Flame spread control

Fire risks and fire hazards are mainly the result of the combination of factors, inclnding ignitability, ease of extinction, flammability of volatiles generated, amonnt of heat released on burning, rate of heat release, flame spread, smoke obscuration, and smoke toxicity. The most important fire risks and Are hazards are the rates of heat release, smoke production, and toxic gas release. An early high rate of heat release causes fast ignition and flame spread, controls a fire s intensity, and is mnch more important than ignitability, smoke toxicity, or flame spread. The time for people to escape a Are is also controlled by the heat release rate. ... 

Figure 8.9 Control volume energy conservation for a thermally thick solid with flame spread steady velocity, Up...

The key to a successful derivation of a particular flame spread phenomena is to establish the mechanism controlling the spread in terms of expressions for 6f and t. We will not continue to develop such approximate expressions, but will show some results that are grounded in data and empirical analyses. 

Loh, H.T. and Fernandez-Pello, A.C., A study of the controlling mechanisms of flow assisted flame spread, Proc. Comb. Inst., 1984, 20, pp. 1575-82. 

The inherent flammability and low melting point of sulfur impose some limitations of SC use. Flammability can be controlled to some extent by the use of additives, and it is fortunate that the DCPD types of additives used to improve the durability of SC also impart a degree of fire resistance. Sulfur concretes are in any case considerably less of a fire hazard than wood. Because of the low thermal conductivity, heat penetration is slow, and SC can survive short exposures to fire without serious damage. Sulfur concretes do not support combustion, and flame spread is essentially zero. 

MATERIAL PARAMETERS CONTROLLING FLAME SPREAD 3.5.1 Definition... 

There are many mechanisms involved in the propagation of a flame through a condensed fuel [13], The problem is extremely complicated therefore, the simplest case will be used here, namely, the opposed-flow flame spread. The tip of the flame controls the opposed-flow flame spread and all the transport mechanisms involved are presented in Figure 3.8. 

It is important to note that the physical parameters controlling opposed flame spread are the same as those controlling ignition, with the added parameter associated with the flame heat flux. Depending on the approach to be followed, the flame input can be either defined by the flame temperature,... 

The analysis of co-current flame spread is very similar to that of opposed flame spread. However, it is further complicated because the flame covers the fuel thus, the flame length is a further parameter that needs to be analyzed. The flame length can be represented empirically as being proportional to the pyrolysis length or can be calculated using boundary layer theory and the assumption of infinitely fast gas-phase chemistry [22], Despite the added complexity, co-current flame spread is controlled by the same physical parameters as ignition or opposed flame spread. 

Femandez-Pello, A.C. and Hirano, T., Controlling mechanisms of flame spread, Combustion Science and Technology, 32,1, 1983. 

The UL 94 standard specihes bench-scale test methods to determine the acceptability of plastic materials for use in appliances or other devices with respect to flammability under controlled laboratory conditions. The test method that is used depends on the intended end-use of the material and its orientation in the device. The standard outlines two horizontal burning tests, three vertical burning tests, and a radiant panel flame spread test. The most commonly used test method described in the UL 94 standard is the 20-mm Vertical Burning Test V-0, V-l, or V-2. The method is also described in ASTM D 3801. A schematic of the test setup is shown in Figure 14.3. 

Chapter 7 is the chapter dealing with Special Conditions and it addresses most of the cables with highly improved fire performance. Thus, Articles 725 (Class 1, Class 2, and Class 3 Remote-Control, Signaling, and Power-Limited Circuits), 760 (Fire Alarm Systems), and 770 (Optical Fiber Cables and Raceways) all use the same two schemes for fire performance of cables, as shown in Figures 21.4 and 21.5. The figures show that the best is NFPA 262,65 a cable fire test for flame spread and smoke, conducted in a modified Steiner tunnel (86 kW or 294,000 BTU/h), for which the requirements in the NEC are that the maximum peak optical density should not exceed 0.5, the maximum average optical density should not exceed 0.15, and the maximum allowable flame travel distance should not exceed 1.52m (5 ft). The next test, in the order of decreasing severity is UL 1666,64 known... 

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... 

Researchers at the Eastern Forest Products Laboratory in Canada have evaluated the urea and melamine amino-resin systems (9, 57, 99-110). Their work demonstrates that both systems show good leach resistance and reduced flame spread. The stability of these resins is controlled by the rate of methylolation of the urea, melamine, and dicyandiamide. The optimum mole ratio for stability of these solutions is 1 3 12 4 for urea or melamine, dicyandiamide, formaldehyde, and orthophosphoric acid. However, even at the optimum mole ratios, the pot life of the melamine system is less than that of the urea system. In both systems the nitrogen is fixed to a greater degree than the phosphorus. However, the degree of fixation of the phosphorus is greater with the melamine than with the urea. The melamine structure may promote formation of compounds with phosphoric acid that are less soluble than those from urea and dicyandiamide. 

The test method exposes a 24-ft (7.32-m) long by 20.25-in. (0.514-m) wide specimen to a controlled air flow and adjusts the observed flame spread to that with the select grade oak for which the flame spreads the entire length of the specimen in S A min. The specimen may consist of sections joined together. 

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