Hazardous Waste Class 3: Flammable Liquids

Posted by author Dawn DeVroom on Thu, Sep 27, 2018

Flammable and combustible liquids are liquids that can burn. They present a risk of personal injury and property damage, so strict storage and disposal are necessary for them and required by law.  

There are certain characteristics that define whether a liquid is considered flammable or combustible. We provide information on these types of liquids


What Is A Flashpoint?


Class 3 flammable liquidsA flashpoint is the temperature at which a particular organic compound gives off sufficient vapor to ignite in air. So, released vapor is the true danger of flammable liquids. Highly volatile liquids, those that are quick to vaporize in various conditions, present the greatest potential danger.

flammable liquid is a liquid having a flash point of not more than 60 °C (140 °F), or any material in a liquid phase with a flash point at or above 37.8 °C (100 °F) that is intentionally heated and offered for transportation or transported at or above its flash point in a bulk packaging.

A combustible liquid is a liquid having a has a flash point above 60.5 °C (141 °F) and below 93 °C (200 °F).

Because of these flashpoints, they are labeled as Class 3 Hazardous Waste by the US Department of Transportation.


Does The Liquid Itself Burn?


Flammable and combustible liquids themselves do not burn. It is the mixture of their vapors and air that burns.


What Is The Danger Of Flashback?

Class 3 flammable liquidsVapors can flow from open liquid containers containing flammables and combustibles. These vapors from  flammable and combustible liquids are heavier than air, so they collect in low areas like sewers, pits, trenches and basements if ventilation is not adequate.

A vapor trail can spread far away from the liquid. If it comes in contact with an ignition source, the fire produced can flash back all the way to the liquid.

Because of this vapor trail, flashback and fire can happen even if the actual liquid is hundreds of feet or several floors away.


Hazard Classifications


Flammable liquids are separated into subcategories by their makeup and flashpoint.

Class 3 “Flammable” liquids are those with a flashpoint above 100 degrees Fahrenheit. Examples of Class 3 Flammable Liquids include acetaldehyde, petroleum ether, and ethyl chloride.

Class 3 “Combustible” liquids are those with a flashpoint above 100 degree and below 200 degrees Fahrenheit. Acetone, benzene, and methyl alcohol are all examples of Class 3 Combustible Liquids. 


Facts About Flammable And Combustible Liquids

To summarize the above information about flammable and combustible liquids:
  • Flammable and combustible liquids ignite easily and burn extremely quickly.
  • Flammability is determined by the flashpoint of the liquid.
  • Flashpoint is the minimum temperature at which a liquid forms a vapor above its surface in sufficient concentration that it can be ignited.
  • Flammable liquids have a flash point of less than 100°F. Liquids with lower flash points ignite easier.
  • Combustible liquids have a flashpoint at or above 100°F.
  • The vapor burns, not the liquid itself and the rate at which a liquid produces flammable vapors depends upon its vapor pressure.
  • The vaporization rate increases as the temperature increases. Therefore, flammable and combustible liquids are more hazardous at elevated temperatures than at room temperature.


Restrictions And Guidelines


Class 3 flammable liquidsBecause their vapors ignite and burn easily, flammable and combustible liquids have strict storage requirements. 

OSHA and the US Department of Transportation offer a long list of requirements for Class 3 substance storage.

Here are some basic storage requirements:

1. Only approved containers and portable tanks shall be used for storage and handling of flammable liquids. Approved safety cans or Department of Transportation approved containers shall be used for the handling and use of flammable liquids in quantities of 5 gallons or less, except that this shall not apply to those flammable liquid materials which are highly viscid (extremely hard to pour), which may be used and handled in original shipping containers. For quantities of one gallon or less, the original container may be used, for storage, use and handling of flammable liquids.

2. Flammable liquids shall not be stored in areas used for exits, stairways, or normally used for the safe passage of people.

3. No more than 25 gallons of flammable liquids shall be stored in a room outside of an approved storage cabinet.

4. Quantities of flammable liquid in excess of 25 gallons shall be stored in an acceptable or approved metal or wood cabinet. 

5. Cabinets shall be labeled in conspicuous lettering, "Flammable-Keep Away from Open Flames."

6. Not more than 60 gallons of Class 3 flammable liquids shall be stored in any one storage cabinet. Not more than three such cabinets may be located in a single storage area. Quantities in excess of this shall be stored in an inside storage room.

7. Inside storage rooms shall be constructed to meet the required fire-resistive rating for their use. Such construction shall comply with the test specifications set forth in Standard Methods of Fire Test of Building Construction and Material, NFPA 251-1969.

You can find more storage requirements on this OSHA website page.

The regulations for transporting and disposing of Class 3 materials are quite extensive. So, if your business has Class 3 flammables that need to be disposed of, we recommend working with an experienced hazardous materials disposal company to make sure you are compliant with DOT regulations.