UN 2204 — Carbonyl sulphide
Placard: Toxic Gas. ERG Guide 119. Training/quick-reference only — use current ERG + SOP/SOG for incident-specific actions.
UN 2204 is Carbonyl sulphide, a toxic flammable liquefied gas assigned to ERG Guide 119. It can collect in low areas and hydrolyze slowly to hydrogen sulfide.
Hazard overview: TOXIC and FLAMMABLE liquefied compressed gas; inhalation may cause serious injury or death. May form explosive mixtures with air and flash back from ignition sources. Gas is heavier than air and may collect in low or confined areas.
Response guidance: For a UN 2204 incident, verify the product with shipping papers, container markings, SDS and ERG Guide 119. Establish incident command, isolate the area, stay upwind, control ignition or incompatibility hazards, prevent runoff or vapor spread and base entry/fire-control actions on monitoring and local SOP.
Firefighter training notes: Training for UN 2204 should emphasize toxic flammable gas behavior, source isolation, downwind monitoring, cylinder cooling, ignition control, Level A decisions and medical coordination. Use ERG 119, SDS and local SOP.
Regulatory context: Carbonyl sulphide 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: Carbonyl sulphide containers should be secured in a cool, ventilated gas storage area away from heat, physical damage and incompatible materials. Toxic, flammable, oxidizing, corrosive or refrigerated gases require leak detection/ventilation and emergency planning according to SDS and local code.
UN 2204 Quick Details
Common Hazards of UN 2204
- TOXIC and FLAMMABLE liquefied compressed gas; inhalation may cause serious injury or death.
- May form explosive mixtures with air and flash back from ignition sources.
- Gas is heavier than air and may collect in low or confined areas.
- Hydrolyzes slowly with water to form hydrogen sulfide and carbon dioxide.
- Contact with liquefied gas may cause frostbite.
- Cylinders exposed to fire may vent, rupture or rocket.
- Fire may produce sulfur oxides, carbon monoxide and other toxic gases.
Chemical Identity & Physical Properties
Colorless gas with a faint sulfide or rotten egg odor at high concentrations. Shipped as a liquefied compressed gas.
| Also known as | Carbon oxide sulfideCarbon oxysulfideCOSCarbonyl sulfide |
| CAS Number | 463-58-1 |
| Appearance | Colorless gas with a faint sulfide or rotten egg odor at high concentrations. Shipped as a liquefied compressed gas. |
| Flash Point | Not applicable (gas) |
| Boiling Point | -50C (-58F) |
| Vapor Density | 2.1 (heavier than air) |
| Water Reactivity | Slowly hydrolyzes in water to form hydrogen sulfide and carbon dioxide |
Fireground Response Guidance — UN 2204
Extinguishing Media
PPE Requirements
Use positive-pressure SCBA for leak, vapor, fire or confined-space exposure. Chemical protective clothing and insulated gloves may be needed for liquefied gas contact.
Isolation & Evacuation
First Actions for a UN 2204 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 gas, vapor, dust, mist, smoke or fumes and avoid skin or eye contact.
- Eliminate ignition sources if safe and treat the release as both toxic and flammable.
- Do not touch damaged containers or spilled/released 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/gas spread, cylinder heating, oxidizer reaction or unknown product identity.
- Use ERG Guide 119, shipping papers, SDS, air monitoring and incident command for protective actions.
📋 Copy & Share Field Card
UN 2204 — Carbonyl sulphideUse 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.