UN 1038 — Ethylene, refrigerated liquid (cryogenic liquid)
Placard: Flammable Gas. ERG Guide 115. Training/quick-reference only — use current ERG + SOP/SOG for incident-specific actions.
Ethylene, refrigerated liquid, is a highly flammable and toxic substance, classified as a DOT Class 2 gas. It is primarily used as a raw material in the production of plastics and other chemicals. First responders may encounter ethylene in various settings, including industrial facilities, transportation accidents, and residential areas. The scale of production and transport of ethylene is significant, with millions of tons being produced and transported annually. Ethylene is a colorless cryogenic liquid or compressed gas with a faint sweet odor, boiling at -104°C (-155°F) at atmospheric pressure. Its widespread use and potential for accidents make it essential for first responders to be familiar with its hazards and response procedures.
Hazard overview: Ethylene is extremely flammable and can be ignited by heat, sparks, or flames. It can also displace oxygen in confined spaces, leading to asphyxiation, and cause cryogenic burns.
Response guidance: In the event of an ethylene spill or leak, first responders should isolate the area 800m in all directions and evacuate if necessary. The use of dry chemical, CO2, or inert gas is recommended for small fires, while foam is ineffective on cryogenic liquids. It is essential to stop the gas flow if safe to do so. First responders should also be aware of the potential for environmental contamination from runoff water. The isolation distance for a tank or rail car involved in a fire is 800m in all directions, with evacuation of the initial 1600m downwind. CHEMTREC should be contacted in the event of a significant spill or leak.
Firefighter training notes: First responders should be trained to recognize the hazards of ethylene and respond accordingly. A common tactical error is the use of foam on cryogenic liquids, which can exacerbate the situation. First responders should be aware of the potential for environmental contamination and take steps to mitigate it. ICS position needs and mutual aid criteria should be established in advance to ensure a coordinated response. First responders should also be trained to use dry chemical, CO2, or inert gas for small fires and to stop the gas flow if safe to do so.
Regulatory context: Ethylene is classified as a DOT Class 2 gas, with a packing group that is not established. The OSHA PEL for ethylene is 200,000 ppm, and it is not listed on the CERCLA list. However, ethylene can still pose a significant environmental hazard if not handled properly.
Storage & handling: Ethylene should be stored in a well-ventilated area, away from incompatible materials such as oxidizers and flammable liquids. The storage temperature should be limited to prevent overheating, and the container should be designed to withstand the pressure of the gas. The top 3 incompatible materials for ethylene are oxidizers, flammable liquids, and other combustible materials.
UN 1038 Quick Details
Common Hazards of UN 1038
- EXTREMELY FLAMMABLE.
- Will be easily ignited by heat, sparks or flames.
- Will form explosive mixtures with air.
- Vapors from liquefied gas are initially heavier than air and spread along ground.
- Vapors may travel to source of ignition and flash back.
- Cylinders exposed to fire may vent and release flammable gas through pressure relief devices.
- Containers may explode when heated.
- Ruptured cylinders may rocket.
Chemical Identity & Physical Properties
Ethylene is a colorless cryogenic liquid or compressed gas with a faint sweet odor. It boils at -104°C (-155°F) at atmospheric pressure and has a flash point of -136°C (-213°F). The vapor density of ethylene is 0.98, which is lighter than air as a gas. Ethylene is typically stored in insulated tanks or containers to maintain its cryogenic temperature.
| Also known as | EtheneEthylene gasRefrigerated liquid ethyleneCryogenic ethyleneLiquid ethylene |
| CAS Number | 74-85-1 |
| Appearance | Colorless cryogenic liquid or compressed gas with a faint sweet odor. Boils at -104°C (-155°F) at atmospheric pressure. Heavier than air as a liquid, lighter than air as a gas. |
| Flash Point | -136C (-213F) |
| Boiling Point | -104C (-155F) |
| Vapor Density | 0.98 (lighter than air as gas) |
| Water Reactivity | No significant reaction with water |
Fireground Response Guidance — UN 1038
Extinguishing Media
PPE Requirements
First responders should wear a minimum of Level B PPE, including SCBA, to respond to an ethylene spill or leak. Insulated gloves and vapor-protective chemical-resistant clothing are also recommended to prevent cryogenic exposure. The use of SCBA is essential to prevent inhalation of toxic gases. First responders should also wear protective clothing to prevent skin contact with the cryogenic liquid.
Isolation & Evacuation
First Actions for a UN 1038 Incident
- Keep unauthorized personnel away.
- Stay upwind, uphill and/or upstream.
- Isolate spill or leak area for at least 100 meters (330 feet) in all directions.
- Consider initial downwind evacuation for at least 800 meters (1/2 mile).
📋 Copy & Share Field Card
UN 1038 — Ethylene, refrigerated liquid (cryogenicUse 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.