What are flammable and combustible liquids?

Many people assume flammable and combustible mean the same thing; however, they are strikingly different. These terms are used to describe the conditions in which dangerous liquids are likely to ignite. What’s even more interesting is that it’s not the liquid that burns, it’s instead the vapors caused by evaporation that ignite.

The National Fire Protection Association defines the differences between flammable and combustible in the NFPA 30 standard. They are as follows:

  • Flammable liquids are characterized by flash points that do not go above 100°F.
  • Combustible liquids are characterized by flash points above 100°F.

This voluntary standard is a best practice method that many businesses choose to incorporate into their safety regimen.

Where there is a voluntary standard, there’s always a mandatory regulation. Changes were made to OSHA’s Hazard Communication Standard in 2015 when it was aligned with GHS. This resulted in changes occurring to OSHA’s Flammable and Combustible Liquids standard 29 CFR 1910.106. We’ll give you a hint–it’s just titled “Flammable Liquids.” There’s no more combustible category.

OSHA’s definition of flammable liquids is characterized by a flash point below 199.4°F.

Facts to Know About Flash Points

Flash points are defined as the lowest temperature a substance can be to let off enough vapors into the air, that when exposed to an ignition source will ignite. There are two different ways these chemicals are ranked within NFPA standards and OSHA regulation.

According to the NFPA, there are six classes that chemical substances can fall into when it comes to being either combustible or flammable. They are as follows:

  • Class IA – The flash point is less than 73°F and the boiling point less than 100°F
  • Class IB – The flash point is less than 73°F and the boiling point equal to or greater than 100°F
  • Class IC – The flash point is equal to or greater than 73°F, but less than 100°F
  • Class II – The flash point is equal to or greater than 100°F, but less than 140°F
  • Class IIIA – The flash point is equal to or greater than 140°F, but less than 200°F
  • Class IIIB – The flash point is equal to or greater than 200°F

As for OSHA’s GHS standard, there are four categories of flammable chemicals that workers must be aware of.

  • Category 1 – These liquids have flash points below 73.4°F and a boiling point at or below 95°F.
  • Category 2 – These liquids have flashpoints below 73.4°F and a boiling point above 95°F.
  • Category 3 – These liquids have flashpoints at or above 73.4°F and at or below 140°F.
  • Category 4 – These liquids have flash points above 140°F and at or below 199.4°F.

The difference between these two authorities exists because OSHA and DOT aligned themselves with the United Nation’s definitions of flammable and combustible material rather than sticking with the NFPA 30 standard. In terms of which one to utilize, a company may use the NFPA 30 standard if they so choose, but they must prove that it is as protective or more than OSHA’s 1910.106 regulation.

Safety Precautions Required for Flammable and Combustible Liquids

There are plenty of safety precautions to take when working around dangerous chemicals like these. However, we’d like to point you towards three specific safety measures you can take to keep yourself safe as well as other co-workers. They are as follows:

  1. Always have the safety data sheets pertaining to the flammable or combustible material on hand. This sheet of information will give you information on handling the chemical, what to wear to protect yourself, how to handle an emergency involving the chemical, the contact information for the manufacturer, and much more relevant information for your safety.
  2. Be aware of the safety labels or the lack thereof. GHS and NFPA 704 labels are two of the most common code compliant labels you may see on flammable or combustible storage tanks. These labels will display easily recognizable information for employees to take quick action when needed.
  3. Wear the right PPE when working around these hazardous materials. The safety data sheets, any labels on the storage tanks, and even signage posted before entering a space, are all great reminders to not only provide but encourage workers to protect themselves in these types of environments.

OSHA Compliant Storage for Hazardous Substances

The standards for storing dangerous flammable and combustible materials thankfully did not change with OSHA’s decision to alter the definition of flammable.

There are three safety measures to remember when storing flammable and combustible liquids:

  1. Never store chemicals together that have a potential to react with each other. You can do this by keeping, for example, oxidizers and flammables in separate safety cabinets.
  2. Make sure the area is adequately ventilated. This is essential as chemical vapors are often heavier than air, causing them to pool in poorly ventilated areas within the space.
  3. Stay informed. A visual workplace is a workplace that actively works to alert employees of the potential dangers within a storage space. This can be done with labels and signage around the area.

You can find more of the specifics on safe flammable chemical storage in OSHA’s 1910.106 regulation here.

These standards and best practice methods are essential to know for workplace safety. Make sure you are familiar with them before allowing workers to enter the area.


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