurement (gas volume percent, relative weight, and relative volume), CF3I is a much more effective firefighting agent than any of the HFCs listed. Whereas HFCs in general require two to three times the weight and volume of Halon 1301, trifluoromethyl iodide requires less volume and only about 40% more weight.
Table 1. Relative Weights and Volumes of Total Flooding Agents Compared to Halon 1301.
Agent Name Formula MW Liquid
DensityCup
burner %Rel. Wt. Rel. Vol. Halon 1301 CF3Br 148.91 1.50 2.90 1.00 1.00 trifluoromethyl iodide CF3I 195.91 2.36 3.00 1.36 0.87 HFC-125 CF3CHF2 120.00 1.23 9.40 2.61 3.19 HFC-134a CF3CH2F 102.00 1.20 10.50 2.48 3.10 HFC-227ea CF3CHFCF3 170.00 1.42 5.90 2.32 2.45 Selection of CF3I
The only FIC with a boiling point below 0°C, and therefore the only FIC suitable for total flooding, is CF3I (boiling point -22.5°C). Selected properties of CF3I are shown in Table 2.
Table 2. Selected Properties of CF3I
Property Value boiling point at 1 atm pressure -22.5°C = -8.5°F bond dissociation energy 54 kcal/mole CAS number 2314-97-8 critical pressure 4.04 MPa critical temperature 395 K critical volume 225 cm3/mole dipole moment 0.92 electron affinity 150 ± 20 kJ/mol heat of formation -141 kcal/mole heat of vaporization 22 kJ/mol liquid density 2.36 at -32.5°C molecular weight 195 refractive index (liquid) 1.379 at -42°C vapor heat capacity, Cp 70.9 J/mol-K vapor pressure at 20°C 85 psia The combustion products of CF3I are HF, CO2, and HI. The only qualitative difference between combustion products of halons and FICs is the production of HI instead of HBr (and, for Halon 1211, HCl). Although the data on toxicity of HI are limited, it appears to be comparable in acute toxicity to other acid gases (such as HF, HBr, and HCl). The facts that the human body requires iodine and can use and excrete it effectively indicate that the long-term effects of HI may be less than those of HBr. It is possible that, because of the lower bond strength in CF3I compared to CF3Br, the quantities of combustion products under given conditions may be greater from FICs than halons. However, given the limited human exposure and the large quantities of toxic gases produced from fuels without any extinguishing agent, combustion products of FICs are not expected to pose a problem. In addition, the lower C-I bond strength in FICs compared to the C-Br bond strength in halons may mean that a larger percentage breaks down in the fire and a smaller amount of agent may be required. The relative ease of decomposition of FICs in flames may especially aid extinguishment of large, hot fires.
Advantages of Blends
Military specifications require an effective temperature range of -65°F (-54°C) to 165°F (74°C). The low end of range is encountered in airborne aircraft and at ground level at higher latitudes. The boiling point of CF3I (-22.5°C or -8.5°F) is much higher than that of Halon 1301 (-56°C or -72°F). This higher boiling point means CF3I is much less volatile than Halon 1301; below -22.5°C CF3I will be discharged as a liquid and will remain as a liquid. Although a liquid can be dispersed finely, it does not fill quickly around obstacles. If a fast response time is required (e.g., a few milliseconds as in tanks and aircraft dry bays) it might not be possible to obtain the necessary inertion speed with a liquid agent. Although it is possible that appropriate engineering (nozzles, pressures) can deliver pure CF3I effectively at low temperatures, adding a blending agent may increase the vapor pressure and improve performance at low temperatures. The ideal blend would be a low-boiling azeotrope in which the components have synergistic suppressant effects (better than expected extinguishment from the combined effects of the components).Optimal Blends
It is possible to design blends that are expected to have the same performance per unit volume as (are isovolumic with) Halon 1301. Examples of such blends are shown in Table 3.
Table 3. Blends Isovolumic with Halon 1301
Blending Agent Mole Fraction
CF3IMole Fraction
Blending AgentRel.Wt. HFC-125 0.93 0.07 1.44 HFC-134a 0.87 0.13 1.50 HFC-227ea 0.93 0.07 1.42 As shown in Table 3, it appears possible to formulate agents with the same performance per unit liquid volume as Halon 1301, with a gain in agent weight of 40% to 50%. It should be noted that these are not necessarily the most attractive blends possible.
