Methyl Ethyl Ketone (MEK) Storage & Tank Compatibility

Storing Methyl Ethyl Ketone (MEK)? Start Here

Methyl ethyl ketone (CAS 78-93-3, C₄H₈O; also called butan-2-one, 2-butanone, or MEK) is a colorless, volatile, polar solvent with a sweet, sharp odor. It is the most widely used industrial ketone after acetone, valued for dissolving paints, lacquers, adhesives, resins, and coatings. With a flash point near 26 °F and a vapor pressure of about 78 mmHg at room temperature, it forms an ignitable vapor-air mixture at ordinary working temperatures and is classified as an NFPA/DOT Class 1B flammable liquid.

Two facts govern how MEK must be stored. First, it is highly flammable - NFPA 704 rates it Flammability 3 - and its vapor is heavier than air, traveling along the floor to remote ignition sources. Second, as a polar ketone solvent it chemically attacks polyethylene and polypropylene, so plastic tanks that handle water and many aqueous chemicals are the wrong container here. Material of construction is therefore a safety-critical decision, not a cost decision.

Why Polyethylene Tanks Are Not Suitable for MEK

Rotomolded high-density polyethylene (HDPE) and crosslinked polyethylene (XLPE) tanks are excellent for water, brines, and many aqueous chemicals, but they are the wrong container for methyl ethyl ketone. Ketones are among the most aggressive solvent classes toward polyolefins: MEK is absorbed into the polyethylene wall, swells and plasticizes the polymer matrix, and softens the structure. The result is a distorted, weakened wall, extraction of resin components into the product, and migration of flammable solvent vapor through the tank shell.

Polypropylene behaves the same way - it is attacked and swollen by ketones and is not a suitable primary container. Because MEK is so flammable, a degrading plastic wall is not a slow nuisance failure; it is a flammable-vapor and structural-failure hazard. For these reasons we do not recommend any polyethylene or polypropylene tank for MEK storage. The correct primary container is grounded and bonded carbon steel or stainless steel, engineered for flammable-liquid service.

Need a tank built for MEK? Our custom fabrication team builds grounded, code-compliant steel and stainless vessels for flammable solvent service. Explore UL-142 aboveground steel tanks, compare 304 vs. 316 stainless, and review our solvent recovery systems, or call our engineers at 866-418-1777.

Material compatibility at a glance

Store methyl ethyl ketone in grounded and bonded carbon steel or stainless steel (304 or 316) built to a recognized aboveground flammable-liquid standard such as UL-142. Polyethylene and polypropylene are not suitable - as a polar ketone, MEK attacks and swells the polymer, softens the wall, and lets flammable vapor permeate the shell. Use PTFE seals and gaskets; many elastomers, including some FKM grades, swell in ketones. Rigorously control ignition sources.

Ratings: S suitable · C conditional / limited · U unsuitable. Verify against the cited resistance charts and your concentration/temperature before specifying.

The safety that actually matters

High flammability. MEK ignites from a small energy input at ordinary temperatures; its vapor is heavier than air and flows to low points and distant ignition sources. Eliminate ignition sources, ground and bond all transfer equipment, use intrinsically safe / explosion-proof electrical gear in the storage area, and provide vapor control. Inert-gas (nitrogen) blanketing of the headspace reduces the in-tank flammable atmosphere.

• Material of construction. Use grounded, bonded carbon steel or stainless steel (304/316) built to a recognized aboveground flammable-liquid standard such as UL-142. Do not use polyethylene or polypropylene tanks.
• Seals and gaskets. PTFE is the safe default; many elastomers, including some FKM (Viton) grades, swell in ketones. Verify every elastomer against MEK at service temperature.
• Static control. MEK can accumulate static charge during transfer; ground and bond containers and use bottom or dip-tube filling to limit splashing and vapor generation.
• Health. Vapor irritates the eyes, nose, and throat and causes drowsiness and dizziness (H319, H335, H336); it is harmful if inhaled (H332) with organ-damage hazard on exposure (H370, H372). Provide ventilation and appropriate PPE; avoid skin contact (H315).

Keep MEK cool, in closed, vented containers away from oxidizers and heat. Store and handle to NFPA 30 and applicable flammable-liquid codes.

Common questions

Can I store methyl ethyl ketone in a polyethylene (poly) tank?

No. MEK is a polar ketone solvent that attacks, swells, and softens polyethylene - including crosslinked (XLPE) tank resin - and polypropylene. The wall distorts, weakens, and lets flammable vapor permeate the shell. Poly tanks are not suitable. Use grounded, bonded carbon steel or stainless steel built for flammable-liquid service.

What is the NFPA 704 rating for methyl ethyl ketone?

Per CAMEO Chemicals (NOAA): Health 1, Flammability 3, Instability 0, no special hazard. The Flammability 3 reflects that MEK ignites under almost all ambient temperature conditions; the Instability 0 reflects that the pure liquid is normally chemically stable.

What material should an MEK tank be made of?

Grounded and bonded carbon steel or stainless steel (304 or 316), built to a recognized aboveground flammable-liquid standard such as UL-142. Stainless is preferred where product purity, cleanability, or corrosion margin matters. Use PTFE seals rather than ketone-sensitive elastomers.

Is MEK flammable, and how should ignition sources be controlled?

Yes - MEK is a Class 1B flammable liquid with a flash point near 26 °F; it forms an ignitable vapor at room temperature and the vapor is heavier than air. Eliminate ignition sources, ground and bond all transfer equipment, use explosion-proof electrical gear, control static during transfer, and consider nitrogen blanketing of the headspace.