U161 RCRA waste code Flammable paint & lacquer solvent with a sharp smell.

Free, no account
Based on 40 CFR 261.33 and EPA guidance
Nothing is stored

U-listed waste
Methyl isobutyl ketone

U-list unused product.

Ignitable U-listed hazardous waste for unused methyl isobutyl ketone, a flammable solvent for paints, lacquers & adhesives.

Is U161 hazardous waste?

Yes, when the listing applies. U161 covers unused methyl isobutyl ketone that is thrown away, including off-specification product and qualifying residues. It is a U-listed waste, not an acute P-listed one, so the listing depends on the product and how it is discarded, not on a TCLP result alone.

An entry with no letter is toxic (T) under 261.33(f), not free of hazard. “Methyl isobutyl ketone (I)” and “4-Methyl-2-pentanone (I)” are ignitable (I). “Pentanol, 4-methyl-” has no letter, so it counts as T.

When it applies, U161 is nonacute hazardous waste. On a required hazardous waste manifest, put U161 in Item 13. For VSQG exemptions and empty-container rules and pharmaceutical containers, follow the linked guides.

What does U161 cover?

This covers unused methyl isobutyl ketone thrown away pure or technical grade, or in a formulation where it is the only active ingredient. Off-specification batches, residues in non-empty containers and spill cleanup residues of those products count too. Inactive ingredients don't stop it being the only active ingredient.

CAS: 108-10-1
Table entries: Methyl isobutyl ketone (I); 4-Methyl-2-pentanone (I); Pentanol, 4-methyl-
Printed hazard annotations: “Methyl isobutyl ketone (I)”: (I); “4-Methyl-2-pentanone (I)”: (I); “Pentanol, 4-methyl-”: unmarked: T (toxic) by default.
Rule: 40 CFR 261.33(f)

Is methyl isobutyl ketone waste always U161?

Code	When it fits
U161	The unused chemical is thrown away, pure or technical grade or as the sole active ingredient. Qualifying product residues count too.
F003	It is spent after solvent use, alone or blended only with F003 solvents before use. Recovery still bottoms count too.
F001–F005	Before use, the blend held an F003 solvent plus at least 10% by volume of total F001, F002, F004 or F005 solvents.
Characteristic waste (D001–D043)	A used chemical or a different formulation meets a hazardous waste characteristic. Any process listings that apply need assessing too.

A listed unused product can also exhibit a characteristic, so both rows can apply. Having this chemical in a manufacturing waste doesn't make the waste U161. What counts is the waste’s origin, formulation and use history. Mixing listed waste with solid waste, or treating it, generally doesn't remove the listing. That takes an applicable exclusion, exception or approved delisting. Using the chemical as an ingredient or reactant doesn't by itself make it a spent F-listed solvent. Each listing has its own before-use blend conditions. The numerical entry “Pentanol, 4-methyl-” is a different chemical from the 2 ketone names. The alphabetical entries are methyl isobutyl ketone.

Which wastes take U161?

Waste	When it’s U161
Unused methyl isobutyl ketone	Pure or technical-grade methyl isobutyl ketone is thrown away, or a product has it as the sole active ingredient

Which codes sit beside U161?

Code	What it is
U157	3-Methylcholanthrene
U158	4,4′-Methylenebis(2-chloroaniline)
U159	Methyl ethyl ketone (MEK)
U160	Methyl ethyl ketone peroxide
U162	Methyl methacrylate
U163	MNNG
U164	Methylthiouracil
U165	Naphthalene