UN 3526 — Hydrogen selenide, adsorbed
Placard: Toxic Gas. ERG Guide 173. Training/quick-reference only — use current ERG + SOP/SOG for incident-specific actions.
UN 3526 is Hydrogen selenide, adsorbed, an extremely toxic adsorbed hydrogen selenide gas assigned to ERG Guide 173. Low-area vapor and selenium contamination matter.
Hazard overview: EXTREMELY TOXIC hydrogen selenide gas adsorbed on a porous solid; inhalation may be fatal. Gas can cause severe systemic toxicity; odor is not a reliable warning. Released gas is heavier than air and may collect in low or confined areas.
Response guidance: For UN 3526, isolate downwind/low areas, treat as a life-threatening gas release and use Level A/SCBA for entry. Verify exact gas with shipping papers and ERG 173.
Firefighter training notes: Training for UN 3526 should emphasize toxic-gas recognition, Zone A isolation, Level A/SCBA entry, air monitoring, source-control limits and decontamination. Use ERG 173, SDS and local SOP.
Regulatory context: Hydrogen selenide, adsorbed is regulated as a hazardous material for transport and emergency response. Storage, reporting, exposure, waste and incident-notification duties depend on quantity, package type, gas identity and jurisdiction; verify shipping papers, SDS and authority guidance.
Storage & handling: Hydrogen selenide, adsorbed should be stored in secured compatible adsorbed-gas packages away from heat, impact, corrosion, moisture where incompatible and unauthorized access, with ventilation and emergency planning.
UN 3526 Quick Details
Common Hazards of UN 3526
- EXTREMELY TOXIC hydrogen selenide gas adsorbed on a porous solid; inhalation may be fatal.
- Gas can cause severe systemic toxicity; odor is not a reliable warning.
- Released gas is heavier than air and may collect in low or confined areas.
- May burn or decompose in fire to selenium oxides and toxic smoke.
- Soluble gas can form acidic, selenium-contaminated solutions.
- Heating or package damage can release toxic gas from the adsorbent.
- Runoff or debris may carry toxic selenium contamination.
Chemical Identity & Physical Properties
Colorless gas with a foul, garlic-like or rotten horseradish odor. Adsorbed form is gas absorbed onto a solid carrier material in cylinders.
| Also known as | Hydrogen selenideSelenium hydrideSelenaneDihydrogen selenideH2Se |
| CAS Number | 7783-07-5 |
| Appearance | Colorless gas with a foul, garlic-like or rotten horseradish odor. Adsorbed form is gas absorbed onto a solid carrier material in cylinders. |
| Flash Point | Not applicable (gas) |
| Boiling Point | -41.3C (-42.3F) |
| Vapor Density | 2.8 (heavier than air) |
| Water Reactivity | Soluble in water forming acidic solution; no violent reaction |
Fireground Response Guidance — UN 3526
Extinguishing Media
PPE Requirements
Use Level A fully encapsulating chemical protective clothing with positive-pressure SCBA for entry. Zone A toxic gas requires maximum respiratory and skin protection.
Isolation & Evacuation
First Actions for a UN 3526 Incident
- Call 911 and the emergency response number on the shipping paper, if available.
- Keep unauthorized personnel away and establish incident command.
- Stay upwind and avoid low or poorly ventilated areas unless monitoring shows they are safe.
- Treat the release as a life-threatening inhalation hazard until the gas is identified and monitored.
- Do not handle leaking cylinders, adsorbed-gas packages or damaged gas articles without proper training and PPE.
- Ventilate only after monitoring and only if properly trained and equipped.
- Use ERG Guide 173, shipping papers, markings and air monitoring to set isolation, evacuation and entry decisions.
📋 Copy & Share Field Card
UN 3526 — Hydrogen selenide, adsorbedUse 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.