☣️ UN 3399 • CLASS 4
UN 3399 — Organometallic substance, liquid, water-reactive, flammable
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 3399 Quick Details
UN 3399
Product name: Organometallic substance, liquid, water-reactive, flammable
DOT Class: 4
Placard type: Dangerous When Wet
ERG Guide: 138 (check current ERG)
Initial isolation: ERG 138: isolate spill 50m all directions; evacuate 800m downwind if tank/rail car involved in fire
Common Hazards of UN 3399
- 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 | Organometallic liquidWater-reactive organometallic compoundPyrophoric organometallic liquidMetal-organic compound liquid |
| Appearance | Varies by specific compound; typically colorless to pale yellow liquid with distinctive odor. Many are spontaneously flammable in air and react violently with moisture. |
| Flash Point | Not applicable (spontaneously flammable in air) |
| Boiling Point | Varies by compound (typically 50-150C range) |
| Vapor Density | Heavier than air (typically 2-5 times air density) |
| Water Reactivity | Reacts violently with water producing flammable gases; may ignite spontaneously on contact with moisture |
Chemical details are general reference only. Always verify with current SDS, ERG, and SOP/SOG.
Fireground Response Guidance — UN 3399
Extinguishing Media
Dry chemical, dry sand, dry powder only; do NOT use water, foam, or CO2
PPE Requirements
⚠️ Level A required; SCBA mandatory; chemically resistant suit; handle under inert atmosphere
Isolation & Evacuation
ERG 138: isolate spill 50m all directions; evacuate 800m downwind if tank/rail car involved in fire
Always confirm protective actions with the current edition of the Emergency Response Guidebook (ERG Guide 138).
First Actions for a UN 3399 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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📋 Copy & Share Field Card
UN 3399 — Organometallic substance, liquid, water-HAZMAT RADIO NOTE — UN 3399
Product: Organometallic substance, liquid, water-reactive, flammable
Class 4 / Dangerous When Wet / ERG 138
PPE: Level A required; SCBA mandatory; chemically resistant suit; handle under inert atmosphere
ISOLATION: ERG 138: isolate spill 50m all directions; evacuate 800m downwind if tank/rail car involved in fire
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 3399 — Organometallic substance, liquid, water-reactive, flammable
Class: 4 | Placard: Dangerous When Wet | ERG Guide: 138
Appearance: Varies by specific compound; typically colorless to pale yellow liquid with distinctive odor. Many are spontaneously flammable in air and react violently with moisture.
Water Reactivity: Reacts violently with water producing flammable gases; may ignite spontaneously on contact with moisture
Extinguishing: Dry chemical, dry sand, dry powder only; do NOT use water, foam, or CO2
PPE: Level A required; SCBA mandatory; chemically resistant suit; handle under inert atmosphere
Isolation: ERG 138: isolate spill 50m all directions; evacuate 800m downwind if tank/rail car involved in fire
— 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/3399 | Always use current ERG + SOP/SOGIC BRIEFING
Use for: Incident command briefing, staging area whiteboard, or pre-entry team brief. Full chemical + response details.
UN3399 Organometallic substance, liquid, water-reactive, flammable Cls4 ERG138 | allfirefighter.com/hazmat/un/3399SMS / 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/3399
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Frequently Asked Questions about UN 3399
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 A required; SCBA mandatory; chemically resistant suit; handle under inert atmosphere
Water reactivity: Reacts violently with water producing flammable gases; may ignite spontaneously on contact with moisture. Recommended extinguishing: Dry chemical, dry sand, dry powder only; do NOT use water, foam, or CO2.
ERG Guide 138 recommendation: ERG 138: isolate spill 50m all directions; evacuate 800m downwind if tank/rail car involved in fire
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.