Workplace safety is always a priority, particularly when working with hazardous chemicals and liquids. Two of the most prevalent types of dangerous liquids on job sites are those that are flammable and/or combustible. Although these terms may seem interchangeable, there are distinct differences between them. When it comes to protecting your workers and ensuring a safe and flame-free environment, it's imperative to understand the unique properties of both types of liquids.

This article will not only discuss the definitions and classifications of flammable and combustible liquids, but it will also illustrate proper handling techniques and the best personal protective equipment (PPE) for your workers. Here is everything you need to know for proper protection, handling, and storage of these liquids.

What is the Difference Between Flammable and Combustible Liquids?

The first thing you should know about these liquids is that the danger comes from vapors, not the fluid itself. Both flammable and combustible liquids emit fumes that can catch fire. What matters most is the flashpoint, which is the lowest temperature at which a liquid emits a vapor that can ignite. As a rule, combustible liquids can ignite at higher temperatures than flammable ones.

According to the Occupational Health and Safety Administration (OSHA), the rules for both liquids change depending on where they're used. Construction sites have unique definitions compared to all other workplaces. As per OSHA standards, the definitions are as follows:

  • Flammable liquids are those with a flashpoint of 100 degrees Fahrenheit (37.8 degrees Celsius) or less. On construction sites, that flashpoint raises to 140 degrees (60 degrees Celsius).
  • Combustible liquids have a flashpoint above 100 degrees. In construction, combustible liquids have a minimum flashpoint of 140 degrees and a maximum of 200 degrees.

Flammable and Combustible Liquid Classifications

While OSHA's definitions are pretty broad, we can break flammable and combustible liquids down into different categories. Another term to know is the boiling point, which relates to the vapor pressure of a fluid. Essentially, when a liquid is heated to a certain point, it starts to vaporize, like water turning into steam. Only flammable liquids have boiling points, while combustible liquids do not.

The National Fire Protection Association (NFPA) defines three classes for both liquid types. Here is a breakdown of each classification.

Flammable Liquids

  • Class I-A - Flashpoint below 73 degrees F (23 degrees C) and a boiling point below 100 degrees F. Examples of this class include petroleum or diethyl ether.
  • Class I-B - Flashpoint below 73 degrees F and a boiling point at or above 100 degrees F. Examples include acetone or ethanol.
  • Class I-C - Flashpoint between 73- and 100-degrees F with no boiling point. An example of this class is p-xylene.

Combustible Liquids

  • Class II -Flashpoint between 101- and 140-degrees F (39-60 degrees C). Examples include diesel fuel and many cleaning solvents.
  • Class III-A - Flashpoint between 141- and 199-degrees F (61-93 degrees C). Examples include oil-based paints and mineral oil.
  • Class III-B - Flashpoint at or above 200 degrees F (93 degrees C). An example is neatsfoot oil.

Another factor to consider is the upper and lower explosive limits of these chemicals. These limits indicate when vapor is most flammable, and they refer to the concentration of fumes in the air. If the concentration is below the lower limit, it's too "lean" to ignite. If the concentration is above the upper limit, the mixture is too "rich" to ignite. However, rich vapor mixtures can cause health problems like headaches, vomiting, and dizziness, so they're still dangerous at high concentrations.

Regulations Regarding Flammable and Combustible Liquids

OSHA is in charge of regulating flammable and combustible liquids at the federal level, and it outlines rules for the handling, storage, and transportation of these items. While there are far too many regulations to list here, some essential requirements include:

  • All flammable and combustible liquids must be stored in OSHA-approved containers and portable tanks up to five gallons. Hard to pour materials and fluids that come in a one-gallon container or smaller can be kept in their original packaging.
  • No flammable or combustible liquids shall be stored in exits, stairways, entrances, or other passageways.
  • The maximum storage limit for a single room is 25 gallons unless using approved containers or storage materials. If using wood to store flammable or combustible liquids, the wood must be at least one inch thick and laminated to avoid combustion. Most metal shelving and cabinets are okay for storage purposes.
  • All storage containers and cabinets must be labeled with a warning sticker that reads "Flammable - Keep Away From Open Flames."
  • Any materials that can create a fire hazard when mixed with water shall not be stored with flammable or combustible liquids.

You can review a full rundown of OSHA's regulations for these liquids here.

