UN 2257 — Potassium
Placard: Dangerous When Wet. ERG Guide 138. Training/quick-reference only — use current ERG + SOP/SOG for incident-specific actions.
UN 2257 is Potassium, a dangerous-when-wet alkali metal assigned to ERG Guide 138. Water or moisture can produce hydrogen gas, caustic potassium hydroxide and ignition.
Hazard overview: DANGEROUS WHEN WET alkali metal; reacts violently with water or moist air. Water contact produces flammable hydrogen gas and corrosive potassium hydroxide. May ignite spontaneously on contact with moisture and may re-ignite after apparent extinguishment.
Response guidance: For a UN 2257 incident, verify the product with shipping papers, container markings, SDS and ERG Guide 138. Establish incident command, isolate the area, stay upwind, control ignition or incompatibility hazards, prevent runoff, dust or vapor spread and base entry/fire-control actions on monitoring and local SOP.
Firefighter training notes: Training for UN 2257 should emphasize dangerous-when-wet behavior, hydrogen generation, alkali-metal Class D tactics, no-water/no-CO2 rules, re-ignition and caustic runoff control. Use ERG 138, SDS and local SOP.
Regulatory context: Potassium is regulated as a hazardous material for transportation and emergency response purposes. Storage, workplace exposure, emergency planning, spill reporting, waste handling and environmental requirements vary by exact product, concentration, quantity and jurisdiction. Verify current requirements through shipping papers, SDS, container markings and applicable DOT, OSHA, EPA, NFPA, state or local authority guidance.
Storage & handling: Potassium should be stored under dry mineral oil, inert gas or other SDS-approved protection in sealed compatible containers away from water, moisture, oxidizers, acids, halogenated agents and ignition sources. Keep Class D media available.
UN 2257 Quick Details
Common Hazards of UN 2257
- DANGEROUS WHEN WET alkali metal; reacts violently with water or moist air.
- Water contact produces flammable hydrogen gas and corrosive potassium hydroxide.
- May ignite spontaneously on contact with moisture and may re-ignite after apparent extinguishment.
- Water, foam, CO2 and halogenated extinguishing agents can worsen the reaction.
- Molten or burning metal can splatter and cause severe burns.
- Runoff may create fire, explosion and caustic contamination hazards.
- Containers may rupture or fail when heated.
Chemical Identity & Physical Properties
Soft, silvery-white metal with a waxy appearance. Rapidly tarnishes in air forming a gray oxide coating. Highly reactive, must be stored under mineral oil or inert gas.
| Also known as | KaliumPotassium metalK |
| CAS Number | 7440-09-7 |
| Appearance | Soft, silvery-white metal with a waxy appearance. Rapidly tarnishes in air forming a gray oxide coating. Highly reactive, must be stored under mineral oil or inert gas. |
| Flash Point | Not applicable (pyrophoric metal) |
| Boiling Point | 759C (1398F) |
| Vapor Density | Not applicable (solid metal) |
| Water Reactivity | Reacts violently with water, producing flammable hydrogen gas and potassium hydroxide. May ignite spontaneously on contact with water or moist air. |
Fireground Response Guidance — UN 2257
Extinguishing Media
PPE Requirements
Use positive-pressure SCBA for smoke, fire or caustic aerosol exposure. Wear fire-resistant and chemical-resistant protection selected from SDS; protect against molten metal splash and exclude moisture.
Isolation & Evacuation
First Actions for a UN 2257 Incident
- CALL 911. Then call the emergency response telephone number on the shipping paper, if available.
- Keep unauthorized personnel away.
- Stay upwind, uphill and/or upstream.
- Avoid breathing vapors, dust, mist, smoke or fumes and avoid skin or eye contact.
- Keep water, foam, CO2, moisture and incompatible extinguishing agents away from the metal.
- Do not touch damaged containers or spilled material unless properly trained and wearing appropriate protective equipment.
- Ventilate closed spaces before entering, but only if properly trained, equipped, monitored and authorized by incident command.
- Isolate the spill or release area and expand the perimeter for fire involvement, vapor spread, dust generation, water reaction or unknown product identity.
- Use ERG Guide 138, shipping papers, SDS, air monitoring and incident command for protective actions.
📋 Copy & Share Field Card
UN 2257 — PotassiumUse for: Quick radio or face-to-face size-up. Short, structured, field-ready.
Use for: Incident command briefing, staging area whiteboard, or pre-entry team brief.
Use for: Quick text to command or incoming units. Fits in a single SMS.