Flammable Explosive Limits

The term lower flammable limit (LFL) describes the minimum concentration of vapor to air below which propagation of a flame will not occur in the presence of an ignition source. The term upper flammable limit (UFL) is the maximum vapor-to-air concentration above which propagation of flame will not occur. If a vapor-to-air mixture is below the lower flammable limit, it is described as being too lean to burn, and if it is above the upper flammable limit, it is too rich to burn. 

When the vapor-to-air ratio is somewhere between the lower flammable limit and the upper flammable limit, fires and explosions can occur. The mixture is then said to be within its explosive or flammable range. When the mixture happens to be in the intermediate range between the LFL and the UFL, the ignition is more intense and violent than if the mixture were closer to either the upper or lower limits. 

Workers exposed to certain chemicals may suffer immediate (acute) or long-term (chronic) harm. Injury may result from chemicals that are corrosive, reactive, and/or toxic. 

Corrosives are either acids or bases. These are materials that can cause burns and destruction of skin or fatty tissue under the skin. Bases are also referred to as alkaline materials and sometimes as caustic materials. The relevant piece of information needed for evaluation is the pH level. The pH indicates how acidic or basic a material is. A 7.0 pH is neutral, neither an acid nor a base. Zero to 7.0 is the acid range. It is physically possible, but rare, to have an acid with a pH less than 0 or a base with a pH greater than 14. When selecting a chemical, choose one that is closes to a pH of 7.0 for safety reasons. 

Reactive chemicals should be avoided, if possible. Included in this class of reactive chemical hazards are cyanide compounds that can release deadly hydrogen cyanide gas. Carefully read the reactivity section and the fire and explosion section of the MSDS for each product being compared. 

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The autoignition temperature is the minimum temperature required for self-sustained combustion in the absence of an external ignition source. The value depends on specified test conditions. Tht flammable (explosive) limits specify the range of concentration of the vapor in air (in percent by volume) for which a flame can propagate. Below the lower flammable limit, the gas mixture is too lean to burn above the flammable limit, the mixture is too rich. Additional compounds can be found in National Fire Protection Association, National Fire Protection Handbook, 14th ed., 1991. 

Substance Autoignition temperature, °C Flammable (explosive) limits, percent by volume of fuel (25°C, 760 mm) ... 

Lower Flammability (Explosive) Limits (LF.J, trr I FT.) The lowest percentage concentration at which a flash or flame can develop and propagate from the source of ignition when in contact with a source of ignition in a combustible material. 

Le Chatelier s Rule allows the calculation of the lower flammability (explosibility) limits for flammable mixtures ... 

Hazard, i.e. the potential of the material to cause injury under certain conditions (flammability, explosion limits in air, ignition and autoignition temperatures, static electricity (explosions have occurred during drying due to static electricity), dust explosion, boiling point, fire protection (specification of extinguishers, compounds formed when firing), R S (nature of special risk and safety precautions). Table 5.2-5 lists hazards associated with typical chemical reactions. 

Extremely flammable. Explosive limits, 6-32%. Because the gas is supplied in a cylinder, turning off the valve will reduce any fire involving it if possible, cylinders should be removed quickly from an area in which a fire has developed. Fight fire with water spray.2... 

Lower flammable (explosive) limit in air 2.5% v/v upper flammable limit 13% v/v... 

Hazard Narcotic in high concentrations. Flammable, explosive limits in air 12-28.5%. 

These tests cover the methods of determination of the minimum temperature at which vapors in equilibrium with liquid solvent are sufficiently concentrated to form flammable mixtures with air at atmospheric pressure and concentration limits of chemicals. Flammable (explosive) limits are the percent levels, volume by volume, of a flammable vapor or gas mixed in air between which the propagation of a flame or an explosion will occur upon the... 

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). 

The fuel/oxygen criteria are known as the lower and upper flammable (explosive) limits. 

The lower flammable (explosive) limit is the smallest concentration of flammable gas or vapour in air which is capable of ignition and subsequent flame propagation under prescribed test conditions. 

Dichlorobenzene (DCB, o-Dichlorobenzene, ODB, Orthodichlorobenzene), C(,H4Cl2, is a colorless to pale yellow liquid with a pleasant aromatic odor. It is a combustible liquid and can form explosive mixtures with air at or above 151"F. Combustion and thermal decomposition products include hydrogen chloride gas, phosgene and chloro-carbons. Its flammable (explosive) limits are as follows Lower 2.2%, Upper 9.2%. 

Fl.Lim Flammable (explosive) limit in air in percent by volume IT Autoignition temperature in "C... 

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