How is the flash point measured?

You mean specific methods, right? There should be some on this forum; you can look for them. I don’t have any information available at the moment; generally, the open flash point is used for heavy oils, while the closed flash point is used for light oils

Flash points are divided into open flash point and closed flash point, and there are standard methods for determining them, in accordance with the ASTM standards. If measuring the flash point of petroleum products, the brands of such instruments can be inquired about at the analysis center of the Petroleum and Chemical Science Research Institute.

This post was last edited by zbx on 2010-6-13 at 11:18. Analysis method: The closed-cup method involves heating the sample at a slow, constant rate while stirring continuously; at a specified temperature, stirring is stopped temporarily, and the lowest temperature at which a small flame causes the vapor on the sample to ignite is taken as the flash point. Open cup method: The sample is placed in the inner crucible up to the specified mark. First, the temperature of the sample is raised rapidly, after which it is increased slowly. As the temperature approaches the flash point, the heating continues at a constant rate. At specified temperature intervals, the flame is passed over the surface of the sample; the lowest temperature at which vapor from the sample surface ignites defines the flash point according to this method. The test is continued until the lowest temperature at which the flame causes the sample to ignite and burn for at least 5 seconds is determined, and this value serves as the ignition point according to the open cup method

Here are some standard numbers; the original poster can look them up on their own: SH/T 0768-2005 Method for determining flash point (closed cup, constant pressure method); GB/T 3536-1983 Method for determining flash point and ignition point of petroleum products (Cleveland open cup method); GB/T 6489.4-1986 Determination of flash point of industrial phthalates (Cleveland open cup method); SY/T 5645-1993 Apparatus for testing flash point and ignition point of petroleum products (Cleveland open cup method); YB/T 5172-1993 Test methods for wood preservatives – Method for determining flash point; GB/T 21615-2008 Dangerous goods – Method for testing closed cup flash point of flammable liquids; GB/T 5208-2008 Determination of flash point – Rapid equilibrium closed cup method; GB/T 21775-2008 Determination of flash point – Closed cup equilibrium method; GB/T 261-2008 Determination of flash point – Benky-Martin closed cup method; GB/T 3536-2008 Determination of flash point and ignition point of petroleum products (Cleveland open cup method); SN/T 2174-2008 Dangerous goods – Method for testing closed cup flash point of flammable liquids; GB/T 1671-2008 Determination of flash point of plasticizers (Cleveland open cup method); GB/T 6489.4-2001 Determination of flash point of industrial phthalates (Cleveland open cup method); GB/T 14454.10-1993 Flavors – Determination of flash point (closed cup method); SN/T 0735.15-1999 Exported aromatic oils, isolated and synthetic flavors – Method for determining flash point (closed cup method); SN/T 0801.12-1999 Import and export of animal and vegetable fats and oils – Method for testing flash point (closed cup method); SH/T 0733-2004 Method for determining flash point (Teck closed cup method); GB/T 267-1988 Method for determining flash point and ignition point of petroleum products (open cup method)

The standards for determining the flash point of flammable liquids can refer to GB261-77.

Literally, it is the temperature at which the sample flashes. It’s also okay to call the time when lightning appears in the sky the flash point.

