UN 1931 — Zinc hydrosulphite
Placard: Miscellaneous. ERG Guide 171. Training/quick-reference only — use current ERG + SOP/SOG for incident-specific actions.
UN 1931 is Zinc hydrosulphite, a miscellaneous hydrosulfite solid assigned to ERG Guide 171. Moisture or heat can release sulfur dioxide and accelerate decomposition.
Hazard overview: UN 1931 presents sulfur dioxide release, heat generation, dust irritation and possible burning under fire conditions. Avoid large water application and control contaminated runoff.
Response guidance: For a UN 1931 incident, responders should verify the product with shipping papers, package markings, SDS and ERG Guide 171. Establish incident command, isolate the area, stay upwind, control ignition or incompatibility hazards, prevent runoff or vapor spread and choose entry/fire-control actions based on monitoring, SDS and local SOP.
Firefighter training notes: Training for UN 1931 should emphasize moisture-triggered decomposition, sulfur dioxide release, spontaneous ignition, dry-agent selection and re-ignition checks. Use ERG 171, SDS and local SOP.
Regulatory context: Zinc hydrosulphite is regulated as a hazardous material for transportation and emergency response purposes. Transportation, workplace exposure, spill reporting, waste handling, storage and environmental requirements may vary by formulation, 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: Zinc hydrosulphite should be stored dry in compatible sealed containers away from water, moisture, oxidizers, acids where incompatible, ignition sources and unauthorized access. Keep compatible dry extinguishing media available.
UN 1931 Quick Details
Common Hazards of UN 1931
- Miscellaneous hydrosulfite solid; may decompose with moisture or heat and release sulfur dioxide gas.
- May burn under fire conditions, although it may not ignite readily.
- Warm water or contamination can accelerate decomposition and heat generation.
- Dust may irritate eyes, skin and respiratory tissue.
- Fire may produce sulfur oxides and irritating/toxic smoke.
- Runoff may carry sulfite/dithionite contamination.
- Containers may rupture or fail when heated.
Chemical Identity & Physical Properties
White to grayish-white crystalline powder or granular solid. Slight sulfurous odor. Solid at room temperature.
| Also known as | Zinc dithioniteZinc hyposulfiteZinc sulfoxylateDithionous acid zinc salt |
| CAS Number | 7779-86-4 |
| Appearance | White to grayish-white crystalline powder or granular solid. Slight sulfurous odor. Solid at room temperature. |
| Flash Point | Not applicable (non-flammable solid) |
| Boiling Point | Not applicable (decomposes before boiling) |
| Vapor Density | Not applicable (solid) |
| Water Reactivity | Decomposes slowly in water releasing sulfur dioxide and heat; reaction accelerates with warm water |
Fireground Response Guidance — UN 1931
Extinguishing Media
PPE Requirements
Use positive-pressure SCBA for smoke, dust, sulfur dioxide/corrosive vapor or fire exposure. Wear chemical-resistant and fire-appropriate protection selected from SDS; avoid moisture contamination.
Isolation & Evacuation
First Actions for a UN 1931 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, mist, smoke or gas and avoid skin or eye contact.
- Do not touch or walk through spilled 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 leak area and expand the perimeter if vapor, dust, fire involvement, gas accumulation or unknown concentration is present.
- Use ERG Guide 171, shipping papers, SDS, air monitoring and incident command for protective actions.
📋 Copy & Share Field Card
UN 1931 — Zinc hydrosulphiteUse 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.