UN 3341 — Thiourea dioxide
Placard: Spontaneously Combustible. ERG Guide 135. Training/quick-reference only — use current ERG + SOP/SOG for incident-specific actions.
UN 3341 is Thiourea dioxide, a moisture-sensitive spontaneously combustible/reducing solid assigned to ERG Guide 135. Keep dry and avoid incompatible contamination.
Hazard overview: SPONTANEOUSLY COMBUSTIBLE/moisture-sensitive reducing solid; may heat or ignite when damp or contaminated. Dust can irritate eyes, skin and respiratory tract and may spread contamination. Heating can cause decomposition and release sulfur oxides, nitrogen oxides and irritating/toxic gases.
Response guidance: For UN 3341, isolate the area, keep material dry and use SCBA. Use compatible dry media only unless SDS/incident command confirms water compatibility.
Firefighter training notes: Training for UN 3341 should emphasize product verification, SCBA use, exposure control, decontamination, runoff containment and SDS/shipping paper review. Use ERG 135, SDS and local SOP.
Regulatory context: Thiourea dioxide is regulated as a hazardous material for transport and emergency response. Storage, reporting, exposure, waste and incident-notification duties depend on quantity, package type, formulation and jurisdiction; verify shipping papers, SDS and authority guidance.
Storage & handling: Thiourea dioxide should be stored dry in tightly closed compatible containers away from moisture, acids, oxidizers, heat and ignition sources. Keep compatible dry media available.
UN 3341 Quick Details
Common Hazards of UN 3341
- SPONTANEOUSLY COMBUSTIBLE/moisture-sensitive reducing solid; may heat or ignite when damp or contaminated.
- Dust can irritate eyes, skin and respiratory tract and may spread contamination.
- Heating can cause decomposition and release sulfur oxides, nitrogen oxides and irritating/toxic gases.
- Moisture, acids, oxidizers or heat may accelerate decomposition.
- May re-ignite if hot or contaminated residue remains.
- Runoff may carry reducing/contaminated residue.
- Keep material dry and verify SDS before applying water-based tactics.
Chemical Identity & Physical Properties
White to pale yellow crystalline powder. Odorless or slight sulfurous odor. Solid at room temperature.
| 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 |
Fireground Response Guidance — UN 3341
Extinguishing Media
PPE Requirements
Use positive-pressure SCBA for dust, smoke or fire. Wear chemical-resistant gloves, eye/face protection and protective clothing; keep PPE dry where required.
Isolation & Evacuation
First Actions for a UN 3341 Incident
- Call 911 and the emergency response number on the shipping paper, if available.
- Keep unauthorized personnel away and establish incident command.
- Stay upwind, uphill and upstream.
- Avoid breathing vapor, dust, gas, mist, smoke or aerosols and avoid skin or eye contact.
- Keep moisture, acids, oxidizers and incompatible materials away until specialist guidance confirms compatibility.
- Do not touch damaged containers, cylinders, packages or spilled material without proper training and PPE.
- Prevent contaminated liquid, dust, runoff, residue and decontamination waste from spreading.
- Ventilate confined spaces only after monitoring and only if properly trained and equipped.
- Use ERG Guide 135, SDS, shipping papers and monitoring to set isolation, evacuation and entry decisions.
📋 Copy & Share Field Card
UN 3341 — Thiourea dioxideUse 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.