Liquids with flashpoint below 73 °F (22.8 °C) and having a boiling point at or above 100 °F (37.8 °C) are classified as:

• A. Class IB
• B. Class IA
• C. Class IC
• D. Class II

Answer: (A)

Flammable-liquid classification hinges on how easily vapors can ignite (flash point) and how hot the liquid must get to boil (boiling point). A flash point below 73 °F means the liquid can form ignitable vapor at room temperature. A boiling point at or above 100 °F means it does not boil away at typical ambient temperatures, even though its vapors can ignite when heated.

This combination—flash point below 73 °F and boiling point at or above 100 °F—matches Class IB. If the boiling point were below 100 °F, it would be Class IA, so the boiling point threshold is what separates these two.