UN 1777 — Fluorosulphonic acid
Placard: Corrosive. ERG Guide 137. Training/quick-reference only — use current ERG + SOP/SOG for incident-specific actions.
UN 1777 is Fluorosulphonic acid, a corrosive hazardous material assigned to ERG Guide 137. Responders should verify the exact product with shipping papers, container markings and SDS before close action.
Hazard overview: UN 1777 presents corrosive exposure hazards and may create toxic/corrosive gases or runoff in fire or incompatible contact. Use ERG, SDS and incident command to set isolation, PPE and control actions.
Response guidance: For a UN 1777 incident, responders should verify the product with shipping papers, package markings, SDS and ERG Guide 137. 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 1777 should emphasize corrosive exposure routes, water or oxidizer incompatibility where applicable, air monitoring, PPE selection, decontamination and runoff containment. Use ERG 137, SDS and local SOP.
Regulatory context: Fluorosulphonic acid is regulated as a hazardous material for transportation and emergency response purposes. Transportation, workplace exposure, spill reporting, pesticide/waste handling where applicable, 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: Fluorosulphonic 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 1777 Quick Details
Common Hazards of UN 1777
- 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
Colorless to straw-colored fuming liquid with a pungent, irritating odor. Fumes in moist air due to high reactivity with water vapor.
| Also known as | Fluorosulfuric acidFluorosulfonic acidFluosulfonic acidFSO3H |
| CAS Number | 7789-21-1 |
| Appearance | Colorless to straw-colored fuming liquid with a pungent, irritating odor. Fumes in moist air due to high reactivity with water vapor. |
| Flash Point | Not applicable (non-flammable corrosive liquid) |
| Boiling Point | 163°C (325°F) |
| Vapor Density | 3.5 (heavier than air) |
| Water Reactivity | Reacts violently with water generating heat and toxic/corrosive hydrogen fluoride and sulfuric acid fumes. Do not use water directly on material. |
Fireground Response Guidance — UN 1777
Extinguishing Media
PPE Requirements
Use positive-pressure SCBA for vapor, mist, dust, fire or confined-space exposure. Chemical-resistant gloves, boots, eye/face protection and protective clothing should be selected from SDS.
Isolation & Evacuation
First Actions for a UN 1777 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.
- 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 137, shipping papers, SDS, air monitoring and incident command for protective actions.
📋 Copy & Share Field Card
UN 1777 — Fluorosulphonic 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.