☣️ UN 1778 • CLASS 8
UN 1778 — Hydrofluorosilicic acid
Placard: Corrosive. ERG Guide 154. Training/quick-reference only — use current ERG + SOP/SOG for incident-specific actions.
🚒☣️
⚠️ 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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UN 1778 Quick Details
UN 1778
Product name: Hydrofluorosilicic acid
DOT Class: 8
Placard type: Corrosive
ERG Guide: 154 (check current ERG)
Initial isolation: ERG 154: Isolate spill 50m all directions; evacuate downwind 300m for small spills, 800m for large spills during day, consider evacuation up to 1600m at night
Common Hazards of UN 1778
- 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.
Chemical Identity & Physical Properties
| Also known as | Fluorosilicic acidHexafluorosilicic acidSilicofluoric acidHydrofluoric acid silicate |
| CAS Number | 16961-83-4 |
| Appearance | Colorless to straw-colored fuming liquid with a sharp, pungent, irritating odor. Highly corrosive aqueous solution. |
| Flash Point | Not applicable (non-flammable aqueous solution) |
| Boiling Point | Approximately 108-110C (226-230F) with decomposition |
| Vapor Density | Not applicable (releases HF vapors which are heavier than air) |
| Water Reactivity | Miscible with water; solution is highly corrosive and acidic |
Chemical details are general reference only. Always verify with current SDS, ERG, and SOP/SOG.
Fireground Response Guidance — UN 1778
Extinguishing Media
Not recommended; use water spray from distance to reduce vapors, do not direct water into container
PPE Requirements
⚠️ Level A or B required; SCBA mandatory; acid-resistant suit, gloves, and boots essential; protect against HF vapor exposure
Isolation & Evacuation
ERG 154: Isolate spill 50m all directions; evacuate downwind 300m for small spills, 800m for large spills during day, consider evacuation up to 1600m at night
Always confirm protective actions with the current edition of the Emergency Response Guidebook (ERG Guide 154).
First Actions for a UN 1778 Incident
- 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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📋 Copy & Share Field Card
UN 1778 — Hydrofluorosilicic acidHAZMAT RADIO NOTE — UN 1778
Product: Hydrofluorosilicic acid
Class 8 / Corrosive / ERG 154
PPE: Level A or B required; SCBA mandatory; acid-resistant suit, gloves, and boots essential; protect against HF vapor exposure
ISOLATION: ERG 154: Isolate spill 50m all directions; evacuate downwind 300m for small spills, 800m for large spills during day, consider evacuation up to 1600m at night
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 1778 — Hydrofluorosilicic acid
Class: 8 | Placard: Corrosive | ERG Guide: 154
Appearance: Colorless to straw-colored fuming liquid with a sharp, pungent, irritating odor. Highly corrosive aqueous solution.
Water Reactivity: Miscible with water; solution is highly corrosive and acidic
Extinguishing: Not recommended; use water spray from distance to reduce vapors, do not direct water into container
PPE: Level A or B required; SCBA mandatory; acid-resistant suit, gloves, and boots essential; protect against HF vapor exposure
Isolation: ERG 154: Isolate spill 50m all directions; evacuate downwind 300m for small spills, 800m for large spills during day, consider evacuation up to 1600m at night
— 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/1778 | Always use current ERG + SOP/SOGIC BRIEFING
Use for: Incident command briefing, staging area whiteboard, or pre-entry team brief. Full chemical + response details.
UN1778 Hydrofluorosilicic acid Cls8 ERG154 | allfirefighter.com/hazmat/un/1778SMS / 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/1778
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Frequently Asked Questions about UN 1778
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 A or B required; SCBA mandatory; acid-resistant suit, gloves, and boots essential; protect against HF vapor exposure
Water reactivity: Miscible with water; solution is highly corrosive and acidic. Recommended extinguishing: Not recommended; use water spray from distance to reduce vapors, do not direct water into container.
ERG Guide 154 recommendation: ERG 154: Isolate spill 50m all directions; evacuate downwind 300m for small spills, 800m for large spills during day, consider evacuation up to 1600m at night
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.