Some additional properties of CF3I and top candidate blending agents are given in Table 4.
Table 4. Additional Properties of CF3I and Top Candidate Blending Agents
Agent GWP
(CFC-11 = 1.0)Toxicity
(2-hr LC50, ppm)Est. Cost($/lb in 1995) CF3I 0.0027 unknown 30.00 HFC-125 0.58 >700,000 11.00 HFC-134a 0.27 >500,000 7.50 HFC-227ea 0.45 >800,000 12.00 Candidate agents were ranked on the basis of the following criteria (with weightings): extinguishing efficiency (25%), toxicity (25%), materials compatibility (10%), ODP (20%), GWP (10%), and cost (10%). Since all candidates considered have zero or extremely close to zero ODP, all were given full scores in this area. All candidates were also given full scores for materials compatibility on the basis of reported information indicating that all are probably compatible with an acceptably wide range of materials. The areas where agents differed were in extinguishing efficiency, toxicity, GWP, and cost. Weighted rankings for all factors considered are given in Table 5. In Table 5 for simplicity blends are considered to be equal parts of each component.
Table 5. Weighted Rankings of Candidate Halon 1301 Replacements
Ext.
Eff.Toxicity Mat.
Comp.ODP GNP Cost Total % Weighting 25 25 10 20 10 10 100 Rank Candidate 1 CF3I/HFC-227ea 24 23 10 20 8 8 93 2 CF3I/HFC-134a/HFC-125 21 25 10 20 7 9 92 3 CF3I/HFC-134a 20 21 10 20 9 10 90 4 CF3I/HFC-227ea/HFC-125 23 24 10 20 6 7 90 5 neat CF3I 25 20 10 20 10 5 90 6 CF3I/HFC-125 22 22 10 20 5 6 85 The top blends finally recommended for testing are shown in Table 6. All of these blends could also contain a small amount of HFC-125 (perhaps 10% to 30% by moles).
Table 6. Top Halon 1301 Replacement Candidates for Phase II Testing
Component 1 Component 2 Mole Percentages CF3I none 100:0 CF3I HFC-134a 50:50 to 80:20 CF3I HFC-227ea 20:80 to 80:20 The AZEO Program
ETEC has developed a proprietary computer program, called AZEO, that calculates properties of mixtures and predicts azeotrope formation and composition. Mathematical modeling in this program is based upon the theory of corresponding states using a third order virial equation of state (Refs. 1-3). AZEO uses the well-documented Soave modification of the Redlich-Kwong equation of state, specifically fitted to small halogenated hydrocarbons. The Pitzer-Curl method is used to calculate mixture cross-correlation coefficients. The required inputs for each chemical are the molecular weight, normal boiling point, critical temperature, and critical pressure.The AZEO program correctly calculates properties of all known azeotropes tested (including R-500 and R-502) within 1% accuracy. AZEO runs on a PC, works for up to five-component mixtures, and allows a choice of units. It identifies probable azeotropes, near-azeotropes, and non-azeotropes. For azeotropes and near-azeotropes, it gives the approximate azeotropic composition. It calculates vapor pressure curves and gives enthalpies of vaporization and specific heats of liquid and vapor as functions of temperature. AZEO provides pressure-volume-temperature data with an accuracy within 1% and enthalpies of vaporization within 2%. AZEO is only a tool for initial screening to identify attractive blends and possible azeotropes; all results obtained from AZEO must be validated by laboratory measurements.
In the most recent version of the AZEO program, the equation of state can be optionally fitted to experimental vapor pressure data. For pure substances this allows highly accurate modeling, and for mixtures it decreases the error below 5%. This greatly improves the accuracy of modeling without the need for binary interaction coefficients as required in Carnahan-Starling-deSantis (CSD) modeling. If binary interaction coefficients are available and CSD modeling is used, the error can be reduced to about 1%.
