Chemical Burning - Paper Example

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Harvey Mudd College
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The ability of a chemical to either burn or support burning is a potentially disastrous physical hazard. The flashpoint and the autoignition temperature are the two main measures that determine if a chemical will burn. The flashpoint is the lowest temperature at which a liquid will release vapors that form combustible mixtures with air. On the other hand, autoignition is the ability of a material to spontaneously burn with the absence of an ignition source, such as a flame or spark. Combustible chemicals and Flammable chemicals are explained together since the flashpoint is the condition used to classify both materials. The only disparity between a "combustible" and "flammable" liquid is the relative temperature with which the chemical burns or supports burning.

The Hazard Communication Standard (HCS) explanation of a combustible liquid is "any liquid with a flashpoint of 100oF (37.8oC) or beyond, but less than 200oF (93.3oC). Combustible liquids exclude mixtures having flashpoints of 200oF (93.3oC) and above, the total volume of which makes up 99 percent or more of the total volume of the mixture." The HCS also defines flammable liquids as "any liquid having a flashpoint below 100oF (37.8oC), except any mixture having components with flashpoints of 100oF (37.8oC) or higher, the total of which make up 99 percent or more of the total volume of the mixture."

A mixture is not combustible if less than 1% of the total amount of constituents have flashpoints ranging between 100o and 200oF. For instance, if Chemical X has a flashpoint of 170oF and represents 0.6% of the mix and all other components have flashpoints exceeding 200oF, then the mixture is not a combustible chemical. Likewise, a mixture of chemicals will not be classified as flammable if it is made up of at least 99% of constituents with flashpoints beyond 100oF or 38oC. Several mixtures will comprise of more than 1% of a flammable substance, and the mixture will assume a flashpoint of above 100oF.

In instances where information regarding the flashpoint of a chemical is unavailable, an individual can decide to perform tests that determine the chemicals flashpoint. The HCS recommends the following three methods of determining flashpoint. Tagliabue Closed Tester, Pensky-Martens Closed Tester, and the Setaflash Closed Tester methods. If information derived from another testing method is available, then a thorough account of the process should be produced along with the outcome of the test.

When a chemical sparks, the flame produced will move from the ignition source to the nearby surface of the liquid. From a practical perspective, a flammable chemical is probably more dangerous than a combustible chemical. A flammable liquid becomes a potential fire hazard if stored in an open container close to an ignition source in a setting where the temperature is close to or below room temperature. Flammable chemicals having flashpoint temperatures include ethyl ether (-49oF), gasoline (-45oF), acetone (0oF), and ethyl alcohol (55oF). For a chemical to present a fire hazard, the temperature of the substance must lie above normal room temperature. Examples of such chemicals are Stoddard solvent (102o-110oF) and kerosene (100o-162oF).

The lower flammability limit (LFL) and the upper flammability limit (UFL) are the least and maximum vapor concentration that supports combustion in the presence of an external ignition source respectively. To fully comprehend the LFL and the UFL, consider the automobile carburetor. The auto part must be adequately attuned so that the air and gasoline mixture is not too little or too much since the gasoline-air vapor mixture will not ignite in the vehicle engine. The LFL and UFL of gasoline are 1.4% and 7.6% respectively.

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