☣️ UN 1421 • CLASS 4
UN 1421 — Alkali metal alloy, liquid, 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.
Alkali metal alloys, like UN 1421, are highly reactive and can ignite spontaneously when exposed to water or moist air. Handling these substances requires extreme caution and specialized equipment.
Hazard overview: UN 1421 can produce flammable gases when in contact with water, and may ignite on contact with water or moist air.
Response guidance: In the event of a spill, evacuate the area immediately and call for professional assistance. Use dry sand, dry salt, or soda ash to extinguish the fire.
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UN 1421 Quick Details
UN 1421
Product name: Alkali metal alloy, liquid, n.o.s.
DOT Class: 4
Placard type: Dangerous When Wet
ERG Guide: 138 (check current ERG)
Initial isolation: ERG 138: Isolate spill 50m all directions. If tank/container involved in fire, isolate 800m in all directions and evacuate.
Common Hazards of UN 1421
- 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
UN 1421 is a silvery-white or gray metallic liquid at room temperature with no characteristic odor.
| Also known as | Alkali metal alloy liquidLiquid alkali metal mixtureSodium-potassium alloy (NaK)Alkali metal eutectic alloy |
| Appearance | Silvery-white or gray metallic liquid at room temperature. No characteristic odor. Liquid alloy typically of sodium, potassium, or cesium mixtures. |
| Flash Point | Not applicable (pyrophoric material, ignites spontaneously on contact with air or moisture) |
| Boiling Point | Varies by composition; typically 700-900C (1292-1652F) |
| Vapor Density | Not applicable (liquid metal, negligible vapor pressure at ambient temperature) |
| Water Reactivity | Reacts violently and explosively with water, producing flammable hydrogen gas and heat. May ignite spontaneously. Never use water. |
Chemical details are general reference only. Always verify with current SDS, ERG, and SOP/SOG.
Fireground Response Guidance — UN 1421
Extinguishing Media
Dry sand, dry salt (NaCl), soda ash, graphite powder. NO water, foam, CO2, or halogenated agents.
PPE Requirements
⚠️ Level A required for spills; full encapsulation, SCBA. Face shield, rubber gloves, and fire-resistant clothing minimum for handling under inert atmosphere.
Level A protection is required for spills, including full encapsulation, SCBA, face shield, rubber gloves, and fire-resistant clothing.
Isolation & Evacuation
ERG 138: Isolate spill 50m all directions. If tank/container involved in fire, isolate 800m in all directions and evacuate.
Always confirm protective actions with the current edition of the Emergency Response Guidebook (ERG Guide 138).
First Actions for a UN 1421 Incident
- 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 1421 — Alkali metal alloy, liquid, n.o.s.HAZMAT RADIO NOTE — UN 1421
Product: Alkali metal alloy, liquid, n.o.s.
Class 4 / Dangerous When Wet / ERG 138
PPE: Level A required for spills; full encapsulation, SCBA. Face shield, rubber gloves, and fire-resistant clothing minimum for handling under inert atmosphere.
ISOLATION: ERG 138: Isolate spill 50m all directions. If tank/container involved in fire, isolate 800m in all directions and evacuate.
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 1421 — Alkali metal alloy, liquid, n.o.s.
Class: 4 | Placard: Dangerous When Wet | ERG Guide: 138
Appearance: Silvery-white or gray metallic liquid at room temperature. No characteristic odor. Liquid alloy typically of sodium, potassium, or cesium mixtures.
Water Reactivity: Reacts violently and explosively with water, producing flammable hydrogen gas and heat. May ignite spontaneously. Never use water.
Extinguishing: Dry sand, dry salt (NaCl), soda ash, graphite powder. NO water, foam, CO2, or halogenated agents.
PPE: Level A required for spills; full encapsulation, SCBA. Face shield, rubber gloves, and fire-resistant clothing minimum for handling under inert atmosphere.
Isolation: ERG 138: Isolate spill 50m all directions. If tank/container involved in fire, isolate 800m in all directions and evacuate.
— 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 —
• 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
SOURCE: allfirefighter.com/hazmat/un/1421 | Always use current ERG + SOP/SOGIC BRIEFING
Use for: Incident command briefing, staging area whiteboard, or pre-entry team brief.
UN1421 Alkali metal alloy, liquid, n.o.s. Cls4 ERG138 | allfirefighter.com/hazmat/un/1421SMS / 160 CHAR
Use for: Quick text to command or incoming units. Fits in a single SMS.
⚠️ Quick-reference only. Always use current ERG + SOP/SOG for incident-specific actions.
Page: https://allfirefighter.com/hazmat/un/alkali-metal-alloy-liquid-un-1421
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Frequently Asked Questions about UN 1421
Yes, UN 1421 can produce flammable gases on contact with water.
No, never use water to extinguish a UN 1421 fire.
Level A protection is required, including full encapsulation, SCBA, face shield, rubber gloves, and fire-resistant clothing.
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.