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 At a Glance
UN 3526 (Hydrogen selenide, adsorbed) is listed as DOT Class 2 Toxic Gas and is assigned to ERG Guide 173. Use this page to review placard data, common hazards, PPE notes, isolation context, first actions, and related UN numbers.
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.