Flame spread

There are a multiplicity of tests, which cover various aspects of determining the rate of flame advance. UL 94 and oxygen index tests are widely used (and quoted) to characterize materials. 

The most quoted test for comparing specific materials is UL 94, which assigns a flame class based on the burning behaviour at a specified thickness when ignited with a small ignition source (laboratory burner). 

The lowest flame class is HB, which restricts the rate at which a flame can advance along a horizontal test specimen to 75mm/min ( 3.2mm thick) and 38mm/min for thicker samples. There are four classes of vertical test samples V-0, V-1, V-2 and 5V, of which 5V is the most demanding in terms of its ability to self-extinguish. 

These tests measure the minimum oxygen concentration, in an admixture with nitrogen, required to sustain combustion of small samples under specified test conditions. The higher the index, the more difficult it is for the flame to spread. 

Some typical data for flame spread are listed for resins in Table 8.1, and for fibres in Table 8.2. 

FMVSS 302 flammability of interior materials - passenger cars, multi-purpose passenger vehicles, trucks, and buses. Specified in regulation for flammability of 

Measurement of the density of smoke evolved from a burning or smouldering specimen has been widely studied and several tests proposed. They differ mainly in that some measure the density of hot smoke as evolved from the specimen, while others allow the smoke to cool and stabilize before density is measured. Other tests use a gravimetric method for smoke determination. 

1 AS 1530 Part 3 - test lor early fire hazard properties of materials 

A 600x450 mm specimen is mounted vertically and moved at a predetermined rate towards a radiant gas burner. The radiation intensity of the burning specimen is measured for at least 2 minutes after ignition, and a Spread of Flame Index is calculated from the time taken for the radiation intensity to increase by 1.4 kW m .  

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Corrosion Resistant Fiber-Reinforced Plastic (FRP). Fiber glass reinforcement bonded with furfuryl alcohol thermosetting resias provides plastics with unique properties. Excellent resistance to corrosion and heat distortion coupled with low flame spread and low smoke emission are characteristics that make them valuable as laminating resins with fiber glass (75,76). Another valuable property of furan FRP is its strength at elevated temperature. Hand-layup, spray-up, and filament-win ding techniques are employed to produce an array of corrosion-resistant equipment, pipes, tanks, vats, ducts, scmbbers, stacks, and reaction vessels for industrial appHcations throughout the world. 

Antimony oxide and 2inc borate are also used as synergists for unsaturated polyesters. Their combined effect on the flame spread index (25) is ... 

Sb202 Zinc borate Flame spread Oxygen index ... 

ASTM E162-87 radiant panel flame spread... 

ASTM E84, UL 723, UL 910 Steiner tunnel flame spread and smoke... 

The Ohio State University (OSU) calorimeter (12) differs from the Cone calorimeter ia that it is a tme adiabatic instmment which measures heat released dufing burning of polymers by measurement of the temperature of the exhaust gases. This test has been adopted by the Federal Aeronautics Administration (FAA) to test total and peak heat release of materials used ia the iateriors of commercial aircraft. The other principal heat release test ia use is the Factory Mutual flammabiHty apparatus (13,14). Unlike the Cone or OSU calorimeters this test allows the measurement of flame spread as weU as heat release and smoke. A unique feature is that it uses oxygen concentrations higher than ambient to simulate back radiation from the flames of a large-scale fire. 

Tunnel Test. The tunnel test is widely used to test the flame spread potential of building products such as electrical cable (15) and wall coverings (16). The test apparatus consists of a tunnel 7.62 x 0.445 m x 0.305 m ia cross section, one end of which contains two gas burners. The total heat suppHed by the burners is 5.3 MJ/min. The test specimen (7.62 m x 50.8 cm), attached to the ceiling, is exposed to the gas flames for 10 minutes while the maximum flame spread, temperature, and smoke evolved are measured. The use of this and other flame spread test methods has been reviewed (17). 

A. Tewarson, "Heat Release and Surface Flame Spread," lEC TC 89-WG8 Meeting, British Standards Institution, London, Oct. 1992. 

The product contains 12.6% phosphoms and has an OH number in the 450 mg KOH/g range. Fyrol 6 is used to impart a permanent Class 11 E-84 flame spread rating to rigid foam for insulating walls and roofs. Particular advantages are low viscosity, stabiHty in polyol—catalyst mixtures, and outstanding humid aging resistance. Fyrol 6 is used in both spray foam, froth, pour-in-place, and slab stock. 

The surface burning characteristics (flame spread index and smoke developed index) for wood and wood products as measured by American Society for Testing and Materials (44) can be reduced with fire retardant treatments, either chemical impregnation or coatings (48). Fire retardant treatments also reduce the heat release rate of a burning piece of wood (49,50). The heat release rates (51) of the burning materials are an important factor in fire growth. 

Solutions of these fire retardant formulations are impregnated into wood under fliU cell pressure treatment to obtain dry chemical retentions of 65 to 95 kg/m this type of treatment greatly reduces flame-spread and afterglow. These effects are the result of changed thermal decomposition reactions that favor production of carbon dioxide and water (vapor) as opposed to more flammable components (55). Char oxidation (glowing or smoldering) is also inhibited. 

