UN 1229 — Mesityl oxide
Placard: Flammable. ERG Guide 129. Training/quick-reference only — use current ERG + SOP/SOG for incident-specific actions.
UN 1229 is Mesityl oxide, a Class 3 flammable ketone liquid assigned to ERG Guide 129. It can produce solvent vapors that travel, ignite and flash back from distant ignition sources.
Hazard overview: UN 1229 presents flammable vapor, flashback and sewer vapor-explosion hazards. Vapors are heavier than air, and exposure may irritate eyes, skin or respiratory tissue in poorly ventilated areas.
Response guidance: For a UN 1229 incident, responders should confirm the product using shipping papers, container markings, SDS and ERG Guide 129. Establish incident command, isolate the area, stay upwind and uphill, remove ignition sources when safe, keep vapors or runoff out of sewers and use compatible fire-control agents from a protected position.
Firefighter training notes: Training for UN 1229 should emphasize flammable liquid vapor travel, flashback, sewer vapor explosion risk, foam compatibility, container cooling and atmospheric monitoring. Common errors include standing downwind, allowing runoff into drains and ignoring low-area vapor collection. Use ERG 129, SDS and local SOP.
Regulatory context: Mesityl oxide is regulated as a hazardous material for transportation and emergency response purposes. Transportation, workplace exposure, spill reporting, waste handling, storage and environmental requirements may vary by formulation, quantity and jurisdiction. Verify current requirements through shipping papers, SDS, facility documents and applicable DOT, OSHA, EPA, NFPA, state or local authority guidance.
Storage & handling: Mesityl oxide should be stored in tightly closed compatible containers in a cool, dry, well-ventilated flammable-liquid storage area. Keep away from heat, sparks, open flames, oxidizers and incompatible materials, with bonding/grounding, secondary containment and drain protection where required.
UN 1229 Quick Details
Common Hazards of UN 1229
- HIGHLY FLAMMABLE ketone liquid; vapors may ignite easily.
- Vapors may form explosive mixtures with air and flash back to the source.
- Vapors are heavier than air and may collect in low, confined or sewer areas.
- Liquid or vapor may irritate eyes, skin and respiratory tissue.
- Runoff to sewer may create fire or explosion hazards.
- Fire may produce irritating or toxic combustion products.
- Containers may rupture or explode when heated.
Chemical Identity & Physical Properties
Clear, colorless to pale yellow liquid with a strong honey-like or peppermint odor. Oily consistency at room temperature.
| Also known as | Methyl isobutenyl ketoneIsopropylideneacetone4-Methyl-3-penten-2-oneMIBK (alternate)2-Methyl-2-penten-4-one |
| CAS Number | 141-79-7 |
| Appearance | Clear, colorless to pale yellow liquid with a strong honey-like or peppermint odor. Oily consistency at room temperature. |
| Flash Point | 31°C (88°F) |
| Boiling Point | 130°C (266°F) |
| Vapor Density | 3.4 (heavier than air) |
| Water Reactivity | Slightly soluble in water; no significant reaction with water |
Fireground Response Guidance — UN 1229
Extinguishing Media
PPE Requirements
Use positive-pressure SCBA for fire, heavy vapor or confined-space exposure. Chemical-resistant gloves, splash protection and protective clothing should be selected using SDS, product concentration and incident command.
Isolation & Evacuation
First Actions for a UN 1229 Incident
- CALL 911. Then call the emergency response telephone number on the shipping paper, if available.
- Keep unauthorized personnel away.
- Stay upwind, uphill and/or upstream.
- Eliminate ignition sources if it is safe to do so.
- Do not touch or walk through spilled liquid unless properly trained and wearing appropriate protective equipment.
- Ventilate closed spaces before entering, but only if properly trained, equipped and authorized by incident command.
- Isolate the spill or leak area for at least 50 meters (150 feet) in all directions.
- For large spills, fire involvement or strong vapor movement, expand isolation and consider downwind evacuation based on monitoring and incident command.
- Use ERG Guide 129, shipping papers, SDS and local SOP for protective actions and entry decisions.
📋 Copy & Share Field Card
UN 1229 — Mesityl oxideUse for: Quick radio or face-to-face size-up. Short, structured, field-ready.
Use for: Incident command briefing, staging area whiteboard, or pre-entry team brief.
Use for: Quick text to command or incoming units. Fits in a single SMS.