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Fire-Screening Results of Polymers and Composites Usman Sorathia and C. Beck. ABSTRACT Fire-screening tests performed by the U.S. Navy in the course of evaluating composite materials are summarized and the relative flammability charactenshcs of conventional and advanced fiber-reinforced thermoses and thermoplastic composite materials are discussed. The use of composites inside naval submarines is now covered by M~-STD-2031 (SH), Fire and Toxicity Test Methods and Qualification Procedure for Composite Material Systems Used in Hull, Machinery, ant! Structural Applications Inside Naval Submarines. This military standard contains test methods and requirements for flammability characteristics such as flame- spread index (ASTM E-162~; specific optical density of smoke (ASTM E-662; combustion gas generation, heat release, and ignitability as measured by cone calorimeter (ASTM E-13541; oxygen-temperature index; and long-term outgassing. Over the past 5-7 years, the Carderock Division of the Naval Surface Warfare Center (CDNSWC) has evaluated commercially available and development polymers and composites for flammability characteristics, with particular emphasis on heat release rates and ignitability (time to ignition) as determined by cone calorimetry. This paper presents the summary of relative flammability characteristics of conventional and advanced fiber-reinforced, organic matrix thermoses and thermoplastic composite materials suitable for surface ship and submarine applications. The thermoses materials evaluated included viny} esters (VE), epoxies (EP), cyanate ester (CE3, bismaleimides (BMI), phenolics (PH), and polyimides (Pl). Thermoplastic materials evaluated included polyphenylene sulfide (PPS), polyethersulfone, polyarylsulfone, polyetheretherketone (PEEK), and polyetherkeloneketone (PEKK). INTRODUCTION The introduction of composite materials into both the marine and aerospace industries began during the 1940s with the use of polyesters as the primary matrix material. Today, aerospace and aircraft use of composites relies heavily on graphite-reinforced epoxy and high glass transition temperature bismaleimide resins to provide optimum mechanical properties at much reduced weight, and on glass-reinforced phenolic and other thermoplastic materials for interior applications to meet Federal Aviation Requirements (FAR) fire-worthiness criteria. Aircraft and aerospace industries have successfully used the composite materials now for over 25 years. This is due to the premium placed on weight savings in the aircraft business. Current seaborne applications of composite materials in the U.S. Navy have been limited. For submarines, these applications include sonar bow domes and windows, towed array failings, and *Carderock Division, Naval Surface Warfare Center, Annapolis, Maryland. 93
94 Improved Fire- aM Smoke-Resistan! Materials prototype diving plane and control surfaces. The focus for surface ships has been on coastal minehunter (MHC-51) hulls (Gagorik et al., 1991~. Over the past 10 years, however, there has been a growing interest in the development and application of composites for both primary and secondary load-bearing structures such as foundation, deckhouses, and hulls; for machinery components such as composite piping, valves, centrifugal pumps, and heat exchangers; and for auxiliary or support items such as gratings, stanchions, ventilation ducts, and screens (Caplan, 1993~. This new interest in composite materials is due to increased need for a corrosion-free, lightweight, and affordable low-cost alternative to metallic components. A significant technical issue that has limited composite use on board naval ships and submarines is the combustible nature. and hence the fire smoke. and toxicity, of organic matrix composite materials. 7 7 ~ ~ ~ ~ ~ The use of structural composites inside naval submarines is now covered by MIL-STD- 203 1 (SH), Fire and Toxicity Test Methods and Qualification Procedure for Composite Material Systems Used in Hull, Machinery, and Structural Applications Inside Naval Submarines (DOD, 19911. Fire testing specified in this standard is intended to support hazard analyses of the composites for proposed application. The approach philosophy (DeMarco, 1991) taken by the Navy in the development of MIL-STD-2031 (SH) centered on determining the types of fires that could occur, understanding the potential threat from a fire, and determining the bounds of that threat so that performance criteria could be established. It was also established that a sufficient range of material fire testing would be required to understand the performance of composite system and to permit a risk-benefit assessment. Two guiding criteria were established for the use of composite systems aboard naval vessels: (1) The composite system will not be the fire source, that is, it will be sufficiently fire resistant not to be a source of spontaneous combustion. (2) Secondary ignition of the composite system will be delayed until the crew can respond to the primary fire source, that is, the composite system will not result in rapid spreading of the fire. This military standard is significantly more stringent than FAR 25.853, which regulates the materials used for aircraft interiors on the basis of, among other things, flame spread, smoke emission, and heat release rate. The Navy requires the use of ASTM E-1354 (heat release rate using an oxygen consumption calorimeter) to