UN 2281 — Hexamethylene diisocyanate
Placard: Toxic. ERG Guide 156. Training/quick-reference only — use current ERG + SOP/SOG for incident-specific actions.
UN 2281 is Hexamethylene diisocyanate, a toxic diisocyanate liquid assigned to ERG Guide 156. Inhalation can cause severe respiratory sensitization and water reaction can build pressure.
Hazard overview: TOXIC isocyanate liquid; inhalation of vapor or aerosol may cause severe respiratory sensitization and injury. Combustible material: may burn but does not ignite readily. Reacts with water to release carbon dioxide, heat and polymeric solids; pressure buildup may occur in closed containers.
Response guidance: For a UN 2281 incident, verify the product with shipping papers, container markings, SDS and ERG Guide 156. Establish incident command, isolate the area, stay upwind, control ignition or incompatibility hazards, prevent runoff, dust or vapor spread and base entry/fire-control actions on monitoring and local SOP.
Firefighter training notes: Training for UN 2281 should emphasize isocyanate respiratory sensitization, water reaction/CO2 pressure, vapor monitoring, PPE, decontamination and runoff containment. Use ERG 156, SDS and local SOP.
Regulatory context: Hexamethylene diisocyanate is regulated as a hazardous material for transportation and emergency response purposes. Storage, workplace exposure, emergency planning, spill reporting, waste handling and environmental requirements vary by exact product, concentration, quantity and jurisdiction. Verify current requirements through shipping papers, SDS, container markings and applicable DOT, OSHA, EPA, NFPA, state or local authority guidance.
Storage & handling: Hexamethylene diisocyanate should be stored in tightly closed compatible containers in a cool, dry, ventilated area away from water/moisture, amines, alcohols, acids/bases where incompatible and heat. Prevent pressure buildup and humid air exposure.
UN 2281 Quick Details
Common Hazards of UN 2281
- TOXIC isocyanate liquid; inhalation of vapor or aerosol may cause severe respiratory sensitization and injury.
- Combustible material: may burn but does not ignite readily.
- Reacts with water to release carbon dioxide, heat and polymeric solids; pressure buildup may occur in closed containers.
- Skin and eye contact may cause irritation, burns or sensitization.
- Vapors may collect in low or confined areas depending on temperature and formulation.
- Fire may produce nitrogen oxides, isocyanate vapors, hydrogen cyanide-type products and other toxic gases.
- Runoff may spread toxic isocyanate contamination.
Chemical Identity & Physical Properties
Colorless to pale yellow liquid with a sharp, pungent odor. Viscous liquid at room temperature.
| Also known as | HDI1,6-Hexamethylene diisocyanateHexane-1,6-diisocyanate1,6-DiisocyanatohexaneDesmodur H |
| CAS Number | 822-06-0 |
| Appearance | Colorless to pale yellow liquid with a sharp, pungent odor. Viscous liquid at room temperature. |
| Flash Point | 140°C (284°F) |
| Boiling Point | 255°C (491°F) |
| Vapor Density | 6.9 (much heavier than air) |
| Water Reactivity | Reacts with water releasing carbon dioxide gas and heat, forming polyureas; reaction is exothermic but not violent |
Fireground Response Guidance — UN 2281
Extinguishing Media
PPE Requirements
Use positive-pressure SCBA for vapor, aerosol, fire or confined-space exposure. Wear chemical-resistant gloves, boots, eye/face protection and protective clothing selected from SDS; Level A may be needed for heavy vapor, moisture reaction or unknown concentrations.
Isolation & Evacuation
First Actions for a UN 2281 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.
- Avoid breathing vapors, dust, mist, smoke or fumes and avoid skin or eye contact.
- Avoid unnecessary water contact with released product unless incident command confirms a compatible control use.
- Do not touch damaged containers or spilled material unless properly trained and wearing appropriate protective equipment.
- Ventilate closed spaces before entering, but only if properly trained, equipped, monitored and authorized by incident command.
- Isolate the spill or release area and expand the perimeter for fire involvement, vapor spread, dust generation, water reaction or unknown product identity.
- Use ERG Guide 156, shipping papers, SDS, air monitoring and incident command for protective actions.
📋 Copy & Share Field Card
UN 2281 — Hexamethylene diisocyanateUse 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.