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February 2002 — Flammable Liquid Hazards Flammable liquids are liquids with a flash point of less than 100°F. The flash point is the lowest temperature at which a liquid gives off enough vapor to form a flammable mixture with air. Material Safety Data Sheets (MSDS) list flash points and often specifically name materials as "flammable." Flammable liquid vapors in air have a lower and upper explosive limit, commonly called the LEL and UEL, that are also identified in the MSDS. The lower explosive limit, or LEL, is the lowest concentration of vapor in air that will ignite. The upper explosive limit, or UEL, is the highest concentration that will ignite. If the vapor concentration is between the LEL and UEL, there is serious risk of fire or explosion. Everyone knows to avoid ignition sources near flammable liquids, but one of the least understood hazards involves specific gravity. If the MSDS lists the vapor density as greater than "1," the vapor is heavier than air (Air = 1). Vapor will settle in low-lying areas and may travel considerable distance until it finds a low resting place. Therefore, plenty of ventilation to disperse vapors is essential when using flammable liquids. In addition to the flammability hazard, flammable liquids may cause or contribute to a variety of serious and immediate health problems, often involving the respiratory tract, skin, and eyes. Before working with flammable liquids, always read the material's label and MSDS thoroughly, assess contributing hazards in the vicinity, and select and use appropriate personal protective equipment
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