measure heat release rates and ignitability at four different fluxes of 25, 50, 75' and 100 kW/m2. FAR mandates OSU (Ohio State University) apparatus at one heat flux of 35 kW/m2 to measure peak heat release rate, and total heat release for the first 2-minute duration, the requirement for aircraft certification being 65/65. In addition, the Navy requires the ignitability tests, the requirement being 300, 150, 90, and 60 seconds at 25, 50, 75, and 100 kW/m2, respectively. The Navy requires smoke emission (E-662) of no more than 100 for the first 5-minute duration, whereas FAR requires smoke emission of no more than 200 for the first 4 minutes. The Navy requires the flame-spread index (E-162) of 20 or less whereas FAR requires the traditional Bunsen burner test. Table 1 summarizes the requirements of MIL-STD-203 1. The Navy currently has no specific standard for surface ships. The flammability requirements for surface ships are different from those for submarines. Instead of survivability measured in minutes, as it is in submarine fires, the critical issue in surface ship fires is the residual strength of structures at elevated temperatures for a period of 30-60 minutes. During the past decade, the introduction of new or modified resins in both the thermoses and thermoplastic family of polymers has resulted in steady improvement in the upper
Usman Sorathia and C. Beck 95 TABLE 1 Summary of Test Methods and Requirements, MIL-STD-2031 l Fire Test/Characteristic Requirement Test Method Oxygen-temperature index Minimum ASTM D-2863 Modified % oxygen at 25 °C 35 % oxygen at 75 °C 30 % oxygen at 300 °C 21 Flame-spread index 20 (maximum) ASTM E-162 Ignitability (s) Minimum ASTM E-1354 100 kW/m2 irradiance 60 75 kW/m2 irradiance 90 50 kW/m2 irradiance 150 25 kW/m2 irradiance 300 Heat release ~cW/m2) Maximum ASTM E-1354 100 kW/m2 irradiance, peak 150 Average for 300 s 120 75 kW/m2 irradiance, peak 100 Average for 300 s 100 50 kW/m2 irradiance, peak 65 Average for 300 s 50 25 kW/m2 irradiance, peak 50 Average for 300 s 50 Smoke obscuration Maximum ASTM E~62 Ds during 300 s 100 Do,,, 200 Combustion gas generation CO = 200 ppm ASTM E-1354 (25 kW/m2) CO2 = 4 TV HCN = 30 ppm HC1 = 100 ppm N-Gas model smoke toxicity No deaths Modified Screening test Pass NBS11M temperature limits, and hence their thermal stability. The upward temperature limits have also improved fire and smoke properties of these new state-of-the-art polymers and offer the potential of improved fire-resistant composite materials. For the past several years, CDNSWC, Annapolis Detachment (formerly known as DTRC), has been evaluating the fire performance of commercially available and development composite materials under the 6.2 Materials Block Program sponsored by the Office of Naval Technology. This program also included work on thermal barriers to protect the composite structures against fire damage (Sorathia et al., 1992a, b). This paper summarizes small-scale fire performance characteristics of selected state-of-the-art and conventional composite materials and assesses the suitability of these materials for use inside naval submarines. Table 2 lists the composite materials evaluated at CDNSWC and discussed
96 Improved Fire- aru] Smoke-Resistant Materials in this paper. All composite systems have a thickness of approximately 0.175-0.250 inches unless mentioned otherwise. FIRE PERFORMANCE OF COMPOSITE LAMINATES The fire performance of composite materials are those characteristics that describe the response of polymeric materials when exposed to fire (Hilado, 1982~. These include flame spread (fire propagation), smoke evolution (visibility), combustion gas generation (toxicity), fire endurance (residual strength during and after fire exposures, heat release and ignitability (fire growth), and ease of extinguishment (oxygen index). The following sections explain some of the tests used to assess these properties and the results obtained from these tests. Flam - Spread Index (ASTM ~162) Flame spread has been defined as the progress of flame over a surface. It is used to clescnbe the response of materials to heat and flame under controlled laboratory conditions. The rate at which flame will travel along surfaces depends upon the physical and thermal properties of the material, its method of mounting and orientation, type and level of fire or heat exposure, the availability of air, and properties of the surrounding enclosure. The standard radiant pane! test procedure for surface flammability is ASTM E-162. The threat consideration tested in the flame-spread test is that a fire will be controllable in 300 seconds, thereby providing time for active extinguishment efforts. This method uses an inclined 6 x IS in. pane! in front of which a radiant heat source (670 °C or 1238 °F) is placed. A pilot flame, located at the upper edge of the test specimen, ignites the specimen. The orientation of the specimen is such that ignition is forced near its upper edge and the flame front progresses downward. A factor derived from the rate of progress of the flame front and another relating to the rate of heat liberation by the material under test are combined to provide flame-spread index. Table 3 lists the flame-spread index of many composite materials evaluated at CDNSWC. As shown, autociaved cured epoxies, bismaleimides, phenolics, polyimides, and advanced thermoplastics all have low flame-spread characteristics (under 20). Polyethylene and aramid- reinforced phenolic composites had high flame-spread index due to the combustible nature of polymeric fibers. Smoke and Combustion Gas Generation (ASTM ~662) Smoke is defined as the visible, nonluminous, airborne suspension of particles originating from a combustion process. Smoke affects visibility and hinders the ability of the occupants to escape and of fire fighters to locate and suppress the fire. Smoke density is influenced by the degree of ventilation.
