UN 2624 — Magnesium silicide
Placard: Dangerous When Wet. ERG Guide 138. Training/quick-reference only — use current ERG + SOP/SOG for incident-specific actions.
UN 2624 is Magnesium silicide, a dangerous-when-wet solid assigned to ERG Guide 138. Moisture can release flammable and toxic silane-type gases.
Hazard overview: DANGEROUS WHEN WET solid; reacts with water or moisture to release flammable and toxic silane-type gases. Generated gases may ignite spontaneously or form explosive mixtures with air. Dust or solid can ignite from heat, sparks, friction or moisture.
Response guidance: For UN 2624, isolate the area, exclude water/moisture and use SCBA. Use compatible dry media only, monitor for flammable/toxic gas and contain reactive runoff under ERG 138.
Firefighter training notes: Training for UN 2624 should emphasize dangerous-when-wet behavior, silane-type gas generation, no-water/no-foam tactics, dry media, monitoring and re-ignition control. Use ERG 138, SDS and local SOP.
Regulatory context: Magnesium silicide is regulated as a hazardous material for transport and emergency response. Storage, exposure, spill reporting, waste and fire-code duties depend on quantity, concentration and jurisdiction; verify shipping papers, SDS and local authority requirements.
Storage & handling: Magnesium silicide should be stored dry in sealed compatible containers away from water, moisture, acids, oxidizers and ignition sources. Keep compatible dry media available.
UN 2624 Quick Details
Common Hazards of UN 2624
- DANGEROUS WHEN WET solid; reacts with water or moisture to release flammable and toxic silane-type gases.
- Generated gases may ignite spontaneously or form explosive mixtures with air.
- Dust or solid can ignite from heat, sparks, friction or moisture.
- Water, foam and CO2 can worsen the reaction or spread burning material.
- Fire may produce magnesium oxide, silicon oxides and irritating/toxic smoke.
- Runoff may create fire, explosion and caustic contamination hazards.
- Containers may rupture or fail when heated or contaminated with moisture.
Chemical Identity & Physical Properties
Gray to black crystalline powder or solid. Odorless. Stable when dry but decomposes readily in moist conditions.
| Also known as | Magnesium siliconDimagnesium silicideMagnesium silicon alloy |
| CAS Number | 22831-39-6 |
| Appearance | Gray to black crystalline powder or solid. Odorless. Stable when dry but decomposes readily in moist conditions. |
| Flash Point | Not applicable (water-reactive solid) |
| Boiling Point | Not applicable (decomposes before boiling) |
| Vapor Density | Not applicable (solid) |
| Water Reactivity | Reacts vigorously with water producing flammable hydrogen and silane gases; may ignite spontaneously |
Fireground Response Guidance — UN 2624
Extinguishing Media
PPE Requirements
Use positive-pressure SCBA and dry compatible protective clothing. Protect against flammable/toxic gas generation, dust and reaction products; exclude moisture.
Isolation & Evacuation
First Actions for a UN 2624 Incident
- Call 911 and the emergency response number on the shipping paper, if available.
- Keep unauthorized personnel away and establish incident command.
- Stay upwind, uphill and upstream.
- Avoid breathing vapor, dust, gas, mist, smoke or fumes and avoid skin or eye contact.
- Do not touch damaged containers or spilled material without proper training and PPE.
- Keep water or moisture contact controlled when it may increase reaction, fuming or gas generation.
- Ventilate confined spaces only after monitoring and only if properly trained and equipped.
- Use ERG Guide 138, SDS, shipping papers and monitoring to set isolation, evacuation and entry decisions.
📋 Copy & Share Field Card
UN 2624 — Magnesium silicideUse 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.