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It is the temperature of the fuel at which, when heated in a container with a specified structure, it emits flammable gases that mix with the air near the liquid surface; these gases can then be ignited by a spark once they reach a certain concentration. When the vapor emitted by flammable liquids mixes with air to reach a certain concentration, it can ignite in a brief flash when exposed to an open flame. Similarly, when flammable solids are heated to a certain temperature, they can also ignite instantly in a flash when exposed to an open flame; this phenomenon is known as flash ignition. The lowest temperature at which a solid undergoes flash ignition is called the flash point. The flash point is the lowest temperature at which a flammable liquid or solid can release enough vapor to form a flammable mixture with air at the surface of the liquid or solid within its container. The flash point of flammable liquids changes with their concentration. As the temperature rises, more vaporized oil and gas form on the surface of the fuel. When the mixture of these gases with air reaches a certain concentration, it will produce a brief flash of light when exposed to an open flame; this temperature is known as the flash point. There are two methods for determining flash point: the open cup method and the closed cup method. The flash point determined by the open cup method is 15–25°C higher than that obtained using the closed cup method. The level of flash point is related to the molecular composition of the oil as well as the pressure above its surface; higher pressure results in a higher flash point. The flash point is an important indicator for preventing fires involving oil. In an open container, the heating temperature of the oil should be 10 degrees below its flash point℃ ； There is no such limitation when heating in a pressure vessel. The lowest temperature at which a mixture of vapor and air above the oil surface can sustain continuous combustion (for a duration of no less than 5 seconds) when exposed to an open flame is called the ignition point. The ignition point is higher than the flash point. From a fire prevention perspective, it is desirable for the oil to have a high flash point and ignition point, with a large difference between the two. From a combustion perspective, it is desirable to have a low flash point and ignition point, with the difference between the two also being as small as possible.