Ignition, flame propagation

Methyl bromide is nonflammable over a wide range of concentrations in air at atmospheric pressure and offers practically no fire hazard. With an intense source of ignition, flame propagation within a narrow range from 13.5 to 14.5% by volume has been reported. The material has no flash point. Thermal decomposition in a glass vessel begins somewhat above 400°C. 

These values expressed in percent by volume of fuel vapor in air are the ranges of concentration over which a particular vapor or gas mixture with air will burn when ignited. If a mixture within its explosive range of concentrations is ignited, flame propagation will occur. This range will be indicated by lei for lower explosive limit or uel for upper explosive limit. The values given, unless other wise indicated, are for normal conditions of temperature and pressure. 

Moreover, the phenomena of combustion themselves prove to be more complicated. For a long period the study of combustion broke away from chemical kinetics and set itself its own specific tasks. These included especially studies of the influence of instrumental parameters on ignition, flame propagation and limits, i.e., the influence of the diameter and length of tubes, the form of vessels, the direction of propagation, etc. 

Devices utilized on vents for flammable liquid or gas tanks, storage containers, cans, gas lines, or flammable liquid pipelines to prevent flash-back (movement of flame) through the line or into the container when a flammable or explosive mixture is ignited. Flame Propagation... 

Zambon, A.C., Cheiiiah, H.K. Explicit reduced reaction models for ignition, flame propagation, and extinction of C2H4/CH4/H2 and air systems. Combust. Flame 150, 71-91 (2007)... 

Some of the tests and criterion used to define fire resistance may be found in the Hterature (9). Additionally, the compression—ignition and hot manifold tests as defined in MIL-H-19457 and MIL-H-5606, respectively the Wick test as defined by Federal Standards 791, Method 352 flash point and fire point as defined in ASTM D92 autoignition temperature as defined in ASTM D2155 and linear flame propagation rate are defined in ASTM D5306 are used. 

The UL flammability ratings describe the relative ease of ignition and combustibiUty of plastics. Tests include the measurement of flame propagation, time to self-extinguish, melt and drip with and without flame, and oxygen indexes. Some engineering plastics, eg, polyetherimides, are, as ranked by this test, inherently nonflammable. Others can be made nonflammable by compounding with flame retardants (ERs) such as bromine... 

Detonation arresters are typically used in conjunction with other measures to decrease the risk of flame propagation. For example, in vapor control systems, the vapor is often enriched, diluted, or inerted, with appropriate instrumentation and control (see Effluent Disposal Systems, 1993). In cases where ignition sources are present or pre-dic table (such as most vapor destruct systems), the detonation arrester is used as a last-resort method anticipating possible failure of vapor composition control. Where vent collec tion systems have several vapor/oxidant sources, stream compositions can be highly variable and... 

Definition of Dust E losion A dust explosion is the rapid combustion of a dust cloud. In a confined or nearly confined space, the explosion is characterized by relatively rapid development of pressure with a flame propagation and the evolution of large quantities of heat and reaction products. The required oxygen for this combustion is mostly supphed oy the combustion air. The condition necessaiy for a dust explosion is a simultaneous presence of a dust cloud of proper concentration in air that will support combustion and a suitable ignition source. 

Minimum Ignition Energy (MIE) Initiation of flame propagation in a combustible mixture requires an ignition source of adequate energy and duration to overcome heat losses to the cooler surrounding material. Dust and vapor... 

A locally ignited flame must propagate into a surrounding flammable atmosphere. 

Local ignition must be followed by flame propagation into surrounding suspension above powder MEC. 

As mentioned previously, in order to initiate flame propagation, an ignition source of adequate energy and duration is required. Ignition sources can include ... 

The location and energy level of an ignition source has a profound effect on flame propagation and the ability of a DDA to quench the flame. 

Ignition occnrs at the open end of the dnct. The flame propagates into the dnct nntil it reaches the flame arrester element where it is qnenched. In this case, the amonnt of heat that mnst he dissipated hy the arrester is relatively small hecanse the hot comhnstion gases discharge throngh the open end of the dnct. 

---