☣️ UN 3421 • CLASS 8
Potassium hydrogen difluoride, solution
Placard: Corrosive. 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 3421
Class: 8
Placard type: Corrosive
ERG: Guide 154 (check current ERG)
Isolation: ERG 154: isolate spill 25-50m all directions; for large spill isolate 100m; evacuate immediate area if fire involves containers
Chemical & Response Details
| Also known as | Potassium bifluoride solutionPotassium acid fluoride solutionKHF2 solutionPotassium hydrogen fluoride solution |
| CAS Number | 7789-29-9 |
| Appearance | Clear to slightly hazy aqueous solution. Odorless or slight acidic odor. Corrosive liquid at room temperature. |
| Flash Point | Not applicable (aqueous solution, non-flammable) |
| Boiling Point | Approximately 100-110C (212-230F) depending on concentration |
| Vapor Density | Not applicable (aqueous solution) |
| Water Reactivity | Already in aqueous solution; dilution with water generates heat but generally controlled reaction |
| Extinguishing | Water spray to reduce vapors, do not direct stream into solution; dry chemical for surrounding fires |
| PPE | ⚠️ Level B minimum with acid-resistant suit; full face SCBA required; butyl rubber or neoprene gloves; face shield and eye protection mandatory |
| Isolation | ERG 154: isolate spill 25-50m all directions; for large spill isolate 100m; evacuate immediate area if fire involves containers |
Chemical details are general reference only. Always verify with current SDS, ERG, and SOP/SOG.
Common hazards (high level)
- TOXIC and/or CORROSIVE; inhalation, ingestion or skin contact with material may cause severe injury
- Contact with molten substance may cause severe burns to skin and eyes.
- Avoid any skin contact.
- Fire may produce irritating, corrosive and/or toxic gases.
- Runoff from fire control or dilution water may be corrosive and/or toxic and cause environmental
- Non-combustible, substance itself does not burn but may decompose upon heating to produce corrosive
- Some are oxidizers and may ignite combustibles (wood, paper, oil, clothing, etc.).
- Corrosives in contact with metals may evolve flammable hydrogen gas.
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.
- Ventilate closed spaces before entering, but only if properly trained and equipped.
- Isolate spill or leak area in all directions for at least 50 meters (150 feet) for liquids and at least 25 meters
- 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 3421 — Potassium hydrogen difluoride, solution HAZMAT RADIO NOTE — UN 3421
Product: Potassium hydrogen difluoride, solution
Class 8 / Corrosive / ERG 154
PPE: Level B minimum with acid-resistant suit; full face SCBA required; butyl rubber or neoprene gloves; face shield and eye protection mandatory
ISOLATION: ERG 154: isolate spill 25-50m all directions; for large spill isolate 100m; evacuate immediate area if fire involves containers
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 3421 — Potassium hydrogen difluoride, solution
Class: 8 | Placard: Corrosive | ERG Guide: 154
Appearance: Clear to slightly hazy aqueous solution. Odorless or slight acidic odor. Corrosive liquid at room temperature.
Water Reactivity: Already in aqueous solution; dilution with water generates heat but generally controlled reaction
Extinguishing: Water spray to reduce vapors, do not direct stream into solution; dry chemical for surrounding fires
PPE: Level B minimum with acid-resistant suit; full face SCBA required; butyl rubber or neoprene gloves; face shield and eye protection mandatory
Isolation: ERG 154: isolate spill 25-50m all directions; for large spill isolate 100m; evacuate immediate area if fire involves containers
— Key Hazards —
• TOXIC and/or CORROSIVE; inhalation, ingestion or skin contact with material may cause severe injury
• Contact with molten substance may cause severe burns to skin and eyes.
• Avoid any skin contact.
— 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.
• Ventilate closed spaces before entering, but only if properly trained and equipped.
SOURCE: allfirefighter.com/hazmat/un/3421 | Always use current ERG + SOP/SOGIC BRIEFING
Use for: Incident command briefing, staging area whiteboard, or pre-entry team brief. Full chemical + response details.
UN3421 Potassium hydrogen difluoride, solution Cls8 ERG154 | allfirefighter.com/hazmat/un/3421SMS / 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/3421
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FAQ
TOXIC and/or CORROSIVE; inhalation, ingestion or skin contact with material may cause severe injury Contact with molten substance may cause severe burns to skin and eyes. Avoid any skin contact. Fire may produce irritating, corrosive and/or toxic gases. Runoff from fire control or dilution water may be corrosive and/or toxic and cause environmental Non-combustible, substance itself does not burn but may decompose upon heating to produce corrosive Some are oxidizers and may ignite combustibles (wood, paper, oil, clothing, etc.). Corrosives in contact with metals may evolve flammable hydrogen gas.
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 B minimum with acid-resistant suit; full face SCBA required; butyl rubber or neoprene gloves; face shield and eye protection mandatory
No. This is a training/quick-reference aid only. Always consult the current ERG Guide 154 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.