UN 2197 — Hydrogen iodide, anhydrous
Placard: Toxic Gas. ERG Guide 125. Training/quick-reference only — use current ERG + SOP/SOG for incident-specific actions.
UN 2197 is Hydrogen iodide, anhydrous, a toxic corrosive anhydrous hydrogen halide gas assigned to ERG Guide 125. Moisture creates strong acid mist and corrosive runoff.
Hazard overview: TOXIC and CORROSIVE anhydrous hydrogen iodide gas; inhalation may be fatal. Fumes in moist air and dissolves in water to form corrosive hydriodic acid with heat. Gas is much heavier than air and may collect in low or confined areas.
Response guidance: For a UN 2197 incident, verify the product with shipping papers, container markings, SDS and ERG Guide 125. Establish incident command, isolate the area, stay upwind, control ignition or incompatibility hazards, prevent runoff or vapor spread and base entry/fire-control actions on monitoring and local SOP.
Firefighter training notes: Training for UN 2197 should emphasize toxic/corrosive gas isolation, moisture or fluoride acid formation, air monitoring, Level A entry decisions, decontamination and downwind protection. Use ERG 125, SDS and local SOP.
Regulatory context: Hydrogen iodide, anhydrous is regulated as a hazardous material for transportation and emergency response purposes. Storage, workplace exposure, emergency planning, spill reporting, waste handling and environmental requirements vary by exact product, concentration, quantity and jurisdiction. Verify current requirements through shipping papers, SDS, container markings and applicable DOT, OSHA, EPA, NFPA, state or local authority guidance.
Storage & handling: Hydrogen iodide, anhydrous containers should be secured in a cool, ventilated gas storage area away from heat, physical damage and incompatible materials. Toxic, flammable, oxidizing, corrosive or refrigerated gases require leak detection/ventilation and emergency planning according to SDS and local code.
UN 2197 Quick Details
Common Hazards of UN 2197
- TOXIC and CORROSIVE anhydrous hydrogen iodide gas; inhalation may be fatal.
- Fumes in moist air and dissolves in water to form corrosive hydriodic acid with heat.
- Gas is much heavier than air and may collect in low or confined areas.
- Contact with liquefied gas may cause frostbite and severe chemical burns.
- Containers may rupture or rocket when heated.
- Fire may produce irritating, corrosive and/or toxic gases.
- Runoff may become strongly acidic and corrosive.
Chemical Identity & Physical Properties
Colorless gas with a pungent, acrid, irritating odor. May appear as a pale yellow liquid under pressure. Highly corrosive.
| Also known as | Hydriodic acid anhydrousHydrogen monoiodideHI gasAnhydrous hydriodic acid |
| CAS Number | 10034-85-2 |
| Appearance | Colorless gas with a pungent, acrid, irritating odor. May appear as a pale yellow liquid under pressure. Highly corrosive. |
| Flash Point | Not applicable (non-flammable gas) |
| Boiling Point | -35.4°C (-31.7°F) |
| Vapor Density | 4.4 (much heavier than air) |
| Water Reactivity | Dissolves readily in water forming highly corrosive hydriodic acid solution. Generates heat upon contact with moisture. |
Fireground Response Guidance — UN 2197
Extinguishing Media
PPE Requirements
Use positive-pressure SCBA and fully encapsulating chemical protective clothing for close entry or unknown concentrations. Level A may be needed; protect against frostbite where liquefied gas contact is possible.
Isolation & Evacuation
First Actions for a UN 2197 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.
- Treat the release as a serious inhalation hazard and consider downwind protective actions using ERG and monitoring.
- Avoid breathing gas, vapor, dust, mist, smoke or fumes and avoid skin or eye contact.
- Avoid unnecessary water contact with the released product unless incident command confirms a compatible vapor-control use.
- Do not touch damaged containers or spilled/released 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 release area and expand the perimeter for fire involvement, vapor/gas spread, cylinder heating, oxidizer reaction or unknown product identity.
- Use ERG Guide 125, shipping papers, SDS, air monitoring and incident command for protective actions.
📋 Copy & Share Field Card
UN 2197 — Hydrogen iodide, anhydrousUse 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.