UN 1966 — Hydrogen, refrigerated liquid (cryogenic liquid)
Placard: Flammable Gas. ERG Guide 115. Training/quick-reference only — use current ERG + SOP/SOG for incident-specific actions.
UN 1966 is Hydrogen, refrigerated liquid (cryogenic liquid), an extremely flammable cryogenic gas assigned to ERG Guide 115. It vaporizes rapidly and warmed hydrogen may accumulate overhead.
Hazard overview: UN 1966 presents flammable hydrogen cloud, near-invisible flame, cryogenic frostbite, material embrittlement and container rupture hazards.
Response guidance: For a UN 1966 incident, verify the product with shipping papers, container markings, SDS and ERG Guide 115. Establish incident command, isolate the area, stay upwind, control ignition or downwind hazards, cool exposed containers from a protected distance when appropriate and base entry decisions on monitoring and local SOP.
Firefighter training notes: Training for UN 1966 should emphasize gas vapor travel, flashback, cylinder cooling, BLEVE/rocket hazards, source isolation, invisible or low-lying vapor behavior and ignition control. Use ERG 115, SDS and local SOP.
Regulatory context: Hydrogen, refrigerated liquid (cryogenic liquid) is regulated as a hazardous material for transportation and emergency response purposes. Requirements for storage, workplace exposure, emergency planning, spill reporting and waste handling vary by exact product, concentration, quantity and jurisdiction. Verify current requirements through shipping papers, SDS, container markings and applicable DOT, OSHA, EPA, NFPA, state or local authority guidance.
Storage & handling: Hydrogen, refrigerated liquid (cryogenic liquid) should be stored in approved cryogenic containers in a ventilated area away from heat, ignition sources where flammable, confined low spots and physical damage. Provide pressure relief, oxygen/flammable gas monitoring where appropriate and cryogenic handling controls.
UN 1966 Quick Details
Common Hazards of UN 1966
- EXTREMELY FLAMMABLE cryogenic hydrogen; vapors may ignite easily and form explosive mixtures with air.
- Rapid vaporization can create large flammable clouds; hydrogen flames may be nearly invisible.
- Gas is very light when warmed and may accumulate under roofs, canopies or overhead pockets.
- Contact with liquid hydrogen or cold vapor can cause severe frostbite and cryogenic burns.
- Containers exposed to heat may vent, rupture or rocket.
- Liquid hydrogen can embrittle materials and condense oxygen-enriched air on cold surfaces.
- Do not extinguish a leaking hydrogen fire unless the gas flow can be stopped safely.
Chemical Identity & Physical Properties
Colorless, odorless cryogenic liquid stored at extremely low temperature (-253°C). Boils rapidly at ambient temperature, producing large volumes of flammable gas.
| Also known as | Liquid hydrogenLH2Cryogenic hydrogenRefrigerated liquid hydrogen |
| CAS Number | 1333-74-0 |
| Appearance | Colorless, odorless cryogenic liquid stored at extremely low temperature (-253°C). Boils rapidly at ambient temperature, producing large volumes of flammable gas. |
| Flash Point | Not applicable (cryogenic gas) |
| Boiling Point | -253°C (-423°F) |
| Vapor Density | 0.07 (lighter than air) |
| Water Reactivity | No significant reaction with water, but rapid vaporization and extreme cold hazard on contact |
Fireground Response Guidance — UN 1966
Extinguishing Media
PPE Requirements
Use positive-pressure SCBA for leak, vapor, fire or confined-space exposure. Wear flame-resistant protection, eye/face protection and insulated gloves where liquefied or cryogenic gas contact is possible.
Isolation & Evacuation
First Actions for a UN 1966 Incident
- CALL 911. Then call the emergency response telephone number on the shipping paper, if available.
- Keep unauthorized personnel away.
- Stay upwind, uphill and/or upstream.
- Avoid breathing gas, vapor, smoke or mist and avoid skin or eye contact.
- Protect against cryogenic frostbite and avoid low/confined areas until oxygen and flammable gas readings are checked.
- Eliminate ignition sources if safe and keep gas or vapor out of drains, sewers, basements and low areas.
- Do not touch damaged containers or spilled/released material unless properly trained and wearing appropriate protective equipment.
- Ventilate closed spaces before entering, but only if properly trained, equipped, monitored and authorized by incident command.
- Isolate the release area and expand the perimeter for fire involvement, cylinder heating, vapor accumulation, unknown gas identity or downwind exposure.
- Use ERG Guide 115, shipping papers, SDS, air monitoring and incident command for protective actions.
📋 Copy & Share Field Card
UN 1966 — Hydrogen, 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.