☣️ UN 1923 • CLASS 4
Calcium hydrosulphite
Placard: Spontaneously Combustible. 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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Quick details
UN 1923
Class: 4
Placard type: Spontaneously Combustible
ERG: Guide 135 (check current ERG)
Isolation: ERG 135: isolate spill 25-50m all directions; if fire, isolate 800m and consider evacuation 500m downwind
Chemical & Response Details
| 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 |
| Extinguishing | Dry sand, dry chemical, soda ash; do not use water or foam |
| PPE | ⚠️ Level B minimum with SCBA; full chemical protective suit for large spills; avoid moisture contact |
| Isolation | ERG 135: isolate spill 25-50m all directions; if fire, isolate 800m and consider evacuation 500m downwind |
Chemical details are general reference only. Always verify with current SDS, ERG, and SOP/SOG.
Common hazards (high level)
- Flammable/combustible material.
- May ignite on contact with moist air or moisture.
- May burn rapidly with flare-burning effect.
- Some react vigorously or explosively on contact with water.
- Some may decompose explosively when heated or involved in a fire.
- May re-ignite after fire is extinguished.
- Runoff may create fire or explosion hazard.
- Containers may explode when heated.
First actions (field-minded)
- CALL 911. Then call emergency response telephone number on shipping paper. If shipping paper
- Stay upwind, uphill and/or upstream.
- Keep unauthorized personnel away.
- Isolate spill or leak area in all directions for at least 50 meters (150 feet) for liquids and at least 25 meters
- For highlighted materials: see Table 1 - Initial Isolation and Protective Action Distances.
- For non-highlighted materials: increase the immediate precautionary measure distance, in the downwind
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UN 1923 — Calcium hydrosulphite HAZMAT RADIO NOTE — UN 1923
Product: Calcium hydrosulphite
Class 4 / Spontaneously Combustible / ERG 135
PPE: Level B minimum with SCBA; full chemical protective suit for large spills; avoid moisture contact
ISOLATION: ERG 135: isolate spill 25-50m all directions; if fire, isolate 800m and consider evacuation 500m downwind
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 1923 — Calcium hydrosulphite
Class: 4 | Placard: Spontaneously Combustible | ERG Guide: 135
Appearance: White to light gray or beige crystalline powder or granules. May have a slight sulfurous odor. Solid at room temperature.
Water Reactivity: Reacts with water and moisture, generating heat and sulfur dioxide gas; can ignite spontaneously when wet
Extinguishing: Dry sand, dry chemical, soda ash; do not use water or foam
PPE: Level B minimum with SCBA; full chemical protective suit for large spills; avoid moisture contact
Isolation: ERG 135: isolate spill 25-50m all directions; if fire, isolate 800m and consider evacuation 500m downwind
— Key Hazards —
• Flammable/combustible material.
• May ignite on contact with moist air or moisture.
• May burn rapidly with flare-burning effect.
— First Actions —
• CALL 911. Then call emergency response telephone number on shipping paper. If shipping paper
• Stay upwind, uphill and/or upstream.
• Keep unauthorized personnel away.
• Isolate spill or leak area in all directions for at least 50 meters (150 feet) for liquids and at least 25 meters
SOURCE: allfirefighter.com/hazmat/un/1923 | Always use current ERG + SOP/SOGIC BRIEFING
Use for: Incident command briefing, staging area whiteboard, or pre-entry team brief. Full chemical + response details.
UN1923 Calcium hydrosulphite Cls4 ERG135 | ERG 135: isolate spill 25-50m all directions; if fire, isolate 800m and consider | allfirefighter.com/hazmat/un/1923SMS / 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/1923
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FAQ
Flammable/combustible material. May ignite on contact with moist air or moisture. May burn rapidly with flare-burning effect. Some react vigorously or explosively on contact with water. Some may decompose explosively when heated or involved in a fire. May re-ignite after fire is extinguished. Runoff may create fire or explosion hazard. Containers may explode when heated.
CALL 911. Then call emergency response telephone number on shipping paper. If shipping paper Stay upwind, uphill and/or upstream. Keep unauthorized personnel away.
Level B minimum with SCBA; full chemical protective suit for large spills; avoid moisture contact
No. This is a training/quick-reference aid only. Always consult the current ERG Guide 135 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.