Flame spread reduction

This study resulted in a series of reports on a comprehensive evaluation of fire-retardant treatments for wood (2-6). One hundred and thirty single chemicals or combinations of chemicals in the form of various salts were evaluated for flame-spread reduction, smoke, and corrosivity. Diammonium phosphate ranked first in reducing flame spread, followed by monoammonium phosphate, ammonium chloride, ammonium sulfate, borax, and zinc chloride. Zinc chloride, although excellent as a flame retardant, promoted smoke and glowing. Ammonium sulfate was the least expensive, but under certain environmental conditions it was corrosive to metals. None of the 130 compositions tested was considered ideal because of the adverse effects on some of the properties of wood. Several reviews of the subject are available and provide additional background material (J, 7-JO). 

Studies of fire damage from atomic bomb attack and incendiary bomb attack have shown this reduction of flame spread to be a significant and measurable fact. However, variations in burning conditions, types of structures, types of paints, condition of the paint at the time of exposure to fire, etc., will always leave the true value of protective paints open to question and subject to opinion. 

Bromination of vinyl-ester resin imparts fire retardancy as manifested by flame spread and lower RHR [50]. However, this fire-retardant system functions primarily in the gas phase causing incomplete combustion. As such, brominated resins produce dense smoke, and an increase in the yield of CO and HBr. Recent interest in the use of non-halogenated organic-matrix composite materials in US Navy submarines and ships has generated the requirement for significant improvement in the flammability performance of these materials including reduction in the amount of smoke, CO and corrosive combustion products. 

To achieve typical flame retardancy for cables required by the most important international cable fire test (lEC 60332-3-24, Tests on electrical cables imder fire conditions - Part 3-24 Test for vertical flame spread of vertically-mounted bunched wires or cables) demands a high loading of a mineral FR filler such as ATH. 65wt% of ATH with 35% of a suitable polymer like EVA must often be used for cable jackets. A similar compound of EVA (with 28% VA content) with ATH and 5% of a nanocomposite can pass the same test. It was found that the ATH could be reduced to only 45% of the composition. The reduction in the total amount of the fillers results in improved mechanical and rheological properties of typical EVA-based cable compoimds. The char formed is... 

Nelson [136] has reported studies of zinc, zinc oxide, and zinc borate in coatings on or as a filler in modified polyphenylene oxide (m-PPO). Zinc arc spray, or zinc, zinc borate, and zinc/zinc borate in epoxy coatings showed a substantial reduction of flame spread index (ASTM E-162) (I,) for m-PPO. Zinc oxide in epoxy, however, showed a dramatic increase in I, on m-PPO. Zinc arc spray on m-PPO led to enhanced stability in the 500-600°C range in both isothermal and GC/MS experiments. It was speculated that since zinc melts at 420OC, just at the early stage of decomposition of m-PPO, this could allow intimate contact with the charring substrate. As in pure polystyrene, char formation is enhanced in air in m-PPO, and this was thought to be enhanced further by the presence of zinc. Indeed it was observed that volatilization of small molecules is reduced for m-PPO with zinc present at temperatures under 700°C, with preference for volatilization of the triaryl phosphate flame retardant, styrene trimer, and PPO dimers. 

The controlled flame was found to be largely unaffected by moderate swirl (levels up to 40%) although the stability was slightly reduced. Heavy swirl (beyond 75%) led to a further reduction in stability and intermittent formation of soot. The unforced swirling flame was not nearly as efficient in reducing soot formation as the controlled (forced) flame without swirl. The flame was unstable, quite yellow, and spread out to impinge upon the dump diameter... 

From Figures 6, 18, and 20 we see that relative fluorescence measurements for OH, SH, S2, and SO along with the method for data reduction leads to reasonable agreement with the equilibrium expectations. In Figures 19 and 21 there is a somewhat wider spread of the data about the equilibrium expectation. This is probably caused by the use of non-optimal measuring conditions and data reduction for S02 which has a very complex spectrum at flame temperatures. We are expecting a Nd-Yag laser shortly which will operate deeper into the UV than our present flash lamp pumped dye laser and will permit a more extensive characterization of SO2 fluorescence in the flame environment. 

If the diameter of the tube is sufficiently small, the flame dies out after travelling a short distance. Still further reduction in the diameter of the tube renders it impossible for the flame to spread from the point... 

Combustion is understood to be a fast reduction-oxidation reaction between substances, capable of spreading in space at a subsonic speed and usually accompanied by flame and light. An oxidant and reducing agent are necessary for this reaction to occur. Combustion processes are as manifold as the chemical nature of compounds having oxidizing and reducing properties. 

The higher the flame propagation rate, the faster the fire spreads and therefore the more flammable the fluid, as measured by the test. As can be seen this approach ranks the fluids in the same order as the flash point, with H-515 being the most flammable and H-537 the least. There are a variety of methods that can be used to demonstrate flammability and some show the PAO fluids in a better light than others however, the ultimate test of flammability has to be the performance of the fluid in service. US Air Force statistics show quite clearly a significant reduction in aircraft losses since the introduction of the PAO-based H-537 into service. 

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