Usman Sora~hia and C. Beck TABLE 2 Summary of Composite Materials Evaluated at Carderock Division, Naval Surface Warfare Center 97 Composite Identification Glass/VE (1031) Glass/VE (1087) Glass/epoxy (1089) Glass/epoxy (1066) Glass/epoxy (1067) Glass/epoxy (1040) Glass epoxy (1071) Glass/epoxy (1006) Glass/epoxy (1070) Glass/epoxy (1003) Glass/epoxy (1090) Graphite/epoxy (1091) Graphite/epoxy (1092) Graphite/epoxy (1093) Graphite/epoxy (1094) Glass/CE (1046) Graphite/M.BMI (1095) Glass/BMI (1096) Graphite/BMI (1097) Graphite/BMI (1106) Graphite/BMI (1098) Glass/phenolic (1014) Glass/phenolic (1015) Glass/phenolic (1017) Glass/phenolic (1018) Glass/phenolic (1099) Glass/phenolic (1100) Glass/phenolic (1101) Graphite/phenolic (1102) Graphite/phenolic (1103) Graphite/phenolic (1104) PE/phenolic (1073) Aramid/phenolic (1074) Glass/polyimide (1105) Graphite/PNi (1080) Glass/PP (1082) Glass/J-2 (1077) Glass/PPS (1069) Graphite/PPS (1083) Glass/PPS (1084) Graphite/PPS (1085) Graphite/PAS (1081) Graphite/PES (1078) Graphite/PEEK (1086) Glass/PEKK (1079) Glass/vinyl ester, fire retardant, brominated Glass/vinyl ester, non-fire-retardant Glass/epoxy, S2/3501~, (0/90~`, Glass/epaxy, 105/206, RT cure, post-cured Glass/epoxy, 125/226, RT cure, post~ured Glass/epoxy, E-Glass/F155 Glass/epoxy, S2/F155 Glass/epoxy, 7701/7781 Sonar bow dome, MXB7780/3783 RTM, 9405/9470 SL-851-H4, SMC, 50% glass T-300/5208, (0/90)s, 350 °F AS4/LC1, anhydnde-cured Graphite/epoxy, AS4/3501~ P55/ERLX, toughened epoxy Glass/cyanate ester T300/5245C, modified bismaleimide T2E225/F650 T6T145/F650, (0/90)s, Post-cured at 475 °F for 4 hr. T6T145/F655, toughened Compimide HTA-7/65FWR J2027/Phencat 10, RT cure, PC at 140 °F/6 hr. Mark IV, RT cure, PC at 140 °F/6 hr. Fire PRF2-, RT cure, PC at 140 °F/6 hr. 350D66 RT cure, PC at 140 °F/6 hr. Q6399, developmental RT-cunng phenolic system CPH 2265/7781, cure at 250 °F. CPH 2265/7781, post-cured at 350 °F 3C584/F453-1, structural, heat resistant R1620, toughened, structural 402/7781 Polyethylene fibers 1000, 985PT/Mark IV Aramid fibers 49, 900-F1000/Mark IV CPI 2237/6781, PMR-15 polyimide system Graphite/phthalonitrile, NRL Glass/polypropylene Glass/nylon AG 40-70, polyphenylene sulfide AC 40~0, polyphenylene sulfide LG 40-70, polyphenylene sulfide LC 31~0, T300, polyphenylene sulfide T650-42/Radel X, polyarylsulfone 4084/PES-1, IM8/ITA APC-2/AS4, polyetheretherketone S2/PEKK, polyetherketoneketone
98 Improved Fire- aru' Smoke-Resistant Maternal TABLE 3 Flame-Spread Index (ASTM E-162) Composite lddex Glass/VE (1087) Glass/VE (1031) Glass/epoxy (1066) Glass/epoxy (1067) Glass/epaxy (1089) Glass/epoxy (1091) Glass/epaxy (1092) Graphite/M.BMI (1095) Glass/BMI (1096) Graphite/BMI (1097) Graphite/BMI (1098) Glass/phenolic (1099) Glass/phenolic (1100) Glass/phenolic (1101) Glass/phenolic (1014) Glass/phenolic (1015) Glass/phenolic (1017) Glass/phenolic (1018) Graphite/phenolic (1102) Graphite/phenolic (1103) Graphite/phenolic (1104) PE/phenolic (1073) Aramid/phenolic (1074) Glass/polyimide (1105) Glass/J-2 (1077) Glass/PPS (1069) Graphite/PPS (1083) Glass/PPS (1084) Graphite/PPS (1085) Graphite/PAS (1081) Graphite/PEEK (1086) Glass/PEKK (1079) 156 27 43 12 11 11 23 13 17 12 3 1 s 4 4 4 6 4 6 20 3 48 30 2 13 7 3 8 3 9 3 3 Test method ASTM E-662 covers the determination of specific optical density of smoke generated by solid materials. Measurement is made of the attenuation of a light beam by smoke accumulating within a closed chamber due to nonflaming pyrolytic decomposition and flaming combustion. Measurements made with the test relate to light transmission through smoke and are similar to the optical density scale for human vision. Combustion gas generation is defined as the gases evolved from materials during the process of combustion. The most common of gases evolved during combustion are carbon monoxide (CO) and carbon dioxide (CO2), along with hydrogen chloride (HCI), hydrogen cyanide (HCN), and others, depending upon the matrix resin chemistry of a given composite material. The Committee on Fire Toxicology of the National Research Council has concluded that as a basis for judging or regulating materials performance in a fire, combustion product toxicity data must be used only within the context of f~re-hazard assessment. The committee
