extremely flammable
(i) The term extremely flammable shall apply to any substance which has a flashpoint at or below 20 F (6.7 C) as determined by the test method described at 1500.43a, except that, any mixture having one component or more with a flashpoint higher than 20 F (6.7 C) which comprises at least 99 percent of the total volume of the mixture is not considered to be an extremely flammable substance.