How do you check the flashpoint of diesel?

To check the flashpoint of diesel, you can use a closed cup flashpoint tester, such as a Pensky-Martens or a Cleveland open cup tester. The sample is heated while an ignition source is applied periodically until a flash (a momentary flame) occurs above the liquid's surface. The temperature at which this flash occurs is recorded as the flashpoint. Always follow safety protocols and manufacturer guidelines when performing this test.