☣️ UN 2197 • CLASS 2
Hydrogen iodide, anhydrous
Placard: Toxic Gas. Training/quick-reference only — use current ERG + SOP/SOG for incident-specific actions.
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⚠️ This page is a quick-reference aid. For real incidents: stage upwind, isolate, deny entry, request Hazmat early, and consult the current ERG + SOP/SOG.
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Quick details
UN 2197
Class: 2
Placard type: Toxic Gas
ERG: Guide 125 (check current ERG)
Isolation: ERG 125: Initial isolation 100m all directions; protective action distance 300m downwind daytime, 800m downwind nighttime for large spills
Chemical & Response Details
| 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. |
| Extinguishing | Not applicable for fire suppression; use water spray to reduce vapors from distance only |
| PPE | ⚠️ Level A required for direct contact; full-face SCBA, vapor-tight chemical protective suit, butyl rubber gloves. Severe corrosion hazard to skin and respiratory tract. |
| Isolation | ERG 125: Initial isolation 100m all directions; protective action distance 300m downwind daytime, 800m downwind nighttime for large spills |
Chemical details are general reference only. Always verify with current SDS, ERG, and SOP/SOG.
Common hazards (high level)
- TOXIC and/or CORROSIVE; may be fatal if inhaled, ingested or absorbed through skin.
- Vapors are extremely irritating and corrosive.
- Contact with gas or liquefied gas may cause burns, severe injury and/or frostbite.
- Fire will produce irritating, corrosive and/or toxic gases.
- Runoff from fire control or dilution water may cause environmental contamination.
- Some may burn but none ignite readily.
- Vapors from liquefied gas are initially heavier than air and spread along ground.
- Some of these materials may react violently with water.
First actions (field-minded)
- CALL 911. Then call emergency response telephone number on shipping paper. If shipping paper
- Keep unauthorized personnel away.
- Stay upwind, uphill and/or upstream.
- Many gases are heavier than air and will spread along the ground and collect in low or confined areas
- Ventilate closed spaces before entering, but only if properly trained and equipped.
- Isolate spill or leak area for at least 100 meters (330 feet) in all directions.
- For highlighted materials: see Table 1 - Initial Isolation and Protective Action Distances.
- For non-highlighted materials: increase the immediate precautionary measure distance, in the downwind
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UN 2197 — Hydrogen iodide, anhydrous HAZMAT RADIO NOTE — UN 2197
Product: Hydrogen iodide, anhydrous
Class 2 / Toxic Gas / ERG 125
PPE: Level A required for direct contact; full-face SCBA, vapor-tight chemical protective suit, butyl rubber gloves. Severe corrosion hazard to skin and respiratory tract.
ISOLATION: ERG 125: Initial isolation 100m all directions; protective action distance 300m downwind daytime, 800m downwind nighttime for large spills
ACTION: Stage upwind · Isolate · Deny entry · Request HazmatRADIO
Use for: Quick radio or face-to-face size-up. Short, structured, field-ready.
=== IC HAZMAT BRIEFING ===
UN 2197 — Hydrogen iodide, anhydrous
Class: 2 | Placard: Toxic Gas | ERG Guide: 125
Appearance: Colorless gas with a pungent, acrid, irritating odor. May appear as a pale yellow liquid under pressure. Highly corrosive.
Water Reactivity: Dissolves readily in water forming highly corrosive hydriodic acid solution. Generates heat upon contact with moisture.
Extinguishing: Not applicable for fire suppression; use water spray to reduce vapors from distance only
PPE: Level A required for direct contact; full-face SCBA, vapor-tight chemical protective suit, butyl rubber gloves. Severe corrosion hazard to skin and respiratory tract.
Isolation: ERG 125: Initial isolation 100m all directions; protective action distance 300m downwind daytime, 800m downwind nighttime for large spills
— Key Hazards —
• TOXIC and/or CORROSIVE; may be fatal if inhaled, ingested or absorbed through skin.
• Vapors are extremely irritating and corrosive.
• Contact with gas or liquefied gas may cause burns, severe injury and/or frostbite.
— First Actions —
• CALL 911. Then call emergency response telephone number on shipping paper. If shipping paper
• Keep unauthorized personnel away.
• Stay upwind, uphill and/or upstream.
• Many gases are heavier than air and will spread along the ground and collect in low or confined areas
SOURCE: allfirefighter.com/hazmat/un/2197 | Always use current ERG + SOP/SOGIC BRIEFING
Use for: Incident command briefing, staging area whiteboard, or pre-entry team brief. Full chemical + response details.
UN2197 Hydrogen iodide, anhydrous Cls2 ERG125 | allfirefighter.com/hazmat/un/2197SMS / 160 CHAR
Use for: Quick text to command or incoming units. Fits in a single SMS. Includes link to full page.
⚠️ Quick-reference only. Always use current ERG + SOP/SOG for incident-specific actions. Page: https://allfirefighter.com/hazmat/un/2197
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FAQ
TOXIC and/or CORROSIVE; may be fatal if inhaled, ingested or absorbed through skin. Vapors are extremely irritating and corrosive. Contact with gas or liquefied gas may cause burns, severe injury and/or frostbite. Fire will produce irritating, corrosive and/or toxic gases. Runoff from fire control or dilution water may cause environmental contamination. Some may burn but none ignite readily. Vapors from liquefied gas are initially heavier than air and spread along ground. Some of these materials may react violently with water.
CALL 911. Then call emergency response telephone number on shipping paper. If shipping paper Keep unauthorized personnel away. Stay upwind, uphill and/or upstream.
Level A required for direct contact; full-face SCBA, vapor-tight chemical protective suit, butyl rubber gloves. Severe corrosion hazard to skin and respiratory tract.
No. This is a training/quick-reference aid only. Always consult the current ERG Guide 125 and your department SOP/SOG for incident-specific protective actions.
Sources (high level): DOT/PHMSA marking & class concepts + ERG usage principles. This page does not reproduce ERG guide text—always consult the current ERG for incident-specific protective actions.