UN 3500 — Chemical under pressure, n.o.s.
Placard: Non-Flammable Gas. ERG Guide 126. Training/quick-reference only — use current ERG + SOP/SOG for incident-specific actions.
UN 3500 is Chemical under pressure, n.o.s., a pressurized hazardous material assigned to ERG Guide 126. The exact contents should be verified from shipping papers and the SDS before close-range action.
Hazard overview: Primary hazards include toxic exposure, corrosive burns, fire or vapor ignition, container rupture. Chemical under pressure, n.o.s. may release irritating, toxic or corrosive vapors when heated, spilled or involved in fire, so avoid contact, inhalation and incompatible materials.
Response guidance: For a UN 3500 incident, establish incident command, isolate the area, stay upwind and uphill, keep unauthorized personnel away, verify shipping papers/SDS and follow ERG 126. Use extinguishing, cooling, containment and decontamination tactics only when compatible with the material and local SOP.
UN 3500 Quick Details
Common Hazards of UN 3500
- Some may burn but none ignite readily.
- Containers may explode when heated.
- Ruptured cylinders may rocket.
- Vapors may cause dizziness or asphyxiation without warning, especially when in closed or confined areas.
- Vapors from liquefied gas are initially heavier than air and spread along ground.
- Contact with gas or liquefied gas may cause burns, severe injury and/or frostbite.
- Fire may produce irritating, corrosive and/or toxic gases.
Chemical Identity & Physical Properties
Variable appearance depending on specific chemical; typically a liquid or gas under pressure in cylinders or aerosol containers at room temperature. May have various colors and odors depending on contents.
| Also known as | Chemical under pressure NOSCompressed chemicalPressurized chemical mixtureChemical aerosol |
| Appearance | Variable appearance depending on specific chemical; typically a liquid or gas under pressure in cylinders or aerosol containers at room temperature. May have various colors and odors depending on contents. |
| Flash Point | Variable depending on specific chemical; some may be flammable while others are non-flammable |
| Boiling Point | Variable depending on specific chemical and pressure conditions |
| Vapor Density | Variable depending on specific chemical; may be heavier or lighter than air |
| Water Reactivity | Variable depending on specific chemical; consult SDS for specific contents |
Fireground Response Guidance — UN 3500
Extinguishing Media
PPE Requirements
Level B minimum recommended; SCBA and chemical-resistant suit required; consult specific chemical contents for exact PPE requirements
Isolation & Evacuation
First Actions for a UN 3500 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 for at least 100 meters (330 feet) in all directions.
- Consider initial downwind evacuation for at least 500 meters (1/3 mile).
📋 Copy & Share Field Card
UN 3500 — Chemical under pressure, n.o.s.Use 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.