Calculated properties from AZEO for pure CF3I and for blends of 60:40 by moles CF3I:HFC-134a and CF3I:HFC-227ea are given in Tables 7 through 9.
Table 7. Calculated Properties of Pure CF3I
THERMODYNAMIC DATA FOR FILE NAME PURECF3I
DATE: 05-01-1994
TIME: 16:02:18TEMP PRESSURE VOLUME
VAPOR
VgDENSITY
LIQUID
1/VfENTHALPY ENTROPY LIQUID
HfLATENT
HfgVAPOR
HgLIQUID
SfVAPOR
Sg°F psia ft3/lbm lb/ft3 BTU/lb BTU/lb°R -40.0 6.544 3.4141 148.701 0.000 47.10 47.10 0.00000 0.1114 -30.0 8.526 2.676 147.422 0.416 47.23 47.64 0.0010 0.1111 -20.0 11.013 2.105 146.067 1.332 47.34 48.67 0.0032 0.1108 -10.0 14.087 1.6671 144.632 2.325 47.33 49.66 0.0053 0.1104 0.0 17.85 1.339 143.112 3.396 47.21 50.61 0.0076 0.1100 10.0 22.412 1.081 141.507 4.544 46.98 51.52 0.0099 0.1096 20.0 27.892 0.880 139.803 5.770 46.62 52.39 0.0122 0.1091 30.0 34.416 0.722 137.999 7.073 46.15 53.22 0.0146 0.1086 40.0 42.117 0.596 136.091 8.454 45.56 54.02 0.0171 0.1080 50.0 51.132 0.495 134.071 9.912 44.86 54.77 0.0196 0.1074 60.0 61.603 0.413 131.934 11.448 44.04 55.49 0.0222 0.1068 70.0 73.674 0.347 129.629 13.062 43.10 56.17 0.0248 0.1061 80.0 87.490 0.293 127.242 14.752 42.05 56.80 0.0275 0.1054 90.0 103.198 0.248 124.743 16.521 40.88 57.40 0.0302 0.1047 100.0 120.942 0.211 122.055 18.367 39.60 57.96 0.0330 0.1039 110.0 140.866 0.180 119.206 20.290 38.20 58.49 0.0359 0.1031 120.0 163.114 0.154 116.181 22.291 36.68 58.97 0.0388 0.1023 130.0 187.828 0.132 112.963 24.370 35.04 59.41 0.0418 0.1014 140.0 215.152 0.113 109.531 26.526 33.29 59.82 0.0448 0.1005 150.0 245.230 0.097 105.853 28.759 31.42 60.18 0.0479 0.0995 160.0 278.214 0.084 101.878 31.070 29.44 60.51 0.0510 0.0985 170.0 314.260 0.072 97.503 33.459 27.34 60.79 0.0542 0.0975 180.0 353.538 0.062 92.417 35.925 25.12 61.04 0.0575 0.0964
Property = Constant + ....* Tr + ....* Trr**2 + ....* Tr **3 ....* Tr **4 Psat -1.11762E+03 55.125E+02 -8.6197E+03 3.2065E+03 1.7630E+03 Vg 5.35592E+02 -26.599E+02 4.9648E+03 -4.1228E+03 1.2840E+03 Ldens 4.61149E+0l 40.060E+0l -3.8695E+02 0.0000E+00 0.0000E+00 Hf 3.58612E+0l -17.867E+0l 1.9681E+02 0.0000E+00 0.0000E+00 Hfg -6.73910E+0l 36.760E+0l -2.9439E+02 0.0000E+00 0.0000E+00 Hg -1.45296E+Ol 11.945E+Ol -1.8495E+00 -4.1762E+0l 0.0000E+00 Sf -3.34955E-02 -32.272E-03 1.4844E-01 0.0000E+00 0.0000E+00 Sg 9.08407E-02 89.762E-03 -9.294SE-02 0.0000E+00 0.0000E-00 Tmin = -40°F Tmax = 185°F USE CAUTION EXTRAPOLATING ABOVE AND BELOW ENDPOINTS Cpv = .1037254 Cp/Cv = 1.172219 Cpliq = .1768405 at -300(K) Tr = Tabs(I) / T(crit) Tc = 711.7493 (R) or 395.4163 (K) Table 8. Calculated Properties of a 60:40 (by moles) Blend of CF3I and HFC-134a
THERMODYNAMIC DATA FOR FILE NAME 22196040
DATE: 05-02-1994
TIME: 22:03:00TEMP PRESSURE VOLUME
VAPOR
VgDENSITY
