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Flammable and Combustible Liquids Overview

See storage requirements for flammable and combustible liquids in UC San Diego facilities.

Flammable and combustible liquids present a danger of personal injury and property damage, so strict storage requirements are both essential and required by law.

Facts about flammable and combustible liquids

  • Flammable and combustible liquids ignite easily and burn with extreme rapidity.
  • Flammability is determined by the flash point of a material.
  • Flash point is the minimum temperature at which a liquid forms a vapor above its surface in sufficient concentration that it can be ignited.
  • Flammable liquids have a flash point of less than 100°F. Liquids with lower flash points ignite easier.
  • Combustible liquids have a flashpoint at or above 100°F.
  • The vapor burns, not the liquid itself. The rate at which a liquid produces flammable vapors depends upon its vapor pressure.
  • The vaporization rate increases as the temperature increases. Therefore, flammable and combustible liquids are more hazardous at elevated temperatures than at room temperature.
  • Class 1 Flammable Liquids must be bonded and grounded when transferring liquids.

Restrictions and guidelines

Because their vapors ignite and burn easily, flammable and combustible liquids have strict storage requirements. The hazard classification of a liquid determines the type and size of container in which it can be stored. For more information, see:

Hazard classifications

National Fire Protection Association (NFPA) hazard classifications for flammable and combustible liquids are listed below:

Hazard classification for flammable liquids
Class Flash point Boiling point Examples
I-A below 73°F (23°C) below 100°F (38°C) diethyl ether, pentane, ligroin, petroleum ether
I-B below 73°F (23°C) at or above 100°F (38°C) acetone, benzene, cyclohexane, ethanol
I-C 73-100°F (24-38°C) ---- p-xylene
Hazard classification for combustible liquids
II 101-140°F (39-60°C) ---- diesel fuel, motor oil, kerosene, cleaning solvents
III-A 141-199°F (61-93°C) ---- paints (oil base), linseed oil, mineral oil
III-B 200°F (93°C) or above ---- paints (oil base), neatsfoot oil

Regulations and policies