☣️ UN 3502 • CLASS 2
UN 3502 — Chemical under pressure, poisonous, n.o.s.
Placard: Non-Flammable Gas. ERG Guide 123. 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 3502 Quick Details
UN 3502
Product name: Chemical under pressure, poisonous, n.o.s.
DOT Class: 2
Placard type: Non-Flammable Gas
ERG Guide: 123 (check current ERG)
Initial isolation: ERG 123: Isolate spill/leak area immediately for at least 100m in all directions; initial evacuation 800m downwind if large spill
Common Hazards of UN 3502
- TOXIC; may be fatal if inhaled or absorbed through skin.
- Vapors may be irritating and/or 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.
- Cylinders exposed to fire may vent and release toxic and/or corrosive gas through pressure relief
Chemical Identity & Physical Properties
| Also known as | Chemical under pressure poisonous NOSCompressed poisonous chemical NOSPressurized toxic chemical NOS |
| Appearance | Not otherwise specified (n.o.s.) entry covering various toxic chemicals under pressure. May be gas, liquefied gas, or dissolved gas. Physical characteristics vary by specific chemical. |
| Flash Point | Variable depending on specific chemical; refer to SDS |
| Boiling Point | Variable depending on specific chemical; refer to SDS |
| Vapor Density | Variable depending on specific chemical; typically heavier than air for pressurized gases |
| Water Reactivity | Variable depending on specific chemical; may range from no reaction to violent reactivity |
Chemical details are general reference only. Always verify with current SDS, ERG, and SOP/SOG.
Fireground Response Guidance — UN 3502
Extinguishing Media
Do not use water spray; use dry chemical, CO2, or inert gas as appropriate for specific chemical
PPE Requirements
⚠️ Level A required for unknown toxic chemicals; full-face SCBA mandatory; chemical-resistant suit with splash protection minimum
Isolation & Evacuation
ERG 123: Isolate spill/leak area immediately for at least 100m in all directions; initial evacuation 800m downwind if large spill
Always confirm protective actions with the current edition of the Emergency Response Guidebook (ERG Guide 123).
First Actions for a UN 3502 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 3502 — Chemical under pressure, poisonous, n.o.HAZMAT RADIO NOTE — UN 3502
Product: Chemical under pressure, poisonous, n.o.s.
Class 2 / Non-Flammable Gas / ERG 123
PPE: Level A required for unknown toxic chemicals; full-face SCBA mandatory; chemical-resistant suit with splash protection minimum
ISOLATION: ERG 123: Isolate spill/leak area immediately for at least 100m in all directions; initial evacuation 800m downwind 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 3502 — Chemical under pressure, poisonous, n.o.s.
Class: 2 | Placard: Non-Flammable Gas | ERG Guide: 123
Appearance: Not otherwise specified (n.o.s.) entry covering various toxic chemicals under pressure. May be gas, liquefied gas, or dissolved gas. Physical characteristics vary by specific chemical.
Water Reactivity: Variable depending on specific chemical; may range from no reaction to violent reactivity
Extinguishing: Do not use water spray; use dry chemical, CO2, or inert gas as appropriate for specific chemical
PPE: Level A required for unknown toxic chemicals; full-face SCBA mandatory; chemical-resistant suit with splash protection minimum
Isolation: ERG 123: Isolate spill/leak area immediately for at least 100m in all directions; initial evacuation 800m downwind if large spill
— Key Hazards —
• TOXIC; may be fatal if inhaled or absorbed through skin.
• Vapors may be irritating and/or 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/3502 | Always use current ERG + SOP/SOGIC BRIEFING
Use for: Incident command briefing, staging area whiteboard, or pre-entry team brief. Full chemical + response details.
UN3502 Chemical under pressure, poisonous, n.o.s. Cls2 ERG123 | allfirefighter.com/hazmat/un/3502SMS / 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/3502
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Frequently Asked Questions about UN 3502
TOXIC; may be fatal if inhaled or absorbed through skin. Vapors may be irritating and/or 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. Cylinders exposed to fire may vent and release toxic and/or corrosive gas through pressure relief
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 toxic chemicals; full-face SCBA mandatory; chemical-resistant suit with splash protection minimum
Water reactivity: Variable depending on specific chemical; may range from no reaction to violent reactivity. Recommended extinguishing: Do not use water spray; use dry chemical, CO2, or inert gas as appropriate for specific chemical.
ERG Guide 123 recommendation: ERG 123: Isolate spill/leak area immediately for at least 100m in all directions; initial evacuation 800m downwind if large spill
No. This is a training/quick-reference aid only. Always consult the current ERG Guide 123 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.