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(1) It is related to the type of instrument used for the measurement. Generally, the results obtained using an open-cup flash point tester are higher than those obtained using a closed-cup flash point tester, as the vapor generated by the open-cup tester can freely disperse into the air, resulting in some loss of vapor. (2) It is related to the amount of oil sample added. A larger amount of oil sample in the cup of the closed-flash detector yields lower measurement results, while a smaller amount of oil gives higher measurement results than normal. Because the amount of oil affects the volume of space above the liquid level, which in turn influences the concentration of the oil vapor and air mixture. (3) It is related to the size of the flame used for ignition, its height above the liquid surface, and the residence time. If the diameter of the spherical flame used for ignition is larger than specified, the measured results will be lower. Conversely, it is higher than normal. (4) It is related to the heating rate. When the heating rate is high, more heat is supplied to the oil per unit of time, resulting in faster evaporation; this causes the concentration of oil vapor in the air to reach the lower explosive limit sooner, leading to lower measurement results. When the heating rate is too slow, the measurement time is prolonged, and more ignition attempts are required, resulting in some loss of oil vapor. This delays the time it takes for the mixture of oil vapor and air to reach its flash point, leading to higher results. (5) Related to atmospheric pressure: The flash point of oils is related to the external pressure. With low air pressure, oils are more volatile; therefore, the measured flash point is lower. Conversely, when air pressure is high, the measured flash point is higher. The standard specifies that the flash point measured at an atmospheric pressure of 101.3 kPa is the flash point under standard pressure. If there is a deviation in atmospheric pressure, the measured flash point must be corrected for atmospheric pressure. For every 0.133 kPa change in pressure, the flash point changes by an average of 0.033–0.036°C. (6) It is related to the moisture content of the sample; the sample must be dehydrated before its flash point can be determined. The closed-cup flash point method requires dehydration when the moisture content is greater than 0.05%, while the open-cup flash point method requires it when the moisture content is greater than 0.1%. This is because when the oil is heated for testing, the water dispersed in the oil vaporizes to form water vapor; sometimes bubbles are formed on the surface of the liquid, which hinders the normal vaporization of the oil, delays the flash point, and results in higher measurement values. For heavy oils with a high water content, when determining the flash point using an open-flame flash point tester, heating to a certain temperature causes the oil sample to easily overflow out of the cup, rendering the test impossible to conduct.