Usman Sorathia aM C. Beck 99 believed that required smoke toxicity was best obtained with animal exposure methods for purposes of predicting the fire hazard of different materials (NBC, 19861. Table 4 presents smoke density and the relative concentrations of combustion gas generation (Draeger colonmeiric tubed in flaming mode during smoke obscuration test (ASTM E-662) for several composite materials. Figure ~ shows the maximum specific optical density and specific optical density at 300 seconds for selected composite systems in flaming mode only. With the exception of viny} ester, all other composite systems had the specific optical density at 300 seconds of less than 100. Of the thermosets, glass- or graphite-reinforced phenolic composites have very low smoke. This is also true for all advanced thermoplastics, which also have low maximum smoke density. In general, thermoses composite materials give off more carbon monoxide than thermoplastic composites. One interesting observation was that thermoplastic panels evaluates! in this study had slightly expanded or foamed up in the middle during smoke density tests, presumably due to the gases escaping through the softened front face during fire exposure. This may translate into greater structural damage or loss during fire exposure. Residual FIexural Strength (ASTM D~790) FIexural strength was selected to characterize the residual mechanical integrity of composite panels after fire exposure. As part of the testing protocol, all specimens (3 x 3 in.) were exposed at radiant heat source of 25 kW/m2 for a duration of 20 minutes during ASTM E- 662 in a flaming mode. The specimens were reclaimed and cut into I/: x 3 in. coupons, each specimen yielding five coupons. These coupons were tested in accordance with ASTM D-790 using a universal testing machine. Specimens were tested for flexural strength before and after the fire test. Companson of selected composites on the basis of percentage residual flexural strength retained after the fire exposure is shown in Table 5. As shown, graphite/PEEK exhibited the maximum flexural strength retained (75 percent) at this level of fire exposure. Insofar as thermoplastics soften during heating, measurements of flexural strength retained after fire testing may not give true or accurate flexural properties during fire. What is needed is the real-time measurement of flexural integrity of composite structures during exposure to fire. The measurement, analytical prediction, and validation of structural integrity during and after fire exposure is being vigorously pursued by CDNSWC, the University of Washington, and the University of Maryland (Milke and Vizzini, 1991; Ritter et al., 1992; Sorathia et al., 19931. Heat Release and Ignitability (ASTM ~1354) . . . ,_ Heat release is defined as the heat generated in a fire due to various chemical reactions occurring within a given weight or volume of material. The major contributors are those reactions where carbon monoxide and carbon dioxide are generated and oxygen is consumed (Tewarson, 19881. Different levels of radiant flux simulate fire scenarios in which the composite material is itself burning or in which it may be near another burning material. Heat release data
100 TABLE 4 Smoke and Combustion Gas Generation (ASTM E-662) Improved Fire- a~ Smoke-Resistant Mater~als Composite D. D ,,,,,, CO (300 s) (ppm) (% v) CO2 HCN (ppm) (ppm) (ppm) Glass/VE (1031) Glass/VE (1087) Glass/epcxy (1089) Glass/epoxy (1066) Glass/epaxy (1067) Glass/epoxy (1071) Glass/epaxy (1090) Graphite/epaxy (1091) Graphite/epaxy (1092) Graphite/epoxy (1093) Graphite/epaxy (1094) Glass/CE (1046) Graphite/M. BMI (1095) Graphite/BMI (1097) Graphite/BMI (1098) Glass/BMI (1096) Glass/phenolic (1100) Glass/phenolic (1099) Glass/phenolic (1101) Glass/phenolic (1014) Glass/phenolic (1015) Glass/phenolic (1017) Glass/phenolic (1018) Graphite/phenolic (1102) Graphite/phenolic (1103) Graphite/phenolic (1104) PE/phenolic (1073) 1 Aramid/phenolic (1074) 2 Glass/polyimide (1105) Glass/J-2 (1077) Glass/PPS (1069) Graphite/PPS (1083) Glass/PPS (1084) Graphite/PPS (1085) Graphite/PAS (1081) Graphite/PES (1078) Graphite/PEEK (1086) Glass/PEKK (1079) 463 310 56 2 16 17 96 75 66 3 1 4 24 6 9 34 4 576 325 165 408 456 348 155 191 210 353 301 84 158 171 117 127 18 43 23 1 1 1 3 4 1 l 8 2 4 1 2 1 24 138 4 241 62 16 328 87 32 54 26 3 s 1 1 4 230 298 283 200 250 80 50 115 313 160 300 30 175 10 300 300 50 300 300 190 200 200 115 100 600 700 700 200 180 70 100 100 100 55 110 TR 200 0.3 1.5 1.5 2 1 0.5 0.2 0.9 2 0.5 0.6 0.3 0.8 TR 0.1 TR 0.5 0.1 2 1.5 0.5 0.5 0.1 TR ND. ND 0.5 ND 2 ND s s 2 3 ND 15 2 2 3 TR 7 TR TR TR ND TR 1 2 2 2 TR 10 2 1 TR TR TR 1 ND ND ND TRb 0.5 1.5 ND ND TR ND ND TR ND ND 1 ND ND ND ND 2 ND 0.5 ND TR TR ND 1 ND TR aND: not done. b~: trace amounts.
Usman Sorathia and C. Beck ^,600 ~_ ._ U) a) C) ._ o ._ ._ cn 500 400 300 200 100 ~ _ _ ~] Ds(300s) · Dmax O _ ~- ~ a1 CO _ _ ~ ~ ~ ~ CD 8 O O g 8 .- 8 O 8 8 8 8 _ _ _ ~ _ _ _ _ _ _ _ _ _ _ ~ ~. Q Q ~, _ _ _ _ ~ ~-J ~ ~ ~ _-m m m `,, u ', <~ ~ ~ ~ ~ m <' 3 ~ - .t ~ ~ O r~ ~ aD CD ~ ~ r~ _ 0 _ 0 0 0 0 0 0 0_ _ _ _ _ _ _ _ :~: I Q ~J Ct) cn y ~ cn y Q t~ ~ Q Q ~ llJ e' y ~ ~ ~ _ _ Q ~ _ _ Y Q ~ C:, ~ (:J FIGURE 1 Smoke density of selected composites. ~ u, ~ ao _ _ _ _ _ 0 0 _ 0 0 0 __ _ _ _ ~: I I ~ ~ ~ ~ Q _ _ _ _ , . <' ~ ~ ~ ~ ~ TABLE 5 Residual Flexural Strength (ksi) (ASTM D-790) Composite Before After % Retained Glass/VE (1087) 54 17 32 Glass/VE (1088) 59 8 14 Glass/epoxy (1089) 168 9 5 Graphite/epoxy (1091) 104 0 0 Graphite/M.BMI (1095) 125 5 4 Glass/BMI (1096) 148 31 21 Graphite/BMI (1097) 115 18 16 Graphite/BMI (1098) 175 24 14 Graphite/phenolic (1102) 54 29 53 Graphite/phenolic (1103) 41 12 30 Glass/polyimide (1105) 114 51 45 Glass/PPS (1085) 47 17 36 Graphite/PPS (1083) 72 29 41 Graphite/PEEK (1086) 144 109 75 Graphite/PAS (1081) 117 39 34 101 provide a relative fire-hazard assessment for materials in that mater~als with low heat release per unit weight or volume will do less damage to the surroundings than the material with high release rate. The rate of heat release, especially the peak amount, is the primary characteristic determining the size, growth, and suppression requirements of a fire environment (Brown et al., 1988~.
