☣️ UN 3303 • CLASS 2
UN 3303 — Compressed gas, poisonous, oxidizing, n.o.s. (Inhalation Hazard Zone A)
Placard: Toxic Gas. ERG Guide 124. 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.
Compressed gas, poisonous, oxidizing, n.o.s. (Inhalation Hazard Zone A) is a Zone A toxic gas entry with severe inhalation hazard. Releases require immediate isolation, air monitoring and specialized hazmat control.
Hazard overview: Toxic oxidizing compressed gas may be fatal if inhaled and may also be corrosive, oxidizing or flammable depending on the exact gas. Vapors can spread along the ground and threaten downwind areas.
Response guidance: Use ERG Guide 124 and Table 1 distances, stay upwind, deny entry and evacuate downwind as directed. Do not attempt leak control without Level A protection and gas-specific monitoring.
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UN 3303 Quick Details
UN 3303
Product name: Compressed gas, poisonous, oxidizing, n.o.s. (Inhalation Hazard Zone A)
DOT Class: 2
Placard type: Toxic Gas
ERG Guide: 124 (check current ERG)
Initial isolation: ERG 124: Initial isolation 100m in all directions; Protective Action Distance daytime 0.8km, nighttime 2.4km for small spills; 2.5km daytime, 6.4km nighttime for large spills
Common Hazards of UN 3303
- TOXIC and/or CORROSIVE; may be fatal if inhaled or absorbed through skin.
- Fire will produce irritating, corrosive and/or toxic gases.
- Contact with gas or liquefied gas may cause burns, severe injury and/or frostbite.
- Runoff from fire control or dilution water may cause environmental contamination.
- Substance does not burn but will support combustion.
- Vapors from liquefied gas are initially heavier than air and spread along ground.
- These are strong oxidizers and will react vigorously or explosively with many materials including fuels.
- May ignite combustibles (wood, paper, oil, clothing, etc.).
Chemical Identity & Physical Properties
Compressed gas stored under pressure in cylinders or tanks. Physical properties vary depending on specific gas; typically colorless to pale yellow. Extremely hazardous upon release due to combined toxic and oxidizing properties.
| Also known as | Compressed toxic oxidizing gas N.O.S.Poisonous oxidizing gas N.O.S.Toxic oxidizer gas N.O.S.Inhalation Hazard Zone A oxidizing gas |
| Appearance | Compressed gas stored under pressure in cylinders or tanks. Physical properties vary depending on specific gas; typically colorless to pale yellow. Extremely hazardous upon release due to combined toxic and oxidizing properties. |
| Flash Point | Not applicable (compressed gas) |
| Boiling Point | Not applicable (varies by specific gas composition) |
| Vapor Density | Heavier than air (typical for most toxic oxidizing gases); will accumulate in low-lying areas |
| Water Reactivity | Variable depending on specific gas; many oxidizing gases react with water or moisture producing corrosive or toxic vapors |
Chemical details are general reference only. Always verify with current SDS, ERG, and SOP/SOG.
Fireground Response Guidance — UN 3303
Extinguishing Media
Do not use water directly on leak or spill; dry chemical or CO2 for small fires only; evacuate area and let burn if safe to do so
PPE Requirements
⚠️ Level A required; full encapsulating chemical protective suit with SCBA; positive pressure self-contained breathing apparatus mandatory; no skin contact permitted
Level A required; full encapsulating chemical protective suit with SCBA; positive pressure self-contained breathing apparatus mandatory; no skin contact permitted.
Isolation & Evacuation
ERG 124: Initial isolation 100m in all directions; Protective Action Distance daytime 0.8km, nighttime 2.4km for small spills; 2.5km daytime, 6.4km nighttime for large spills
Always confirm protective actions with the current edition of the Emergency Response Guidebook (ERG Guide 124).
First Actions for a UN 3303 Incident
- CALL 911, then contact the emergency response telephone number shown on shipping papers, if available.
- 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.
- See Table 1 - Initial Isolation and Protective Action Distances.
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📋 Copy & Share Field Card
UN 3303 — Compressed gas, poisonous, oxidizing, n.HAZMAT RADIO NOTE — UN 3303
Product: Compressed gas, poisonous, oxidizing, n.o.s. (Inhalation Hazard Zone A)
Class 2 / Toxic Gas / ERG 124
PPE: Level A required; full encapsulating chemical protective suit with SCBA; positive pressure self-contained breathing apparatus mandatory; no skin contact permitted
ISOLATION: ERG 124: Initial isolation 100m in all directions; Protective Action Distance daytime 0.8km, nighttime 2.4km for small spills; 2.5km daytime, 6.4km nighttime for large spills
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 3303 — Compressed gas, poisonous, oxidizing, n.o.s. (Inhalation Hazard Zone A)
Class: 2 | Placard: Toxic Gas | ERG Guide: 124
Appearance: Compressed gas stored under pressure in cylinders or tanks. Physical properties vary depending on specific gas; typically colorless to pale yellow. Extremely hazardous upon release due to combined toxic and oxidizing properties.
Water Reactivity: Variable depending on specific gas; many oxidizing gases react with water or moisture producing corrosive or toxic vapors
Extinguishing: Do not use water directly on leak or spill; dry chemical or CO2 for small fires only; evacuate area and let burn if safe to do so
PPE: Level A required; full encapsulating chemical protective suit with SCBA; positive pressure self-contained breathing apparatus mandatory; no skin contact permitted
Isolation: ERG 124: Initial isolation 100m in all directions; Protective Action Distance daytime 0.8km, nighttime 2.4km for small spills; 2.5km daytime, 6.4km nighttime for large spills
— Key Hazards —
• TOXIC and/or CORROSIVE; may be fatal if inhaled or absorbed through skin.
• Fire will produce irritating, corrosive and/or toxic gases.
• Contact with gas or liquefied gas may cause burns, severe injury and/or frostbite.
— First Actions —
• CALL 911, then contact the emergency response telephone number shown on shipping papers, if available.
• 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/compressed-gas-poisonous-oxidizing-un-3303 | Always use current ERG + SOP/SOGIC BRIEFING
Use for: Incident command briefing, staging area whiteboard, or pre-entry team brief.
UN3303 Compressed gas, poisonous, oxidizing, n.o.s. (Inhalation Hazard Zone A) Cls2 ERG124 | allfirefighter.com/hazmat/un/compressed-gas-poisonous-oxidizing-un-3303SMS / 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/compressed-gas-poisonous-oxidizing-un-3303
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Frequently Asked Questions about UN 3303
UN 3303 is Compressed gas, poisonous, oxidizing, n.o.s. (Inhalation Hazard Zone A), assigned to ERG Guide 124 and placarded as Toxic Gas.
Yes. Toxic oxidizing compressed gas presents a serious toxic exposure hazard; avoid inhalation, ingestion, skin contact and contaminated runoff.
Yes, corrosive effects are possible. Avoid skin and eye contact and use chemical-resistant protection.
Gas can spread downwind, collect in low or confined areas, displace oxygen or create toxic exposure depending on the material.
Use caution. Variable depending on specific gas; many oxidizing gases react with water or moisture producing corrosive or toxic vapors
Do not use water directly on leak or spill; dry chemical or CO2 for small fires only; evacuate area and let burn if safe to do so.
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.