UN 1561 — Arsenic trioxide
Placard: Toxic. ERG Guide 151. Training/quick-reference only — use current ERG + SOP/SOG for incident-specific actions.
UN 1561 is Arsenic trioxide, a toxic arsenic material assigned to ERG Guide 151. The key responder concern is preventing inhalation of dust or fumes and preventing contaminated runoff.
Hazard overview: UN 1561 presents arsenic dust, fume and ingestion hazards. Heating or fire can create toxic arsenic oxide fumes, and dry powder can contaminate clothing, equipment and surfaces.
Response guidance: For a UN 1561 incident, responders should verify the product with shipping papers, package markings, SDS and ERG Guide 151. Establish incident command, isolate the area, stay upwind, prevent dust or vapor exposure, control runoff and choose entry or cleanup actions based on monitoring, SDS and local SOP.
Firefighter training notes: Training for UN 1561 should emphasize arsenic dust/fume exposure, contamination control, SCBA use, runoff containment and decontamination. Common errors include treating nonflammable toxic solids as low risk and spreading dust during cleanup. Use ERG 151, SDS and local SOP.
Regulatory context: Arsenic trioxide is regulated as a toxic arsenic hazardous material. Transportation, workplace exposure, spill reporting, waste handling, storage and environmental requirements may vary by compound, concentration, quantity and jurisdiction. Verify current requirements through shipping papers, SDS, facility documents and applicable DOT, OSHA, EPA, NFPA, state or local authority guidance.
Storage & handling: Arsenic trioxide should be stored in tightly closed compatible containers in a secure, cool, dry, well-ventilated toxic-material area away from food, incompatible chemicals, heat and unauthorized access. Prevent dust release, leaks and contaminated runoff.
UN 1561 Quick Details
Common Hazards of UN 1561
- HIGHLY TOXIC arsenic material; may be fatal if inhaled, ingested or absorbed through skin.
- Dust or powder can create a serious inhalation and contamination hazard.
- Avoid skin contact and prevent dust from becoming airborne.
- Fire or heating may produce toxic arsenic oxide fumes.
- Runoff from fire control or spill control may pollute waterways.
- Containers may rupture or fail when heated.
- Specific toxicity and solubility depend on the exact arsenic compound.
Chemical Identity & Physical Properties
White, odorless crystalline powder or solid. Exists as amorphous or crystalline forms. Stable at room temperature.
| Also known as | Arsenous oxideArsenic(III) oxideArsenous acid anhydrideWhite arsenicArsenious oxide |
| CAS Number | 1327-53-3 |
| Appearance | White, odorless crystalline powder or solid. Exists as amorphous or crystalline forms. Stable at room temperature. |
| Flash Point | Not applicable (non-combustible solid) |
| Boiling Point | 465C (869F) - sublimes |
| Vapor Density | Not applicable (solid, but vapors heavier than air when heated) |
| Water Reactivity | Slightly soluble in water, no violent reaction but forms toxic solutions |
Fireground Response Guidance — UN 1561
Extinguishing Media
PPE Requirements
Use positive-pressure SCBA for dust, mist, fumes, fire or confined-space exposure. Chemical-resistant gloves, eye/face protection and protective clothing should be selected from SDS; avoid all skin contact and contaminated dust.
Isolation & Evacuation
First Actions for a UN 1561 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 vapors, fumes, dust or mist and avoid all skin or eye contact.
- Do not touch or walk through spilled material unless properly trained and wearing appropriate protective equipment.
- Avoid creating dust clouds; cover or contain dry material only using methods directed by SDS and incident command.
- Ventilate closed spaces before entering, but only if properly trained, equipped, monitored and authorized by incident command.
- Isolate the spill or leak area and expand the perimeter if vapor, dust, fire involvement or unknown concentration is present.
- Use ERG Guide 151, shipping papers, SDS, air monitoring and incident command for protective actions.
📋 Copy & Share Field Card
UN 1561 — Arsenic trioxideUse 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.