UN 1250 — Methyltrichlorosilane
Placard: Flammable. ERG Guide 155. Training/quick-reference only — use current ERG + SOP/SOG for incident-specific actions.
UN 1250 is Methyltrichlorosilane, a flammable water-reactive corrosive liquid assigned to ERG Guide 155. It fumes in moist air and can release corrosive hydrogen chloride when exposed to water.
Hazard overview: UN 1250 presents flammable vapor, corrosive fume and water-reactivity hazards. Water or moisture can generate heat and dense acid fumes, while vapors may travel to ignition sources and flash back.
Response guidance: For a UN 1250 incident, responders should confirm the product using shipping papers, container markings, SDS and ERG Guide 155. Establish incident command, isolate the area, stay upwind and uphill, remove ignition sources when safe, keep vapors or runoff out of sewers and use compatible fire-control agents from a protected position.
Firefighter training notes: Training for UN 1250 should emphasize dangerous-when-wet behavior, flammable gas generation, corrosive fumes, dry-agent selection and runoff control. Common errors include applying water or foam directly, entering without SCBA and ignoring re-ignition after apparent knockdown. Use ERG 155, SDS and hazmat SOP.
Regulatory context: Methyltrichlorosilane 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: Methyltrichlorosilane should be stored in tightly closed compatible containers in a cool, dry, well-ventilated area away from water, moisture, heat, ignition sources, oxidizers and incompatible materials. Protect containers from corrosion, impact and unauthorized access, with dry spill-control materials available where required.
UN 1250 Quick Details
Common Hazards of UN 1250
- HIGHLY FLAMMABLE and WATER-REACTIVE; vapors may form explosive mixtures with air.
- Reacts with water or moisture to release heat and corrosive hydrogen chloride fumes.
- Vapors are heavier than air and may travel to ignition sources and flash back.
- Liquid and fumes are corrosive to eyes, skin and respiratory tissue.
- Fire may produce irritating, corrosive and/or toxic gases.
- Runoff or water contact may spread corrosive contamination.
- Containers may rupture or explode when heated or contaminated with water.
Chemical Identity & Physical Properties
Colorless to pale yellow fuming liquid with a pungent, acrid odor. Fumes in moist air due to reaction with atmospheric moisture.
| Also known as | TrichloromethylsilaneMethyl trichlorosilaneSilane, trichloromethyl-Methylsilicon trichloride |
| CAS Number | 75-79-6 |
| Appearance | Colorless to pale yellow fuming liquid with a pungent, acrid odor. Fumes in moist air due to reaction with atmospheric moisture. |
| Flash Point | -9C (15F) |
| Boiling Point | 66C (151F) |
| Vapor Density | 5.2 (heavier than air) |
| Water Reactivity | Reacts violently with water producing heat, hydrogen chloride fumes, and flammable hydrogen gas. Keep away from water. |
Fireground Response Guidance — UN 1250
Extinguishing Media
PPE Requirements
Use positive-pressure SCBA for vapor, fire or confined-space exposure. Chemical-resistant protective clothing, gloves, boots and eye/face protection should be selected from SDS and incident command because fumes and liquid may be corrosive, toxic and water-reactive.
Isolation & Evacuation
First Actions for a UN 1250 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 touch spilled material or damaged containers unless properly trained and equipped.
- Keep water, foam and moisture away from the released material unless incident command confirms a compatible cooling or control use.
- Ventilate closed spaces before entering, but only if properly trained, equipped and authorized by incident command.
- Isolate the spill or leak area for at least 50 meters (150 feet) in all directions.
- For large spills, fire involvement or violent reaction, expand isolation and consider downwind evacuation based on monitoring and incident command.
- Use ERG Guide 155, shipping papers, SDS and local SOP for protective actions and entry decisions.
📋 Copy & Share Field Card
UN 1250 — MethyltrichlorosilaneUse 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.