☣️ UN 3131 • CLASS 4
UN 3131 — Water-reactive solid, corrosive, n.o.s.
Placard: Dangerous When Wet. ERG Guide 138. 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 3131 Quick Details
UN 3131
Product name: Water-reactive solid, corrosive, n.o.s.
DOT Class: 4
Placard type: Dangerous When Wet
ERG Guide: 138 (check current ERG)
Initial isolation: ERG 138: Initial isolation 50m in all directions; protective action distance 100m for small spills, 300m for large spills during day, 800m at night; evacuate immediate area if fire involves this material
Common Hazards of UN 3131
- Produce flammable gases on contact with water.
- May ignite on contact with water or moist air.
- Some react vigorously or explosively on contact with water.
- May be ignited by heat, sparks or flames.
- May re-ignite after fire is extinguished.
- Some are transported in highly flammable liquids.
- Runoff may create fire or explosion hazard.
- Inhalation or contact with vapors, substance or decomposition products may cause severe injury or
Chemical Identity & Physical Properties
| Also known as | Water-reactive solid, corrosive, NOSDangerous when wet solid, corrosiveClass 4.3 corrosive solid |
| Appearance | Generic entry covering various solid materials that react with water and have corrosive properties. Physical appearance varies depending on specific chemical; typically solid form at room temperature with varying colors and no characteristic odor until wetted. |
| Flash Point | Not applicable (water-reactive solid) |
| Boiling Point | Not applicable (varies by specific substance) |
| Vapor Density | Not applicable (solid material) |
| Water Reactivity | Reacts with water producing flammable gases and heat; may ignite spontaneously. Do NOT use water except in flooding quantities to cool containers. Keep material dry. |
Chemical details are general reference only. Always verify with current SDS, ERG, and SOP/SOG.
Fireground Response Guidance — UN 3131
Extinguishing Media
Dry sand, dry chemical, soda ash, or lime only. NO WATER or water-based agents including foam.
PPE Requirements
⚠️ Level B minimum with full face SCBA; acid-resistant protective clothing required due to corrosive properties; avoid moisture contact on PPE
Isolation & Evacuation
ERG 138: Initial isolation 50m in all directions; protective action distance 100m for small spills, 300m for large spills during day, 800m at night; evacuate immediate area if fire involves this material
Always confirm protective actions with the current edition of the Emergency Response Guidebook (ERG Guide 138).
First Actions for a UN 3131 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 in all directions for at least 50 meters (150 feet) for liquids and at least 25 meters
- Consider initial downwind evacuation for at least 300 meters (1000 feet).
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UN 3131 — Water-reactive solid, corrosive, n.o.s.HAZMAT RADIO NOTE — UN 3131
Product: Water-reactive solid, corrosive, n.o.s.
Class 4 / Dangerous When Wet / ERG 138
PPE: Level B minimum with full face SCBA; acid-resistant protective clothing required due to corrosive properties; avoid moisture contact on PPE
ISOLATION: ERG 138: Initial isolation 50m in all directions; protective action distance 100m for small spills, 300m for large spills during day, 800m at night; evacuate immediate area if fire involves this material
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 3131 — Water-reactive solid, corrosive, n.o.s.
Class: 4 | Placard: Dangerous When Wet | ERG Guide: 138
Appearance: Generic entry covering various solid materials that react with water and have corrosive properties. Physical appearance varies depending on specific chemical; typically solid form at room temperature with varying colors and no characteristic odor until wetted.
Water Reactivity: Reacts with water producing flammable gases and heat; may ignite spontaneously. Do NOT use water except in flooding quantities to cool containers. Keep material dry.
Extinguishing: Dry sand, dry chemical, soda ash, or lime only. NO WATER or water-based agents including foam.
PPE: Level B minimum with full face SCBA; acid-resistant protective clothing required due to corrosive properties; avoid moisture contact on PPE
Isolation: ERG 138: Initial isolation 50m in all directions; protective action distance 100m for small spills, 300m for large spills during day, 800m at night; evacuate immediate area if fire involves this material
— Key Hazards —
• Produce flammable gases on contact with water.
• May ignite on contact with water or moist air.
• Some react vigorously or explosively on contact with water.
— 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/3131 | Always use current ERG + SOP/SOGIC BRIEFING
Use for: Incident command briefing, staging area whiteboard, or pre-entry team brief. Full chemical + response details.
UN3131 Water-reactive solid, corrosive, n.o.s. Cls4 ERG138 | allfirefighter.com/hazmat/un/3131SMS / 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/3131
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Frequently Asked Questions about UN 3131
Produce flammable gases on contact with water. May ignite on contact with water or moist air. Some react vigorously or explosively on contact with water. May be ignited by heat, sparks or flames. May re-ignite after fire is extinguished. Some are transported in highly flammable liquids. Runoff may create fire or explosion hazard. Inhalation or contact with vapors, substance or decomposition products may cause severe injury or
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 full face SCBA; acid-resistant protective clothing required due to corrosive properties; avoid moisture contact on PPE
Water reactivity: Reacts with water producing flammable gases and heat; may ignite spontaneously. Do NOT use water except in flooding quantities to cool containers. Keep material dry.. Recommended extinguishing: Dry sand, dry chemical, soda ash, or lime only. NO WATER or water-based agents including foam..
ERG Guide 138 recommendation: ERG 138: Initial isolation 50m in all directions; protective action distance 100m for small spills, 300m for large spills during day, 800m at night; evacuate immediate area if fire involves this material
No. This is a training/quick-reference aid only. Always consult the current ERG Guide 138 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.