☣️ UN 2303 • CLASS 3
UN 2303 — Isopropenylbenzene
Placard: Flammable. ERG Guide 128. Training/quick-reference only — use current ERG + SOP/SOG for incident-specific actions.
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⚠️ This page is a quick-reference aid. For real incidents: stage upwind, isolate, deny entry, request Hazmat early, and consult the current ERG + SOP/SOG.
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UN 2303 Quick Details
UN 2303
Product name: Isopropenylbenzene
DOT Class: 3
Placard type: Flammable
ERG Guide: 128 (check current ERG)
Initial isolation: ERG 128: Initial isolation 50m in all directions; if tank/rail car involved in fire, isolate 800m in all directions
Common Hazards of UN 2303
- HIGHLY FLAMMABLE: Will be easily ignited by heat, sparks or flames.
- Vapors may form explosive mixtures with air.
- Vapors may travel to source of ignition and flash back.
- Most vapors are heavier than air. They will spread along the ground and collect in low or confined areas
- Vapor explosion hazard indoors, outdoors or in sewers.
- Those substances designated with a (P) may polymerize explosively when heated or involved in a fire.
- Runoff to sewer may create fire or explosion hazard.
- Containers may explode when heated.
Chemical Identity & Physical Properties
| Also known as | alpha-Methylstyrene2-PhenylpropeneAMSIsopropenyl benzeneCumene styrene |
| CAS Number | 98-83-9 |
| Appearance | Colorless to pale yellow liquid with a sharp, penetrating aromatic odor. Insoluble in water, soluble in organic solvents. |
| Flash Point | 53°C (127°F) |
| Boiling Point | 165°C (329°F) |
| Vapor Density | 4.1 (heavier than air) |
| Water Reactivity | No significant reaction; insoluble in water |
Chemical details are general reference only. Always verify with current SDS, ERG, and SOP/SOG.
Fireground Response Guidance — UN 2303
Extinguishing Media
AFFF foam, alcohol-resistant foam, CO2, dry chemical powder
PPE Requirements
⚠️ Level B minimum recommended; SCBA required in confined spaces or high vapor concentrations; chemical-resistant gloves and boots
Isolation & Evacuation
ERG 128: Initial isolation 50m in all directions; if tank/rail car involved in fire, isolate 800m in all directions
Always confirm protective actions with the current edition of the Emergency Response Guidebook (ERG Guide 128).
First Actions for a UN 2303 Incident
- CALL 911. Then call emergency response telephone number on shipping paper. If shipping paper
- Keep unauthorized personnel away.
- Stay upwind, uphill and/or upstream.
- Ventilate closed spaces before entering, but only if properly trained and equipped.
- Isolate spill or leak area for at least 50 meters (150 feet) in all directions.
- Consider initial downwind evacuation for at least 300 meters (1000 feet).
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📋 Copy & Share Field Card
UN 2303 — IsopropenylbenzeneHAZMAT RADIO NOTE — UN 2303
Product: Isopropenylbenzene
Class 3 / Flammable / ERG 128
PPE: Level B minimum recommended; SCBA required in confined spaces or high vapor concentrations; chemical-resistant gloves and boots
ISOLATION: ERG 128: Initial isolation 50m in all directions; if tank/rail car involved in fire, isolate 800m in all directions
ACTION: Stage upwind · Isolate · Deny entry · Request HazmatRADIO
Use for: Quick radio or face-to-face size-up. Short, structured, field-ready.
=== IC HAZMAT BRIEFING ===
UN 2303 — Isopropenylbenzene
Class: 3 | Placard: Flammable | ERG Guide: 128
Appearance: Colorless to pale yellow liquid with a sharp, penetrating aromatic odor. Insoluble in water, soluble in organic solvents.
Water Reactivity: No significant reaction; insoluble in water
Extinguishing: AFFF foam, alcohol-resistant foam, CO2, dry chemical powder
PPE: Level B minimum recommended; SCBA required in confined spaces or high vapor concentrations; chemical-resistant gloves and boots
Isolation: ERG 128: Initial isolation 50m in all directions; if tank/rail car involved in fire, isolate 800m in all directions
— Key Hazards —
• HIGHLY FLAMMABLE: Will be easily ignited by heat, sparks or flames.
• Vapors may form explosive mixtures with air.
• Vapors may travel to source of ignition and flash back.
— First Actions —
• CALL 911. Then call emergency response telephone number on shipping paper. If shipping paper
• Keep unauthorized personnel away.
• Stay upwind, uphill and/or upstream.
• Ventilate closed spaces before entering, but only if properly trained and equipped.
SOURCE: allfirefighter.com/hazmat/un/2303 | Always use current ERG + SOP/SOGIC BRIEFING
Use for: Incident command briefing, staging area whiteboard, or pre-entry team brief. Full chemical + response details.
UN2303 Isopropenylbenzene Cls3 ERG128 | ERG 128: Initial isolation 50m in all directions; if tank/rail car involved in f | allfirefighter.com/hazmat/un/2303SMS / 160 CHAR
Use for: Quick text to command or incoming units. Fits in a single SMS. Includes link to full page.
⚠️ Quick-reference only. Always use current ERG + SOP/SOG for incident-specific actions.
Page: https://allfirefighter.com/hazmat/un/2303
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Frequently Asked Questions about UN 2303
HIGHLY FLAMMABLE: Will be easily ignited by heat, sparks or flames. Vapors may form explosive mixtures with air. Vapors may travel to source of ignition and flash back. Most vapors are heavier than air. They will spread along the ground and collect in low or confined areas Vapor explosion hazard indoors, outdoors or in sewers. Those substances designated with a (P) may polymerize explosively when heated or involved in a fire. Runoff to sewer may create fire or explosion hazard. Containers may explode when heated.
CALL 911. Then call emergency response telephone number on shipping paper. If shipping paper Keep unauthorized personnel away. Stay upwind, uphill and/or upstream.
Level B minimum recommended; SCBA required in confined spaces or high vapor concentrations; chemical-resistant gloves and boots
Water reactivity: No significant reaction; insoluble in water. Recommended extinguishing: AFFF foam, alcohol-resistant foam, CO2, dry chemical powder.
ERG Guide 128 recommendation: ERG 128: Initial isolation 50m in all directions; if tank/rail car involved in fire, isolate 800m in all directions
No. This is a training/quick-reference aid only. Always consult the current ERG Guide 128 and your department SOP/SOG for incident-specific protective actions.
Sources (high level): DOT/PHMSA marking & class concepts + ERG usage principles.
This page does not reproduce ERG guide text—always consult the current ERG for incident-specific protective actions.