Chemistry and Chemical Disasters. A liquid having a closed cup flash point below 100°F (37.8°C) and having a vapour pressure not exceeding 40 psia (2068 mm Hg) at 100°F (37.8°C). Class I liquids are subdivided as follows: Class I A: Those having flash points below 73° F (22.8°C) and having a boiling point below 100°F (37.8°C). Class I B: Those having flash points below 73°F (22.8°C) and having a boiling point at or above 100°F (37.8°C). Class I C: Those having flash points at or above 73°F (22.8°C) and below 00°F (37.8°C)