UN 3208 — Metallic substance, waterreactive, n.o.s.
Placard: Dangerous When Wet. ERG Guide 138. Training/quick-reference only — use current ERG + SOP/SOG for incident-specific actions.
UN 3208 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 3208 Quick Details
Common Hazards of UN 3208
- 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
Solid metallic powder, granules, or chunks; appearance varies widely by specific metal (gray, silvery, or dark); may be odorless or have metallic smell; typically shipped in sealed containers to prevent moisture contact.
| Also known as | Water-reactive metalMetal powder water-reactiveReactive metallic substancePyrophoric metal compound |
| Appearance | Solid metallic powder, granules, or chunks; appearance varies widely by specific metal (gray, silvery, or dark); may be odorless or have metallic smell; typically shipped in sealed containers to prevent moisture contact. |
| Flash Point | Not applicable (ignites spontaneously on contact with water) |
| Boiling Point | Not applicable (varies by specific metal constituent) |
| Vapor Density | Not applicable (solid material) |
| Water Reactivity | Reacts violently with water producing flammable hydrogen or other gases; may ignite spontaneously; DO NOT USE WATER |
Fireground Response Guidance — UN 3208
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 3208 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 3208 — Metallic substance, waterreactive, n.o.sUse 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.