☣️ UN 3543 • CLASS 4
UN 3543 — Articles containing a substance which in contact with water emits flammable gases, n.o.s.
Placard: Dangerous When Wet. ERG Guide 138. Training/quick-reference only — use current ERG + SOP/SOG for incident-specific actions.
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⚠️ 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 3543 is Articles containing a substance which in contact with water emits flammable gases, n.o.s., assigned to ERG Guide 138. This entry should be verified with shipping papers, labels and the SDS before responders commit to close-range action.
Hazard overview: Articles containing a substance which in contact with water emits flammable gases, n.o.s. can generate flammable gas when water contacts the contained material. Moisture, damaged packaging, heat or ignition sources can create fire, flashback or explosion hazards.
Response guidance: Use ERG Guide 138, isolate the area, keep people upwind and avoid incompatible agents. Keep water away unless incident command confirms it is safe for the specific material.
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UN 3543 Quick Details
UN 3543
Product name: Articles containing a substance which in contact with water emits flammable gases, n.o.s.
DOT Class: 4
Placard type: Dangerous When Wet
ERG Guide: 138 (check current ERG)
Initial isolation: ERG 138: Initial isolation 100m in all directions; if tank/rail car involved in fire isolate 800m in all directions; evacuate downwind areas if flammable gas ignition occurs
Common Hazards of UN 3543
- Produce flammable gases on contact with water.
- May ignite on contact with water or moist air.
- Some react vigorously or explosively on contact with water.
- May be ignited by heat, sparks or flames.
- May re-ignite after fire is extinguished.
- Some are transported in highly flammable liquids.
- Runoff may create fire or explosion hazard.
- Inhalation or contact with vapors, substance or decomposition products may cause severe injury or
Chemical Identity & Physical Properties
Various articles or manufactured items containing substances that react with water to produce flammable gases. Physical appearance varies depending on the specific article and contained substance.
| Also known as | Water-reactive articles n.o.s.Articles containing water-reactive substancesDangerous when wet articlesWater-activated flammable gas generating articles |
| Appearance | Various articles or manufactured items containing substances that react with water to produce flammable gases. Physical appearance varies depending on the specific article and contained substance. |
| Flash Point | Not applicable (articles containing reactive substances) |
| Boiling Point | Not applicable (articles containing reactive substances) |
| Vapor Density | Not applicable (articles containing reactive substances) |
| Water Reactivity | Reacts with water to produce flammable gases; may ignite spontaneously on contact with water or moist air; some react vigorously or explosively with water. Keep dry at all times. |
Chemical details are general reference only. Always verify with current SDS, ERG, and SOP/SOG.
Fireground Response Guidance — UN 3543
Extinguishing Media
Do not use water, foam, or water-based agents; use dry sand, dry chemical, soda ash, or lime to cover and control; may require dry agent smothering
PPE Requirements
⚠️ Level B minimum with SCBA required; chemical-resistant suit; avoid contact with moisture; maintain dry environment during response operations
Level B minimum with SCBA required; chemical-resistant suit; avoid contact with moisture; maintain dry environment during response operations. Select final PPE using ERG guidance, SDS, monitoring and incident command.
Isolation & Evacuation
ERG 138: Initial isolation 100m in all directions; if tank/rail car involved in fire isolate 800m in all directions; evacuate downwind areas if flammable gas ignition occurs
Always confirm protective actions with the current edition of the Emergency Response Guidebook (ERG Guide 138).
First Actions for a UN 3543 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
- Consider initial downwind evacuation for at least 300 meters (1000 feet).
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UN 3543 — Articles containing a substance which inHAZMAT RADIO NOTE — UN 3543
Product: Articles containing a substance which in contact with water emits flammable gases, n.o.s.
Class 4 / Dangerous When Wet / ERG 138
PPE: Level B minimum with SCBA required; chemical-resistant suit; avoid contact with moisture; maintain dry environment during response operations
ISOLATION: ERG 138: Initial isolation 100m in all directions; if tank/rail car involved in fire isolate 800m in all directions; evacuate downwind areas if flammable gas ignition occurs
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 3543 — Articles containing a substance which in contact with water emits flammable gases, n.o.s.
Class: 4 | Placard: Dangerous When Wet | ERG Guide: 138
Appearance: Various articles or manufactured items containing substances that react with water to produce flammable gases. Physical appearance varies depending on the specific article and contained substance.
Water Reactivity: Reacts with water to produce flammable gases; may ignite spontaneously on contact with water or moist air; some react vigorously or explosively with water. Keep dry at all times.
Extinguishing: Do not use water, foam, or water-based agents; use dry sand, dry chemical, soda ash, or lime to cover and control; may require dry agent smothering
PPE: Level B minimum with SCBA required; chemical-resistant suit; avoid contact with moisture; maintain dry environment during response operations
Isolation: ERG 138: Initial isolation 100m in all directions; if tank/rail car involved in fire isolate 800m in all directions; evacuate downwind areas if flammable gas ignition occurs
— Key Hazards —
• Produce flammable gases on contact with water.
• May ignite on contact with water or moist air.
• Some react vigorously or explosively on contact with water.
— 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/articles-containing-a-substance-un-3543 | Always use current ERG + SOP/SOGIC BRIEFING
Use for: Incident command briefing, staging area whiteboard, or pre-entry team brief.
UN3543 Articles containing a substance which in contact with water emits flammable gases, n.o.s. Cls4 ERG138 | allfirefighter.com/hazmat/un/articles-containing-a-substance-un-3543SMS / 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/articles-containing-a-substance-un-3543
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Frequently Asked Questions about UN 3543
UN 3543 is Articles containing a substance which in contact with water emits flammable gases, n.o.s., assigned to ERG Guide 138.
ERG Guide 138 applies for initial isolation, protective actions and first response guidance.
Articles containing a substance which in contact with water emits flammable gases, n.
Level B minimum with SCBA required; chemical-resistant suit; avoid contact with moisture; maintain dry environment during response operations.
ERG 138: Initial isolation 100m in all directions; if tank/rail car involved in fire isolate 800m in all directions; evacuate downwind areas if flammable gas ignition occurs.
Water compatibility depends on the specific contents and incident conditions. Check ERG 138, SDS and incident command before applying water.
Verify shipping papers, container markings, SDS, package condition and whether contents are leaking, burning or exposed.
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.