☣️ UN 3341 • CLASS 4
Thiourea dioxide
Placard: Spontaneously Combustible. Training/quick-reference only — use current ERG + SOP/SOG for incident-specific actions.
🚒☣️
⚠️ 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 3341
Class: 4
Placard type: Spontaneously Combustible
ERG: Guide 135 (check current ERG)
Isolation: ERG 135: isolate spill/leak area immediately 25-50m in all directions; evacuate 800m downwind if fire; keep material dry
Chemical & Response Details
| Also known as | Formamidine sulfinic acidThioxTDOAminoiminomethanesulfinic acid |
| CAS Number | 1758-73-2 |
| Appearance | White to pale yellow crystalline powder. Odorless or slight sulfurous odor. Solid at room temperature. |
| Flash Point | Not applicable (combustible solid, no traditional flash point) |
| Boiling Point | Not applicable (decomposes before boiling at approximately 126C/259F) |
| Vapor Density | Not applicable (solid) |
| Water Reactivity | Reacts with moisture and moist air; may ignite spontaneously when wet |
| Extinguishing | Dry chemical, dry sand, soda ash; avoid water-based agents due to moisture sensitivity |
| PPE | ⚠️ Level B minimum; SCBA required; chemical-resistant gloves and protective clothing to prevent moisture contact |
| Isolation | ERG 135: isolate spill/leak area immediately 25-50m in all directions; evacuate 800m downwind if fire; keep material dry |
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 3341 — Thiourea dioxide HAZMAT RADIO NOTE — UN 3341
Product: Thiourea dioxide
Class 4 / Spontaneously Combustible / ERG 135
PPE: Level B minimum; SCBA required; chemical-resistant gloves and protective clothing to prevent moisture contact
ISOLATION: ERG 135: isolate spill/leak area immediately 25-50m in all directions; evacuate 800m downwind if fire; keep material dry
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 3341 — Thiourea dioxide
Class: 4 | Placard: Spontaneously Combustible | ERG Guide: 135
Appearance: White to pale yellow crystalline powder. Odorless or slight sulfurous odor. Solid at room temperature.
Water Reactivity: Reacts with moisture and moist air; may ignite spontaneously when wet
Extinguishing: Dry chemical, dry sand, soda ash; avoid water-based agents due to moisture sensitivity
PPE: Level B minimum; SCBA required; chemical-resistant gloves and protective clothing to prevent moisture contact
Isolation: ERG 135: isolate spill/leak area immediately 25-50m in all directions; evacuate 800m downwind if fire; keep material dry
— 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/3341 | Always use current ERG + SOP/SOGIC BRIEFING
Use for: Incident command briefing, staging area whiteboard, or pre-entry team brief. Full chemical + response details.
UN3341 Thiourea dioxide Cls4 ERG135 | ERG 135: isolate spill/leak area immediately 25-50m in all directions; evacuate | allfirefighter.com/hazmat/un/3341SMS / 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/3341
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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; SCBA required; chemical-resistant gloves and protective clothing to prevent 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.