UN 2202 — Hydrogen selenide, anhydrous
Placard: Toxic Gas. ERG Guide 117. Training/quick-reference only — use current ERG + SOP/SOG for incident-specific actions.
UN 2202 is Hydrogen selenide, anhydrous, an extremely toxic flammable gas assigned to ERG Guide 117. Odor fatigue can occur, so monitoring is essential.
Hazard overview: EXTREMELY TOXIC and FLAMMABLE gas; inhalation may be fatal at very low concentrations. Odor may be irritating or foul at first, but smell is not a reliable warning. Gas is heavier than air and may collect in low or confined areas.
Response guidance: For a UN 2202 incident, verify the product with shipping papers, container markings, SDS and ERG Guide 117. 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 2202 should emphasize toxic flammable gas behavior, source isolation, downwind monitoring, cylinder cooling, ignition control, Level A decisions and medical coordination. Use ERG 117, SDS and local SOP.
Regulatory context: Hydrogen selenide, anhydrous 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: Hydrogen selenide, anhydrous 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 2202 Quick Details
Common Hazards of UN 2202
- EXTREMELY TOXIC and FLAMMABLE gas; inhalation may be fatal at very low concentrations.
- Odor may be irritating or foul at first, but smell is not a reliable warning.
- Gas is heavier than air and may collect in low or confined areas.
- Contact with liquefied gas may cause frostbite and severe injury.
- Cylinders exposed to fire may vent toxic/flammable gas, rupture or rocket.
- Fire may produce toxic selenium oxides and other irritating/corrosive gases.
- Runoff and decontamination water may carry toxic selenium contamination.
Chemical Identity & Physical Properties
Colorless gas with a highly offensive odor resembling decayed horseradish or rotten eggs at low concentrations. Odor fatigue occurs rapidly, deadening the sense of smell.
| Also known as | Selenium hydrideDihydrogen selenideSelenaneHydrogen selenide gas |
| CAS Number | 7783-07-5 |
| Appearance | Colorless gas with a highly offensive odor resembling decayed horseradish or rotten eggs at low concentrations. Odor fatigue occurs rapidly, deadening the sense of smell. |
| Flash Point | Not applicable (flammable gas) |
| Boiling Point | -41.3C (-42.3F) |
| Vapor Density | 2.8 (heavier than air) |
| Water Reactivity | Reacts with water to form selenious acid; not violent but toxic products formed |
Fireground Response Guidance — UN 2202
Extinguishing Media
PPE Requirements
Use positive-pressure SCBA and fully encapsulating chemical protective clothing for close entry or unknown concentrations. Level A may be needed; protect against frostbite where liquefied gas contact is possible.
Isolation & Evacuation
First Actions for a UN 2202 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 117, shipping papers, SDS, air monitoring and incident command for protective actions.
📋 Copy & Share Field Card
UN 2202 — Hydrogen selenide, anhydrousUse 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.