The Flaming Truth About Ignitability

Author: ACTenviro Corporate
Date: February 3, 2024

As we noted in “Understanding the Four Characteristics of Hazardous Waste,” the first step in managing your hazardous waste is determining that it is, in fact, a waste, as defined by the EPA. Suppose your waste does not appear on one of the EPA’s four lists of hazardous wastes; you still need to check if it exhibits any of the four characteristics established by the Resource Conservation and Recovery Act (RCRA): ignitability, corrosivity, reactivity, and toxicity. Additionally, certain states, including California and Washington, have state-specific requirements that expand on the RCRA hazard characteristic definitions.

The RCRA definition of “ignitable” wastes is in 40 CFR 261.21. Wastes that are determined to be ignitable are assigned the EPA hazardous waste code D001. The characteristic of ignitability is evaluated differently for solids, liquids, and gases.

Liquid Flash Point

Liquid wastes

Liquid wastes are evaluated based on “flashpoint,” which is the lowest temperature at which a liquid will ignite if there is an ignition source. This is different from the autoignition temperature, which is the temperature at which liquids will catch fire without any obvious source of ignition. A liquid waste with a flashpoint of less than 140 degrees Fahrenheit (60 degrees Celsius) is considered “ignitable.”

  • Test methods for measuring flashpoint are found in EPA SW-846.
  • The procedures for measuring flashpoint (EPA methods 1010 and 1020) were revised in 2020 (effective Sept. 8, 2020) to reflect current test standards, add guidance for sampling mixtures of liquids and solids, and clarify an exemption for aqueous liquids that contain alcohols.

Examples of ignitable liquids are organic solvents used in painting or for cleaning parts, as well as waste gasoline and kerosene.

Solid wastes

The definition of ignitable solids is more complicated. To be an ignitable solid, first, the waste must be solid, then it must be “capable of causing fire through friction, moisture or spontaneous chemical change.” When ignited, it must burn “so vigorously and persistently that it creates a hazard.”

Whether a waste is “solid” can be evaluated using the “paint filter test” (EPA method 9095B). Free liquids (or liquid components of waste) will pass through the paint filter within 5 minutes; solid components will not. Wastes that contain free liquids must be evaluated as liquid waste.

Once a waste is determined to be “solid,” the next step is to determine if it is “capable of causing fire through friction, moisture or spontaneous chemical change.” EPA method 1050 can be used to evaluate whether a waste is air-reactive or self-heating, but there is no guidance from the EPA on whether a waste is “capable of causing fire” by other means. Generators can look to U.S. DOT hazardous materials classification procedures (for example, Division 4.2 self-heating/pyrophoric, or Division 4.3 dangerous when wet), or rely on their generator knowledge.

Solids that are “capable of causing fire” through friction or other means must also burn “vigorously and persistently” (based on a burn rate of greater than 2.2 mm/sec when tested per EPA method 1030) in order to be classified as an ignitable waste.

Classification of solids is more complicated than liquids, but the bottom line is: The ability to burn does not mean something is ignitable by RCRA standards. To be considered an ignitable solid, a waste needs to catch fire very easily or burn vigorously — or both.

Many types of materials and wastes, such as wood, paper and plastic, may be capable of burning (and may be subject to workplace safety, fire code or other regulations), but they would not be considered” ignitable” hazardous wastes. Examples of ignitable solid wastes include certain powdered metals, as well as other air- and water-reactive materials.

Gas wastes

Ignitability also applies to compressed gas wastes that have a “lower flammable limit” (LFL) of 13% or less, or where the flammable range (the difference between the lower flammable limit and upper flammable limit) is 12 % or more. Wastes meeting the definition of DOT “flammable” gas (Hazard Class/Division 2.1) in 49 CFR 173.115 are considered “ignitable.” Methane, propane, hydrogen and acetylene are all examples of gases that would be considered ignitable for waste-classification purposes.

To summarize, oxidizers, such as certain perchlorates, permanganates, inorganic peroxides and nitrates, are also considered ignitable for waste classification. These are substances that can yield oxygen and stimulate combustion of other materials. The hazardous waste definition of oxidizer also includes organic peroxides, subject to exclusions for materials that are highly reactive or potentially explosive (which will generally be considered “reactive” for waste classification) and for materials that have lower hazards. As with ignitable solids, the definition does not reference specific EPA test methods. Instead, generators must rely on safety data sheets (SDS) and generator knowledge.

ACTenviro can assist generators in making their determinations. If you have any questions about hazardous waste — from classification to management to disposal — please e-mail us at [email protected]. We’re happy to help!

James Kapin is Principal Advisor for safety, health and environmental compliance for ACTenviro.  Jim is a Certified Industrial Hygienist (CIH) and a Certified Safety Professional (CSP) with over 25 years of workplace safety and environmental protection experience.   Do you have any hazardous waste questions for Jim?  Or any other workplace safety or environmental compliance questions?  Let us know at [email protected]


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