☣️ UN 3423 • CLASS 8
UN 3423 — Tetramethylammonium hydroxide, solid
Placard: Corrosive. ERG Guide 153. Training/quick-reference only — use current ERG + SOP/SOG for incident-specific actions.
🚒☣️
⚠️ Verification required:
Broad or variable material category; verify exact product, SDS and shipping papers.
⚠️ 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.
UN 3423 is Tetramethylammonium hydroxide, solid, a highly alkaline corrosive material used in electronic and chemical applications. Even small exposures can be serious because TMAH is both corrosive and systemically toxic.
Hazard overview: UN 3423 can cause severe chemical burns to skin and eyes and may produce toxic effects after skin absorption. The solid dissolves in water with heat generation, producing a very high-pH solution. Fire can generate irritating or toxic nitrogen-containing fumes.
Response guidance: For UN 3423, isolate the spill, avoid dust, keep unprotected personnel away and prevent product from entering drains. Use dry chemical, CO2 or dry sand for small fires where appropriate, and cool exposures from a protected distance without spreading the solid.
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UN 3423 Quick Details
UN 3423
Product name: Tetramethylammonium hydroxide, solid
DOT Class: 8
Placard type: Corrosive
ERG Guide: 153 (check current ERG)
Initial isolation: ERG 153: isolate spill/leak area immediately for at least 25-50m in all directions; if tank/rail car involved in fire, isolate 800m in all directions
Common Hazards of UN 3423
- TOXIC and/or CORROSIVE; inhalation, ingestion or skin contact with material may cause severe injury
- Methyl bromoacetate (UN2643) is an eye irritant/lachrymator (causes flow of tears).
- 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
- Combustible material: may burn but does not ignite readily.
- When heated, vapors may form explosive mixtures with air: indoors, outdoors and sewers explosion
Chemical Identity & Physical Properties
UN 3423 is a white to off-white crystalline solid or pellets. It is hygroscopic and can develop a faint amine-like odor when exposed to moisture.
| Also known as | TMAHTetramethylammonium hydroxideHydroxide de tetramethylammoniumTMAOHTetramethyl ammonium hydroxide |
| CAS Number | 75-59-2 |
| Appearance | White to off-white crystalline solid or pellets at room temperature. Hygroscopic material with no distinct odor or faint amine-like odor when exposed to moisture. |
| Flash Point | Not applicable (solid) |
| Boiling Point | 130C (266F) with decomposition |
| Vapor Density | Not applicable (solid) |
| Water Reactivity | Dissolves readily in water, generating heat; highly alkaline solution (pH >14) |
Chemical details are general reference only. Always verify with current SDS, ERG, and SOP/SOG.
Fireground Response Guidance — UN 3423
Extinguishing Media
Dry chemical, CO2, or dry sand; water spray may be used to cool containers but avoid direct contact with solid
PPE Requirements
⚠️ Level B minimum; SCBA required; full face shield, chemical-resistant suit, neoprene or butyl rubber gloves; extreme corrosive hazard to skin and eyes
Use SCBA with full chemical-resistant clothing, face shield, eye protection and compatible gloves. Because of the severe corrosive and systemic toxicity risk, avoid all skin contact and decontaminate promptly.
Isolation & Evacuation
ERG 153: isolate spill/leak area immediately for at least 25-50m in all directions; if tank/rail car involved in fire, isolate 800m in all directions
Always confirm protective actions with the current edition of the Emergency Response Guidebook (ERG Guide 153).
First Actions for a UN 3423 Incident
- 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 3423 — Tetramethylammonium hydroxide, solidHAZMAT RADIO NOTE — UN 3423
Product: Tetramethylammonium hydroxide, solid
Class 8 / Corrosive / ERG 153
PPE: Level B minimum; SCBA required; full face shield, chemical-resistant suit, neoprene or butyl rubber gloves; extreme corrosive hazard to skin and eyes
ISOLATION: ERG 153: isolate spill/leak area immediately for at least 25-50m in all directions; if tank/rail car involved in fire, isolate 800m in all directions
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 3423 — Tetramethylammonium hydroxide, solid
Class: 8 | Placard: Corrosive | ERG Guide: 153
Appearance: White to off-white crystalline solid or pellets at room temperature. Hygroscopic material with no distinct odor or faint amine-like odor when exposed to moisture.
Water Reactivity: Dissolves readily in water, generating heat; highly alkaline solution (pH >14)
Extinguishing: Dry chemical, CO2, or dry sand; water spray may be used to cool containers but avoid direct contact with solid
PPE: Level B minimum; SCBA required; full face shield, chemical-resistant suit, neoprene or butyl rubber gloves; extreme corrosive hazard to skin and eyes
Isolation: ERG 153: isolate spill/leak area immediately for at least 25-50m in all directions; if tank/rail car involved in fire, isolate 800m in all directions
— Key Hazards —
• TOXIC and/or CORROSIVE; inhalation, ingestion or skin contact with material may cause severe injury
• Methyl bromoacetate (UN2643) is an eye irritant/lachrymator (causes flow of tears).
• Contact with molten substance may cause severe burns to skin and eyes.
— First Actions —
• 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
SOURCE: allfirefighter.com/hazmat/un/tetramethylammonium-hydroxide-solid-un-3423 | Always use current ERG + SOP/SOGIC BRIEFING
Use for: Incident command briefing, staging area whiteboard, or pre-entry team brief.
UN3423 Tetramethylammonium hydroxide, solid Cls8 ERG153 | allfirefighter.com/hazmat/un/tetramethylammonium-hydroxide-solid-un-3423SMS / 160 CHAR
Use for: Quick text to command or incoming units. Fits in a single SMS.
⚠️ Quick-reference only. Always use current ERG + SOP/SOG for incident-specific actions.
Page: https://allfirefighter.com/hazmat/un/tetramethylammonium-hydroxide-solid-un-3423
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Frequently Asked Questions about UN 3423
UN 3423 is Tetramethylammonium hydroxide, solid. It should be identified from shipping papers, markings and the SDS before responders work near the release.
ERG Guide 153 applies to UN 3423 for initial isolation, protective actions and first-response guidance.
UN 3423 is not primarily classified as flammable, but fire may produce toxic or corrosive gases and containers may become dangerous when heated.
Use SCBA with full chemical-resistant clothing, face shield, eye protection and compatible gloves. Because of the severe corrosive and systemic toxicity risk, avoid all skin contact and decontaminate promptly.
UN 3423 can cause severe chemical burns to skin and eyes and may produce toxic effects after skin absorption.
For UN 3423, isolate the spill, avoid dust, keep unprotected personnel away and prevent product from entering drains.
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.