UN 2477 — Methyl isothiocyanate
Placard: Toxic. ERG Guide 131. Training/quick-reference only — use current ERG + SOP/SOG for incident-specific actions.
UN 2477 is Methyl isothiocyanate, a toxic flammable isothiocyanate assigned to ERG Guide 131. Vapor irritation, skin exposure and fire products require strict controls.
Hazard overview: TOXIC and FLAMMABLE isothiocyanate liquid; inhalation, ingestion or skin absorption may cause severe injury or death. Vapors irritate eyes, skin and respiratory tract and may act as a strong lachrymator. Vapors may ignite and form explosive mixtures with air.
Response guidance: For UN 2477, isolate the area, eliminate ignition sources, keep vapors out of drains and use SCBA. Select foam, dry chemical or CO2 based on SDS and contain contaminated runoff.
Firefighter training notes: Training for UN 2477 should emphasize vapor travel, sewer flashback, toxic/corrosive exposure, SCBA use, decontamination, runoff control and foam selection. Use ERG 131, SDS and local SOP.
Regulatory context: Methyl isothiocyanate 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: Methyl isothiocyanate should be stored in approved flammable/toxic or corrosive-liquid containers with ventilation, secondary containment and separation from heat, ignition sources, oxidizers and incompatible materials.
UN 2477 Quick Details
Common Hazards of UN 2477
- TOXIC and FLAMMABLE isothiocyanate liquid; inhalation, ingestion or skin absorption may cause severe injury or death.
- Vapors irritate eyes, skin and respiratory tract and may act as a strong lachrymator.
- Vapors may ignite and form explosive mixtures with air.
- Vapors are heavier than air and may collect in low or confined areas.
- Slow water decomposition can release toxic vapors; runoff may spread contamination.
- Fire may produce nitrogen oxides, sulfur oxides and other toxic gases.
- Containers may rupture or explode when heated.
Chemical Identity & Physical Properties
Colorless to pale yellow liquid with a pungent, irritating odor. May have a sharp, mustard-like or lachrymatory smell at room temperature.
| Also known as | MITCMethyl mustard oilIsothiocyanatomethaneMethylisothiocyanateMethanisothiocyanate |
| CAS Number | 556-61-6 |
| Appearance | Colorless to pale yellow liquid with a pungent, irritating odor. May have a sharp, mustard-like or lachrymatory smell at room temperature. |
| Flash Point | 32°C (90°F) |
| Boiling Point | 119°C (246°F) |
| Vapor Density | 2.5 (heavier than air) |
| Water Reactivity | Slowly decomposes in water; not violently reactive but produces toxic vapors |
Fireground Response Guidance — UN 2477
Extinguishing Media
PPE Requirements
Use positive-pressure SCBA for vapor, dust, mist, fire or confined-space exposure. Wear chemical-resistant gloves, boots, eye/face protection and protective clothing.
Isolation & Evacuation
First Actions for a UN 2477 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.
- Eliminate ignition sources if this can be done safely.
- Avoid breathing vapor, dust, mist, smoke or fumes and avoid skin or eye contact.
- Do not touch damaged containers or spilled material without proper training and PPE.
- Ventilate confined spaces only after monitoring and only if properly trained and equipped.
- Use ERG Guide 131, SDS, shipping papers and monitoring to set isolation, evacuation and entry decisions.
📋 Copy & Share Field Card
UN 2477 — Methyl isothiocyanateUse 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.