Fire and Polymers: An Overview - ACS Publications - American

Chapter 1

Fire and Polymers:

An Overview

Gordon L. Nelson

Downloaded by OAKLAND UNIV on May 3, 2015 | http://pubs.acs.org Publication Date: July 21, 1995 | doi: 10.1021/bk-1995-0599.ch001

Florida Institute of Technology, 150 West University Boulevard, Melbourne, FL 32901-6988

Our environment is largely one of polymers and all polymers burn whether natural or synthetic. The issue is not whether polymers burn but rather if a given polymer has a property profile appropriate to provide for an acceptable level of risk in a given application. How we make polymers flame retardant, whatflameretardant means, and how codes achieve an acceptable level of risk are the subjects of this overview. Fire is an ever present hazard in the built environment. In A.D. 64, during Nero's reign, ten of the fourteen districts of Rome burned in eight days. In 1666 the Great Fire of London destroyed 13,200 homes, 94 churches, and countless public buildings. In 1842, 4200 buildings were destroyed in Hamburg, Germany, by afirewhich killed 100 and rendered 20% of the population homeless. The Chicago Fire of 1871 killed 766 and destroyed 17,500 buildings. San Francisco (1906), Tokyo (1923) and Yokohama were almost totally destroyed byfiresafter damaging earthquakes. In the San Francisco fire alone 28,000 buildings (10km ) were destroyed and over 1000 lives lost. In a 1908firestorm in Chelsea, Massachusetts, some 3500 buildings were lost. And lest we think fire is forgotten in the last years of the 20th century, the Oakland, California, hills fire leapedfreewaysand destroyed nearly 6000 buildings. When the lessons learned of construction, materials, building separation, and urban defense strategies are ignored, thenfiresof significant consequence remain possible. Most fire deaths are not the consequence of largefires,however, butfiresin single structures and involve 1 or 2 fatalities. In the U.S. some 6,000 people die from fire each year, some 30,000 people are injured in 2.5 millionfirescausing $10 billion in property damage. With improved building design and materials the fire death rate in the US has fallen from 9.1 per 100,000 in 1913 to 2.0 in 1988. Even though the rate has fallen it remains twice that of European countries and thatfiredeath rate has stalled. The early 1980's brought smoke detectors to 80% of American homes. Unfortunately only 60% of those are operational now. A simple, cost effective strategy is defeated by indifference and a "fires only happen to someone else" attitude. 2

0097-6156/95/0599-0001$13.50/0 © 1995 American Chemical Society In Fire and Polymers II; Nelson, G.; ACS Symposium Series; American Chemical Society: Washington, DC, 1995.

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FIRE AND POLYMERS II

In fact we have a 40% chance that a fire big enough to cause a call to the fire department will occur in our household during our lifetime. One-third of all fire deaths involve residential furnishings as the first item ignited (smoking 27%, open flame 5%). The advent of cigarette resistant furniture is aimed at the former scenario. Indeed analysis offireincidents has played an important role in pinpointing important scenarios and has allowed the development of defense strategies/ Our environment is largely one of polymers and all polymers burn whether natural or synthetic. The issue is not whether polymers burn but rather if a given polymer has a proper profile appropriate to provide for an acceptable level ofriskin a given application. How we make polymers flame retardant, what flame retardant means, and how codes achieve an acceptable level of risk are the subjects of this overview. The reader should note that hazard is the potential for harm, with the probability of the event (fire) equal to one and the probability of exposure (e.g. people) equal to one. Risk is the product of the probability of the event times the probability of exposure, times the potential for harm.