LIQUID
1/VfENTHALPY ENTROPY LIQUID
HfLATENT
HfgVAPOR
HgLIQUID
SfVAPOR
Sg°F psia ft3/lbm lb/ft3 BTU/lb BTU/lb°R -40.0 6.912 3.998 122.733 0.000 56.84 56.84 0.0000 0.1345 -30.0 8.963 3.145 121.687 0.490 57.02 57.51 0.0012 0.1341 -20.0 11.505 2.493 120.582 1.490 57.26 58.75 0.0035 0.1337 -10.0 14.634 1.992 119.414 2.587 57.36 59.95 0.0060 0.1333 0.0 18.451 1.604 118.178 3.783 57.32 61.11 0.0085 0.1329 10.0 23.066 1.302 116.871 5.076 57.14 62.21 0.0110 0.1324 20.0 28.597 1.064 115.489 6.467 56.81 63.28 0.0137 0.1318 30.0 35.172 0.875 114.027 7.956 56.34 64.30 0.0165 0.1312 40.0 42.924 0.724 112.480 9.543 55.73 65.27 0.0193 0.1306 50.0 51.997 0.602 110.843 11.228 54.98 66.20 0.0222 0.1299 60.0 62.535 0.504 108.937 13.011 54.08 67.09 0.0252 0.1292 70.0 74.691 0.424 107.273 14.891 53.04 67.93 0.0283 0.1284 80.0 88.617 0.358 105.324 16.869 51.86 68.73 0.0314 0.1276 90.0 104.470 0.303 103.133 18.945 50.53 69.48 0.0347 0.1267 100.0 122.409 0.258 100.945 21.119 49.07 70.19 0.0380 0.1258 110.0 142.592 0.220 98.718 23.391 47.46 70.85 0.0414 0.1249 120.0 165.179 0.188 96.222 25.760 45.71 71.47 0.0449 0.1239 130.0 190.332 0.161 93.555 28.228 43.81 72.04 0.0484 0.1229 140.0 218.213 0.139 90.640 30.793 41.78 72.57 0.0521 0.1218 150.0 248.990 0.119 87.576 33.456 39.60 73.06 0.0558 0.1207 160.0 282.833 0.103 84.258 36.217 37.28 73.50 0.0596 0.1195 170.0 319.920 0.088 80.628 39.075 34.82 73.89 0.0635 0.1183
Property = Constant + ....* Tr + ....* Trr**2 + ....* Tr **3 ....* Tr **4 Psat -7.18695E+02 30.371E+02 -3.0516E+03 -2.0749E+03 3.4690E+03 Vg 6.65970E+02 -32.686E+02 6.0349E+03 -4.9612E+03 1.5308E+03 Ldens 5.08014E+0l 28.717E+0l -2.7981E+02 0.0000E+00 0.0000E+00 Hf 5.17715E+0l -23.104E+01 2.3979E+02 0.0000E+00 0.0000E+00 Hfg -8.73097E+0l 44.596E+01 -3.4362E+02 0.0000E+00 0.0000E+00 Hg -1.07300E+0l 11.455E+0l 3.0355E+0l -5.9297E+0l 0.0000E+00 Sf -1.79342E-02 -95.279E-03 2.0476E-01 0.0000E+00 0.0000E+00 Sg 1.09118E-01 10.557E-02 -1.0539E-01 0.0000E+00 0.0000E+00 Tmin = -40°F Tmax = 170°F USE CAUTION EXTRAPOLATING ABOVE AND BELOW ENDPOINTS Cpv = .1254605 Cp/Cv = 1.179785 Cpliq = .2076032 at 300 (K) Tr = Tabs(I) / T(crit) Tc = 696.024 (R) or 386.68 (K) Table 9. Calculated Properties of a 60:40 (by moles) Blend of CF3I and HFC-227ea
THERMODYNAMIC DATA FOR FILE NAME 22936040
DATE: 05-02-1994
TIME: 22:07:16TEMP PRESSURE VOLUME
VAPOR
VgDENSITY
LIQUID
1/VfENTHALPY ENTROPY LIQUID
HfLATENT
HfgVAPOR
HgLIQUID
SfVAPOR
