UN 1779 — Formic acid, with more than 85% acid
Placard: Corrosive. ERG Guide 153. Training/quick-reference only — use current ERG + SOP/SOG for incident-specific actions.
UN 1779 is Formic acid, with more than 85% acid, a Class 8 corrosive combustible acid assigned to ERG Guide 153. It can burn tissue, irritate the respiratory tract and generate heat when diluted.
Hazard overview: UN 1779 presents corrosive acid, combustible vapor, heat-on-dilution and hydrogen gas hazards with some metals. Fire may produce toxic carbon monoxide and corrosive runoff.
Response guidance: For a UN 1779 incident, responders should verify the product with shipping papers, package markings, SDS and ERG Guide 153. Establish incident command, isolate the area, stay upwind, prevent incompatible contact, control runoff and choose entry or fire-control actions based on monitoring, SDS and local SOP.
Firefighter training notes: Training for UN 1779 should emphasize corrosive exposure routes, water or oxidizer incompatibility where applicable, air monitoring, PPE selection, decontamination and runoff containment. Use ERG 153, SDS and local SOP.
Regulatory context: Formic acid, with more than 85% 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 concentration, formulation, 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: Formic acid, with more than 85% 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 1779 Quick Details
Common Hazards of UN 1779
- CORROSIVE and combustible acid liquid; skin, eye or respiratory contact may cause severe burns.
- Vapors may irritate eyes and respiratory tissue and can be heavier than air.
- Combustible liquid; vapors may ignite when heated.
- Dilution with water may generate heat and increase fuming.
- Corrosive liquid may react with some metals to release flammable hydrogen gas.
- Fire may produce irritating and toxic gases including carbon monoxide.
- Runoff may be acidic and corrosive.
Chemical Identity & Physical Properties
Colorless fuming liquid with a pungent, penetrating odor. Corrosive and miscible with water. Fumes in moist air.
| Also known as | Methanoic acidFormylic acidHydrogen carboxylic acidAminic acid |
| CAS Number | 64-18-6 |
| Appearance | Colorless fuming liquid with a pungent, penetrating odor. Corrosive and miscible with water. Fumes in moist air. |
| Flash Point | 69C (156F) closed cup |
| Boiling Point | 101C (214F) |
| Vapor Density | 1.6 (heavier than air) |
| Water Reactivity | Miscible with water; exothermic dilution generates heat but no violent reaction |
Fireground Response Guidance — UN 1779
Extinguishing Media
PPE Requirements
Use positive-pressure SCBA for vapor, mist, fire or confined-space exposure. Wear chemical-resistant gloves, boots, eye/face protection and protective clothing selected from SDS for corrosive liquid contact.
Isolation & Evacuation
First Actions for a UN 1779 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 or spray and avoid skin or eye contact.
- Eliminate ignition sources if safe and keep vapors or runoff out of drains, sewers and low areas.
- 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, water reaction 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 1779 — Formic acid, with more than 85% 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.