UN 2879 — Selenium oxychloride
Placard: Corrosive. ERG Guide 157. Training/quick-reference only — use current ERG + SOP/SOG for incident-specific actions.
UN 2879 is Selenium oxychloride, a toxic corrosive moisture-reactive liquid assigned to ERG Guide 157. Water releases HCl and selenium dioxide fumes.
Hazard overview: TOXIC and CORROSIVE moisture-reactive liquid; vapor or liquid contact can cause severe injury. Reacts vigorously with water or moist air, releasing heat, hydrogen chloride and selenium dioxide fumes. Fumes are much heavier than air and may collect in low or confined areas.
Response guidance: For UN 2879, isolate downwind/low areas, use SCBA with chemical protection and control water contact/runoff. Cool containers from protection and follow SDS and ERG 157.
Firefighter training notes: Training for UN 2879 should emphasize exposure routes, SCBA use, vapor/dust monitoring, decontamination, runoff containment and SDS/package verification. Use ERG 157, SDS and local SOP.
Regulatory context: Selenium oxychloride is regulated as a hazardous material for transport and emergency response. Storage, reporting, exposure, waste and incident-notification duties depend on package type, quantity, formulation and jurisdiction; verify shipping papers, SDS or authority guidance.
Storage & handling: Selenium oxychloride should be stored in compatible corrosion-resistant containers/cylinders, segregated from water, moisture, fuels, reducing agents and unauthorized access, with ventilation and emergency planning.
UN 2879 Quick Details
Common Hazards of UN 2879
- TOXIC and CORROSIVE moisture-reactive liquid; vapor or liquid contact can cause severe injury.
- Reacts vigorously with water or moist air, releasing heat, hydrogen chloride and selenium dioxide fumes.
- Fumes are much heavier than air and may collect in low or confined areas.
- Non-flammable, but heating can produce toxic/corrosive selenium and chlorine-containing gases.
- Runoff may be acidic, selenium-contaminated, corrosive and toxic.
- Containers may rupture when heated or contaminated with water.
- Avoid direct water contact with released product.
Chemical Identity & Physical Properties
Colorless to pale yellow liquid with a pungent, irritating odor. Fumes in moist air due to hydrolysis.
| Also known as | Selenium oxydichlorideSeleninyl chlorideSelenious oxychlorideSelenium chloride oxide |
| CAS Number | 7791-23-3 |
| Appearance | Colorless to pale yellow liquid with a pungent, irritating odor. Fumes in moist air due to hydrolysis. |
| Flash Point | Not applicable (non-flammable liquid) |
| Boiling Point | 176C (349F) |
| Vapor Density | 7.0 (much heavier than air) |
| Water Reactivity | Reacts vigorously with water releasing toxic and corrosive hydrogen chloride and selenium dioxide fumes; generates heat |
Fireground Response Guidance — UN 2879
Extinguishing Media
PPE Requirements
Use positive-pressure SCBA and chemical-resistant protective clothing. Level A may be needed for heavy vapor, fuming, dust, splash risk or unknown concentrations.
Isolation & Evacuation
First Actions for a UN 2879 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, gas, mist, smoke or aerosols and avoid skin or eye contact.
- Keep water or moisture contact controlled because toxic/corrosive acids or fumes may form.
- Do not touch damaged containers or spilled material without proper training and PPE.
- Prevent contaminated liquid, dust, runoff and decontamination waste from spreading.
- Ventilate confined spaces only after monitoring and only if properly trained and equipped.
- Use ERG Guide 157, SDS, shipping papers and monitoring to set isolation, evacuation and entry decisions.
📋 Copy & Share Field Card
UN 2879 — Selenium oxychlorideUse 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.