☣️ UN 3503 • CLASS 2
UN 3503 — Chemical under pressure, corrosive, n.o.s.
Placard: Non-Flammable Gas. ERG Guide 125. 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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UN 3503 Quick Details
UN 3503
Product name: Chemical under pressure, corrosive, n.o.s.
DOT Class: 2
Placard type: Non-Flammable Gas
ERG Guide: 125 (check current ERG)
Initial isolation: ERG 125: isolate spill/leak area immediately for at least 100m in all directions; keep unauthorized personnel away; stay upwind and uphill; evacuate downwind areas if large spill
Common Hazards of UN 3503
- 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.
Chemical Identity & Physical Properties
| Also known as | Compressed corrosive chemicalPressurized corrosive substanceAerosol corrosive chemicalCorrosive gas under pressure |
| Appearance | Variable appearance depending on specific chemical; may be colorless to colored gas or liquefied gas under pressure. Contact with liquefied gas causes frostbite. Vapors are extremely irritating and corrosive to eyes, skin, and respiratory tract. |
| Flash Point | Not applicable (pressurized gas mixture) |
| Boiling Point | Variable depending on specific chemical and pressure |
| Vapor Density | Variable; typically heavier than air for corrosive gases |
| Water Reactivity | Variable depending on specific chemical; may react violently with water or moisture producing corrosive vapors |
Chemical details are general reference only. Always verify with current SDS, ERG, and SOP/SOG.
Fireground Response Guidance — UN 3503
Extinguishing Media
Do not use water or foam; use dry chemical or CO2 if appropriate for specific chemical; consult shipping papers for specific agent
PPE Requirements
⚠️ Level A required for unknown corrosive gases; full encapsulating suit with SCBA; avoid all contact with gas or liquid; extreme inhalation and skin contact hazard
Isolation & Evacuation
ERG 125: isolate spill/leak area immediately for at least 100m in all directions; keep unauthorized personnel away; stay upwind and uphill; evacuate downwind areas if large spill
Always confirm protective actions with the current edition of the Emergency Response Guidebook (ERG Guide 125).
First Actions for a UN 3503 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.
- 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 3503 — Chemical under pressure, corrosive, n.o.HAZMAT RADIO NOTE — UN 3503
Product: Chemical under pressure, corrosive, n.o.s.
Class 2 / Non-Flammable Gas / ERG 125
PPE: Level A required for unknown corrosive gases; full encapsulating suit with SCBA; avoid all contact with gas or liquid; extreme inhalation and skin contact hazard
ISOLATION: ERG 125: isolate spill/leak area immediately for at least 100m in all directions; keep unauthorized personnel away; stay upwind and uphill; evacuate downwind areas if large spill
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 3503 — Chemical under pressure, corrosive, n.o.s.
Class: 2 | Placard: Non-Flammable Gas | ERG Guide: 125
Appearance: Variable appearance depending on specific chemical; may be colorless to colored gas or liquefied gas under pressure. Contact with liquefied gas causes frostbite. Vapors are extremely irritating and corrosive to eyes, skin, and respiratory tract.
Water Reactivity: Variable depending on specific chemical; may react violently with water or moisture producing corrosive vapors
Extinguishing: Do not use water or foam; use dry chemical or CO2 if appropriate for specific chemical; consult shipping papers for specific agent
PPE: Level A required for unknown corrosive gases; full encapsulating suit with SCBA; avoid all contact with gas or liquid; extreme inhalation and skin contact hazard
Isolation: ERG 125: isolate spill/leak area immediately for at least 100m in all directions; keep unauthorized personnel away; stay upwind and uphill; evacuate downwind areas if large spill
— 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/3503 | Always use current ERG + SOP/SOGIC BRIEFING
Use for: Incident command briefing, staging area whiteboard, or pre-entry team brief. Full chemical + response details.
UN3503 Chemical under pressure, corrosive, n.o.s. Cls2 ERG125 | allfirefighter.com/hazmat/un/3503SMS / 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/3503
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Frequently Asked Questions about UN 3503
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 unknown corrosive gases; full encapsulating suit with SCBA; avoid all contact with gas or liquid; extreme inhalation and skin contact hazard
Water reactivity: Variable depending on specific chemical; may react violently with water or moisture producing corrosive vapors. Recommended extinguishing: Do not use water or foam; use dry chemical or CO2 if appropriate for specific chemical; consult shipping papers for specific agent.
ERG Guide 125 recommendation: ERG 125: isolate spill/leak area immediately for at least 100m in all directions; keep unauthorized personnel away; stay upwind and uphill; evacuate downwind areas if large spill
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.