UN 2055 — Styrene monomer, stabilized
Placard: Flammable. ERG Guide 128P. Training/quick-reference only — use current ERG + SOP/SOG for incident-specific actions.
UN 2055 is Styrene monomer, stabilized, a flammable inhibited monomer assigned to ERG Guide 128P. Vapor flashback and heat/contamination polymerization are key risks.
Hazard overview: FLAMMABLE liquid; vapors may form explosive mixtures with air. Vapors are heavier than air and may travel to ignition sources and flash back. May polymerize exothermically if heated, contaminated or if inhibitor is depleted.
Response guidance: For UN 2055, isolate the area, eliminate ignition sources and keep vapors out of drains. Cool containers, monitor polymerization risk and contain runoff under ERG 128P.
Firefighter training notes: Training for UN 2055 should emphasize flammable vapor control, polymerization warning signs, container cooling, SCBA use, decontamination and runoff control. Use ERG 128P, SDS and local SOP.
Regulatory context: Styrene monomer, stabilized is regulated as a hazardous material for transport and emergency response. Storage, reporting, exposure, waste and incident-notification duties depend on quantity, concentration, package type and jurisdiction; verify shipping papers, SDS and authority guidance.
Storage & handling: Styrene monomer, stabilized should be stored cool in approved flammable-liquid containers away from ignition sources, heat, oxidizers and polymerization triggers; maintain inhibitor/stabilizer controls where applicable.
UN 2055 Quick Details
Common Hazards of UN 2055
- FLAMMABLE liquid; vapors may form explosive mixtures with air.
- Vapors are heavier than air and may travel to ignition sources and flash back.
- May polymerize exothermically if heated, contaminated or if inhibitor is depleted.
- Inhalation can irritate respiratory tract and affect the nervous system.
- Containers may rupture or explode if polymerization or heating occurs.
- Fire may produce carbon monoxide, styrene smoke and irritating/toxic gases.
- Runoff may carry flammable and toxic organic contamination.
Chemical Identity & Physical Properties
Styrene monomer, stabilized physical appearance should be verified from SDS, package labels and shipping papers.
| Also known as | StyreneVinylbenzeneEthenylbenzenePhenylethylene |
| CAS Number | 100-42-5 |
| Flash Point | 31°C (88°F) |
| Boiling Point | 145°C (293°F) |
| Vapor Density | 3.6 |
Fireground Response Guidance — UN 2055
Extinguishing Media
PPE Requirements
Use positive-pressure SCBA for vapor, fire or confined-space exposure. Wear chemical-resistant gloves, eye/face protection and protective clothing.
Isolation & Evacuation
First Actions for a UN 2055 Incident
- Call 911 and the emergency response number on the shipping paper, if available.
- Keep unauthorized personnel away and establish incident command.
- Stay upwind, uphill and upstream.
- Eliminate ignition sources if this can be done safely.
- Watch for polymerization, container heating or pressure buildup.
- Avoid breathing vapor, gas, mist, smoke or fumes and avoid skin or eye contact.
- Do not touch damaged containers or spilled material without proper training and PPE.
- Prevent contaminated liquid, runoff and decontamination waste from spreading.
- Ventilate confined spaces only after monitoring and only if properly trained and equipped.
- Use ERG Guide 128P, SDS, shipping papers and monitoring to set isolation, evacuation and entry decisions.
📋 Copy & Share Field Card
UN 2055 — Styrene monomer, stabilizedUse 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.