Sg°F psia ft3/lbm lb/ft3 BTU/lb BTU/lb°R -40.0 6.087 3.871 129.148 0.000 51.34 51.34 0.0000 0.1214 -30.0 7.985 3.014 123.383 0.576 51.34 51.91 0.0013 0.1211 -20.0 10.405 2.347 122.182 1.553 51.49 53.04 0.0036 0.1208 -10.0 13.419 1.846 120.901 2.634 51.49 54.12 0.0060 0.1204 0.0 17.134 1.466 119.536 3.817 51.34 55.16 0.0085 0.1199 10.0 21.669 1.175 118.089 5.104 51.04 56.15 0.0111 0.1194 20.0 27.150 0.949 116.538 6.493 50.60 57.09 0.0138 0.1189 30.0 33.714 0.773 114.887 7.986 50.00 57.99 0.0165 0.1183 40.0 41.508 0.633 113.139 9.582 49.26 58.84 0.0194 0.1177 50.0 50.683 0.522 111.267 11.280 48.37 59.65 0.0223 0.1170 60.0 61.397 0.433 109.288 13.082 47.33 60.41 0.0253 0.1163 70.0 73.815 0.361 107.163 14.987 46.14 61.13 0.0285 0.1156 80.0 88.104 0.302 104.915 16.994 44.80 61.80 0.0317 0.1148 90.0 104.436 0.254 102.523 19.105 43.32 62.42 0.0350 0.1139 100.0 122.988 0.214 99.973 21.319 41.68 63.00 0.0384 0.1130 110.0 143.937 0.181 97.246 23.636 39.90 63.53 0.0418 0.1121 120.0 167.468 0.153 94.309 26.056 37.97 64.02 0.0454 0.1111 130.0 193.771 0.129 91.071 28.578 35.89 64.46 0.0491 0.1101 140.0 223.044 0.109 87.565 31.204 33.66 64.86 0.0528 0.1091 150.0 255.497 0.093 83.705 33.933 31.28 65.21 0.0566 0.1080 160.0 291.354 0.078 79.166 36.765 28.75 65.52 0.0606 0.1068 170.0 330.862 0.066 73.149 39.700 26.07 65.77 0.0646 0.1056
Property = Constant + ....* Tr + ....* Trr**2 + ....* Tr **3 ....* Tr **4 Psat -3.27640E+02 70.061E+0l 2.2604E+03 -7.5292E+03 5.5982E+03 Vg 6.89689E+02 -33.907E+02 6.2645E+03 -5.1489E+03 1.5872E+03 Ldens 1.59034E+0l 40.715E@0l -3.7726E+02 0.0000E+00 0.0000E+00 Hf 5.71950E+0l -24.710E+0l 2.5181E+02 0.0000E+00 0.0000E+00 Hfg -9.46044E+0l 45.798E+0l -3.5881E+02 0.0000E+00 0.0000E@00 Hg -1.51102E+0l 12.098E+0l 1.2752E+0l -5.2703E+0l 0.0000E+00 Sf -9.4338SE-03 -12.044E-02 2.236SE-01 0.0000E+00 0.0000E+00 Sg 9.51206E-02 10.772E-02 -1.0626E-01 0.0000E+00 0.0000E+00 Tmin = -40°F Tmax = 175°F USE CAUTION EXTRAPOLATING ABOVE AND BELOW ENDPOINTS Cpv= .1127048 Cp/Cv = 1.170613 Cpliq = .2110773 at 300 (K) Tr = Tabs(I) / T(crit) Tc = 696.4921 (R) or 366.94 (K) Streaming Agents
The observation that perfluoropropyl iodide should be an excellent Halon 1211 replacement has been published (Refs. 2 and 3) . Table 10 shows properties of selected streaming agents. Table 10 shows that perfluoro-n-propyl iodide is a much more effective firefighting agent than HCFC-123 or perfluorohexane. While HCFC-123 and perfluorohexane require about two to three times the weight and volume of Halon 1211, perfluoro-n-propyl iodide is predicted to require only about 80% more weight and 60% more volume. These estimates are of necessity very crude because they cannot take into account deliverability factors or effects of larger, hotter fires. There are several reasons why FICs are expected to be even more effective on larger, hotter fires. The weaker C-I bond will result in a higher fraction decomposing in the flames, and some may undergo photolysis. Heat also makes C-I bonds more susceptible to photolysis.