102 Improved Fire- and Smoke-Resistant Materials Test method ASTM E-1354 (oxygen consumption cone calorimeter) covers the measurement of the response of materials exposed to controlled levels of radiant heating and is used to determine the heat release rates, ignitability, mass-Ioss rates, effective heat of combustion, and visible smoke development. These values are becoming increasingly important in determining fire growth and are needed in the venous fire models that are being developed. Specific thermal insults of 25, 50, 75, and 100 kW/m2 are required. These thermal insults correspond to a small Class A fire, a large trash can fire, a significant fire, and a pool of! fire. The test method utilizes the oxygen consumption principle in which the heat release rate is computed from the measurements of mass flow rate and oxygen depletion in the gas flow. Table 6 presents heat release and ignitability data on thermoses and thermoplastic composites. Figures 2, 3, and 4 show, respectively, the peak heat release rates, time to ignition, and weight loss (percentages at 25, 50, 75, and 100 kW/m2 for the selected composite material systems. Of all the materials evaluated, phenolics, modified polyimides, and phthalonitrile exhibited the highest resistance to ignition at 100 kW/m2. Thermoplastics, in general, exhibited lower heat release rates. TABLE 6 Heat Release and Ignitability of Composite Materials Average Heat Weight Peak Heat Release, Total Heat Extinction Irradiance Loss Ignitability Release 300 s Release Area Material System (kW/m2) (%) (s) (kW/m2) QcWlm2) (MJ/m2) (m2/kg) Thermosets Glass/VE (1031) 25 14 278 75 29 11 1,185 50 26 74 119 78 25 1,721 75 29 34 139 80 27 1,791 100 28 18 166 22 1,899 Glass/VE (1087) 25 36 281 377 180 55 1,188 50 ~ 75 34 22 499 220 68 1,218 100 33 11 557 64 1,466 Glass/epoxy (1089) 25 - 535 39 30 10 470 50 - 105 178 98 30 580 75 - 60 217 93 28 728 100 - 40 232 93 24 541 Glass/epoxy (1066) 25 20 140 231 158 52 1,096 50 23 48 266 154 48 1,055 75 24 14 271 157 48 1,169 100 24 9 489 - 46 1,235
Usman Sorathia and C. Beck TABLE 6 (continued) 103 - Average Heat Weight Peak Heat Release, Total Heat Extinction Irradiance Loss Ignitability Release 300 s Release Area Material System (kW/m23 (%) (s) (kW/m2~) (kW/m2) (MJ/m2) (mung) Glass/epoxy (1067) 25 18 209 230 120 41 1,148 50 20 63 213 127 39 1,061 75 21 24 300 138 43 1,109 100 20 18 279 - 32 1,293 Glass/epoxy (1040) 25 50 19 18 40 2 29 566 75 21 13 246 1 38 605 100 23 9 232 5 47 592 Glass/epaxy (1071) 25 7 128 20 4 1 1,356 50 5 34 93 - 3 1,757 75 23 18 141 99 30 1,553 100 25 10 202 108 34 1,310 Glass/epoxy (1006) 25 14 159 81 63 28 2,690 50 28 49 181 108 39 1,753 75 24 23 182 -- 35 1,917 100 29 14 229 131 41 1,954 Glass/epoxy (1070) 25 23 229 175 95 45 1,119 50 28 63 196 143 49 1,539 75 27 30 262 133 43 1,440 100 30 23 284 - 36 1,640 Glass/epoxy (1003) 25 17 198 159 93 36 1,162 50 22 50 294 135 43 1,683 75 22 73 191 121 41 1,341 100 22 19 335 122 37 1,535 Glass/epoxy (1090) 25 19 479 118 67 38 643 50 28 120 114 90 55 803 75 34 54 144 115 64 821 100 34 34 173 150 71 1,197
104 TABLE 6 (continued) Improved Fire- arm Smok;e-Resistar~t Materials Average Heat Weight Peak Heat Release, Total Heat Extinction Irradiance Loss Ignitability Release 300 s Release Area Matenal System (kW/m23 (%) (s) ~W/m2) (kW/m2) (MJ/m2) (m2/kg) Graphite/epaxy 25 7 NI NI NI NI 601 (1091) 50 ~ 75 25 53 197 90 30 891 100 38 28 241 - 28 997 Graphite/epaxy 25 - 275 164 99 32 525 (1092) 50 _ 76 189 116 37 593 75 - 32 242 112 37 363 100 - 23 242 113 71 235 Graphite/epoxy 25 13 338 105 69 (1093) 50 24 94 171 93 - - 75 23 44 244 147 - - 100 22 28 202 115 - - Glass/CE (1046) 25 8 199 121 74 30 794 50 22 58 130 71 49 898 75 23 20 196 116 58 1,023 100 24 10 226 141 47 1,199 Graphite/M.BMI 25 19 237 160 103 32 645 (1095) 50 - - - - - - 75 24 42 213 115 36 685 100 26 22 270 124 38 706 Graphite/BMI 25 5 NI NI NI NI 238 (1097) 50 - - - 75 30 66 172 130 45 933 100 31 37 168 130 41 971 Graphite/BMI 25 - NI NI NI NI NI (1098) 50 13 110 74 51 14 228 75 15 32 91 65 17 370 100 16 27 146 75 22 383