Determination of flash point and ignition point of petroleum products – Open cup method 1. Scope of application This method is applicable to the determination of the flash point and ignition point of lubricants and dark-colored petroleum products. 2. Principle of the method The sample is placed at the marked line in the crucible. First, the temperature of the sample is raised rapidly, after which it is increased slowly. When approaching the flash point, a small igniter flame is passed over the surface of the sample at specified temperature intervals; the lowest temperature at which the vapor on the surface of the sample ignites due to this flame is considered the flash point using the open cup method. Continue the tests until the lowest temperature at which the igniter flame causes the sample to ignite and burn for at least 5 seconds is determined, which serves as the flash point by the open cup method. 3. Reagents: Lead-free gasoline 4. Instruments and materials 4.1 Open flash point and ignition point tester 4.2 Thermometer: 0–400°C, minimum resolution: 1°C Note 9.1 4.3 Alcohol lamp or electric furnace (an electric furnace must be used when testing samples with a flash point higher than 200°C). 5. Preparation 5.1 When the moisture content of the sample is greater than 0.1%, dehydration is necessary. Dehydration treatment involves adding newly calcined and cooled table salt, sodium sulfate, or anhydrous calcium chloride to the sample. Samples with a flash point below 100°C do not require heating during dehydration, while other samples may be heated to 50–80°C before using a dehydrating agent for dehydration. 5.2 After washing the inner crucible with solvent oil, it is heated in an electric furnace or over a lit alcohol flame to remove any remaining solvent oil. Once the inner crucible has cooled to room temperature, it is placed inside an outer crucible filled with fine sand (calcined), such that the surface of the sand is about 12 mm away from the edge of the opening in the inner crucible; meanwhile, a layer of sand with a thickness of 5–8 mm remains between the bottom of the inner crucible and the bottom of the outer crucible. When testing specimens with a flash point above 300°C, the thickness of the sand layer between the bottoms of the two crucibles may be reduced as appropriate, but the heating rate specified in 6.1.1 must be maintained during the test. 5.3 When injecting the sample into the inner crucible, for samples with a flash point of 210°C or below, the liquid level should be 12 mm away from the edge of the crucible opening (i.e., at the lower mark on the inner crucible). ) Note: 9.1, 9.2, 9.3 5.4 Place the crucible containing the sample steadily in the electric furnace located on the stand of the open-flame flash point apparatus. Then fix the thermometer vertically in the thermometer holder, ensuring that the mercury bulb of the thermometer is positioned at the center of the inner crucible, at roughly equal distances from the bottom of the crucible and the surface of the sample. 5.5 The testing apparatus should be placed in a wind-protected or darker area and surrounded by a shielding screen to allow for clearer observation in the event of a flash fire. 6. Test procedures 6.1 Flash point 6.1.1 Heat the crucible to gradually raise the temperature of the sample; when the sample temperature reaches 60°C below the expected flash point, adjust the heating rate so that when the temperature is 40°C below the flash point, the heating rate can be controlled at 4±1°C per minute. 6.1.2 When the sample temperature reaches 10°C below the expected flash point, place the flame of the igniter at a distance of 10–14 mm from the surface of the sample liquid, and move it in a straight line along the inner diameter of the crucible at that horizontal level. The time taken to move from one side of the crucible to the other is 2–3 seconds. The ignition test should be repeated once for every 2°C increase in the sample temperature. The flame length of the igniter should be pre-adjusted to 3–4 mm. 6.1.3 As soon as a blue flame first appears above the surface of the sample solution, the temperature is immediately read from the thermometer to determine the flash point, while the atmospheric pressure is also recorded. 6.2 Ignition Point 6.2.1 Continue with the previous steps to heat the outer crucible, such that the temperature of the sample rises at a rate of 4±1°C per minute. Then, conduct the ignition test using the flame of the igniter as described in 6.1.2. 6.2.2 The sample should catch fire immediately upon contact with the flame and continue to burn for at least 5 seconds; at this point, the temperature is read from the thermometer immediately, and this value is taken as the ignition point of the sample. 7. Correction for the effect of atmospheric pressure on flash point and ignition point 7.1 When the atmospheric pressure is below 99.3 KPa (745 mmHg), the flash point and ignition point to (°C) obtained from the tests are corrected using the following formula (to 1°C accuracy). To = t + △t. Here, to represents the flash point or ignition point in °C under an atmospheric pressure of 101.3 KPa (760 mmHg). t—Flash point or ignition point measured under test conditions, in °C. △t—Correction value in °C: For an atmospheric pressure of 7.2, within the range of 72.0–101.33 KPa (540–760 mmHg), the correction value △t (°C) can be calculated using equations ① or ②. △t=（0.00015＋0.028） （101.3—P）7.5……………………① △t=（0.00015＋0.028） （760—P1）………………………… ○2 Where ； P – Atmospheric pressure under test conditions, in kPa; t – Flash point or ignition point measured under test conditions (still considered to be 300°C if it is above 300°C), in °C. 0.00015, 0.028 – Test constants; 7.5 – Conversion factor for atmospheric pressure; P1 – Atmospheric pressure under test conditions, in mmHg. In addition, the correction values can also be found in the table below: Flash point or ignition point in °C: 100, 125, 150, 175, 200, 225, 250, 275, 300. The correction value △t in °C at that atmospheric pressure [kPa (mmHg)] is as follows: 93.3 (700): 2, 3, 3, 3, 4, 4, 4, 4, 4; 96.0 (720): 2, 2, 2, 2, 2, 2, 3, 3, 3; 98.6 (740): 1, 1, 1, 1, 1, 1, 1, 1, 1. Allowable deviation: 8.1. The flash point of the sample is taken as the arithmetic mean of the two flash points obtained from repeated measurements and adjusted for atmospheric pressure; the difference between the two flash points measured by the same operator should not exceed the values specified below ； Flash point, °C; Repeatability, °C: ≤150 for 4 values, ≥150 for 6 values. 8.2 The arithmetic average of the two flash points obtained from repeated measurements and corrected for atmospheric pressure is taken as the flash point of the sample; the difference between the two flash points measured by the same operator should not exceed 6°C. 9 Notes: 9.1 Thermometers must be calibrated regularly. 9.2 If the sample remains inside the crucible (on its inner and outer surfaces), the sample should be poured out, the crucible cleaned, and then reinserted. 9.3 Air bubbles on the surface of the sample must be removed. 9.4 The flash ignition of the sample vapor should not be confused with that of the igniter. If the flash phenomenon is not obvious enough, ignition must be repeated by raising the sample by 2°C to confirm it.