☣️ UN 3303 • CLASS 2
Compressed gas, poisonous, oxidizing, n.o.s. (Inhalation Hazard Zone A)
Placard: Toxic Gas. 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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Quick details
UN 3303
Class: 2
Placard type: Toxic Gas
ERG: Guide 124 (check current ERG)
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
Chemical & Response Details
| 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 |
| 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 |
Chemical details are general reference only. Always verify with current SDS, ERG, and SOP/SOG.
Common hazards (high level)
- 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.).
First actions (field-minded)
- 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.
- See Table 1 - Initial Isolation and Protective Action Distances.
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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 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/3303 | Always use current ERG + SOP/SOGIC BRIEFING
Use for: Incident command briefing, staging area whiteboard, or pre-entry team brief. Full chemical + response details.
UN3303 Compressed gas, poisonous, oxidizing, n.o.s. (Inhalation Hazard Zone A) Cls2 ERG124 | allfirefighter.com/hazmat/un/3303SMS / 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/3303
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FAQ
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.).
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; full encapsulating chemical protective suit with SCBA; positive pressure self-contained breathing apparatus mandatory; no skin contact permitted
No. This is a training/quick-reference aid only. Always consult the current ERG Guide 124 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.