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The Basics of Storing Flammable Liquids

To prevent fires, hazardous liquids, particularly those that are flammable, need special precautions taken for their storage, handling and use.

Is it a flammable liquid?

To handle flammables appropriately, you must know what a flammable is. As defined by OSHA, a flammable is:  "any liquid having a flashpoint below 100 deg. F. (37.8 deg. C.), except any mixture having components with flashpoints of 100 deg. F. (37.8 deg. C.) or higher, the total of which make up 99 percent or more of the total volume of the mixture." (Note, liquids that have a flashpoint above 100oF are combustible liquids. While still requiring caution in how they are handled and stored, combustible liquids have less-stringent storage requirements than do flammable liquids.)

Flammable liquids are also called Class I liquids and fall into three subclasses:

  • Class IA: Liquids having flashpoints below 73°F and having boiling points below 100°F. Examples of Class IA flammables include acetaldehyde, ethyl ether, and cyclohexane.
  • Class IB: Liquids having flashpoints below 73° F and having boiling points at or above 100°F. Acetone, benzene, and toluene are Class 1B.
  • Class IC: Liquids having flashpoints at or above 73° F and below 100°F. Hydrazine, styrene, and turpentine are Class 1C liquids.

As can be seen, flashpoint and boiling point are used to classify flammable materials. This is because boiling point determines at what point the material will produce vapors—vapors are what ignite when there is an ignition source. Producing vapors is not enough, though; there has to be enough vapor. The flashpoint is the point at which the liquid produces enough vapor to ignite (under given test circumstances). So, the lower the boiling point, the lower the temperature at which the material produces vapor, and the lower the flashpoint, the more easily it will catch fire.

In order to tell if you have a flammable liquid, the best thing to do is look at the material safety data sheet (MSDS). It will tell you what the flashpoint is, what the boiling point is, and generally, it will also tell you what class it is. In addition, product labels often will provide information as to whether or not the material is a flammable.

Limits on storage quantities

Regulations limit the amount of flammable liquids that can be stored in a single container:

 

 Container Type
 Class IA Class IB
 Class IC
 Glass or approved plastic
 1 pt.  1 qt.
 1 gal.
 Metal (non DOT drum)  1 gal.
 5 gal.
 5 gal.
 Safety Cans
 2 gal.
 5 gal.
 5 gal.
 Metal Drum (DOT spec.)
 60 gal.
 60 gal.
 60 gal.
 Approved Metal Tanks
 660 gal.
 660 gal.
 660 gal.

 

OSHA regulations limit the amount of flammable liquids that can be stored outside of an inside storage room or a safety cabinet in any one "fire area" of a building to 25 gallons for Class IA liquids in containers, 120 gallons for Class IB and Class IC in containers, and 660 gallons for Class IB and Class IC in a single portable tank.

OSHA also limits the amount of flammable Class I liquids in a storage cabinet to no more than 60 gallons. (While OSHA does not discuss the number of storage cabinets that may be in an area, the National Fire Protection Agency (NFPA) standard is that no more than three cabinets may be located in a single fire area or, if there is no distinct fire area, groups of cabinets (up to three) must be separated by at least 100 feet.)

What's a fire area?

While OSHA uses the term "fire area," it doesn't define it. NFPA, however, does. It is:"An area of a building separated from the remainder of the building by construction having a fire resistance of at least 1 hour and having all communicating openings properly protected by an assembly having a fire resistance rating of at least 1 hour."

Flammable storage cabinets

A flammable storage cabinet is designed and constructed specifically for the storage of flammable and combustible liquids to reduce the risk of fire and explosion as a result of storing the flammable liquids. OSHA does not require that flammable liquids be stored in a flammable storage cabinet—but local fire codes often do.

Per 29 CFR 1910.106, a flammable storage cabinet has the following construction:

  • Bottom, top, and sides of cabinet constructed of at least No. 18 gauge sheet steel
  • Doubled walled with 1½ inches airspace 
  • Joints that are riveted, welded, or made tight by some equally effective means 
  • Door that have a three point latch (and while OSHA does not require it, the NFPA requires self-closing doors)
  • The door sill is to raised at least 2 inches above the cabinet bottom to retain spilled liquid within the cabinet

OSHA regulations also allow for wood flammable storage cabinets that are constructed as follows:
  • Bottom, top, and sides of cabinet constructed of exterior grade plywood at least 1-inch thick
  • Plywood cannot break down or delaminate under fire conditions 
  • Joints that are rebated 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 equipped with latches and hinges that are mounted to not lose their holding capacity when subjected to fire 
  • Door sill or pan that is raised at least 2 inches above the cabinet bottom to retain spilled liquid within the cabinet
Whether wood or metal, the cabinet must have be labeled conspicuously with the words "Flammable—Keep Fire Away."

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