Flame spreading rate

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. 

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. 

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

Furthermore, it has been shown that the time period until ignition occurs, in the Cone calorimeter, is proportional to the inverse of the flame spread rate [16]. The Cone calorimeter can also be used to provide the mass loss rate information required for the simplified classification into categories of toxic hazard [1] quick toxic hazard assessment. Thus, the NBS Cone calorimeter is a very useful tool to overcome some of the disadvantages associated with measuring a single property at a time. 

Figure 8.16 Flame spread rate over thick PMMA sheets as a function of the opposed forced flow velocity for several flow oxygen mass fractions (Femandez-Pello, Ray and Glassman [6])...

The flame spread rate can be represented in terms of the pyrolysis front (xp) from Equation (8.7a) ... 

Some manufacturers of internal cooling tower components, specifically fill material and drift eliminators, have products produced from less easily ignited plastic that have been tested by a nationally recognized testing laboratory and determined to have sufficient fire resistance or reduced flame spread ratings that when, and only when, used in an otherwise noncombustible cooling tower, do not require fixed automatic fire protection. 

Theoretical studies are primarily concentrated on the treatment of flame blow-off phenomenon and the prediction of flame spreading rates. Dunskii [12] is apparently the first to put forward the phenomenological theory of flame stabilization. The theory is based on the characteristic residence and combustion times in adjoining elementary volumes of fresh mixture and combustion products in the recirculation zone. It was shown in [13] that the criteria of [1, 2, 5] reduce to Dunskii s criterion. Longwell et al. [14] suggested the theory of bluff-body stabilized flames assuming that the recirculation zone in the wake of the baffle is so intensely mixed that it becomes homogeneous. The combustion is described by a second-order rate equation for the reaction of fuel and air. 

Flame Spread Rate—Rate of flame propagation across a fuel pool. 

The flame spread rate of methanol is about two-thirds that of gasoline. This measure applies primarily to how fast flame will traverse a pool of fuel, and the difference between methanol and gasoline is not really significant since both will be engulfed in flame before any actions could be taken to stop flame propagation. 

Flame Spread Rate, m/s slower than slower than gasoline 4-6c... 

The flame-spread number is derived relative to red oak (with an arbitrary flame-spread rating of 100) and to asbestos-cement board (rated zero). Natural wood products (1-inch lumber) usually have flame-spread ratings of 100 to 150 in the test furnace of Underwriters1 Laboratories, Inc. (35). Some exceptions are poplar (170-185), western hemlock (60-75), redwood (70), and northern spruce (65). 

Wood well treated with current commercial fire-retardant impregnation treatments will have flame-spread ratings of 25 or less. Many treated wood products have obtained a special marking or designation "FR-S" from UL (36) for having a flame-spread, fuel-contributed, and smoke-developed classification of not over 25 and no evidence of significant progressive combustion in an extended 30-minute ASTM E84 (34) test procedure. The fuel-contributed and smoke-developed classifications are also calculated relative to performance of red oak and asbestos-cement board. 

In flame spread tests, the specimen is ignited at the hot end by a nonimpinging premixed acetylene-air pilot flame. Flame spread rate over the surface is then monitored as a function of distance x. Thus, one experiment yields information on flame spread rate over a whole range of heat flux levels (or surface temperatures). Information to this extent can be obtained in one run owing to the particular shape of the flux invariant, which is the result of the specific geometry and specimen-panel arrangement shown in Figure 14.7. 

In this test, a small sample of material (127 mm x 13 mm, or 5 in. x 0.5 in.) is exposed vertically to a small Bunsen burner-type flame from underneath (in the UL 94 V test) and the results show a rating, ranging from V-0 (best), through V-l, V-2 to B (for Burn). Materials with a B rating on the UL 94 Vertical test can also be tested in the less severe UL 94 HB (for horizontal burning), where the assessment is whether a flame spread rate of 4in./min is achieved. It is the most widely used fire-test specification for plastic materials, especially fire-retarded ones, and forms the basis of the famous Yellow Card used by ULs to list the plastic materials. The results from these tests are almost invariably found in a variety of specifications and data sheets. 

The theory advanced by De Ris belongs to the first group. In his model of flame spread along a horizontal surface it is assumed that the diffusion flame contacts the surface at the point where the polymer vaporization (gasification) begins. Reactant diffusion to the narrow zone of chemical reaction controls the heat generation process. If heat is transferred from the laminar diffusion flame to the surface by conduction, then the flame spread rate follows the Equations a) for thermally thin materials... 

From Eqs. (2.11) and (2.12) it follows that the flame spread rate in the first case is inversely proportional to the material thickness and is independent of the incoming oxidant flow velocity. In the second case it is proportional to v, and does not depend on the material thickness. The functional relationship between v and the initial material temperature T is also different. Preheating of the material reduces AT = T — T, thereby promoting flame spread. 

This model assumes the critical ignition temperature to be equal to T, temperature at which the fuel is gasified in combustion. The temperature T is assumed to be equal to that of the adiabatic flame with a stoichiometric fuel/oxidant ratio. De Ris noted important features of flame spread along a material surface, but the fact that T, must be determined experimentally reduces the potential of the method for predicting the flame spread rates. 

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