Skip Navigation
Oklahoma State University

Flammable and Combustible Liquid Safety

Flammable liquids are among the most common hazardous chemicals found in a laboratory.  The primary hazard associated with flammable liquids is their ability to readily ignite and burn.  The National Fire Protection Association (NFPA) defines a flammable liquid as a liquid whose flash point does not exceed 100°F (38°C).  Combustible liquids are defined as liquids having flash points at or above 100°F (37°C).

Flammable and combustible liquids exhibit multiple health hazards besides fire.  Examples of health hazards that are associated with various flammable solvents are listed in Table 1. The manufacturer’s safety data sheets (SDS’s) must always be reviewed to identify the specific hazards of chemicals, recommended personal protective equipment, and the best practices for storage. 

Flammabke Groups Exhibiting Similar Helalth Effects


  • When receiving flammable or combustible liquids from the manufacturer or a distributor, record the chemical information in the OSU online chemical inventory that is part of the Chemical Safety Assistant.
  • If the flammable liquid is a peroxide forming compound, the appropriate labeling guidelines and disposal timeframes can be found in the Peroxide Former link.


  • The Globally Harmonized System (GHS) hazard pictogram for flammable liquids should be incorporated
    with other hazard pictograms at the entrance of areas containing flammable materials. (Figure 1)
  • Flammable liquids (not in active use) should be stored inside fire resistant
    flammable storage cabinets when available.
  • Always segregate flammable and combustible liquids from other hazardous chemicals such as corrosives or oxidizers.
  • Flammable liquid storage areas should be labeled with a font size that is no less than one inch in height.
  • Laboratory entrances containing hazardous chemicals should display a NFPA diamond labeled
    with appropriate hazard class ratings. (Figure 2)


Hazard sign matrix

  • Flammable liquids that require refrigeration must be stored in a certified explosion-proof refrigerator.  Never store flammable chemicals in a standard household refrigerator.  There are several ignition sources located inside a standard refrigerator that can cause a fire or explosion.
  • Minimize the amount of flammable liquids stored in the laboratory. Use Table 2. to determine the amount of flammable liquids that can be stored.

Maximum Quantity per 100 ft

  • Metal drums used for storing and dispensing flammable chemicals must be properly grounded or bonded.  Ground cables shall be available and utilized in laboratories using metal storage containers for flammable liquid storage.
  • Container size restrictions for storing flammable and combustible liquids are based on the container type and the flammability of the liquid, as shown in Table 3.

Container Size of Flammable and Combustible Liquids

  • Flammable liquids in quantities greater than four liters should be kept in certified metal safety cans such as the one in Figure 2.
     These cans should only be used as recommended by the manufacturer, including the following safety practices:
    • Never disable the spring-loaded closure.
    • Always keep flame-arrestor screen in place; replace if punctured or damaged.
  • Specific areas should be designated for waste containers. The area should be labeled with font height no less than one inch in height.


Usage and Handling

  • Label all chemical containers with the identity of the contents and associated hazard warning information.
  • When utilizing flammable liquids in the laboratory, flame retardant lab coats should be worn.
  • Flammable liquids must be handled in a fume hood, unless it is known that the permissible exposure limit (PEL) and lower explosion limit (LEL) will not be exceeded.  The minimum concentration of a particular flammable or combustible vapor necessary to support combustion in air is defined as the Lower Explosive Limit (LEL).  Below this level, the mixture is too “lean” to burn.  The maximum concentration of a gas or vapor that will burn in air is defined as the Upper Explosive Limit (UEL).  Above this level, the mixture is too “rich” to burn.  The range between the LEL and UEL is known as the flammable range for that gas or vapor.  It is never safe to work in conditions that exceed the UEL.  Table 4. lists LEL and UEL conditions for several common flammable chemicals.  

LEL and UEL %

  • Before handling flammable liquids consider all potential sources of ignition.  Flammable vapors are generally heavier than air and tend to settle - traveling along lab benches and the floor.
  • The transfer of material to and from a container can result in an accumulation of static charge on the container.  When transferring flammable liquids, this static charge could generate a spark, thereby igniting the liquid.  To make these transfers safer, flammable liquid dispensing and receiving containers should be bonded together before pouring.  
  • Keep flammable and combustible liquids away from strong oxidizing agents, such as chromic acid, permanganates, chlorates, perchlorates, and peroxides.
  • Large containers (such as drums) must also be grounded when used as dispensing or receiving vessels.  All grounding and bonding connections must be on conductive surfaces.
  • Never heat flammable liquids with an open flame.  Use steam baths, water baths, oil baths, hot air baths, sand baths, or heating mantles.
  • Use caution when handling miscible solvent/water mixtures.  These mixtures can still be flammable depending on the partial pressures involved.
  • Treat water contaminated with water-immiscible solvents carefully.  Hydrocarbon sheens provide adequate surface area for volatilization and ignition.
  • When volatile materials are present, use only non-sparking explosion-proof electrical equipment such as explosion-proof refrigerators.
  • Laboratory desks and furniture should be constructed of fire-retardant materials.
  • Avoid wearing clothing made of synthetic materials (e.g. Polyester) while handling highly flammable materials. In the event of a fire, synthetic materials will melt and stick to the skin.
  • When transporting organic solvent bottles, use secondary containers to prevent breakage and contain spills in case a bottle is dropped or strikes a surface.
  • Use only ventilated explosion proof ovens for flammable or combustible liquids, or materials that contain residual flammable or combustible liquids.
  • A spill containment kit should be available in the event of an accidental release.  Kits should include appropriate absorbent material.

Waste Disposal

Almost all flammable and combustible liquid waste is considered hazardous.  Flammable and combustible hazardous waste must be disposed of according to local, state, and federal regulations.  OSU guidelines for disposal of flammable and combustible liquid waste are presented below.

  • It is best practice to utilize approved waste disposal cans similar to Figure 3.
  • Do not use consumer goods containers (such as old milk) jugs to store waste aggregation for disposal. 
  • If specialized wastes cans are not utilized, it is best to return the material to the original container and clearly label as waste.
  • Rags or paper towels soiled with flammable or combustible liquids should be segregated from common garbage. These materials should be placed in a disposal can similar to Figure 4, and disposed of according to hazardous waste guidelines.
  • Flammable and combustible liquid waste must be segregated according to the guidelines below:
    • Type A, “CHO” waste are hydrocarbons and oxygenated hydrocarbons.
    • Type B, “Nitrogenated Hydrocarbons” include hydrocarbons with nitrogen containing functional groups.
    • Type C, “Halogenated Hydrocarbons” include hydrocarbons incorporated with halogens.
    • (A+B=B), [(A&/or B) + C=C]
  • A Chemical Surplus Removal Request form is required before any chemical can be picked up.  Each container must be sealed and labeled with a Hazardous Chemical Surplus Tag (Form HM95-2).