Flammable liquids are present in nearly every workplace. Gasoline, diesel fuel, and many common products like solvents, thinners, cleaners, adhesives, paints, and polishes can be flammable—they are part of our everyday life. However, if these liquids are used or stored improperly, it could present serious hazards that could result in injuries and even death.

The purpose of this article is to discuss the requirements of the flammable liquids standard in general industry and to better understand how to avoid serious hazards.

The flammable liquids standard (29 CFR 1910.106) was revised in 2012, in response to U.S. OSHA’s revising the Hazard Communication standard to incorporate the Globally Harmonized System (GHS).

The standard’s title was changed from “Flammable and Combustible Liquids” to “Flammable Liquids.” One significant change is that the revised regulation lists liquids as “categories” rather than “classes.”

Defining flammables

To understand OSHA requirements for the safe storage of flammables, we must define flammable liquid. The flashpoint and boiling point determine the category of a liquid.

OSHA defines a flammable liquid as any liquid having a flashpoint at or below 199.4°F (93°C). Flammable liquids are divided into four categories:

• Category 1: Liquids with flashpoints below 73.4°F (23°C) and boiling point at or below 95°F (35°C) (1910.106(a)(19)(i)). Examples: acetaldehyde and ethyl ether.
• Category 2: Liquids with flashpoints below 73.4°F (23°C) and boiling points at or above 95°F (35°C) (1910.106(a)(19)(ii)). Examples: acetone, benzene, and toluene.
• Category 3: Liquids with flashpoints at or above 73.4°F (23°C) and at or below 140°F (60°C). When a Category 3 liquid with a flashpoint at or above 100°F (37.8°C) is heated for use to within 30°F (16.7°C) of its flashpoint, it must be handled as a Category 3 liquid with a flashpoint below 100°F (37.8 °C) (1910.106(a)(19)(iii)).
• Category 4: Includes liquids having flashpoints above 140°F (60°C) and at or below 199.4°F (93°C). When a Category 4 flammable liquid is heated for use to within 30°F (16.7°C) of its flashpoint, it must be handled as a Category 3 liquid with a flashpoint at or above 100°F (37.8°C) (1910.106(a)(19)(iv)).

Note: The term combustible liquid is no longer considered a class or category in the revised standard.

Whether liquids are Category 1 or 4 is not the only factor you should consider when determining your safe storage needs. You also need to consider ignition temperature, explosive limits (LEL or UEL), vapor pressure, specific gravity, and vapor density if you want to design a truly safe storage system.

Safety cans

One technique to reduce the hazards associated with flammables is the use of safety cans. OSHA defines a safety can as “an approved container, of not more than 5 gallons capacity, having a spring-closing lid and spout cover and so designed that it will safely relieve internal pressure when subjected to fire exposure” (29 CFR 1910.106(a)(29)).

The standard limits the amount of liquid in a single safety can and other portable containers.

Maximum allowable size of containers and portable tanks for flammable liquids

Storage cabinets

Another fundamental means of fire protection is the use of flammable storage cabinets. OSHA requires flammable cabinets to be designed and constructed to specific requirements. Metal cabinets must be constructed in the following manner (29 CFR 1910.106(d)(3)(ii)(a)):

• Bottom, top, and sides of cabinet must be at least No. 18 gage sheet steel.
• Cabinet must be double-walled with 1½-inch airspace.
• Joints must be riveted, welded, or made tight by some equally effective means.
• Door must have a three-point latch.
• Door sill must be raised at least 2 inches above the cabinet bottom to retain spilled liquid within the cabinet.
• Cabinet must be labeled in conspicuous lettering “Flammable—Keep Fire Away.”

These regulations also provide an option for wood cabinets at 29 CFR 1910.106(d)(3)(ii)(b). Wood cabinets must be constructed in the following manner:

• Bottom, top, and sides of cabinet must be constructed of exterior grade plywood at least 1 inch thick.
• Plywood must not break down or delaminate under fire conditions.
• Joints must be rabbeted and fastened in two directions with flathead wood screws.
• When more than one door is used, they should have a rabbeted overlap of not less than 1 inch.
• Doors must be equipped with latches and hinges that are mounted to not lose their holding capacity when subjected to the fire test.
• Cabinet must be labeled in conspicuous lettering “Flammable—Keep Fire Away.”

The total amount of liquids that may be kept outside a storage cabinet or storage room are listed at 29 CFR 1910.106(e)(2)(ii)[b]. These limits are only applicable to those portions of an industrial plant where the use and handling of flammables is only incidental to the principal business. The quantity of liquid that may be stored outside of an inside storage room or flammables storage cabinets in any one fire area of a building cannot exceed:

• 25 gallons of Category 1 liquids in containers
• 120 gallons of Category 2, 3, or 4 liquids in containers
• 660 gallons of Category 2, 3, or 4 liquids in a single portable tank

The maximum capacity of liquid that may be stored in storage cabinets is stated in 29 CFR 1910.106 (d)(3)(i): “Not more than 60 gallons of Category 1, 2, or 3 liquids, nor more than 120 gallons of Category 4 liquids may be stored in a storage cabinet.”

Containers and storage cabinets FAQs

Q: Are 5-gallon plastic gas cans OSHA-approved for storage and/or transportation of unleaded fuel?

A: OSHA’s regulations state the following:

“29 CFR 1910.106(a)(29). Safety can shall mean an approved container, of not more than 5 gallons capacity, having a spring-closing lid and spout cover and so designed that it will safely relieve internal pressure when subjected to fire exposure.”

“29 CFR 1910.106(a)(35). Approved unless otherwise indicated, approved, or listed by a nationally recognized testing laboratory. Refer to 1910.7 for definition of nationally recognized testing laboratory.”

Q: Does an aerosol can of flammable brake cleaner need to be stored in a flammable cabinet at the end of the shift instead of leaving it out on the work table?

A: Check the safety data sheet for the brake cleaner for any special storage requirements and for the flammability category. Then, apply the OSHA requirement for the category and quantity. The OSHA rule at 29 CFR 1910.106(e)(2)(ii)(b) allows the following:

“25 gallons of Category 1 liquids in containers or 120 gallons of Category 2, 3, or 4 liquids in containers may be stored outside of an inside storage room or storage cabinet in a building or in any one fire area of a building.”