April 15, 2019

Modernizing the Definition of “Ignitable” Hazardous Waste

EPA is proposing a number of changes to the ignitability characteristic found in §261.21. [April 2, 2019; 84 FR 12539] This section has been revised only slightly since its original promulgation in 1980. As a result, some of the test methods and Department of Transportation (DOT) references included in the definition of D001 have been out-of-date for years. As proposed, the five primary changes would:

  1. Update the required flash point test methods,
  2. Codify existing guidance regarding the alcohol-content exclusion,
  3. Codify existing sampling guidance for multiphase wastes,
  4. Update cross-references to DOT regulations and remove obsolete information, and
  5. Provide alternatives to the use of mercury thermometers in the flash point tests and other SW–846 methods.

Flash Point Test Update

While the Pensky-Martens and Setaflash flash point test methods currently found in §261.21(a)(1) represented the best practices and technologies in 1980, scientific and technological advances have made these methods outdated, presenting several challenges to the regulated community. For example, these methods require mercury thermometers, which are being phased out due to environmental health and safety concerns for mercury. And certified reference standards for these tests may no longer be commercially available. Furthermore, newer heating elements and electric-spark ignition devices have been developed that may improve the accuracy and precision of flash point testing. EPA is proposing to allow the use of up-to-date (2018) flash point test methods that reflect these improvements and do not require mercury thermometers. However, to provide flexibility to generators and laboratories, the older test methods would still be options in §261.21(a)(1). A summary of the current and proposed flash point tests is given in the table below.

Current and Proposed ASTM and SW–846 Flash Point Tests Referenced in §261.21(a)(1)

Flash point test
common name




EPA SW–846
test method


EPA SW–846
test method


D 93-79 or D 93-80


D 8175-18



D 3278-78


D 8174-18


ASTM = American Society for Testing and Materials.

Source: Adapted from 84 FR 12544.

Alcohol-Content Exclusion Changes

The original (and still current) definition of an ignitable liquid hazardous waste excludes “an aqueous solution containing less than 24 percent alcohol by volume.” Subsequent EPA guidance has clarified how the words “alcohol” and “aqueous” are to be defined, the scope of the alcohol-content exclusion, and how the exclusion interfaces with DOT regulations. [55 FR 22543 and RO 11060, 12274, 13548] However, EPA has become aware that the exclusion may inadvertently apply in ways the agency had not intended. For example, the exclusion may apply to an aqueous waste stream that contains a small concentration of ignitable alcohol and a large concentration of ignitable nonalcoholic component.

To get the exclusion more in line with its original intent, EPA proposes to remove the word “aqueous” and rephrase the regulations to exclude “a solution containing less than 24 percent of any alcohol or combination of alcohols (except if the alcohol has been used for its solvent properties and is one of the alcohols specified in EPA Hazardous Waste No. F003 or F005) by volume and at least 50 percent water by weight.” In addition to the proposed regulatory language, EPA is seeking comment on how much waste is generated that currently enjoys this exclusion, the experiences of state-authorized programs that manage excluded alcohol-containing wastes, and whether the final rule should specify the waste streams that are excluded or narrow the types of alcohol that would qualify for the exclusion.

Multiphase Waste Testing

Section 262.11(a) states that a hazardous waste determination must be made at the point of generation and at any time in the course of its management that the waste has, or may have, changed its properties in a way that may impact its classification under RCRA. EPA’s long-standing sampling guidance states that for multiphase wastes, a sample should be separated into phases and each individual phase analyzed appropriately for the characteristic of ignitability. [RO 13759, 14834] The agency’s proposal would simply codify this guidance into a new §261.21(a)(5) to read “It is a multiphase mixture, where any liquid phase has the flash point described in paragraph (a)(1) of this section, or any non-liquid phase has the properties described in paragraph (a)(2) of this section.”

Related to this issue, EPA requested comment on adding the following language, which reflects EPA’s longstanding position on determining free liquids, to SW-846 as guidance:

‘‘The definitive procedure for determining if a waste contains a liquid for the purposes of the ignitability and corrosivity characteristics is the pressure filtration technique specified in Method 1311. However, if one obtains a free liquid phase using Method 9095, then that liquid may instead be used for purposes of determining ignitability and corrosivity. However, wastes that do not yield a free liquid phase using Method 9095 should then be assessed for the presence of an ignitable or corrosive liquid using the pressure filtration technique specified in Method 1311.’’ [60 FR 3092, January 13, 1995]

DOT/RCRA Interface

The definition of an ignitable hazardous waste under RCRA includes ignitable compressed gases and oxidizers/organic peroxides as defined in the DOT regulations—see §261.21(a)(3) and (4), respectively. In essence, these sections define D001 to include a waste ignitable compressed gas that, when shipped, would be a DOT hazard class 2.1 flammable compressed gas or a waste oxidizer/organic peroxide that, when shipped, would be a DOT hazard class 5.1/5.2 material. However, the current RCRA D001 definition uses the 1980 version of DOT’s regulations. Thus, EPA’s proposal would better align the RCRA definitions with the current DOT regulations.

Specifically, EPA proposed to replace outdated Bureau of Explosives test method references with the more-current ASTM E 681-85 method or an approved equivalent. Additionally, references to outdated DOT Class A and B explosives would be replaced with the current hazard class 1.1, 1.2, and 1.3 designations. Finally, EPA would remove the obsolete notes at the end of §261.21.

Removing the Requirement to Use Mercury Thermometers

Several existing EPA analytical methods, including the current flash point tests in §261.21(a)(1), require the use of mercury thermometers for temperature measurement. Updating the flash point tests to allow the use of non-mercury temperature devices was discussed previously. To eliminate the negative health effects resulting from mercury exposure, EPA is also proposing modifications to SW–846 Methods 0010, 0011, 0020, 0023A, and 0051 to allow the use of non-mercury temperature device alternatives. According to the agency, the removal of the mercury thermometer requirement does not change the underlying technology of the methods, which are used for air sampling and stack testing.

State Authorization

The proposed rule would be promulgated under the base RCRA program, meaning the proposed changes would not take effect in RCRA-authorized states (all states other than Alaska and Iowa) until the state adopts them. Moreover, the proposed revisions to several test methods are considered to be neither more nor less stringent than the existing regulations; thus, authorized states could, but would not be required to, adopt these changes.

Submitting Comments

The preferred method of submitting comments on this proposed rule is through Docket ID: EPA-HQ-OLEM-2018-0830 at regulations.gov. Comments must be received by June 3, 2019.


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