0

Flame Retardant Chemistry Polymer combustion occurs in a continuous cycle (Figures 1-2). Heat generated in the flame is transferred back to the polymer surface producing volatile polymer fragments, or fuel. These fragments diffuse into theflamezone where they react with oxygen by free-radical chain processes. This in turn produces more heat and continues the cycle. Flame retardancy is achieved by interrupting this cycle. There are two ways to interrupt the cycle. One method, solid phase inhibition, involves changes in the polymer substrate. Systems that promote extensive polymer crosslinking at the surface, form a carbonaceous char upon heating. Char insulates the underlying polymer from the heat of the flame, preventing production of new fuel and further burning. Other systems evolve water during heating, cooling the surface and increasing the amount of energy needed to maintain the flame. The second way of interrupting the flame cycle, vapor phase inhibition, involves changes in theflamechemistry. Reactive species are built into the polymer which are transformed into volatilefree-radicalinhibitors during burning. These materials diffuse into theflameand inhibit the branching radical reaction. (Figure 3) As a result, increased energy is required to maintain the flame and the cycle is interrupted. Of course, for many materials both solid and vapor phase inhibition are involved. Polymers vary a great deal in their inherentflammabilityand can be divided roughly into three classes (Table I ). The first group consists of relatively flame retardant structures containing either high halogen, or aromatic groups that confer high thermal stability as well as the ability to form char on burning. Second are the lessflameretardant materials, many of which can be made moreflameretardant by appropriate chemistry. The third class consists of quiteflammablepolymers which are more difficult to makeflameretardant because they decompose readily, forming large quantities of fuel, but these can be made appropriately flame retardant for particular applications by the addition of additives. (3)

In Fire and Polymers II; Nelson, G.; ACS Symposium Series; American Chemical Society: Washington, DC, 1995.

Overview of Fire and Polymers


NELSON

LOW TEMP PYROLYSIS ZONE

ι

I

^

^

Λ Λ *m—

BURNMG FRONT

VOLATILE DFFUSON ZONE HEAT

CONDENSED PHASE DECOMPOSmON

FUEL

• VAPOR PHASE OXIDATION

Figure 1. Polymer combustion process and cycle.


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region

Figure 2. A typicalflameinvolving organic fuel showing decomposition region where volatilized fuel decomposes before combustion. For many (most) fuels oxygen is not involved in fuel generation. For other materials like PTFE oxygen plays an important role in polymer decomposition. After reference 2


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What Happens When Something Burns?

How Do Vapor-Phase Flame Retardants Affect Burning?

Figure 3. The combustion process and the role of flame retardants. Reference 3.


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Less Flame Retardant Silicones Polycarbonates Polysulfone Wool Polysulfones

Flammable Polystyrene Polyacetal Acrylics Polyethylene terephthalate Polyolefins Cellulose (wood, cotton, paper) Polyurethanes

Polymers and Flammability Classification

Intrinsically Flame Retardant Polytetrafluoroethylene Aromatic polyethersulfone All-aromatic polyimides All-aromatic polyamides All-aromatic polyesters All-aromatic polyethers Polyvinylidene dichloride Reference 3

Table I.



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Intrinsically Flame Retardant Polymers. High temperature materials are intrinsically flame retardant. Some of these intrinsically flame retardant polymers are stable for a few minutes at extreme temperatures, 600-1000°C, while others can perform at 200-300 °C for long periods of time. There are three general types of structures: linear single-strand polymers such as aromatic polyimides and polyamides based on benzenoid systems, ladder polymers consisting of an uninterrupted sequence of cyclic aromatic or heterocyclic structures, and spiro polymers in which one carbon is common to two rings. Behind each type of structure is the premise that polymers with high aromatic character and very strong connecting linkages between rings produce more char on heating, retaining most of the potential fuel of the original polymer as residue. A good example is polyphenylene, a crystalline, high-melting substance, with thermal degradation beginning at 500 to 550 °C and continuing to 900 °C with only 20-30% weight loss. In practice, the choice of a polymer depends on cost and on the importance of flame retardancy in relation to its final use. Intrinsically flame retardant and high temperature materials are quite expensive. Less costly materials in the less-flame retardant or flammable classes can be made sufficiently flame retardant either by adding flame retardant chemicals or by modifying the polymer backbone. Additive Approach. Flame retardant additives used with synthetic polymers include organic phosphorus compounds, organic halogen compounds, and combinations of organic halogen compounds with antimony oxide. Inorganic flame retardants include hydrated alumina, magnesium hydroxide, borates to mention only a few. Not all retardants function well in all polymers. Components may interact - components such as fillers, stabilizers, and processing aids must be considered. To be effective, the flame retardant must decompose near the decomposition temperature of the polymer in order to do the appropriate chemistry as the polymer decomposes, yet be stable at processing temperatures. Most organic phosphorus compounds flame retard by solid phase inhibition, decomposing to form phosphorus acids and anhydrides to promote carbonaceous char. In other phosphorus compounds, reaction cooling is accomplished by endothermic reduction of phosphorus species by carbon. A few phosphorus compounds act as vapor phase inhibitors. Most organic halogen compounds are vapor phase inhibitors and decompose to yield HBr or HC1 which quench chain-branchingfreeradical reactions in the flame. Also, in the solid state, some halogen acids catalyze char formation, particularly with polyolefins. Combinations of antimony oxide with organic halogen compounds are even more effective vapor phasefree-radicalinhibitors than halogens alone. Antimony oxide reacts with the organic halogen compound producing antimony trihalide, which carries the halogen into the flame where it is released as hydrogen halide. The end product involving antimony is thought to be antimony oxide infinelydivided form in the flame. Injecting fine particles into the reaction zone is known to reduce flame propagation rates. Flame retardants in order of commercial importance are phosphorus




