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Safe Storage of Combustibles to Avoid Lab Fires

Laboratory fires are all too common and can be devastating, not only for the source lab, but surrounding labs as well.

Vince McLeod, CIH

Vince McLeod is an American Board of Industrial Hygiene-certified industrial hygienist and the senior industrial hygienist with Ascend Environmental + Health Hygiene LLC in Winter Garden, Florida. He has more...

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Safe Use of Flammable Solvents in the Lab

One event we constantly try to prevent is a laboratory fire. Unfortunately, they are all too common and even “small” ones can cause tremendous damage and adversely impact not only the immediate lab where the fire occurred but also most adjoining labs. And large fires can be devastating, destroying the source lab and sometimes the whole building. So, whenever we encounter the use of flammable solvents, our antennae go up and we take extra notice.

Flammable solvents are those that can easily catch fire and burn. This article will focus on liquids because, according to Prudent Practices, the most common fire hazard in the typical research lab is a flammable liquid or the vapor produced by one.1 And the laboratory violation we hand out most often deals with use and storage of flammable liquids.

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If we recall our safety training regarding flammable solvent use and the basic “fire triangle,” three conditions must exist simultaneously for a fire to occur: an oxidizing atmosphere (usually air), a source of ignition, and a concentration of flammable gas or vapor within its flammability limits. If any one of these is absent, a fire will not occur. Controlling flammable vapors and gases and eliminating potential ignition sources are the best ways to reduce the fire hazard, since air is nearly always present.

Flammable and combustible substances—different physical properties

There are a few important concepts to understand at the outset. The first is the difference between flammable and combustible materials. The differentiation is based on flash point—the lowest temperature at which there will be enough flammable vapor to ignite when an ignition source is applied. Flammable liquids are more dangerous, because they have a flash point below 100°F (37.8°C). Combustible liquids have flash points between 100°F and 200°F (93°C). A closely related term is vapor pressure. Every liquid has a vapor pressure, which is a function of that liquid's temperature. As the temperature increases, the vapor pressure increases. As the vapor pressure increases, the concentration of flammable liquid vapor in the air increases. Therefore, temperature determines the concentration of vapor in the flammable liquid in the air. A certain concentration of vapor in the air is necessary to sustain combustion, and that concentration is different for each flammable liquid.

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The next important concept is the flammable range— the range between the upper and lower flammable limits. Flammable limits are expressed as percent volume in air. Concentrations above the upper flammable limit (UFL) are too rich to burn (too much vapor) and concentrations below the lower flammable limit (LFL) are too lean to burn (not enough vapor). The most dangerous materials are those with the lowest flash point and widest flammable ranges.

The National Fire Protection Association’s (NFPA) Flammable and Combustible Liquids Code, NFPA 30, is an excellent resource and introduction to the hazards of these materials.2 And if you are interested in details, NFPA 30 further classifies flammables as Class I and divides them into Class IA, IB, and IC, while combustible materials are classified as Class II, IIA, and IIB, all based on flash points and boiling points. NFPA 30 also rates the fire hazard of flammable and combustible materials on a scale of 0 to 4 based on flash point. This rating helps you quickly assess the potential danger of a substance. Zero is the least hazardous and indicates the material will not burn. A rating of 1 is given to materials with flash points above 200°F and indicates the material needs to be preheated to burn, while flammables with flash points below 73°F are rated a 4 and are extremely flammable and the most dangerous.

Important guidelines for storage of flammable and combustible materials

The one issue we see cited most frequently is having excessive flammable solvents in the lab. NFPA 45, Fire Protection for Laboratories Using Chemicals, is the first reference we turn to as it provides universal guidelines for safe storage.3 The maximum quantity of flammable and combustible materials that can be stored in the lab is set in NFPA 45, and this is how labs are classified. Chapter 4 of NFPA 45 classifies laboratories into four fire hazard categories based on the amount of flammable and combustible material in the lab. These are Class A (high fire hazard), Class B (moderate), Class C (low) and Class D (minimal). Examples of Class D are high school educational laboratories, while college level undergraduate labs are usually limited to Class C. Class A labs are allowed up to 10 gallons (38L) of Class I flammable liquid per 100 square feet or 20 gallons (76L) total of Class I, II, and III flammable and combustible liquid combined. These quantities can be doubled to 20 gallons of Class I liquid and 40 gallons (150L) of Class I, II, and III liquids, combined with the use of safety cans or storage cabinets.

NFPA 45 also addresses the maximum capacities for different storage container types. For example, for Class IA flammable liquids, the largest allowed container is one pint (500ml) for glass, one gallon (4L) for metal and approved plastic or polyethylene, and 2.6 gallons (10L) for safety cans. Safely storing flammable and combustible liquids in laboratories or stockrooms is risky business. However, by paying attention to the hazard class of the material, the largest container size, and the total quantities, you can minimize that risk. In addition, here are some general guidelines for safe flammable and combustible storage:

  • √ Do substitute nonflammable materials whenever possible.
  • √ Do post the work area with appropriate signs, e.g., “No Smoking” and “No Open Flames.”
  • √ Do store flammable liquids in approved storage cabinets, explosion-proof refrigerators, and safety cans.
  • √ Do clear the area of all ignition sources.
  • √ Do transfer flammable liquids with extreme caution.
  • Do not store large, heavy containers of liquids on high shelves or in high cabinets. A good rule is to store them at shoulder-level or below.
  • Do not store bottles on the floor unless they are in some type of secondary containment.
  • Do not store flammable or combustible solvents near heat sources or in direct sunlight.


1. Prudent Practices in the Laboratory: Handling and Disposal of Chemicals. National Research Council. National Academy Press. Washington, D.C. Latest edition.

2. NFPA 30: Flammable and Combustible Liquids Code. 2008 edition. National Fire Protection Association, Quincy, MA. 2008. 

3. NFPA 45: Standard on Fire Protection for Laboratories Using Chemicals. 2004 edition. National Fire Protection Association, Quincy, MA. 2004.

Additional resources

NFPA 704: Standard System for the Identification of the Hazards of Materials for Emergency Response, National Fire Protection Association, Publication 704. 

NIOSH Pocket Guide to Chemical Hazards. National Institute of Occupational Safety and Health. Publication 2005- 149.

OSHA Hazard Communication Standard. 

Laboratory Safety Manual, University of Florida, Division of Environmental Health and Safety. 2003.