UN 1923 — Calcium hydrosulphite
Placard: Spontaneously Combustible. ERG Guide 135. Training/quick-reference only — use current ERG + SOP/SOG for incident-specific actions.
UN 1923 is Calcium hydrosulphite, a spontaneously combustible hydrosulfite/dithionite solid assigned to ERG Guide 135. Moisture can cause heat, sulfur dioxide release and ignition.
Hazard overview: UN 1923 presents spontaneous ignition, moisture reaction, sulfur dioxide, re-ignition and dry-agent hazards. Keep it dry and avoid water or foam on the product.
Response guidance: For a UN 1923 incident, responders should verify the product with shipping papers, package markings, SDS and ERG Guide 135. 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 1923 should emphasize moisture-triggered decomposition, sulfur dioxide release, spontaneous ignition, dry-agent selection and re-ignition checks. Use ERG 135, SDS and local SOP.
Regulatory context: Calcium 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: Calcium 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 1923 Quick Details
Common Hazards of UN 1923
- SPONTANEOUSLY COMBUSTIBLE dithionite/hydrosulfite solid; may ignite on contact with moist air or moisture.
- Reacts with water or moisture, releasing heat and sulfur dioxide gas.
- May burn rapidly and may re-ignite after apparent extinguishment.
- Some decomposition can become vigorous when heated, contaminated or confined.
- Fire may produce sulfur oxides and irritating/toxic smoke.
- Water or foam may worsen the reaction and spread contamination.
- Containers may rupture or explode when heated.
Chemical Identity & Physical Properties
White to light gray or beige crystalline powder or granules. May have a slight sulfurous odor. Solid at room temperature.
| Also known as | Calcium dithioniteCalcium hydrosulfiteCalcium sulfoxylateDithionous acid calcium salt |
| CAS Number | 10118-76-0 |
| Appearance | White to light gray or beige crystalline powder or granules. May have a slight sulfurous odor. Solid at room temperature. |
| Flash Point | Not applicable (spontaneously combustible solid) |
| Boiling Point | Not applicable (decomposes before boiling) |
| Vapor Density | Not applicable (solid) |
| Water Reactivity | Reacts with water and moisture, generating heat and sulfur dioxide gas; can ignite spontaneously when wet |
Fireground Response Guidance — UN 1923
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 1923 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.
- Keep water, foam and moisture away from released product unless incident command confirms a compatible control use.
- 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 135, shipping papers, SDS, air monitoring and incident command for protective actions.
📋 Copy & Share Field Card
UN 1923 — Calcium 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.