compounds (including poly(vinyl chloride) plasticizers), halogen compounds (chlorine and bromine compounds), and combinations of halogen materials with antimony oxide. In addition, certain nitrogen and boron compounds as well as alkali metal salts and hydrates of metal oxides are important asflameretardants in specific polymers. As reported in this volume increased understanding of specific degradation chemistry now allows one to use additives which will direct that chemistry to increase char or to alter vapor phase reactions. The use of metals, copper in PVC for example, is of particular interest in that regard and is discussed a chapter in this volume (Starnes, et al.). Backbone Incorporation. Although the additive approach may be "simple," incorporatingflameretardant chemical units directly into a polymer backbone may be more effective. The main advantages are the ability to bestow permanent flame retardancy and at the same time better maintain the original physical properties of the polymer. Monomelic additives may not be permanent and often change the polymer's physical characteristics. Flame retardant monomers used in backbone modification contain reactive functional groups to allow the monomers to be incorporated directly into the polymer chain. Many are halogen compounds, the source of the resulting improvement inflameretardancy. Generally 10-25% halogen is necessary to impart suitable flame retardancy in polymers, either by additive or backbone modification. The examples of phosphorus comonomers in Nylon 6,6 or polycarbonate are discussed in this volume. Testing and Regulation In many respects, to say a material is flame retardant is a misnomer. Fire is a sequence of events or phases (Figure 4). Depending upon the application different fire properties are important. These properties are: 1. Ease of ignition - how readily will a material ignite? to what kind of ignition source? a cigarette, a match, a large open flame? 2.

Flame spread - how rapidly willfirespread across a polymer surface? horizontal, upward, downward, across a ceiling?

3.

Rate of heat release - how much heat is released? how quickly?

4.

Fire endurance - how rapidly willfirepenetrate a wall,floor,or ceiling, or other barrier (fire penetration)?

5.

Ease of extinction - how easily will thefirego out?

6.

Smoke Release - how much smoke is released? how quickly?

7.

Toxic gas evolution - how potent and how rapidly are toxic gases released? Are they irritating? Are they corrosive? Fire starts with an ignition source and afirstitem to be ignited. For an electrical



