UN 2561 — Methyl butene
Placard: Flammable. ERG Guide 128. Training/quick-reference only — use current ERG + SOP/SOG for incident-specific actions.
Methyl butene is a very volatile flammable hydrocarbon liquid shipped as UN 2561. Vapor travel, flashback and low-area explosion hazards dominate the response.
Hazard overview: Because of its low boiling point and very low flash point, methyl butene can generate flammable vapor readily. Vapors can move to ignition sources and flash back to the release.
Response guidance: Remove ignition sources, isolate the release and monitor for flammable vapor. Use AFFF, dry chemical or CO2 for fire; water spray may cool containers but will not dissolve the product.
Firefighter training notes: Train responders on very volatile flammable liquids, vapor cloud movement and ignition source control. Include sewer/drain isolation and combustible gas monitoring.
Regulatory context: UN 2561 is transported as Methyl butene, Class 3 flammable liquid. Verify exact isomer, quantity and packing details from shipping papers.
Storage & handling: Store in closed, grounded pressure-rated or flammable liquid containers as specified by the SDS, away from heat, sparks and oxidizers.
UN 2561 Quick Details
Common Hazards of UN 2561
- Methyl butene is an extremely flammable, very volatile liquid.
- Vapors may form explosive mixtures with air at normal temperatures.
- Vapor can travel along the ground to ignition sources and flash back.
- Liquid floats on water and may spread fire across surfaces or drains.
- Vapors can collect in low or confined areas and create explosion hazards.
- Containers may rupture violently when heated.
- Fire may produce irritating smoke and carbon oxides.
Chemical Identity & Physical Properties
Methyl butene is a colorless, gasoline-like hydrocarbon liquid. It is insoluble in water, floats and evaporates readily.
| Also known as | Isopropylethylene3-Methylbutene-1IsoamyleneIsopentene |
| CAS Number | 563-45-1 |
| Appearance | Colorless liquid with a gasoline-like or hydrocarbon odor. Volatile organic compound at room temperature. |
| Flash Point | -54C (-65F) |
| Boiling Point | 20C (68F) |
| Vapor Density | 2.4 (heavier than air) |
| Water Reactivity | No significant reaction; insoluble in water, floats and forms flammable layer |
Fireground Response Guidance — UN 2561
Extinguishing Media
PPE Requirements
Use SCBA for vapor, fire or confined-space response. Wear splash protection and compatible gloves for liquid contact.
Isolation & Evacuation
First Actions for a UN 2561 Incident
- Call 911 and the emergency response number on the shipping papers.
- Keep unauthorized personnel away and eliminate ignition sources if safe.
- Stay upwind, uphill and upstream; avoid low areas where vapor may collect.
- Avoid breathing vapor and prevent liquid contact.
- Do not touch damaged containers or spilled liquid without PPE.
- Ventilate confined spaces only with trained personnel and combustible gas monitoring.
- Use ERG 128, SDS and shipping papers to confirm evacuation, vapor control and foam tactics.
📋 Copy & Share Field Card
UN 2561 — Methyl buteneUse 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.