☣️ UN 3221 • CLASS 4
Self-reactive liquid type B
Placard: Flammable Solid. 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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Quick details
UN 3221
Class: 4
Placard type: Flammable Solid
ERG: Guide 149 (check current ERG)
Isolation: ERG 149: isolate 800m (1/2 mile) all directions if tank/rail car involved in fire; initial isolation 60m in all directions for small spills
Chemical & Response Details
| Also known as | Self-reactive liquid type BOrganic peroxide type B liquidSelf-accelerating decomposition liquidSADT liquid |
| Appearance | Variable appearance depending on specific formulation; typically clear to colored liquids that are thermally unstable organic compounds capable of exothermic decomposition without external oxygen. |
| Flash Point | Variable by formulation, typically <23C (<73F) for flammable self-reactive liquids |
| Boiling Point | Variable by formulation, many decompose before boiling |
| Vapor Density | Variable by formulation, typically >1 (heavier than air) |
| Water Reactivity | Generally no violent water reaction, but avoid introducing water which may affect thermal stability |
| Extinguishing | Foam may be used for fire control; avoid extinguishing agents that cause shock or increase temperature; dry chemical, CO2 acceptable |
| PPE | ⚠️ Level B minimum with SCBA required; full encapsulation if decomposition or fire threatens; thermal protective clothing for fire involvement |
| Isolation | ERG 149: isolate 800m (1/2 mile) all directions if tank/rail car involved in fire; initial isolation 60m in all directions for small spills |
Chemical details are general reference only. Always verify with current SDS, ERG, and SOP/SOG.
Common hazards (high level)
- Self-decomposition, self-polymerization, or self-ignition may be triggered by heat, chemical
- May be ignited by heat, sparks or flames.
- Some may decompose explosively when heated or involved in a fire.
- Those substances designated with a (P) may polymerize explosively when heated or involved in a fire.
- May burn violently. Decomposition or polymerization may be self-accelerating and produce large
- Vapors or dust may form explosive mixtures with air.
- Inhalation or contact with vapors, substance or decomposition products may cause severe injury or
- May produce irritating, toxic and/or corrosive gases.
First actions (field-minded)
- CALL 911. Then call emergency response telephone number on shipping paper. If shipping paper
- Keep unauthorized personnel away.
- Stay upwind, uphill and/or upstream.
- Isolate spill or leak area in all directions for at least 50 meters (150 feet) for liquids and at least 25 meters
- Consider initial evacuation for at least 250 meters (800 feet) in all directions.
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UN 3221 — Self-reactive liquid type B HAZMAT RADIO NOTE — UN 3221
Product: Self-reactive liquid type B
Class 4 / Flammable Solid / ERG 149
PPE: Level B minimum with SCBA required; full encapsulation if decomposition or fire threatens; thermal protective clothing for fire involvement
ISOLATION: ERG 149: isolate 800m (1/2 mile) all directions if tank/rail car involved in fire; initial isolation 60m in all directions for small spills
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 3221 — Self-reactive liquid type B
Class: 4 | Placard: Flammable Solid | ERG Guide: 149
Appearance: Variable appearance depending on specific formulation; typically clear to colored liquids that are thermally unstable organic compounds capable of exothermic decomposition without external oxygen.
Water Reactivity: Generally no violent water reaction, but avoid introducing water which may affect thermal stability
Extinguishing: Foam may be used for fire control; avoid extinguishing agents that cause shock or increase temperature; dry chemical, CO2 acceptable
PPE: Level B minimum with SCBA required; full encapsulation if decomposition or fire threatens; thermal protective clothing for fire involvement
Isolation: ERG 149: isolate 800m (1/2 mile) all directions if tank/rail car involved in fire; initial isolation 60m in all directions for small spills
— Key Hazards —
• Self-decomposition, self-polymerization, or self-ignition may be triggered by heat, chemical
• May be ignited by heat, sparks or flames.
• Some may decompose explosively when heated or involved in a fire.
— 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.
• Isolate spill or leak area in all directions for at least 50 meters (150 feet) for liquids and at least 25 meters
SOURCE: allfirefighter.com/hazmat/un/3221 | Always use current ERG + SOP/SOGIC BRIEFING
Use for: Incident command briefing, staging area whiteboard, or pre-entry team brief. Full chemical + response details.
UN3221 Self-reactive liquid type B Cls4 ERG149 | allfirefighter.com/hazmat/un/3221SMS / 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/3221
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FAQ
Self-decomposition, self-polymerization, or self-ignition may be triggered by heat, chemical May be ignited by heat, sparks or flames. Some may decompose explosively when heated or involved in a fire. Those substances designated with a (P) may polymerize explosively when heated or involved in a fire. May burn violently. Decomposition or polymerization may be self-accelerating and produce large Vapors or dust may form explosive mixtures with air. Inhalation or contact with vapors, substance or decomposition products may cause severe injury or May produce irritating, toxic and/or corrosive gases.
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 with SCBA required; full encapsulation if decomposition or fire threatens; thermal protective clothing for fire involvement
No. This is a training/quick-reference aid only. Always consult the current ERG Guide 149 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.