☣️ UN 3299 • CLASS 2
UN 3299 — Ethylene oxide and tetrafluoroethane mixture, with not more than 5.6% ethylene oxide
Placard: Non-Flammable Gas. ERG Guide 126. 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 3299 Quick Details
UN 3299
Product name: Ethylene oxide and tetrafluoroethane mixture, with not more than 5.6% ethylene oxide
DOT Class: 2
Placard type: Non-Flammable Gas
ERG Guide: 126 (check current ERG)
Initial isolation: ERG 126: Initial isolation 100m all directions; protective action distance 300m downwind (small spill day), 800m (large spill night); evacuate area if container rupture imminent
Common Hazards of UN 3299
- Some may burn but none ignite readily.
- Containers may explode when heated.
- Ruptured cylinders may rocket.
- Vapors may cause dizziness or asphyxiation without warning, especially when in closed or confined areas.
- Vapors from liquefied gas are initially heavier than air and spread along ground.
- Contact with gas or liquefied gas may cause burns, severe injury and/or frostbite.
- Fire may produce irritating, corrosive and/or toxic gases.
Chemical Identity & Physical Properties
| Also known as | ETO/R-134a mixtureEthylene oxide-tetrafluoroethane blendEO-HFC134a sterilant mixture |
| Appearance | Colorless liquefied gas mixture under pressure. Ethylene oxide component has a sweet ether-like odor at high concentrations; tetrafluoroethane (R-134a) is nearly odorless. Stored as compressed liquid, releases as gas at ambient temperature. |
| Flash Point | Not applicable (compressed gas mixture) |
| Boiling Point | Approximately -26C (-15F) for R-134a component; -10.7C (12.7F) for ethylene oxide component |
| Vapor Density | 3.5-3.8 (heavier than air) |
| Water Reactivity | No significant reaction with water; gas will dissolve slightly |
Chemical details are general reference only. Always verify with current SDS, ERG, and SOP/SOG.
Fireground Response Guidance — UN 3299
Extinguishing Media
CO2, dry chemical, water spray for cooling containers; foam generally not needed for gas
PPE Requirements
⚠️ Level B minimum with SCBA mandatory; ethylene oxide is highly toxic by inhalation and carcinogenic; chemical-resistant gloves and suit required
Isolation & Evacuation
ERG 126: Initial isolation 100m all directions; protective action distance 300m downwind (small spill day), 800m (large spill night); evacuate area if container rupture imminent
Always confirm protective actions with the current edition of the Emergency Response Guidebook (ERG Guide 126).
First Actions for a UN 3299 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.
- Consider initial downwind evacuation for at least 500 meters (1/3 mile).
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📋 Copy & Share Field Card
UN 3299 — Ethylene oxide and tetrafluoroethane mixHAZMAT RADIO NOTE — UN 3299
Product: Ethylene oxide and tetrafluoroethane mixture, with not more than 5.6% ethylene oxide
Class 2 / Non-Flammable Gas / ERG 126
PPE: Level B minimum with SCBA mandatory; ethylene oxide is highly toxic by inhalation and carcinogenic; chemical-resistant gloves and suit required
ISOLATION: ERG 126: Initial isolation 100m all directions; protective action distance 300m downwind (small spill day), 800m (large spill night); evacuate area if container rupture imminent
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 3299 — Ethylene oxide and tetrafluoroethane mixture, with not more than 5.6% ethylene oxide
Class: 2 | Placard: Non-Flammable Gas | ERG Guide: 126
Appearance: Colorless liquefied gas mixture under pressure. Ethylene oxide component has a sweet ether-like odor at high concentrations; tetrafluoroethane (R-134a) is nearly odorless. Stored as compressed liquid, releases as gas at ambient temperature.
Water Reactivity: No significant reaction with water; gas will dissolve slightly
Extinguishing: CO2, dry chemical, water spray for cooling containers; foam generally not needed for gas
PPE: Level B minimum with SCBA mandatory; ethylene oxide is highly toxic by inhalation and carcinogenic; chemical-resistant gloves and suit required
Isolation: ERG 126: Initial isolation 100m all directions; protective action distance 300m downwind (small spill day), 800m (large spill night); evacuate area if container rupture imminent
— Key Hazards —
• Some may burn but none ignite readily.
• Containers may explode when heated.
• Ruptured cylinders may rocket.
— 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/3299 | Always use current ERG + SOP/SOGIC BRIEFING
Use for: Incident command briefing, staging area whiteboard, or pre-entry team brief. Full chemical + response details.
UN3299 Ethylene oxide and tetrafluoroethane mixture, with not more than 5.6% ethylene oxide Cls2 ERG126 | allfirefighter.com/hazmat/un/3299SMS / 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/3299
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Frequently Asked Questions about UN 3299
Some may burn but none ignite readily. Containers may explode when heated. Ruptured cylinders may rocket. Vapors may cause dizziness or asphyxiation without warning, especially when in closed or confined areas. Vapors from liquefied gas are initially heavier than air and spread along ground. Contact with gas or liquefied gas may cause burns, severe injury and/or frostbite. Fire may produce irritating, corrosive and/or toxic gases.
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 B minimum with SCBA mandatory; ethylene oxide is highly toxic by inhalation and carcinogenic; chemical-resistant gloves and suit required
Water reactivity: No significant reaction with water; gas will dissolve slightly. Recommended extinguishing: CO2, dry chemical, water spray for cooling containers; foam generally not needed for gas.
ERG Guide 126 recommendation: ERG 126: Initial isolation 100m all directions; protective action distance 300m downwind (small spill day), 800m (large spill night); evacuate area if container rupture imminent
No. This is a training/quick-reference aid only. Always consult the current ERG Guide 126 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.