Table 10. Relative Weights and Volumes of Streaming Agents Compared to Halon 1211.
Agent Name Formula MW Liquid
DensityCup
burner %Rel. Wt. Rel. Vol. Halon 1211 CF2ClBr 165.37 1.85 3.2 1.00 1.00 Halon 2402 CF2BrCF2Br 259.82 2.16 2.1 1.03 0.88 HCFC-123 CHCl2CF3 152.93 1.46 6.3 1.81 2.29 perfluorohexane C6Fl4 338.06 1.70 4.4 2.82 3.07 perfluoro-n-propyl iodide CF3CF2CF2I 295.93 2.10 3.2 1.79 1.58 dibromofluoromethane CHBr2F 191.80 2.42 1.8 0.65 0.50 Other Uses of FICs
Although the effort described in this paper was limited to the examination of total-flooding firefighting agents, the potential usefulness of FICs is not limited to this area. As described above, 1-C3F7I shows strong potential as a streaming agent. FICs and blends containing FICs also show excellent potential as general CFC replacements in many applications. The author and his co-inventor Lance Lankford have successfully demonstrated several other promising uses of FICs. For example, a mixture of 52% by moles CF3I and 48% HFC-152a has been shown to be a nonflammable, high-performance drop-in replacement for CFC-12 in refrigeration without changing the mineral oil lubricant (Ref. 7). Trifluoromethyl iodide, both alone and in blends, has been successfully demonstrated as a foam blowing agent (Ref. 8). Calculations predict that rigid foams blown with FICs will have insulating abilities 10% to 40% greater than those blown with conventional agents and will have a payback period of less than one year for refrigerators. Tests by the author using two FICs (perfluoro-n-butyl iodide and perfluoro-n-hexyl iodide) as solvents have shown that they are effective cleaners for oils and greases, are miscible with a wide range of common solvents, and can render mixtures with other common solvents nonflammable (Ref. 9).The Ikon Corporation has been formed to promote testing, development, manufacture, and use of FIC technologies, provide know-how and technical support, license FIC technologies, and make available the benefits of FIC technologies worldwide.
Additional Validation Work Required
Since the first and second interim reports for this effort were submitted in March and June 1993 (Refs. 10 and 11) and a paper and talk were presented on the subject (Ref 1), several of the recommendations made have already been implemented. Laboratory testing of the thermal stability of CF3I is underway at both the National Institute of Standards and Technology (NIST) and NMERI. Acute toxicity tests of CF3I have been completed by the U.S. Air Force at Armstrong Laboratories. Two pilot plants to manufacture CF3I have come into operation, and the price has already dropped by over 75% (from over $600/lb to less than $150/lb). It is estimated that bulk costs of production of CF3Iwill be in the range of $5 to $10/lb.It is recommended that cup-burner tests on the top-ranking blends identified in this effort begin immediately. The purpose of these tests will be to determine the optimum concentrations of components in the recommended blends for greatest ease of delivery and firefighting effectiveness at the lowest cost. Each pair or triad of agents should be tested at the range of concentrations specified, with special attention paid to detecting possible synergism. Tests for formation of binary and ternary azeotropes among the top recommended chemicals (CF3I and HFCs 125, 134a, and 227ea) should also be carried out.
After the optimal blends have been identified through cup-burner and azeotrope testing, cardiotoxicity testing should be carried out on the most attractive blend(s) identified so that approval for use under the EPA SNAP program can be requested.
