UN 1787 — Hydriodic acid
Placard: Corrosive. ERG Guide 154. Training/quick-reference only — use current ERG + SOP/SOG for incident-specific actions.
UN 1787 is Hydriodic acid, a Class 8 corrosive acid assigned to ERG Guide 154. It can release irritating acid fumes and cause severe burns to eyes, skin and respiratory tissue.
Hazard overview: UN 1787 presents corrosive liquid, acid fume, heat-on-dilution and acidic-runoff hazards. Contact with some metals may release flammable hydrogen gas, and vapors can accumulate in poorly ventilated areas.
Response guidance: For a UN 1787 incident, responders should verify the product with shipping papers, package markings, SDS and ERG Guide 154. 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 1787 should emphasize corrosive exposure routes, water or oxidizer incompatibility where applicable, air monitoring, PPE selection, decontamination and runoff containment. Use ERG 154, SDS and local SOP.
Regulatory context: Hydriodic 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: Hydriodic 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 1787 Quick Details
Common Hazards of UN 1787
- CORROSIVE acid solution; inhalation, ingestion or skin/eye contact may cause severe injury.
- Fumes may contain hydrogen iodide and can injure eyes and respiratory tissue.
- Dilution with water may generate heat and increase fuming.
- Contact with some metals may release flammable hydrogen gas.
- Fire may produce irritating, corrosive and/or toxic gases.
- Runoff may be strongly acidic and corrosive.
- Vapors may collect in poorly ventilated or low areas depending on concentration and conditions.
Chemical Identity & Physical Properties
Colorless to pale yellow aqueous solution with a pungent, acrid odor. Fumes strongly in moist air. Typically supplied as 47-57% solution in water.
| Also known as | Hydrogen iodide solutionHydroiodic acidHI solutionIodhydric acid |
| CAS Number | 10034-85-2 |
| Appearance | Colorless to pale yellow aqueous solution with a pungent, acrid odor. Fumes strongly in moist air. Typically supplied as 47-57% solution in water. |
| Flash Point | Not applicable (aqueous solution) |
| Boiling Point | 127C (261F) for azeotropic mixture |
| Vapor Density | 4.4 (heavier than air) |
| Water Reactivity | Miscible with water; generates heat on dilution |
Fireground Response Guidance — UN 1787
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 1787 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 154, shipping papers, SDS, air monitoring and incident command for protective actions.
📋 Copy & Share Field Card
UN 1787 — Hydriodic 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.