UN 0226 — HMX; Octogen, wetted
Placard: Explosive 1.1D. ERG Guide 112. Training/quick-reference only — use current ERG + SOP/SOG for incident-specific actions.
UN 0226, known as HMX or Octogen, is a white crystalline high explosive supplied in a wetted state with water or alcohol to reduce its sensitivity to heat, shock, and friction. The wetted formulation stabilizes this extremely powerful explosive, but it remains capable of mass detonation if the wetting agent is lost or the material is mishandled.
Hazard overview: UN 0226 presents a Class 1.1D mass explosion hazard, meaning the entire load can detonate simultaneously, producing catastrophic blast overpressure and fragmentation over a wide area. HMX is highly sensitive to heat, shock, and friction, making any unwetted or dried-out material extremely dangerous and unpredictable.
Response guidance: Emergency responders must not attempt to fight a fire involving UN 0226 — the area should be evacuated immediately and the material allowed to burn from a safe distance, using water spray only if absolutely necessary and from maximum standoff range. Initial isolation of 500 meters in all directions is required, expanding to a 1-mile evacuation radius if containers are exposed to fire or if detonation is considered possible.
UN 0226 Quick Details
Common Hazards of UN 0226
- Mass explosion hazard — entire load may detonate simultaneously.
- Severe blast overpressure and fragmentation.
- Sensitive to heat, shock, and friction.
- Secondary fire and debris hazard.
Chemical Identity & Physical Properties
UN 0226 HMX is a white, odorless crystalline solid that is shipped wetted with water or alcohol to suppress its sensitivity, remaining stable only as long as adequate moisture is maintained.
| Also known as | OctogenCyclotetramethylenetetranitramine1,3,5,7-Tetranitro-1,3,5,7-tetraazacyclooctaneHMX wettedHigh Melting Explosive |
| CAS Number | 2691-41-0 |
| Appearance | White crystalline solid, odorless. Supplied wetted with water or alcohol to reduce sensitivity. Stable when properly wetted. |
| Flash Point | Not applicable (explosive solid, wetted formulation) |
| Boiling Point | Not applicable (decomposes at approximately 280C/536F) |
| Vapor Density | Not applicable (solid) |
| Water Reactivity | No significant reaction with water; wetting agent maintains stability |
Fireground Response Guidance — UN 0226
Extinguishing Media
PPE Requirements
Responders approaching UN 0226 must wear a minimum of Level B protection with SCBA and full blast-resistant protective equipment, and must never approach any material suspected of being unwetted or dried out.
Isolation & Evacuation
First Actions for a UN 0226 Incident
- CALL 911. Then call emergency response telephone number on shipping paper.
- Establish large isolation zone — minimum 500 meters in all directions.
- Stage upwind, uphill; limit personnel to essential responders only.
- Request Hazmat + law enforcement + additional resources immediately.
- Do not fight fire — evacuate and isolate; let burn if no life safety risk.
- Protect exposures only if safe and directed by command.
- Consult current ERG Guide 112 and follow SOP/SOG.
📋 Copy & Share Field Card
UN 0226 — HMX; Octogen, wettedUse 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.