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appliance one wants a material which will resist a small electrical arc or a small short duration flame. One does not want the appliance to be the source of fire. But one does not expect an appliance to survive a house fire. Ignition resistance is what is required. Given ignition of an initial item thenfirebegins to spread and heat is released. For a wall covering, for example, flame spread should not be rapid. And indeed wall coverings and other interiorfinishare regulated for rate of flame spread. As fire spreads from item to item and more heat is released and combustible gases rise, a point is reached when fire engulfs the upper part of the room (flashover). The upper part of the room exceeds 600 °C. If a door is open, fire moves downfromthe ceiling and begins to exit the room. Thefireis fully developed. Given a fully developedfirethe issue then is the ability of barriers to contain the compartment fire. Can the assembly of materials resist penetration (fire endurance) to allow for evacuation and to protect adjacent property? Walls and floors/roofs are rated for theirfireendurance. The answer as to whether a material is flame retardant totally depends upon the application. A material suitable as an appliance enclosure because of its ignition resistance would be totally unsuitable as a seal in a wall or floor where the expectation might be the resistance to a room burnout on the other side of the wall of several hours duration. It should not be surprising that there are hundreds of tests which are used in this country alone to access one or more aspects of the flammability of materials or assemblies. Tests by ASTM, UL, NFPA, the building codes, Federal standards, are only a portion of the test methods available. Some tests are very specific to applications, others provide data which can be used more broadly, for example in mathematical fire models. It is important for anyone interested in flame retardant materials to understand what tests measure and why they are being used. Ignition. For ignition one might want to determine the temperature at which a material will ignite, the flux that will sustain ignition, or determine whether an ignition source such as a prescribed flame of specific duration will cause self-sustained ignition. The Setchkin Apparatus (ASTM D1929) is used to heat a material in a furnace to determine the temperature at which a material will generate sufficient volatiles to ignite in the presence or absence of a pilot flame under specific conditions. Thermal analysis (TGA) can determine decomposition temperature, and if interfaced to an infrared or GC/MS can determine decomposition products. One can also determine other thermal properties (Table II), for example, whether a material will bear a load at a given temperature. The decomposition temperatures, or the flash or self-ignition temperatures from ASTM D1929 for polymers are well below flame temperatures, which are 800-1200 °C. Most materials will ignite by direct flame exposure. While cigarettes are used to test upholstered furniture, and incendiary pills (methenamine) are used to test carpets and rugs, the most common ignition tests use Bunsen burners, whether the sample is horizontal, at 45°, at 60°, or vertical. A test series of particular importance in the plastics industry is the test series



After Reference 5

Polyethylene (Low Density) (High Density) Polypropylene Polystyrene ABS PVC (rigid) Polyvinylidene chloride Polytetrafluoroethylene Polymethyl methacrylate Polyamide (Nylon 6) Polyethylene terephthalate Polycarbonate Polyoxymethylene

Polymer

Table II

80 -18 -113,127 105 75 70 149 -85

-125,-20 26,-35 100

100 125 140 90 95 75 150 300 95 150 150 140 140 75 145 88 110 70-80

85-110 200 80 150-155 170

80 100 100 80 80 60 260 70 80-120 130 100 80-100

340-440 330-410 300-400 250-350 200-300 225-275 510-540 170-300 310-350 285-305 420-600 220

340 350-370 345-360 390 390 >530 560 300 420 440 520 350-400

350 390-410 490 480 455 >530 580 450 450 480 no ignition 400

46500 46000 42000 36000 20000 10000 4500 26000 32000 21500 31000 17000

Glass Transition Temperature resistance Vicat-softening Decomposition Flash-ignition Self-ignition Heat of point Β range temperature temperature Combustion ASTM D1929 ASTM D1929 ΔΗ Tg {kJ/kg} TO TO TO TO TO TO TO Short term Long term

