☣️ UN 3526 • CLASS 2
UN 3526 — Hydrogen selenide, adsorbed
Placard: Toxic Gas. ERG Guide 173. Training/quick-reference only — use current ERG + SOP/SOG for incident-specific actions.
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⚠️ This page is a quick-reference aid. For real incidents: stage upwind, isolate, deny entry, request Hazmat early, and consult the current ERG + SOP/SOG.
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UN 3526 Quick Details
UN 3526
Product name: Hydrogen selenide, adsorbed
DOT Class: 2
Placard type: Toxic Gas
ERG Guide: 173 (check current ERG)
Initial isolation: ERG 173: isolate 100m all directions initially; evacuate 800m downwind if large spill; toxic inhalation hazard zone
Common Hazards of UN 3526
- TOXIC; may be fatal if inhaled or absorbed through skin.
- Vapors may be irritating.
- Contact with gas may cause burns and injury.
- Fire will produce irritating, corrosive and/or toxic gases.
- Runoff from fire control or dilution water may cause environmental contamination.
- Some gases may burn or be ignited by heat, sparks or flames.
- May form explosive mixtures with air.
- Oxidizers may ignite combustibles (wood, paper, oil, clothing, etc.) but NOT readily due to low
Chemical Identity & Physical Properties
| 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 |
Chemical details are general reference only. Always verify with current SDS, ERG, and SOP/SOG.
Fireground Response Guidance — UN 3526
Extinguishing Media
Do not use water spray; inert gas blanketing or dry chemical if appropriate
PPE Requirements
⚠️ Level A required; full encapsulating chemical protective suit with SCBA; extremely toxic gas
Isolation & Evacuation
ERG 173: isolate 100m all directions initially; evacuate 800m downwind if large spill; toxic inhalation hazard zone
Always confirm protective actions with the current edition of the Emergency Response Guidebook (ERG Guide 173).
First Actions for a UN 3526 Incident
- CALL 911. Then call emergency response telephone number on shipping paper. If shipping paper
- Keep unauthorized personnel away.
- Stay upwind, uphill and/or upstream.
- Many gases are heavier than air and will spread along the ground and collect in low or confined areas
- Ventilate closed spaces before entering, but only if properly trained and equipped.
- Isolate spill or leak area for at least 100 meters (330 feet) in all directions.
- See Table 1 - Initial Isolation and Protective Action Distances.
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📋 Copy & Share Field Card
UN 3526 — Hydrogen selenide, adsorbedHAZMAT RADIO NOTE — UN 3526
Product: Hydrogen selenide, adsorbed
Class 2 / Toxic Gas / ERG 173
PPE: Level A required; full encapsulating chemical protective suit with SCBA; extremely toxic gas
ISOLATION: ERG 173: isolate 100m all directions initially; evacuate 800m downwind if large spill; toxic inhalation hazard zone
ACTION: Stage upwind · Isolate · Deny entry · Request HazmatRADIO
Use for: Quick radio or face-to-face size-up. Short, structured, field-ready.
=== IC HAZMAT BRIEFING ===
UN 3526 — Hydrogen selenide, adsorbed
Class: 2 | Placard: Toxic Gas | ERG Guide: 173
Appearance: Colorless gas with a foul, garlic-like or rotten horseradish odor. Adsorbed form is gas absorbed onto a solid carrier material in cylinders.
Water Reactivity: Soluble in water forming acidic solution; no violent reaction
Extinguishing: Do not use water spray; inert gas blanketing or dry chemical if appropriate
PPE: Level A required; full encapsulating chemical protective suit with SCBA; extremely toxic gas
Isolation: ERG 173: isolate 100m all directions initially; evacuate 800m downwind if large spill; toxic inhalation hazard zone
— Key Hazards —
• TOXIC; may be fatal if inhaled or absorbed through skin.
• Vapors may be irritating.
• Contact with gas may cause burns and injury.
— First Actions —
• CALL 911. Then call emergency response telephone number on shipping paper. If shipping paper
• Keep unauthorized personnel away.
• Stay upwind, uphill and/or upstream.
• Many gases are heavier than air and will spread along the ground and collect in low or confined areas
SOURCE: allfirefighter.com/hazmat/un/3526 | Always use current ERG + SOP/SOGIC BRIEFING
Use for: Incident command briefing, staging area whiteboard, or pre-entry team brief. Full chemical + response details.
UN3526 Hydrogen selenide, adsorbed Cls2 ERG173 | allfirefighter.com/hazmat/un/3526SMS / 160 CHAR
Use for: Quick text to command or incoming units. Fits in a single SMS. Includes link to full page.
⚠️ Quick-reference only. Always use current ERG + SOP/SOG for incident-specific actions.
Page: https://allfirefighter.com/hazmat/un/3526
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Frequently Asked Questions about UN 3526
TOXIC; may be fatal if inhaled or absorbed through skin. Vapors may be irritating. Contact with gas may cause burns and injury. Fire will produce irritating, corrosive and/or toxic gases. Runoff from fire control or dilution water may cause environmental contamination. Some gases may burn or be ignited by heat, sparks or flames. May form explosive mixtures with air. Oxidizers may ignite combustibles (wood, paper, oil, clothing, etc.) but NOT readily due to low
CALL 911. Then call emergency response telephone number on shipping paper. If shipping paper Keep unauthorized personnel away. Stay upwind, uphill and/or upstream.
Level A required; full encapsulating chemical protective suit with SCBA; extremely toxic gas
Water reactivity: Soluble in water forming acidic solution; no violent reaction. Recommended extinguishing: Do not use water spray; inert gas blanketing or dry chemical if appropriate.
ERG Guide 173 recommendation: ERG 173: isolate 100m all directions initially; evacuate 800m downwind if large spill; toxic inhalation hazard zone
No. This is a training/quick-reference aid only. Always consult the current ERG Guide 173 and your department SOP/SOG for incident-specific protective actions.
Sources (high level): DOT/PHMSA marking & class concepts + ERG usage principles.
This page does not reproduce ERG guide text—always consult the current ERG for incident-specific protective actions.