UN 1940 — Thioglycolic acid
Placard: Corrosive. ERG Guide 153. Training/quick-reference only — use current ERG + SOP/SOG for incident-specific actions.
UN 1940 is Thioglycolic acid, a hazardous material assigned to ERG Guide 153. Responders should verify the exact product with shipping papers, package markings and SDS before close action.
Hazard overview: UN 1940 presents hazards that depend on formulation, packaging and incident conditions. Use ERG, SDS and incident command to set isolation, PPE and control actions.
Response guidance: For a UN 1940 incident, responders should verify the product with shipping papers, package markings, SDS and ERG Guide 153. 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 1940 should emphasize exposure routes, air monitoring, PPE selection, decontamination, runoff containment and ERG/SDS verification. Use ERG 153, SDS and local SOP.
Regulatory context: Thioglycolic acid 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: Thioglycolic acid should be stored in tightly closed compatible containers in a secure, cool, dry, well-ventilated hazardous-material area according to SDS and local procedures.
UN 1940 Quick Details
Common Hazards of UN 1940
- CORROSIVE material; inhalation, ingestion or skin/eye contact may cause severe injury.
- Fire may produce irritating, corrosive and/or toxic gases.
- Runoff may be corrosive and may pollute waterways.
- Containers may rupture or fail when heated.
- Specific hazards depend on the exact product, concentration and SDS.
Chemical Identity & Physical Properties
Clear to slightly yellow liquid with a strong, unpleasant sulfur-like or rotten egg odor. Corrosive and toxic organic acid.
| Also known as | Mercaptoacetic acid2-Mercaptoacetic acidTGAThioglycollic acid2-Sulfanylacetic acid |
| CAS Number | 68-11-1 |
| Appearance | Clear to slightly yellow liquid with a strong, unpleasant sulfur-like or rotten egg odor. Corrosive and toxic organic acid. |
| Flash Point | 129C (264F) |
| Boiling Point | 123C (253F) at 29 mmHg; decomposes at higher temperatures |
| Vapor Density | 3.2 (heavier than air) |
| Water Reactivity | Soluble in water; no violent reaction but solution is corrosive and toxic |
Fireground Response Guidance — UN 1940
Extinguishing Media
PPE Requirements
Use protective equipment selected from SDS, monitoring results and incident command.
Isolation & Evacuation
First Actions for a UN 1940 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 153, shipping papers, SDS, air monitoring and incident command for protective actions.
📋 Copy & Share Field Card
UN 1940 — Thioglycolic acidUse 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.