P or U? RCRA Waste Codes for Chemical Products

Posted on 6/8/2020 by Anthony Cardno, CHMM

Under the Resource Conservation and Recovery Act (RCRA), unused commercial chemical products listed at 40 CFR 261.33 (e) and (f) are hazardous waste when discarded.

The Environmental Protection Agency (EPA) divides this list of chemicals into two groups:
  • Chemicals assigned a code starting with the letter “P” (listed in paragraph (e); and
  • Chemicals assigned a code starting with the letter “U” (listed in paragraph (f)).
So how does waste code assignment really work for unused, discarded commercial chemical products? The thought process can be complicated and confusing.

What is a RCRA Commercial Chemical Product?

Before we try to assign waste codes, let's confirm that our waste meets EPA's definition of a “commercial chemical product.”

Found at 40 CFR 261.33, the definition describes four scenarios:
  • Any on-specification commercial chemical product or manufacturing chemical intermediate having the generic name listed in 40 CFR 261.33(e) or (f)
  • Any off-specification commercial chemical product having the same name
  • Any residue of a listed chemical remaining in a container or inner liner
  • Any residue or contaminated soil, water or other debris resulting from the cleanup of a spill of a listed chemical.
This means that any individual chemical which can be found on either part of the list by its name and Chemical Abstract Services (CAS) number will be a hazardous waste when discarded, regardless of whether it is on-spec or off-spec, and regardless of whether you already used part of the chemical in the container but not all of it or whether you spilled the unused chemical and must discard it upon cleaning it up.

Popular misconception: Many believe that spilled chemicals are considered “used.” In EPA’s eyes, spilling does not constitute use of a chemical.

Lion's live RCRA workshops return to Texas in August! Join us in Houston or Dallas to keep your hazardous waste training current and learn the latest RCRA rules that Texas must adopt.  

“P” Codes

Chemicals which the EPA has listed on the “P” part of the list are considered by the Agency to be “acutely hazardous.” That means they could be, or are known to be, fatal to humans or animals in low doses.

Some “P”-coded wastes pose hazards in addition to being acutely hazardous (such as posing the characteristics of reactivity or toxicity), but every chemical that gets a “P” code is acutely hazardous regardless of which hazardous waste characteristics it might also present. A lot of your nastier poisons and pesticides can be found on the “P” list, including things like acrolein, aldrin, methomyl, methyl isocyanate, and nitroglycerine.

“U” Codes

Chemicals the EPA has listed on the “U” part of the list are still bad for human health or the environment – just not as bad as those that get a “P” code.

Most of the chemicals on the “U” part of the list are toxic, but some pose additional hazards or are on the list because they’re not toxic but pose a different hazard, for instance ignitability. Most of your solvents are on the “U” list, along with a variety of carcinogens, mutagens and chemicals that bioaccumulate in the environment. This includes things like acetone, benzene, methyl ethyl ketone, formaldehyde, hydrazine, and sulfur phosphide.

What About Unlisted Chemicals?

You won't find every single chemical manufactured in or imported into the US on the “P” and “U” lists.  Potassium Hydroxide, for instance, does not appear on either list. In cases like this, the generator would need to determine whether the unused chemical exhibited any of the characteristics of hazardous waste defined in 40 CFR 261.21–.24.

In this regard, the characteristics serve as a catch-all to prevent unlisted chemicals from being disposed in a landfill without a second thought.

Formulations and Sole Active Ingredient 

Everything named on the P and U lists is an individual chemical. But many discarded unused commercial chemical products are actually formulations. So how do the P and U codes apply to those?

EPA is pretty adamant that P and U codes are only assigned to individual chemicals or to formulations in which that chemical is the sole (read: only) active ingredient. If the manufacturer identifies multiple active ingredients on the label or safety data sheet (SDS), then the generator cannot apply a P or U code. EPA simply does not allow it.

That said, a few states, including Washington, require multiple P/U codes to be assigned to formulations despite what the EPA says about the issue. Always check your state regulations for extra requirements like this. 

Active Ingredient vs. Hazardous Ingredients 

The tricky part is remembering that active ingredients and hazardous ingredients are not necessarily the same things. A formulation could consist of more than one ingredient found on the P or U lists. The question is how many of them are considered “active” – that is, which ingredient(s) are there to get the job done, and which are there to make the product look nice, smell nice, taste nice, or act as a binding or delivery agent?

For comparison, most solvent blends consist of more than one active ingredient because there are multiple solvents in the blend and they are all there to provide their solvent qualities. Many pesticides, on the other hand, have one active ingredient (job: kill the pest) combined with multiple inactive ingredients (job: delivery mechanism, color, or smell).

So assigning the proper P or U codes to unused commercial chemical products we intend to discard or dispose of is not as straightforward as it first seems to be. It takes a familiarity with the definition and lists at 40 CFR 261.33 as well as an understanding of how to identify whether the product has a sole active ingredient or multiple active ingredients.

Online RCRA Trainingonline RCRA training

Lion makes it easy to keep your annual RCRA training up to date, even in these difficult times. Get effective, comprehensive hazardous waste training with a self-paced online course or a live webinar at

RCRA Hazardous Waste Management (Online Course) 
RCRA Hazardous Waste Management Refresher (Online Course) 
RCRA Hazardous Waste Management Refresher (Webinar) 

Courses are packed with original graphics, professional narration, and engaging exercises–so you learn by seeing, by hearing, and by doing. When we learn something in multiple ways, we retain more information and are better prepared to apply our knowledge to real world situations.

See all online Lion's RCRA training options at

Tags: chemicals, hazardous waste, RCRA, waste codes

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