UN 2644 — Methyl iodide
Placard: Toxic. ERG Guide 151. Training/quick-reference only — use current ERG + SOP/SOG for incident-specific actions.
UN 2644 is Methyl iodide, a highly toxic dense volatile liquid assigned to ERG Guide 151. Low-area vapor and skin exposure require strict control.
Hazard overview: HIGHLY TOXIC dense volatile liquid; inhalation, ingestion or skin absorption may cause severe injury. Vapors are much heavier than air and can collect in low or confined areas. Liquid is denser than water and may sink or form a separate layer, spreading contamination.
Response guidance: For UN 2644, isolate the area, avoid skin contact and use SCBA where dust, vapor, mist or fire is present. Prevent spread of contaminated runoff, cool containers from protection and verify controls with SDS and ERG 151.
Firefighter training notes: Training for UN 2644 should emphasize toxic exposure routes, skin absorption, SCBA use, dust/vapor control, decontamination, runoff containment and SDS verification. Use ERG 151, SDS and local SOP.
Regulatory context: Methyl iodide 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 iodide should be stored in tightly closed compatible containers with ventilation, secondary containment, restricted access and separation from heat, oxidizers and incompatible materials.
UN 2644 Quick Details
Common Hazards of UN 2644
- HIGHLY TOXIC dense volatile liquid; inhalation, ingestion or skin absorption may cause severe injury.
- Vapors are much heavier than air and can collect in low or confined areas.
- Liquid is denser than water and may sink or form a separate layer, spreading contamination.
- Non-flammable liquid, but heating or fire may produce hydrogen iodide and iodine-containing toxic fumes.
- Turns darker on light exposure; decomposition products may increase irritation hazards.
- Runoff may carry toxic iodinated contamination.
- Avoid all skin contact and vapor exposure.
Chemical Identity & Physical Properties
Colorless to pale yellow liquid with a characteristic sweet, ether-like odor. Density greater than water. Turns brown on exposure to light.
| Also known as | IodomethaneMonoiodomethaneHalon 10001MeI |
| CAS Number | 74-88-4 |
| Appearance | Colorless to pale yellow liquid with a characteristic sweet, ether-like odor. Density greater than water. Turns brown on exposure to light. |
| Flash Point | Not applicable (non-flammable liquid) |
| Boiling Point | 42.5C (108.5F) |
| Vapor Density | 4.9 (much heavier than air) |
| Water Reactivity | Slightly soluble in water; undergoes slow hydrolysis but no vigorous reaction |
Fireground Response Guidance — UN 2644
Extinguishing Media
PPE Requirements
Use positive-pressure SCBA and full chemical protective clothing. Level A may be needed for heavy vapor, dust, splash risk or unknown concentrations; prevent all skin contact.
Isolation & Evacuation
First Actions for a UN 2644 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, mist, smoke or fumes and avoid skin or eye contact.
- Do not touch damaged containers or spilled material without proper training and PPE.
- Prevent contaminated dust, liquid, runoff and decontamination waste from spreading.
- Ventilate confined spaces only after monitoring and only if properly trained and equipped.
- Use ERG Guide 151, SDS, shipping papers and monitoring to set isolation, evacuation and entry decisions.
📋 Copy & Share Field Card
UN 2644 — Methyl iodideUse 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.