Usman Sorathia and C. Beck TABLE 6 (continued) 105 Average Heat Weight Peak Heat Release, Total Heat Ext~nction Irradiance Loss Ign~tability Release 300 s Release Area Matenal System ~W/m23 (%) (s) (kW/m3 (kW/m2) (MJ/m2) (m2/kg) Glass/BMI 25 17 503 128 105 40 324 (1096) 50 25 141 176 161 60 546 75 30 60 245 199 76 604 100 30 36 285 219 73 816 Glass/phenolic 25 - NI NI NI NI NI (1099) 50 _ 121 66 43 18 4 75 - 33 102 86 33 85 100 - 22 122 95 40 - Glass/phenolic 25 - NI NI NI NI NI (1100) 50 _ 125 66 48 17 308 75 - 20 120 63 21 365 100 - 40 163 74 21 441 Glass/phenolic 25 - NI NI NI NI NI (1101) 50 - 210 47 38 14 176 75 - 55 57 40 16 161 100 - 25 96 70 22 620 Glass/phenolic 25 - NI NI NI NI NI (1014) 50 12 214 81 40 17 83 75 16 73 97 54 20 246 100 16 54 133 78 21 378 Glass/phenolic 25 - NI NI NI NI NI (1015) 50 6 238 82 73 15 75 75 8 113 76 37 7 98 100 13 59 80 62 12 58 Glass/phenolic 25 - NI NI NI NI NI (1017) 50 10 180 190 139 43 71 75 14 83 115 84 17 161 100 18 43 141 73 19 133 Glass/phenolic 25 - NI NI NI NI NI (1018) 50 3 313 132 22 12 143 75 11 140 56 44 11 74 100 13 88 68 58 13 66
106 TABLE 6 (continued) ·mproved Fire- aru] Smoke-Resistant Mater~als Average Heat Weight Peak Heat Release, Total Heat Extinction Irradiance Loss Ignitability Release 300 s Release Area Material System (kW/m) (%) (s) (kW/m23 (kW/m2) (MJ/m2!) (m2/kg) Graphite/phenolic 25 4 NI NI NI NI NI (1102) 50 ~ 75 28 79 159 80 28 261 100 - 45 196 - - - Graphite/phenolic 25 - NI NI NI NI NI (1103) 50 28 104 177 112 50 253 75 27 34 183 132 50 495 100 29 20 189 142 51 493 Graphite\phenolic 25 - NI NI NI NI NI (1104) 50 9 187 71 41 14 194 75 11 88 87 - 11 194 100 11 65 101 - 11 232 PE/phenolic 25 30 714 NI NI NI NI (1073) 50 61 129 98 83 107 294 75 60 28 141 92 104 500 100 67 10 234 131 96 580 Aramid/phenolic 25 4 1,110 NI NI NI NI (1074) 50 43 163 51 40 57 156 75 40 33 93 54 45 240 100 65 15 104 72 95 333 Glass/polyimide 25 - NI NI NI NI NI (1105) 50 11 175 40 27 21 170 75 13 75 78 49 22 131 100 14 55 85 60 20 113 Graphite/PNi 25 (1080) 50 - _ _ _ _ _ 75 - - - _ _ _ 100 13 75 118 36 12 610
Usman Sora~hia and C. Beck TABLE 6 (continued) 107 Average Heat Weight Peak Heat Release, Total Heat Extinction Irradiance Loss Ignitability Release 300 s Release Area Material System (kW/m2) (%) (s) (kW/m23 ~WIm2) (MJ/m23 (m2/kg) Thermoplastics Glass/PP (1082) 25 37 168 187 153 88 702 50 36 47 361 248 82 959 75 37 23 484 265 82 1,077 100 36 13 432 - 82 1,120 Glass/J-2 (1077) 25 _ 193 67 38 _ 803 50 - 53 96 49 - 911 75 - 21 116 48 - 866 100 - 13 135 76 - 1,011 Glass/PPS (1069) 25 _ NI NI NI NI NI 50 12 105 52 25 32 585 75 12 57 71 56 24 575 100 14 30 183 106 41 749 Graphite/PPS 25 - NI NI NI NI NI (1083) 50 - - 75 - 34 69 81 60 37 431 100 23 26 141 80 37 752 Glass/PPS (1084) 25 _ NI NI _ _ _ 50 13 244 48 28 39 690 75 15 70 88 67 35 954 100 16 48 150 94 35 613 Graphite/PPS 25 - NI NI (1085) 50 16 173 94 70 26 604 75 17 59 66 50 23 - 100 26 33 126 88 33 559 Graphite/PAS 25 - NI NI NI NI NI (1081) 50 3 122 24 8 1 79 75 18 40 47 32 14 211 100 18 19 60 44 14 173
108 TABLE 6 (continued) Imp roved Fire- and Smoke-Resistant Materials Average Heat Weight Peak Heat Release, Total Heat Extinction Irradiance Loss Igmtability Release 300 s Release Area Matenal System (kW/m23 (%) (s) (kW/m23 ~WIm2) (MJ/m2) (m2/kg) Graphite/PES 25 - NI NININI NI (1078) 50 _ 172 1163 145 75 - 47 412322 88 100 - 21 653923 189 Graphite/PEEK 25 - NI NININI NI (1086) 50 2 307 1483 69 75 18 80 543035 134 100 16 42 855628 252 Glass/PEKK (1079) 25 - NI NININI NI 50 6 223 211015 274 75 10 92 452420 - 100 6 53 744624 891 Oxygen-Temperature Index The test method employing oxygen-temperature index is basically the same as ASTM D-2863 for limiting oxygen index but with a series of oxygen index determination.s over the temperature range from ambient to 300 °C. Limiting oxygen index is defined as the minimum concentration of oxygen in an oxygen-nitrogen atmosphere necessary to sustain flaming combustion. The purpose of the test is to rank ignitability over a range of temperatures. As the temperature of a material increases, ignition of the material requires less oxygen. Thirty-f~ve percent oxygen is the level above which materials have proven to be good fire performers. Table 7 presents the oxygen index for venous thermoses and thermoplastic composites. During fire extinguishment, composites should be cooled below the temperature corresponding to an oxygen index of 21 to prevent re-ignition. _ ~ ~ ~ O ~. DISCUSSION Fire performance characteristics of composites are dependent on the chemical nature and amount of the resin matrix used; the type, amount, and orientation of the fiber; additives or modifiers present in the system; and the processing or fabrication techniques employed.
