(1) "Extremely flammable" applies to a substance which has a flash point at or below 20 degrees F, as determined by the Tagliabue open cup tester.
(2) "Flammable" applies to a substance which has a flash point above 20 degrees to and including 80 degrees F, as determined by the Tagliabue open cup tester.
(3) "Combustible" applies to a substance which has a flash point above 80 degrees to and including 150 degrees F, as determined by the Tagliabue open cup tester.
(4) The flammability or combustibility of solids and the contents of self-pressurized containers shall be determined by methods found by the department to be generally applicable to the materials or containers, respectively, and established by rules issued by the department, which rules shall also define the terms "flammable", "combustible", and "extremely flammable" in accord with the methods used.