Flash point of pressure vessel media

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The flash point is the minimum temperature at which, under normal pressure, a sufficient amount of vapor is released from the liquid surface in a container to form a flammable mixture with air. Flash point is primarily applicable to liquids, but some solids, such as camphor and naphthalene, also have a certain degree of volatility at room temperature; therefore, they too have a flash point. The flash point is different from the ignition point; the flash point is slightly lower than the ignition point. The determination of flash point is divided into the closed-cup method (C.C.) and the open-cup method (O.C.), with the open-cup flash point often being higher than that of the closed-cup method. Liquids are classified according to their flash point in terms of flammability: Category 1 has a flash point of <28°C; Category 2 has a flash point of 28°C ≤ flash point ≤ 45°C; Category 3 has a flash point of 45°C < flash point ≤ 120°C; and Category 4 has a flash point >120°C. Liquids in Categories 1 and 2 are considered flammable liquids, while those in Categories 3 and 4 are considered combustible liquids.