Usman Sorathia and C. Beck 350 300 Cal ~ 2SO - a) cts 200 a) a) lo: ~ lSO a, ~ I cows 1 00 50 . . . . . . . . ~ 25 50 75 Flux, kW/m2 100 FIGURE 2 Pealc heat release versus flux for selected composite materials. Ignition Delay Time, Sec , 00 1 0 . . . . . . . . . . 1 ::: -:: ~ 25 50 75 100 Flux, kW/m2 FIGURE 3 Ignitability of composite materials. 109 -OLIVE (1031) I GL/EP(1089) GLJBMI(1096) ° GLIPH(1101) ~ GLJPMR(1 105) + GLJPPS(1069) G R./ PE EK( 1086) ~ GL/PEKK(1079) -OR/PAS (1081) GRIPES (1078) GR/EP( 1093) 5} GLICE(1046) GRIPPS(25) -GL/J-2(1077) + GL/EP(1040) S P/PH(1073) GL/VE(1 03 1) GLIEP(1089) GLIBMI(1096) GLIPH(1 101) GLIPMR(1 105) GLIPPS(106s) GRIPEEK(1086) GlJPEKK(1079) GRIPAS(1081) GRIPES(1078) GRIPPS(l 083) GLfJ-2(1077) GLIEP(1040) SPIPH(1 073) GIIcE(1 046)
110 100 80 60 a_ an an o - 40 2D / , ~ . 44~ 50 75 1 00 Flux, kW/m2 FIGURE 4 Weight loss (%) for selected composites. TABLE 7 Oxygen Index for Selected Composites Composite Oxygen Index Glass/VE (1031) Graphite/epoxy (1092) Glass/BMI (1096) Graphite/BMI (1097) Graphite/BMI (1098) Glass/PPS (1069) Graphite/PEEK (1086) Graphite/PAS (1081) 34 33 65 55 60 64 58 66 Improved Fire- aM Smoke-Resistant Materials GLEE (1031) GL/EP(1 066) GL/BM 1~1 096) GL/P H (1 014) GL/PMR(1 105) GL/PPS(1 069) GR/PEEK(1 086) GL/P E KK(1 079) GR/PAS(1081 ) Kev/PH(1 074) GR/EP(1093) GL/CE(1046) GR/PPS(1083) GL/EP(1040) S P/P H (1 073) There are basically two types of matrix resins used in composite industry. These are thermosets and thermoplastics. Thermosets are cross-linked polymer chains in which composites degrade, thermally decompose, or char, but do not melt or drip. Thermoplastics are mostly linear polymeric chains that tend to soften when exposed to higher temperatures. Low- temperature thermoplastics also tend to drip. The fiber most commonly used for naval
Usman Sorathia and C. Beck applications is glass, and graphite fiber is used predominantly for aerospace applications. Special applications such as ballistic armor employ aramid, and radome-related applications may use polyethylene fibers. The extinguishment of fire depends on the fire-propagation rate, physico- chemical properties of the materials, and the rate of application and the concentration of extinguishing agents. Water applied through sprinklers is the most widely used liquid extinguishing agent (Macaione and Tewarson, 1990~. Heat Release and Ignitability The "authors" of MTL-STD-2031 extensively discussed the significance and effects of heat release rates with researchers inside the navy laboratories and also outside the Department of Defense community, ant! came to a conclusion that materials that exhibit peak and integrated heat releases per unit time below 50-60 kW/m2 are considered as "good" materials. There appears to be a significant difference in the burning mechanisms of thermoplastics and thermoses materials. Thermoplastics (AS-4/PEEK, AS-4/PPS) burn, after ignition, for a longer period of time but produce lower peak heat release rates. The thermoses materials, in general, burn for a shorter period of time and produce much higher heat release rates. If the heat released per unit time during a fire is low, the ability of the fire to spread is limited. Furthermore, a lower heat released per unit time also protects the sailors aboard submarines who must respond to fires quickly and who often use fire extinguishers requiring a close approach to fire. Ignitability is defined as the ease of ignition. The higher the heat flux, the shorter the time before ignition. In general, time to ignition may also be looked upon as the thermal resistance of the polymeric material to participation in the fire scenario. It is in this area of material development where great strides have been made in the past 10 years due to the need to use higher and higher glass transition temperatures for higher and higher speeds in the aircraft industry. The ability of a material to resist ignition is an important consideration for ensuring adequate response time and minimizing the spread of the fire. For submarine interior materials, the Navy criteria at thermal insults of 25, 50, 75, and 100 kW/m2 are minimum ignition times of 300, 150, en c! 90, and 60 seconds, respectively. The ignition time criteria were established from "typical" response and fire-fighting times aboard submarines. Influence of Fiber Reinforcement The type of fiber reinforcement can also influence the fire performance. Composites with glass fiber or graphite fiber reinforcement smoke less and give less heat output than composites with organic fibers such as ultra high molecular weight polyethylene or aramid fiber due to their combustible nature. Also, heat transfer through the thickness of the composite results in higher temperature gradient for glass-reinforced composites than with graphite-reinforced composites due to differences in thermal conductivity. Thick reinforced composites have also shown a tendency to reflash if not cooled properly when extinguishing the fire.
112 Improved Fire- arm Smoke-Resistant Materials Effect of Resin Matrix and Additives Companson of flammability data for previous thermoses composites shows that phenolic and polyimide composites smoke less, have low flame spread, have high ignition delay (more difficult to initiate), have low peals heat release, have low total heat release, and have a high oxygen index. Also, thermoses composites char during fire exposure due to a high degree of cross-linking. The char formation, highly pronounced in phenolic composites, tends to insulate the core of composite structure and thus render less structural damage. Companson of flammability data for various thermoplastics shows that all advanced thermoplastics, in general, have low flame spread, low smoke density, and low heat release values. However, thermoplastics have low ignition delay limes, with PEEK and PEKK being the exception. The repeat unit of PEEK is very similar to that of phenolic resin, which is inherently fire resistant due to the high cross-linked cure structure. It is assumed that the fire resistance is primarily due to the aromatic character. However, the pendant phenolic (-OH) group may also contribute to the fire performance. The argument about the aromatic character is in agreement with thermoplastics such as PEEK or PPS. Both have benzene linkages with pendant groups in polymer chains. However, phenolics are cured via polycondensation reactions in which water is released. This causes higher void content, and thus phenolic matrix composites are not suitable for primary structures. A number of U.S. corporations have begun some research work in the past few years to alter the cure chemistry of phenolic resins from polycondensation to addition reactions in which no volatiles are released during curing. These include work in phenol triazine (PT) resin technology that is based on the thermally and chemically stable network derived from the cyclotrimenzation of cyanate ester groups, and polycondensation of phenol-free phenolic resins with bisoxazolines without producing volatiles during the curing cycle (SAMPE, 19881. The type of matrix resin used has a significant impact on the toxicity of combustion gas generation en c} corrosivity of gases on surrounding equipment or instruments. The most common of toxic gases evolved during combustion is carbon monoxide. I:n addition to carbon monoxide, fluorocarbons will produce hydrogen fluoride (HF), chlorinated resins will produce HCI, sulfur- containing materials will produce hydrogen sulfide (H2S), and nitrogen-containing materials will produce HCN. The nature of the combustion mechanism during fire exposure may also have a significant impact on the toxicity of combustion gas generation; this is the case with phenolic composites, which tend to char and smolder, giving off higher amounts of carbon monoxide due to incomplete combustion. Modification of resin matrix can also have a significant impact on fire performance of composites. This modification can be in the form of additives, such as rubber for toughening the epoxy-basec! composites, fire retardants for viny! esters, or chemical reformulation such as replacing aliphatic ciiamine with aromatic diamine. Addition of antimony trioxide and hydrated alumina to the polyester and epoxy resin systems significantly decreases (improves) flammability characteristics but causes a marked increase in smoke evolution. Additives also cause reduction in toad-bearing characteristics of composite structures. Chemical modification offers a viable alternative to improving flammability characteristics. Chemical modification of polyimide increased the ignition delay times from 75 to 123 seconds and from 55 to 68 seconds, respectively, when exposed to radiant heat fluxes of 75 and 100 kW/m2 during Cone Calorimeter heat release testing.