Thermal characteristics of thermoplastics


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of Underwriters Laboratories, UL-94. In the horizontal test, a specimen is mounted horizontally and ignited at one end by a flame. Specimens which burn slower than prescribed or don't burn to a line during the test achieve an HB rating. In the vertical test specimens are mounted vertically and ignited at the bottom end by a flamefroma burner. Time to extinguish is measured upon flame withdrawal and the presence or absence of flaming drippingfromthe specimen is noted. The resultant data allows one to assign V-2, V - l , or V-0 ratings. In a third test, a larger flame is used on a vertical specimen with the burner inclined 20° from the vertical. This latter test allows assignment of a 5-V test rating. Such tests are ignitability tests. They don't measure flame spread, or heat release, or ease of extinction, but whether ignition is achieved by a sample subjected to a small burner flame under prescribed conditions. Such tests are not relevant for carpets, or wall coverings, or roof tiles, but are very relevant for polymers used in or as enclosures for appliances, where one wants to insure that the appliance is not a source of fire. Televisions are a good example. In the early 1970's the US Consumer Product Safety Commission found that there were 800 life threatening TV fires in the US per year (about 20,000 total fires) out of 120 million units in place. This 7 in a million rate was determined to be of unreasonable risk. At the time the antenna bracket, turner bracket, and TV enclosure were nonignition resistant (HB) plastic, while other materials in the set were V-2. While a mandatory process was undertaken by CPSC, the voluntary standards process of UL moved more quickly with V-2 (July 1, 1975), V - l (July 1, 1977) and V - 0 (July 1, 1979) rated materials being required by enclosures, antenna brackets, and turner brackets by UL Standard 1410. Having done an extensive series of TV tests at the time, the author's personal view was that with V-0 materials the incidence of TV fires should fall by 1 to 2 orders of magnitude, which has been the case. Fire deaths due to TVfireshave dropped from 200 per year to 10-20. There are other such success stories for Bunsen burner ignitability tests. The user needs to understand such tests are only ignitability tests and understand the applications for which they are relevant. Other Bunsen burner tests include ASTM D-635, which is similar to UL-94 (HB) and used for light transmitting plastics in US building codes. For aircraft FAR Part 25 tests include a horizontal test (transparencies), a vertical test (seat backs, wall liners), a 45° test (cargo and baggage compartment liners), and a 60° test (wire and cable). While other tests are also used, open flame ignitability tests have a broad range of applications. (6)

Flame Spread Given sustained ignition one is concerned about spread of flame from the point of origin. This is particularly important for wall or ceiling materials in buildings where flame spread on a material could carry fire rapidly away from the itemsfirstinvolved. In the US the Tunnel Test (ASTM E-84) is used to measure surface flame spread of building materials. Specimens are mounted on the ceiling of a 25 foot long tunnel and subject to a flame from a large gas burner. Flame spread is measured visually. Material performance is put into categories and it is these categories which are used to classify interior materials in US building codes. Materials or assembly surfaces are rated A (1) 0-25flamespread, B(2) 26-75, and C(3) 76-225. Wood is



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nominally class C (red oak 100, plywood 150). Enclosed vertical exitways require class A, and rooms in certain public buildings class B. Such ratings have been established and justified by experience. Smoke is also measured in the Tunnel Test and a smoke developed limit of 450 required in each of the above classes. While 20 inch wide 25ft long specimens are justified for wall linings, for many other products such samples don't exist. The ASTM E-162 radiant panel test was developed to provide an assessment of downwardflamespread for 6" by 18" samples facing a 670°C radiant panel, with the sample inclined at an angle of 30° from the panel. Since irradiance decreases down the specimen, the time progress of ignition down the specimen serves to measure critical ignition energy (flame spread, F). Thermocouples in the stack above the specimen serve as a measure of heat release rate (Q). FxQ is used as an index, I». Mathematics have been adjusted to give numerical results comparable to the Tunnel Test for coated wood products. ASTM Ε162 is used for a variety of applications. It is cited in UL 1950 for large computer room computer parts (over 10 sq. ft.) for example. Given the need for horizontalflamespread information for vertical surfaces for use in computer fire models, another apparatus, a lateral ignition andflametravel (LIFT) apparatus has been developed (ASTM E1317 and E1321). Whether E84, E162 or E1321, allflamespread tests have problems testing the surface flame spread characteristics of thermoplastics. Thermoplastics, other than floor mounted tend to melt and flow carrying heat andflameaway from the source and making results difficult to compare with other materials. One solution is to test materials on the floor of the Tunnel Test, for example. A bench scale radiant panel test apparatus is used to test carpets in a horizontal mode. ASTM E648 is used to access the critical radiantflux(minimum heatfluxat whichfirepropagates) for carpets used for institutional occupancies. Heat Release Rate Much recent fire test work has focused on heat release rate apparatus. Rate of heat release determines the size of a fire. Heat release rate data are key to computer fire models. Thefirstpractical heat release rate apparatus was developed by Professor Edwin Smith at Ohio State University. ASTM E906 tests specimens in a horizontal or vertical mode to a range of heatfluxes(up to 100kw/m ). Heat release rate curves, smoke release rate curves, and ignitability data are obtained (Figure 5). A more sophisticated apparatus, ASTM El354, the cone calorimeter was subsequently developed at NIST. A key feature of the NIST work is the recognition that for most materials the amount of heat released per unit of oxygen consumed is nearly a constant. Given that oxygen concentrations are far more easily determined than heat output over time, the oxygen depletion calorimeter has proved more versatile. Many E906 units have also been modified for oxygen depletion assessment. A multitude of materials have been tested and data reported using both apparatus. E906 results are now used for the selection of wall and ceiling linings for transport category commercial aircraft (FAR Part 25) (not using oxygen depletion). The cone calorimeter has been considered in Europe as a tool for the regulation of ceiling and wall linings in buildings and is under active study for furniture, as discussed elsewhere in this volume. 2



