Nearly every facet of industry—be it research and development, production, manufacturing, or logistics—handles, transfers, stores, or otherwise uses some amount of flammable liquids. As a result of widespread use and the materials' hazards, flammable liquids are regulated by OSHA under several standards. The OSHA Standard we will focus on in particular in this article falls under the General Industry Flammable Liquids Standard at 29 CFR 1910.106.
A popular misconception synonymous with flammable liquids is that it’s the liquid component of the material that catches fire and burns. It’s important to keep in mind that this is NOT the case. It is actually the vapors coming off the liquid that ignite. So, a liquid’s ability to give off vapor (known as “volatility”) directly correlates with the material’s hazard severity.
Flash Point and Volatility for Flammable Liquids
When addressing the inherent hazard associated with flammable liquids, we typically look to the material’s flash point temperature. Is it “really low” or on the “higher” side? The reason we refer to the flash point has to do with the characteristic of volatility that we just mentioned. The two are essentially interrelated. Perhaps it is no surprise then that one of the two parameters used to classify flammable liquids is in fact the material’s flash point. The other parameter is boiling point.
For all of these reasons and more, specific safeguards need to be taken when handling and storing flammable liquids. In this article, we’ll summarize the main points from OSHA’s General Industry Flammable Liquids Standard as it relates to the use of flammable storage cabinets. Before we get into a discussion on the cabinets themselves, let’s take a quick look at how OSHA groups flammable liquids based on the characteristics of flash point and boiling point.
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OSHA’s Classification of Flammable Liquids
You’re likely familiar with both “categories” of flammable liquids and “classes” of flammable liquids. Simply put, OSHA uses the term “category” in its definition of flammable liquids, while the NFPA uses the term “class.” OSHA has four broad categories of flammable liquids ranging from Category 1 through Category 4. Each category’s flash point and boiling point values is summarized in the table below. [29 CFR 1910.106(a)(19)]
||Flash Point (°F)
||Boiling Point (°F)
||≥ 73.4 and ≤ 140
||PG III or Combustible
||IC or II
||> 140 and ≤ 199.4
By comparison, the NFPA broadly uses the terms “Class I,” “Class II,” and “Class III,” each of which has subgroups denoted by the letters “A,” “B,” and “C.” For instance, an NFPA Class IB liquid is defined as having a flash point below 73°F and a boiling point at or above 100°F. Referencing the OSHA table above, we can see that a Class IB as defined by the NFPA would fall under Category 2 according to OSHA’s standards.
For more about classifying flammable liquids under OSHA and US DOT PHMSA requirements, check out Burning Love: How DOT and OSHA Regulate Flammable Materials.
Storing Flammable Liquids in Cabinets
Now that we have a sense of how flammable liquids are defined/categorized, let’s turn our attention to the safe storage of these materials in the workplace. If your facility makes use of flammable storage cabinets, you’ll want to make sure they meet OSHA’s specifications for design and construction. In addition, HOW
you store your flammable liquids, that is to say, where and how much, is also regulated by OSHA. Let’s start with a brief discussion of permissible quantities.
When dealing with flammable liquids falling into Categories 1, 2, or 3, no more than 60 gallons
of liquid may be stored inside a cabinet. Let’s apply this to an example scenario. Say you have numerous 2-liter bottles on hand that are full of flammable liquids. You’re looking to finally put them away in the storage cabinets in your area. How many should you put in each cabinet?
When converting from liters to gallons, we want to keep in mind that 2 L equals approximately 1/2 gallon (0.53 gal.). If we do a bit of math, we arrive at a value of 113, which means that no more than 113 bottles of the 2 L size would be allowed in a storage cabinet. Now it’s more likely that your flammable liquid bottles are of all different sizes, so you will need to take this into account when making sure you are not exceeding the maximum volume of flammable liquids allowed in each cabinet.
As for the Category 4 flammable liquids, remember, here we’re talking about liquids with higher flash points, so it should be no surprise that the maximum allowable volume is increased. OSHA allows no more than 120 gallons
of Category 4 flammable liquids to be stored in flammable storage cabinets.
Flammables Cabinets: OSHA Design and Construction Requirements
Let’s move on to the design and construction requirements for these cabinets. OSHA provides specifications for two distinct types of cabinets: metal and wood. Due to their widespread popularity, however, we’ll be focusing on cabinets constructed of metal.
The bottom, top, door, and sides of the cabinet shall be at least No. 18 gage sheet iron and double-walled with 1.5-inch air space. All joints must be riveted, welded, or made tight by some equally effective means. The cabinet door must be equipped with a three-point lock with the door sill raised at least 2 inches above the bottom of the cabinet. The design and construction of the cabinets shall effectively limit the internal temperature to not more than 325°F within the cabinet when subjected to a 10-minute fire test. In addition, all joints and seams shall remain tight and the door securely closed during the fire test. The exterior cabinet doors must be labeled "Flammable - Keep Fire Away." [29 CFR 1910.106(d)(3)(ii)]
While ensuring you have an OSHA-compliant cabinet for your flammable liquids is a good place to start, there is much more to be aware of when it comes to flammable liquid storage.
Other factors to consider include limits on how much liquid you can have stored outside of a flammable storage cabinet, the number of cabinets you can have in a single storage area, the proximity of fire extinguishers to the storage area, etc. For additional information on these topics and more, see OSHA's Standards for flammable liquids at 29 CFR 1910.106.
Hazmat Safety and OSHA HazCom Training
DOT and OSHA each maintain requirements for how to communicate flammability, combustibility, and other types of hazards. They also have rules for what to do in an emergency and for how to store, handle, transport, and use flammable and combustible materials safely.
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