S has been approximated for flames stabili2ed by a steady uniform flow of unbumed gas from porous metal diaphragms or other flow straighteners. However, in practice, S is usually determined less directly from the speed and area of transient flames in tubes, closed vessels, soap bubbles blown with the mixture, and, most commonly, from the shape of steady Bunsen burner flames. The observed speed of a transient flame usually differs markedly from S. For example, it can be calculated that a flame spreads from a central ignition point in an unconfined explosive mixture such as a soap bubble at a speed of (p /in which the density ratio across the flame is typically 5—10. Usually, the expansion of the burning gas imparts a considerable velocity to the unbumed mixture, and the observed speed will be the sum of this velocity and S. ... 

In any gas burner some mechanism or device (flame holder or pilot) must be provided to stabilize the flame against the flow of the unbumed mixture. This device should fix the position of the flame at the burner port. Although gas burners vary greatly in form and complexity, the distribution mechanisms in most cases are fundamentally the same. By keeping the linear velocity of a small fraction of the mixture flow equal to or less than the burning velocity, a steady flame is formed. From this pilot flame, the main flame spreads to consume the main gas flow at a much higher velocity. The area of the steady flame is related to the volumetric flow rate of the mixture by equation 18 (81,82)... 

Finishes Thermal insulations require an external covering (finish) to provide protection against entry of water or process fluids, mechanical damage, and ultraviolet degradation of foamed materials. In some cases the finish can reduce the flame-spread rating and/or provide fire protection. 

Many combustible dusts produced by industrial processes are explosible when they are suspended as a cloud in air. A spark may be sufficient to ignite them. After ignition, flame spreads rapidly through the dust cloud as successive layers are heated to ignition temperature. 

To simulate the effect of small flames that may result from faulty conditions within electronic equipment, the lEC 695-2-2 Needle Elame Test may be used. In this case a small test flame is applied to the sample for a specified period and observations made concerning ability to ignite, extent of burning along the sample, flame spread onto adjacent material and time of burning. 

These materials not only have a good resistance to burning and flame spread but are also able to withstand service temperatures of up to 150°C. At the same time polyisocyanurate foams have the very good hydrolytic stability and low thermal conductivity associated with rigid polyurethane foams. 

Protective clothing - Protection against heat and flame - Limited flame spread materials and matenal assemblies. Superseded BS 6249 Part 1 1982... 

Fire safety Incombustibility Flame spread rate Toxic gases Fuel content... 

When plastics are used, their behavior in fire must be considered. Ease of ignition, the rate of flame spread and of heat release, smoke release, toxicity of products of combustion, and other factors must be taken into account. Some plastics bum readily, others only with difficulty, and still others do not support their own combustion A plastic s behavior in fire depends upon the nature and scale of the fire as well as the surrounding conditions. Fire is a highly complex, variable phenomenon, and the behavior of plastics in a fire is equally complex and variable (Chapter 5, FIRE). 

A fire, followed by an explosion at Huddersfield in 1900 was also caused by detonation of iron picrate (presumably Fe++). The iron picrate had been formed on the surface of steam pipes located in the Picric Acid drier shop. It ignited when a plumber, unaware of the fact, struck one of the pipes with a hammer. The flame spread along the pipe and set the drying Picric Acid on fire... 

During this period, the mass discharge rate through the motor nozzle increases as the flame spreads over the propellant, causing an increase in the chamber pressure (as shown in Fig. 2) which is described by... 

A knowledge of the ignition characteristics of the propellant and the heat-transfer characteristics of the igniter permits the igniter designer to determine the propellant ignition-delay for a particular system. The next question is How fast does the flame spread across the propellant surface The answer to this question determines the burning area on the propellant surface as a function of time this is the function AB(t) required to solve Eq. (6) for the chamber pressure as a function of time. 

Nonpremixed edge flames (a) 2D mixing layer (From Kioni, P.N., Rogg, B., Bray, K.N.C., and Linan, A., Combust. Flame, 95, 276, 1993. With permission.), (b) laminar jet (From Chung, S.H. and Lee, B.J., Combust. Flame, 86, 62,1991.), (c) flame spread (From Miller, F.J., Easton, J.W., Marchese, A.J., and Ross, H.D., Proc. Combust. Inst., 29, 2561, 2002. With permission.), (d) autoignition front (From Vervisch, L. and Poinsot, T., Annu. Rev. Fluid Mech., 30, 655, 1998. With permission.), and (e) spiral flame in von Karman swirling flow (From Nayagam, V. and Williams, F.A., Combust. Sci. Tech., 176, 2125, 2004. With permission.). (LPF lean premixed flame, RPF rich premixed flame, DF diffusion flame). 

P. N. Kioni, B. Rogg, K. N. C. Bray, and A. Linan, Flame spread in laminar mixing layers The triple flame. Combust. Flame 95 276-290,1993. 

F. J. Miller, J. W. Easton, A. J. Marchese, and H. D. Ross, Gravitational effects on flame spread through non-homogeneous gas layers, Proc. Combust. Inst. 29(2) 2561-2567, 2002. 

I. Wichman, Theory of opposed-flow flame spread, Prog. Energy Combust. Sci. 18 553-593,1992. 

F.H. Wright and E.E. Zukowsky 1962, Flame spreading from bluff-body flame holders, Proc. Combust. Inst. 8 933-943. 

Increasing the surface area of a combustible solid enhances the ease of ignition. Hence dust burns more rapidly than the corresponding bulk solid combustion of dust layers can result in rapid flame spread by train firing . Solid particles less than about 10 pm in diameter settle slowly in air and comprise float dust (see p. 51 for settling velocities). Such particles behave, in some ways, similarly to gas and, if the solid is combustible, a flammable dust-air mixture can form within certain limits. Larger particles also take part, since there is a distribution of particle sizes, and ignition can result in a dust explosion. 

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