The concentrations of combustion products of FICs should be measured in a realistic fire scenario using established procedures, to determine possible firefighter exposures.
Additional studies of the tropospheric and stratospheric reactions of FICs should be carried out. These studies should be aimed at quantitative determination of the atmospheric lifetimes, effects of FICs on smog, and the extent of stratospheric ozone depletion that would occur if FICs were released directly into the stratosphere by high-flying aircraft.
It is recommended that CF3CF2CF2I and its blends be tested as streaming firefighting agents (Halon 1211 replacements). Work is underway on this through the efforts of Dr. Charles Kibert and Tyndall AFB. Dr. Kibert is also to be commended for his efforts in forming the "Ad Hoc CF3I Working Group" to exchange information among researchers.
A comprehensive toxicity testing program, possibly a new Program for Alternative Fluorocarbon Toxicity Testing (PAFT), should be undertaken to investigate the chronic and subchronic toxicities of CF3I and other FICs.
Because of the great promise of FICs hold as general CFC and halon replacements, it is recommended that acute toxicity testing be started as soon as possible on the other most promising FICs, including CF3CF2CF2I, CF3(CF2)3I, and CF3(CF2)5I. It is recommended that additional testing and validation of FICs and FIC-containing blends as refrigerants, solvents, foam-blowing agents, aerosol propellants, and hydraulic fluids be carried out. This effort will help aid the Air Force, other Department of Defense (DoD) and government agencies, and industrial users and consumers in their efforts to phase out ozone-depleting substances quickly and with minimum disruption of operations.
Acknowledgments
The author is grateful for support of work involving Halon 1301 replacements by the U.S. Air Force through McClellan AFB under contract F04699-93-C-0004. The support and encouragement of the project officer John Carroz, Lt. Col. Tom Duval, and General John Phillips are also gratefully acknowledged.References
- Nimitz, J. S. "The Ultimate Halon Replacements are in Sight," Proceedings of the 1993 Halon Alternatives Working Conference, University of New Mexico, Albuquerque, NM, May 11-13, 1993.
- Nimitz, J. S., High-Performance, Environmentally Sound Replacements for Halon 1301, Prepared for McClellan AFB under contract F04699-93-C-0004, December 1993, ETEC 93-3.
- Nimitz, J. S., and Lankford, L. H., "Fluoroiodocarbons as Halon Replacements," Proceedings of the 1993 International CFC and Halon Alternatives Conference, Washington DC, October 20-22, 1993.
- Skaggs, S. R., Dierdorf, D. S., and Tapscott, R. E., "Update on Iodides as Fire Extinguishing Agents," Proceedings of the 1993 CFC and Halon Alternatives Conference, Washington, DC, October 20-22, 1993, pp. 800-809.
- Personal communication from Dr. Susan Solomon, NOAA, Boulder, CO, to Dr. Jon Nimitz, ETEC, Albuquerque, NM, 1994.
- Personal communication from Major Gary Jepson, Armstrong Labs, Wright-Patterson AFB, OH, to Dr. Jon Nimitz, ETEC, Albuquerque, NM, 1994.
- Lankford, L. H., and Nimitz, J. S., "A New Class of High-Performance, Environmentally Sound Refrigerants" Proceedings of the 1993 International CFC and Halon Alternatives Conference, Washington DC, October 20-22,1993.
- Hurley, B., "FICs May be Next CFC and Halon Replacements," Global Environmental Change Report, Vol. 5, No. 19, October 8, 1993, pp. 1-3.
- Nimitz, J. S., and Lankford, L. H., "A New Class of Nonflammable, Environmentally Safe Solvents," Fourth Annual International Workshop on Solvent Substitution, Phoenix, AZ, Dec. 7-10, 1993.
- Nimitz, J. S., Non-Halon Fire Suppressants: First Interim Report, Prepared for McClellan AFB under contract F04699-93-C-0004, March 1993, ETEC 93-1.
- Nimitz, J. S., Non-Halon Fire Suppressants: Second Interim Report, Prepared for McClellan AFB under contract F04699-93-C-0004, June 1993, ETEC 93-2.