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Hazards

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Ignition sources Ignitability

Ignition Flame spread Heat release

Fire penetration Fire endurance

Smoke, irritation, toxicity, corrosivity Figure 4. Sequence of events or phases in fire. Not allfiresinvolve all phases. For example, afiremay ignite, spread to a limited area and go out. In othersfirespreads, flashover is reached, and thefireis contained only by the ability of the compartment to resist penetration or thefirevents through openings. After reference 4 Glowing Combustion Completed or sample burnout

Sample Burning Rate Fully Developed

o— (if present)

Time Figure 5. Sample heat release rate versus time curve.


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Oxygen depletion calorimetry can be used for more than bench scale tests. If products are tested under a hood and oxygen measured in the stack exiting the hood the rate of heat release of a variety of actual products, whether TV's, business machines, chairs, cables, etc., can be assessed and compared. Such tests have been used to show the effects of flame retardants on thefireperformance of real products substantially lower peak heat release rates. Oxygen depletion techniques have also been applied successfully to full scale compartment or room tests. What is required is an exhaust hood at the exit to the compartment which captures all the combustion productsfromthe room. Fire Endurance The ASTM E l 19 wasfirstdeveloped in 1918. The test is probably the most widely used and recognized in the United States for determining the degree of fire endurance of walls, columns, floors, and other building members. The timetemperature curve used in this test, Figure 6, is achieved by a series of burners appropriate for the application. Ratings generated by this test specification are based on time intervals of 30 min, 45 min, 60 min, 90 min, 2 hr, and there after, in hourly increments. These time ratings apply to tests of bearing and non-bearing walls and partitions, tests of columns, alternative tests of protection for structural steel columns, tests of floors and roofs, tests of loaded restrained beams, alternative classification procedures for loaded beams, alternative tests for protection of solid structural beams and girders, and performance of protective membranes in walls, partitions, floor, or roof assemblies. The ratings given refer to the time - temperature curve used. If the time temperature curve in real scale is different, then the assembly performance will be different accordingly. Ease Of Extinction One of the most common tests used for plastics is the Oxygen Index test (ASTM D2863). In the oxygen index test the minimum percentage of oxygen in an oxygen/nitrogen mixture is determined for a top ignited specimen that will just sustain combustion. At a lower oxygen percentage the specimen will go out. The standard test is used for rigid plastics and for fabrics and films. The test has also been run on powders and liquids. While some have called the oxygen index an ignition test, the ignition parameters are not rigidly controlled and what is measured is after sustained ignition, i.e. , under what percentage of oxygen does the sample burn for at least 3 minutes. Oxygen index is a measure of ease of extinction. Some call oxygen index the "limiting oxygen index" or "LOI". The oxygen index is already a limit so the word "limiting" is redundant. The oxygen index is sensitive to the presence offillers,to thickness, and to the melt/flow characteristics of the polymer being tested. If the sample is heated then the oxygen index falls. At 300°C the 01 is about 50% of that at room temperature. Some have used a bottom ignited sample rather than the standard top ignition. The OI is substantially lower for a bottom ignited sample, as expected, due to heat feedback to the specimen. In Europe an alternative form of the test is to determine the temperature at which the 01 is 21% (the percentage of oxygen in air) Oxygen index readily shows the effects of flame retardants, and of changes in


