UN 3138 — Ethylene, acetylene and propylene mixture, refrigerated liquid containing at least 71.5% ethylene with not more than 22.5% acetylene and not more than 6% propylene
Placard: Flammable Gas. ERG Guide 115. Training/quick-reference only — use current ERG + SOP/SOG for incident-specific actions.
UN 3138 is a refrigerated liquefied mixture of ethylene, acetylene and propylene. The main concerns are flash fire, vapor explosion, cryogenic burns and container failure.
Hazard overview: The mixture releases flammable vapors that can travel to ignition sources and flash back. Cold vapor can collect low at first, and fire exposure can cause pressure relief venting or violent rupture.
Response guidance: Isolate widely, remove ignition sources and do not extinguish a leaking gas fire unless the leak can be stopped safely. Cool exposed containers from maximum distance and use dry chemical for small incipient flame control.
Firefighter training notes: Train crews on BLEVE/rocket hazards, vapor cloud control and the danger of extinguishing gas fires before shutting off the leak. Establish hot zones early.
Regulatory context: UN 3138 is a Class 2 flammable gas entry. Verify mixture limits, container type and emergency contact information from shipping papers and SDS.
Storage & handling: Keep refrigerated containers secured, grounded where required, well ventilated and protected from heat, impact and ignition sources. Do not store near oxidizers.
UN 3138 Quick Details
Common Hazards of UN 3138
- Extremely flammable refrigerated hydrocarbon gas mixture.
- Vapors can form explosive mixtures with air and may flash back to the release point.
- Cold vapors may initially travel along the ground and collect in low or confined areas.
- Cryogenic liquid contact can cause frostbite and brittle failure of some materials.
- Containers exposed to fire may vent, rupture or rocket.
- Acetylene content increases instability concerns if the container is heated or damaged.
- Ignition sources, static discharge and confined spaces create severe explosion hazards.
Chemical Identity & Physical Properties
The material is a colorless cryogenic liquid that boils rapidly to flammable vapor. Vapor behavior changes as it warms, but cold clouds can spread along the ground near the release.
| Also known as | Refrigerated ethylene-acetylene-propylene mixtureCryogenic hydrocarbon gas mixtureLiquefied C2-C3 olefin blendEthylene-rich refrigerated gas mixture |
| Appearance | Colorless cryogenic liquid with a faint sweet odor. Boils at extremely low temperature, producing flammable vapors. Refrigerated to maintain liquid state during transport. |
| Flash Point | Not applicable (cryogenic flammable gas mixture, auto-ignites well below normal temperatures) |
| Boiling Point | Approximately -104°C (-155°F) for ethylene component; mixture boils at cryogenic temperatures |
| Vapor Density | 0.98 (slightly lighter than air at normal temperature, but cold vapors are heavier) |
| Water Reactivity | No significant reaction with water, but rapid vaporization creates extreme fire/explosion hazard |
Fireground Response Guidance — UN 3138
Extinguishing Media
PPE Requirements
Use SCBA, flame-resistant protective clothing, antistatic precautions and cryogenic hand/face protection for liquid exposure. Operate from protected positions.
Isolation & Evacuation
First Actions for a UN 3138 Incident
- Call 911 and the emergency response number shown on the shipping paper, if available.
- Keep unauthorized personnel away and establish incident command before close approach.
- Stay upwind, uphill and upstream; avoid low areas where vapors or gases may collect.
- Avoid breathing vapors, dust, mist or fire gases and avoid skin or eye contact.
- Do not touch damaged containers or spilled material without proper PPE and training.
- Ventilate confined spaces only after atmospheric monitoring and only with trained, equipped personnel.
- Use ERG guidance, SDS, shipping papers and monitoring results for final protective actions.
📋 Copy & Share Field Card
UN 3138 — Ethylene, acetylene and propylene mixturUse for: Quick radio or face-to-face size-up. Short, structured, field-ready.
Use for: Incident command briefing, staging area whiteboard, or pre-entry team brief.
Use for: Quick text to command or incoming units. Fits in a single SMS.