Best Practices for Storage and Handling of Flammable and Combustible Liquids

While following OSHA's requirements is an excellent place to start, you should also implement best practices for storing and handling any flammable or combustible liquids. Here are some top recommendations of how to keep your workplace and employees safe:

  • Knowledge - Make sure that all workers understand the dangers of these chemicals and what can happen if they mishandle them. All signs and Safety Data Sheets (SDS) should be available in various languages to ensure all employees understand them. For example, if some workers speak Spanish, the SDS should include a Spanish translation.
  • Training - All employees should be trained on proper safety and handling techniques. This training can involve the use of personal protective equipment (PPE) and transportation methods. For example, workers may need to lift or carry five-gallon drums in pairs to avoid drops and spills. Training can also include how to react to fires if they happen.
  • Ventilation - Since vapor is the most dangerous element of a flammable or combustible liquid, all storage facilities must have adequate ventilation to prevent vapor buildup. Another potential hazard is a flashback, which is when vapor travels from its source. Once ignited, the flames can return to the source and ignite the remaining liquid, even if it's stored hundreds of feet away. Flashback can even occur between building floors.
  • Ignition - Flammable and combustible liquids should always be kept away from ignition sources, including hot pipes and electronics. Workers must never smoke near these liquids, even if they are stored in airtight containers.
  • Materials - Be sure to use OSHA-approved storage materials for all fluids, including anything in the same room. For example, paper and cardboard boxes can be highly combustible, so keep them out of storage rooms where flammable or combustible liquids are present.

Best PPE for Flammable Liquids

Since these liquids are so dangerous, all workers should wear the proper personal protective equipment. Make sure that all PPE meets minimum fire safety ratings and use non-flammable materials as much as possible. Employees should have the following PPE when handling or transporting flammable and combustible liquids.

  • Eye Protection - Vapors can irritate the eyes, creating unsafe conditions. Some vapors are corrosive, so eye protection must be rated to withstand any corrosive elements. Examples of eye PPE include goggles, glasses, and face shields.
  • Gloves - Not only should the gloves be non-flammable, but they should also be non-absorbent. Many flammable and combustible liquids can absorb into various materials, which can create potential hazards. The gloves should also allow for flexibility and grip to avoid drops and spills.
  • Protective Clothing - When it comes to fire safety, extra layers can protect workers. For example, employees may use flame retardant coveralls or HAZMAT suits over their regular clothing.
  • Footwear - Boots should be non-flammable and non-absorbent if possible. These boots should also have sufficient traction to avoid slips and falls while transporting or handling flammable and combustible liquids.
  • Headwear - Helmets and other headgear may be necessary to protect against falling objects. These items can also keep hair out of the face, which can prevent vision impairment. Hair is also highly flammable, so keeping it covered can help avoid potential ignition.
  • Breathing Apparatus - When employees work with flammable and combustible liquids, they need to avoid breathing in harmful vapors. A face mask should offer sufficient protection in some cases, but workers may need an oxygen supply when vapor levels are high or if the fumes are corrosive.

Browse PPE for Chemical and Flame Protection:

How to Reduce Fire Risk When Working with Flammable and Combustible liquids

We've already gone over best practices for storing and handling flammable and combustible liquids, but here are some additional tips on how to protect your workers and keep a safe workplace.

  • Use Non-Static Clothing - Some liquids are so flammable that they can ignite from a single spark, so all workers should wear non-static clothing.
  • Keep Liquids Out of Sunlight - Heating a flammable or combustible liquid can cause it to vaporize. Liquids stored in airtight containers may build pressure and explode. Even if containers are ventilated, sunlight could cause vapor-rich air mixtures, leading to health hazards for workers.
  • Bond and Ground Metal Containers - Bonding is the act of connecting two conductive objects so that they have the same electrical potential. Grounding means that the objects have zero electrical potential because the energy flows into the ground. Be sure to bond and ground all metal containers when storing or transporting them to avoid any sparks or electrical discharge.

Protect Workers with PPE From International Enviroguard

Protecting your workers is easy when you can buy fire-rated PPE from International Enviroguard. We have chemical and flame-retardant PPE to ensure that your employees stay safe and healthy at a job site. Our vast collection of PPE provides varying levels of protection that can be enhanced with accessories such as chemical splash sleeves, disposable shoe covers, bouffant caps / hair nets, and more.