Usman Sorathia arm C. Beck ~3 Resin content of composites can also have a significant impact on composite fire performance. In general, the higher the resin content, the higher the smoke and heat release. Various fabrication techniques can influence the fire performance of composites. Autoclave composites have, in general, a higher volume fraction of fiber and better fire performance; also, thermally cured composites, in general, have better fire performance than room temperature- cured composites due to higher degree of cross-linking. Residual Strength Advanced composite designs take advantage of different ply orientations to maximize load-bearing characteristics. For epoxy-based composites, this results in poor residual flexural strength due to resin charring and subsequent loss of interiaminar strength between plies. Woven roving as the structural reinforcement provides higher residual flexural strength during fire exposure for marine structures. As noted earlier, since thermoplastics soften during heating, measurements of flexural strength retained after fire testing may not give true or accurate flexural properties during fire. The potential for increased use of organic matrix composite structures will not be realized until the measurement, analytical prediction, and validation techniques for structural integrity during and after fire exposure have been established. ACKNOWLEDGMENTS The authors wish to acknowledge the contributions of many people at CDNSWC for their technical assistance. These include lames Morris, Charles Rolihauser, Michael McFarland, Thomas Gracik, Timothy Dapp, Thomas Nixon, and Dr. Gene Camponeschi. The authors also wish to thank ant] acknowledge the constant support and encouragement of Dr. Eugene Fischer, Ivan Caplan, and Terry Morton. REFERENCES Brown, I.E., E. Braun, and W.H. Twilley. 1988. Cone Calorimeter Evaluation of the Flammability of Composite Materials. NBS TR 88-3733, March 1988. Gaithersburg, Maryland: National Institute of Standards and Technology. Caplan, IN 1993. Marine Composites, The U.S. Navy Experience. Paper presented at the First International Workshop on Composite Materials for Offshore Operations, Houston, Texas, October 26-28. DeMarco, R.A. 1991. Composite applications at sea: Fire-related issues. Pp. 1928-1938 in 36th International SAMPE Symposium and Exhibition, How Concept Becomes Reality. I. Stinson, R. Adsit, and F. Gordaninejad, eds. Covina, California: Society for the Advancement of Materials and Process Engineering.
114 Improved Fire- arm Smoke-Resistant Materials DOD. 1991. Fire and Toxicity Test Methods and Qualification Procedure for Composite Material Systems Used in Hull, Machinery, and Structural Applications Inside Naval Submarines. MIL-STD-2031 (SH). Washington, D.C.: U.S. Department of Defense. Gagorik, I.E., I.A. Corrado, and R.W. Kornbau. 1991. An overview of composite developments for naval surface combatants. Pp. 1855-1867 in 36th International SAMPE Symposium and Exhibition, How Concept Becomes Reality. I. Stinson, R. Adsie, and F. Gordaninejad, eds. Covina, California: Society for the Advancement of Materials and Process Engineering. Hilado, C.~. 1982. Flammability Handbook for Plastics, 3rd ed. Westport, Connecticut: Technomic. Macaione, D.P., and A. Tewarson. 1990. Flammability characteristics of composite materials. Pp. 542-565 in Fire and Polymer. G.~. Nelson, ed. ACS Symposium Series 425. Washington, D.C.: American Chemical Society. Milke, I.A., and A.~. Vizzini. 1991. Thermal response of fire exposed composites. journal of Composites Technology & Research 13~3~:145-151. NRC. 1986. Fire and Smoke: Understanding the Hazards. Committee on Fire Toxicology, Board on Environmental Studies and Toxicology, National Research Council. Washington, D.C.: National Academy Press. Ritter, G.A., R. Coriett, et al. 1992. Real-Time Measurement of FIexural Rigidity in Fire- Impacted Composite Plates. Paper presented at Fire and Materials Ist International Conference and Exhibition, Washington, D.C., September. SAMPE. 1988. International Symposium and Exhibition, Volume 33, Materials-Pathway to the Future. Covina, California: Society for the Advancement of Materials and Process . · - . ~ng~neenng. Sorathia, U., T. Dapp, and C. Beck. 1992a. Fire performance of composites. Materials Engineering 109~9~:10-12. Sorathia, U., C. RolIhauser, and W.A. Hughes. 1992b. Improved fire safety of composites for naval applications. Fire and Materials 16:~19-125. Sorathia, U., C. Beck, and T. Dapp. 1993. Residual strength of composites during and after fire exposure. Journal of Fire Sciences Il(31:255-270. Tewarson, A. 1988. Generation of heat and chemical compounds in fires. Pp. 179-199 in The SFPE Handbook of Fire Protection Engineering. Quincy, Massachusetts: National Fire Protection Association Press.
