UN 3209 — Metallic substance, waterreactive, self-heating, n.o.s.
Placard: Dangerous When Wet. ERG Guide 138. Training/quick-reference only — use current ERG + SOP/SOG for incident-specific actions.
UN 3209 covers metallic water-reactive material. It may be powder, granules or pieces, and exact composition determines the safest control method.
Hazard overview: The key danger is water contact. Moisture can create heat, flammable gas and ignition, especially with powders or self-heating materials.
Response guidance: Isolate the release, keep it dry and prevent runoff. Use dry sand, soda ash, dry limestone or approved dry chemical media; keep water and foam away from the product.
Firefighter training notes: Train crews to recognize dangerous-when-wet placards, keep product dry, deny entry to low areas, and avoid using hose streams on unknown reactive solids or liquids.
Regulatory context: Class 4 dangerous-when-wet entries require strict moisture control, compatible packaging and product-specific SDS verification during transport and storage.
Storage & handling: Store dry, tightly sealed and away from water, humidity, sprinklers, acids and incompatible extinguishing agents. Keep spill control media dry and dedicated.
UN 3209 Quick Details
Common Hazards of UN 3209
- Water-reactive metallic material can generate flammable hydrogen or other gases.
- Moisture or humid air may cause ignition, heat generation or violent reaction.
- Fine powders may burn rapidly and re-ignite after knockdown.
- Containers may rupture when heated or contaminated with water.
- Fire can produce metal oxides and irritating or toxic smoke depending on composition.
- Wet runoff can spread reaction and fire hazards.
- Exact metal or alloy must be verified before selecting extinguishing media.
Chemical Identity & Physical Properties
Metallic solid or powder, appearance varies by specific metal. May be gray, silver, or dark colored. Odorless in dry state.
| Also known as | Water-reactive metalSelf-heating metallic materialPyrophoric metal substance |
| Appearance | Metallic solid or powder, appearance varies by specific metal. May be gray, silver, or dark colored. Odorless in dry state. |
| Flash Point | Not applicable (reacts with water to produce flammable gas) |
| Boiling Point | Not applicable (solid metal, varies by specific substance) |
| Vapor Density | Not applicable (solid material) |
| Water Reactivity | Reacts with water producing flammable hydrogen or other gases; may ignite spontaneously on contact with moisture or humid air |
Fireground Response Guidance — UN 3209
Extinguishing Media
PPE Requirements
Use SCBA, face/eye protection and chemical-resistant protective clothing. Avoid carrying wet tools or applying wet absorbents near the release.
Isolation & Evacuation
First Actions for a UN 3209 Incident
- Call 911 and the emergency response number on the shipping paper, if available.
- Keep unauthorized personnel away and establish incident command before close approach.
- Stay upwind, uphill and upstream; avoid low areas where vapors or gases may collect.
- Avoid breathing vapors, dust, smoke or decomposition products and avoid skin or eye contact.
- Do not touch damaged containers or spilled material without appropriate PPE and monitoring.
- Ventilate confined spaces only if trained, equipped and authorized by incident command.
- Use ERG, SDS, shipping papers and atmospheric/radiation monitoring for final isolation and control decisions.
📋 Copy & Share Field Card
UN 3209 — Metallic substance, waterreactive, self-Use 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.