UN 1238 — Methyl chloroformate
Placard: Toxic. ERG Guide 155. Training/quick-reference only — use current ERG + SOP/SOG for incident-specific actions.
Methyl chloroformate is a colorless liquid with a pungent, irritating odor and is highly flammable. It can be easily ignited by heat, sparks, or flames, causing a fire or explosion.
Hazard overview: Methyl chloroformate is highly flammable and vapors form explosive mixtures with air, posing a significant risk of fire or explosion. The substance is also toxic and can cause severe health effects, including respiratory problems and skin irritation.
Response guidance: In case of a methyl chloroformate spill, evacuate the area immediately and isolate the spill to prevent further damage. Emergency responders should wear Level A or B protective gear, including full-face SCBA, to minimize exposure to the substance.
UN 1238 Quick Details
Common Hazards of UN 1238
- HIGHLY FLAMMABLE: Will be easily ignited by heat, sparks or flames.
- Vapors form explosive mixtures with air: indoors, outdoors and sewers explosion hazards.
- Most vapors are heavier than air. They will spread along the ground and collect in low or confined areas
- Vapors may travel to source of ignition and flash back.
- Those substances designated with a (P) may polymerize explosively when heated or involved in a fire.
- Substance will react with water (some violently) releasing flammable, toxic or corrosive gases and runoff.
- Corrosives in contact with metals may evolve flammable hydrogen gas.
- Containers may explode when heated or if contaminated with water.
Chemical Identity & Physical Properties
Methyl chloroformate is a colorless liquid with a pungent, irritating odor and is denser than water and volatile at room temperature.
| Also known as | Chloromethyl formateFormic acid chloromethyl esterMethyl chlorocarbonateMethylchloroformateMCF |
| CAS Number | 79-22-1 |
| Appearance | Colorless liquid with a pungent, irritating odor. Denser than water and volatile at room temperature. |
| Flash Point | 12°C (54°F) |
| Boiling Point | 71°C (160°F) |
| Vapor Density | 3.3 (heavier than air) |
| Water Reactivity | Reacts slowly with water, releasing HCl and CO2; avoid direct water contact, use water spray carefully |
Fireground Response Guidance — UN 1238
Extinguishing Media
PPE Requirements
Emergency responders should wear Level A or B minimum protective gear, including full-face SCBA, to minimize exposure to methyl chloroformate.
Isolation & Evacuation
First Actions for a UN 1238 Incident
- Keep unauthorized personnel away.
- Stay upwind, uphill and/or upstream.
- Ventilate closed spaces before entering, but only if properly trained and equipped.
- Isolate spill or leak area in all directions for at least 50 meters (150 feet) for liquids and at least 25 meters
- For highlighted materials: see Table 1 - Initial Isolation and Protective Action Distances.
- For non-highlighted materials: increase the immediate precautionary measure distance, in the downwind
📋 Copy & Share Field Card
UN 1238 — Methyl chloroformateUse 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.