UN 1346 — Silicon powder, amorphous
Placard: Flammable Solid. ERG Guide 170. Training/quick-reference only — use current ERG + SOP/SOG for incident-specific actions.
UN 1346 is Silicon powder, amorphous, a Class 4 flammable metal material assigned to ERG Guide 170. Firefighters should think about dust ignition, intense metal fire, re-ignition and incompatible extinguishing agents.
Hazard overview: UN 1346 presents flammable metal and dust hazards. Fine particles or heated metal can ignite, burn intensely and may react dangerously with water or incompatible fire agents, especially if dry or dispersed.
Response guidance: For a UN 1346 incident, responders should verify the product with shipping papers, package markings, SDS and ERG Guide 170. Establish incident command, isolate the area, stay upwind, avoid unnecessary disturbance of powder or damaged packaging, and use only extinguishing agents compatible with the specific material.
Firefighter training notes: Training for UN 1346 should emphasize metal fire behavior, dust cloud prevention, incompatible extinguishing agents, re-ignition, dry-agent application and safe standoff. Common errors include using water or foam on burning metal, disturbing powder and underestimating metal oxide fumes. Use ERG 170, SDS and metal-fire SOP.
Regulatory context: Silicon powder, amorphous is regulated as a hazardous material for transportation and emergency response purposes. Transportation, workplace exposure, spill reporting, waste handling, storage and environmental requirements may vary by formulation, quantity and jurisdiction. Verify current requirements through shipping papers, SDS, facility documents and applicable DOT, OSHA, EPA, NFPA, state or local authority guidance.
Storage & handling: Silicon powder, amorphous should be stored in compatible containers away from heat, ignition sources, oxidizers, moisture where incompatible and physical damage. Prevent dust release, container damage and contact with incompatible extinguishing agents or water-reactive conditions as described in the SDS.
UN 1346 Quick Details
Common Hazards of UN 1346
- FLAMMABLE metal solid or powder; may be ignited by heat, sparks, friction or flames.
- Dusts or fine particles may burn rapidly or form explosive mixtures in air.
- Metal fires can burn with intense heat and may re-ignite after apparent extinguishment.
- Water or incompatible agents may react with hot or dry metal powder and generate flammable hydrogen.
- Metal oxide fumes from fire may be hazardous to breathe.
- Containers may rupture or explode when heated.
- Avoid creating dust clouds or spreading powder during response.
Chemical Identity & Physical Properties
Dark gray to black fine powder with no odor. Exists as a solid at room temperature in amorphous (non-crystalline) form.
| Also known as | Amorphous siliconSilicon dustSilicium powderNon-crystalline silicon |
| CAS Number | 7440-21-3 |
| Appearance | Dark gray to black fine powder with no odor. Exists as a solid at room temperature in amorphous (non-crystalline) form. |
| Flash Point | Not applicable (combustible solid, ignites at approximately 1414C/2577F) |
| Boiling Point | 2355C (4271F) |
| Vapor Density | Not applicable (solid) |
| Water Reactivity | May react with water, especially when hot or finely divided, releasing hydrogen gas |
Fireground Response Guidance — UN 1346
Extinguishing Media
PPE Requirements
Use positive-pressure SCBA for fire, smoke or dust exposure. Protective clothing, gloves and eye/face protection should follow SDS and metal-fire SOP; PPE does not protect against violent metal fire, dust explosion or container rupture hazards.
Isolation & Evacuation
First Actions for a UN 1346 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.
- Eliminate ignition sources if it is safe to do so.
- Do not create dust clouds or disturb spilled powder unless properly trained and equipped.
- Keep water, foam, CO2 and halogenated agents away from burning or reactive metal unless incident command confirms compatibility.
- Use dry Class D agents, dry sand or other compatible dry media when directed by incident command.
- Isolate the spill or fire area and expand the perimeter if metal powder is burning, dry or dispersed.
- Use ERG Guide 170, shipping papers, SDS and metal-fire SOP for protective actions and entry decisions.
📋 Copy & Share Field Card
UN 1346 — Silicon powder, amorphousUse 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.