Flammability ranges upper explosive limit

Flammable or Explosive Limits — the upper and lower vapor eoneentrations at whieh a mixture will bum or explode. The lower explosive limit of p-xylene is 1.1 pereent by volume in air, whereas the upper explosive limit is 7.0 percent in air. A mixture of p-xylene vapor and air having a coneentration of <1.1 pereent in air is too lean in p-xylene vapor to bum. Conversely, a mixture containing more than 7.0 percent is too rieh in p-xylene to bum. By subtraetion (7.0 - 1.1), p-.xylene is said to have a flammable range of 5.9. Materials having low explosive limits and wide flammable ranges are extremely dangerous. 

Flanumbility limits (or explosion limits) for a flammable gas define tlie concentration range of a gas-air ini. ture witliin wliich an ignition source can start a self-propagating reaction. Tlie minimmn and maximmn fuel concentrations in air tliat will produce a self-sustaining reaction mider given conditions are called tlie lower Jlammability limit (LFL) and tlie upper Jlammability limit (UFL). (The abbreviations LEL and UEL, for lower and upper explosivity limits, are sometimes used.) The flanunability limits are functions of... 

The lower and upper explosive limits (LEL and UEL) of gases (really gas-air mixtures) are determined in small-scale equipment by spark ignition at ambient temperature and pressure. The flammability range established by this method may deviate from the actual range at the commercial scale. At elevated temperatures, the flammability range is expected to increase. A similar phenomenon occurs at higher pressures, while at lower pressures, ignition may become impossible. 

Explosive nature of chemical substances is described with upper and lower explosion limits. The explosiveness of vapour cloud depends especially on the lower explosion limit (LEL). The LEL is the concentration of vapour, at which the vapour cloud is possible to ignite. The wider range between explosion limits means, that it is more probable that the formed vapour cloud is in the flammable region, i.e. the higher tendency for explosion. Edwards and Lawrence (1993) have used explosive limits to determine the explosiveness of chemical substances. 

Flammable (explosive) Range The range of gas or vapor concentration (percentage by volume in air) that will burn or explode if an ignition source is present. Limiting concentrations are commonly called the lower explosive limit and the upper explosive limit. Below the lower explosive limit, the mixture is too lean to burn above the upper explosive limit, the mixture is to rich to burn. 

Upper Explosive Limit Also known as Upper Flammable Limit. Is the highest concentration (expressed in percent of vapor or gas in the air by volume) of a substance that will burn or explode when an ignition source is present. Theoretically above this limit the mixture is said to be too rich to support combustion. The difference between the LEL and the UEL constitutes the flammable range or explosive range of a substance. That is, if the LEL is one ppm and the UEL is five ppm, then the explosive range of the chemical is one ppm to Five ppm. (See also LEL)... 

Flammable vapor burns in air only over a limited range of fuel-to-air concentrations. The flammable range is defined by two parameters the Lower flammable limit (LFL) and the upper flammable limit (UFL). These two terms are also called the lower explosive limit (LEL) and the upper explosive limit (UEL). 

When a combustible substance is mixed with air, the mixture will explode only when it is neither too rich nor too lean. The lower explosion limit (LEL) is the minimum volume percent of the substance in air with flammability, which is separated from the upper explosion limit (UEL) by the explosive concentration range. The tabulations in handbooks are based on experimental data, and sometimes derived from estimation methods based on the elemental composition of the fuel as CmEtxOy. Figure 6.11 shows the LEL for the series of normal paraffins and of 1-alcohols versus the number of carbon atoms. There are two ways to plot the results, which show that, for paraffins, the volume percent shows a steeply declining trend, but the weight percent shows a mildly increasing trend. One may conclude that a smaller volume percent of higher paraffin... 

For a large number of flammable dusts, the lower explosion limit lies between 0.02 and 0.06 kg/m3. The upper explosion limit is in the range of 2-6 kg/m3, but this number is of limited importance. 

The flammable properties of substances in air include their flash point, vapor pressure, autoignition temperatures, and flammability range (i.e., their lower and upper explosive limits). Liquids that have a flash point of <100°F (37.8°C) are termed flammable, whereas liquids that have a flash point of 100-200°F (37.8-93.3°C) are termed combustible. These terms are explained in detail... 

The third component of a fire is the vapour, which can mix with air, over the surface of a flammable liquid. Solvent vapours will only burn in air over a restricted concentration range bounded by the UEL (upper explosive limit) and LEL (lower explosive limit). Table 9.2 sets out for a typical range of flammable solvents their UEL and LEL values and their flash points, which are effectively the temperatures at which the solvent-saturated air attains the LEL. 

Combustion can occur only if the mixture of fuel and oxygen lies within a certain range. This is described by the lower and upper explosion limits (LEL and UEL). In older references theses Umits are referred to as the lower and upper limits of flammability (LFL and UFL) (vid. [4]). They represent the volume ratio of fuel vapour in air. Below the lower explosion limit the mixture is too lean, above the upper limit it is too rich for combustion to occur. The explosion Umits are not fixed values. They depend on whether we deal with a mixture with air or with oxygen. Furthermore they are influenced by (vid. [4, 5]) ... 

With an increase in temperature the range between the lower and upper explosion limits widens for all flammable gases. The relative change of the lower and upper limits is similar for many flammable gases. Hence, it may well be approximated by the following linear relationship... 

Dust-air mixtures are flammable only within a certain range of concentrations just like gas-air mixtures. This range is marked by the lower explosion limit (LEL) and the upper explosion limit (UEL). 

Flammable Several data are used to evaluate the dangers of solvent explosion and flammability. Flash point and autoignition temperature are used to determine a solvent s flammability and its potential for ignition. The flash points for hydrocarbons correlate with their initial boiling points. Lower and upper explosive limits determine the safe ranges of solvent concentration. 

The minimum (lower) and maximum (upper) concentration of vapor or gas in air or oxygen below or above which explosion or propagation of flame does not occur in the presence of a source of ignition. The explosive or flammable limits are usually expressed in terms of percentage by volume of vapor or gas in air. In reality, explosive limits for a material vary since they depend on many factors such as air temperature. Therefore, the values given on a Material Safety Data Sheet (MSDS) are approximate. The difference between the lower and upper flammable (explosive) limits is the range, expressed in terms of percentage by volume of vapor or gas in air. See also Lower Explosive Limit (LEL) Upper Explosive Limit (UEL). 

Explosive limits n. When combustible vapor is mixed with air in the proper proportions, ignition will produce an explosion. This proper proportion is called the explosive range. The explosive range includes all concentrations of a mixture of flammable vapor or gas in air, in which a flash will occur or a flame will travel if the mixture is ignited. The lowest percentage at which this occurs is the lower explosive limit and the highest percentage, the upper explosive limit. Explosive limits are express in percent by volume of vapor in air and, unless otherwise specified, under normal conditions of temperature and pressure. 

Flammable Limits The mixture of fuel and standard air necessary for combustion of fuel vapors must be within certain limits. The lower flammable limit (LFL) is the minimum concentration of vapor-to-air, below which propagation of a flame will not occur in the presence of an ignition source. The upper flammable limit (UFL) is the maximum vapor-to-air mixture above which propagation will not occur. Mixtures below the lower flammable limit are too lean, with too little fuel. Those above the upper flammable limit are too rich, with too much fuel. The term lower explosive limit is equivalent to LFL. The upper explosive limit is equivalent to UFL. Flammable limits vary somewhat with temperature and pressure. The flammable range is the mixture of fuel and air between LFL and UFL. Table 16-4 includes LFL and UFL values. 

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