Because the low flash point means that the volatility is high, the vapor density is low, and it is easy to emit. Spontaneous combustion is generally the first fire of the material vapor, and then the liquid is ignited. Materials with high flash point have high vapor density and are not easy to dissipate. They accumulate together to a certain concentration and can spontaneously ignite at a certain temperature. So the higher the flash point, the lower the auto-ignition point.
The temperature at which the oil is heated under specified conditions to the point at which it begins to flash over by a flame. The flash point of oil is mainly related to its evaporability; the lighter the fraction, the easier it is to evaporate, and the lower the flash point. The lower the flash point of the oil, the easier it is to be ignited by flames and cause combustion, and the greater the risk of fire.
Therefore, the flash point can be regarded as a fire safety indicator. Whether various liquids are flammable or combustible is grouped according to their flash points. Measure the flash point of heavy oil such as lubricating oil, if it is found that the flash point drops sharply, it can be judged that it is mixed with light fuel oil. The bitumen is heated in a specified flash point apparatus to the lowest temperature at which a flash fire which is extinguished instantaneously occurs.
Extended information
The flash point depends on the density of the flammable liquid, the pressure of the liquid surface, or whether the flammable liquid is mixed with light components and the content of light components. If the flash point of the flammable liquid is suddenly lowered during use, light oil mixing accident or hydrolysis (for some synthetic oils) may occur, and attention must be paid.
The flash point of a flammable liquid varies with its concentration. The flash point is related to the molecular composition of the oil and the pressure on the oil surface. The higher the pressure, the higher the flash point.
Flash point is an important indicator to prevent oil fire. In an open container, the heating temperature of the oil should be 10°C lower than the flash point; there is no such limit for heating in a pressure container.
From the point of view of fire prevention, it is hoped that the flash point and ignition point of the oil are higher, and the difference between the two is larger. From the point of view of combustion, it is hoped that the flash point and ignition point should be lower, and the difference between the two should be as small as possible.