Flaming combustion, flammability

The most widely accepted theory of the mechanism of fire-retardant chemicals in reducing flaming combustion of wood is that the chemicals alter the pyrolysis reactions with formation of less flammable gases and tars and more char and water (4,5,8,21,24-29). Some fire retardants start and end the chemical decomposition at lower temperatures. Heat of combustion of the volatiles is reduced. Shafizadeh (21) suggests that a primary function of fire retardants is to promote dehydration and charring of cellulose. 

As one can see from the above discussion, establishing correlation between bench-scale flammability and cable flame tests is a difficult task because of complicated chemical and physical processes involved in the burning and combustion of polymer materials and cables. Much research is still needed to understand fundamental processes governing the flaming combustion of wire and cable compounds in actual cable designs and cable bundles in a given environment. 

The retarding effect of metal compounds on the flaming combustion of polymers must be primarily attributed to the decrease of the yield of flammable volatile pyrolysis products. There are two alternative paths 1) catalysis of the formation of non-combustible products (COj, HjO) 2) inhibition of polymer decomposition at the high temperatures developed during steady-state combustion (high-temperature stabilization)... 

Flammable Range Those concentrations of a combustible gas or vapor in air, measured as volume percent in air, at which flaming combustion can occur. The flammable range has an upper and lower limit. The flammable range is bounded by an upper flammable limit (UFL) and a lower flammable limit (LFL). 

Fourth was the idea, in 1948, of replacing flame combustion by catalytic oxidation. In this case it was with the thought of relieving the engineer of the limitations imposed on him by the laws which govern the flammability of air-fuel mixtiu es. 

EXPLOSION and FIRE CONCERNS combustible flammable when exposed to heat or flame NFPA rating Health 1, Flammability 2, Reaetivity 0 can react vigorously with oxidizing materials reacts violently with nitric acid at room temperature to form an explosive product ignites on contact with chromium trioxide incompatible with oxidants heating to decomposition emits smoke and fumes use alcohol foam, dry chemical, water spray, or carbon dioxide for firefighting purposes. 

EXPLOSION and FIRE CONCERNS combustible liquid NFPA rating Health 3, Flammability 2, Reactivity 0 flammable liquid when exposed to heat or flame moderate explosion hazard polymerizes explosively upon contact with strong mineral acids or alkalies mixture with sodium hydrogen carbonate ignites spontaneously keep away from heat and open flames combustion produces irritating fumes and toxic gases use water spray, dry chemical, alcohol foam, or carbon dioxide for firefighting purposes. 

NO regulations have become more severe each year throughout the world. Therefore, low NO combustion technologies for gas turbines, such as water/steam injection, lean diffusion flame combustion, and lean premixed flame combustion, have been developed and used for commercial gas turbines. However, NO levels are still not low enough to meet some of the more severe regulations in some areas. In such cases, catalytic combustion is considered to be the best method to achieve the reqired NO levels. Catalysts support stable combustion with a lower flame temperature than the flammable limit, and NO is not produced at such a flame temperature. 

Catalytic combustion has received an increasing interest as an ultra-low emission technology for gas turbines. The main advantage with catalytic combustion is the possibility to decrease, and for some fuels to increase, the fuel-to-air ratio beyond the limits of flammability. Hence the combustion process and the temperature evolution in a gas turbine combustion chamber can be better controlled and stabilized. This flexibility gives the possibility to reduce emissions of unwanted pollutants compared with conventional flame combustion. Depending on fuel characteristics, emissions such as thermal and fuel-NOx, CO and hydrocarbons as well as soot can be reduced to ultra-low levels. Other advantages are lower noise levels and less vibrations. 

To determine relative flammability of plastic by measuring the minimum concentration of oxygen in a flowing mixture of oxygen and nitrogen that will just support flaming combustion. The apparatus is shown in Fig. 10.60... 

The aforementioned definitions imply that flammabihty tests are concerned with a lower level of performance. Passing a flammability tests does not mean that a material will be less hazardous when involved in a fire. This is consistent with one definition of the term flammable, which in ASTM E176, Terminology of Fire Standards, is described as, subject to easy ignition and rapid flaming combustion (25). 

The flammability of natural and synthetic polymer materials is determined by the ability of such materials to ignite and spread the combustion process. Combustion is defined as a fast, self-accelerating exothermal redox process that is able to spread in the environment and is accompanied by luminosity and the formation of a flame. Combustion may be of either a chain or a thermal nature, depending on the cause of initiation and development accumulation of active particles in the system or the liberation of heat. 

Flammable A combustible material that ignites very easily, burns intensely, or has a rapid rate of flame spread. Flammable is used in a general sense without reference to specific limits... 

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