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2400 2200


2000 1800 1600

F I UJ I-

1400 1200 1000 800 600 400 200 0 I ι 0 1

• 2

ι 3

4

ι 5

. 6

ι

I 7 8

HOURS

Figure 6. ASTM El 19 time-temperature curve. Reference?. Copyright ASTM. Reprinted with Permission


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flame chemistry. For example the oxygen indices (Table III) for a series of polymethylenes range from 15.6 for pentane to 17.4 for polypropylene. A series of polyphenyls rangefrom16.3 for benzene to 32.0 for polyphenyl. The effectiveness of halogens are easily accessed. Oxygen index has been widely used as a research tool, since it uses small samples of material, and as a quality control tool. It has been used for specification purposes in the telecommunications industry. Table IV presents 01 values on a large number of polymers. A correlation has been made with UL-94 ratings, Figure 7. HB materials generally have an 01 less than 23. V-2 and V - l materials have a narrow range, OI's of 24-30, and V-0 materials, as to be expected, cover a broad rangefrom25 and above. Smoke Smoke is here defined as visual obscuration. Smoke is measured for construction materials in the Tunnel Test (E-84). As an alternative for light transmitting plastics, Rohm and Haas Co. was instrumental in gaining acceptance of the XP-2 smoke chamber, ASTM D2843. The loss of transmission in a horizontal light beam is measured over time as a small sample is exposed to a small flame source. NBS (now NIST) developed the NBS Smoke Chamber (ASTM E-662) to resolve some of the technical issues presented by the XP-2 smoke chamber. Samples are exposed to a radiant flaming exposure, with or without a pilot flame, resulting in either a flaming or smoldering condition depending on the ignitability of the sample. The light beam is vertical rather than horizontal to avoid effects of smoke layering. The NBS smoke chamber is probably in the most extensively used test for smoke, both here in the USA and in some countries in Europe. It provides both a flaming condition and a smoldering condition, and some materials (e.g. wood) perform differently depending on this condition. (The E84 tunnel would be aflamingcondition for wood. ) Improvements to the NBS smoke chamber are underway, e.g., horizontal specimen mounting, cone radiant heater, mass loss. From its inception the NBS smoke chamber was controversial. Cellulosic products tend to give high smoke under non-flaming conditions while high performance plastics give maximum smoke under flaming conditions. Which conditions represent real conditions? Wood products which give low smoke in the Tunnel Test now showed high smoke under the smoldering test condition. The Arapahoe smoke apparatus (ASTM D4100) measures smoke gravimetrically. Smoke is collected on filter paperfroma small sample exposed to a small burner. Results correlate with NBS smoke chamber data under flaming conditions. Its use versus the other three ASTM tests has been minimal. Corrosivity Of special concern for polymers used in high technology applications is the generation of corrosive gases. A detailed chapter is given elsewhere in this volume. Readers are referred to that extensive discussion and analysis. Large Scale Tests Full scale validation testing is expensive, but is the prime mechanism to be assured that bench scale results translate to real product performance. Many companies have evaluated their products through full scale: TV's, computers, aircraft interiors, rail car interiors, building products, to name a few.


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Table ΙΠ Contribution to Oxygen Index of major organic structural features Polyphenyl and Polymethylene 01 Benzene Biphenyl p-Terphenyl Quaterphenyl Polyphenyl

16 18 19 26 32

Pentane Hexane Cyclohexane Decane Hexadecane Mineral oil (USP) Paraffin wax Polyethylene Polypropylene

16 16 16 16 16 16 17 17 17

Relative effectiveness of halogen based on units of six carbons Alliphatic materials 01 /atom F Cl Br I

Aromatic materials 01 /atom

Fire and Polymers: An Overview - ACS Publications - American

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