“Flammable” means any substance which has a flashpoint of above 20 degrees to and including 80 degrees Fahrenheit as determined by the Tagliabue Open Cup Tester, and “extremely flammable” means any substance which has a flashpoint at or below 20 degrees Fahrenheit as determined by the Tagliabue Open Cup Tester, and “combustible” means any substance which has a flashpoint above 80 degrees Fahrenheit to and including 150 degrees, as determined by the Tagliabue Open Cup Tester; except that the flammability or combustibility of solids and of the contents of self-pressurized containers shall be determined by methods found by the Director to be generally applicable to such materials or containers, respectively, and established by regulations issued by him, which regulations shall also define the terms “flammable”, “combustible”, and “extremely flammable” in accord with such methods.