☣️ UN 1966 • CLASS 2
Hydrogen, refrigerated liquid (cryogenic liquid)
Placard: Flammable 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 1966
Class: 2
Placard type: Flammable Gas
ERG: Guide 115 (check current ERG)
Isolation: ERG 115: isolate 800m all directions; evacuate 1600m downwind if tank/rail car involved in fire
Chemical & Response Details
| 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 |
| Extinguishing | Do not use water or foam; use dry chemical, CO2, or allow to burn under controlled conditions |
| PPE | ⚠️ Level B minimum with cryogenic-rated gloves and face shield; SCBA required; protect skin from cryogenic burns |
| Isolation | ERG 115: isolate 800m all directions; evacuate 1600m downwind if tank/rail car involved in fire |
Chemical details are general reference only. Always verify with current SDS, ERG, and SOP/SOG.
Common hazards (high level)
- 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.
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
- 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).
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UN 1966 — Hydrogen, refrigerated liquid (cryogenic HAZMAT RADIO NOTE — UN 1966
Product: Hydrogen, refrigerated liquid (cryogenic liquid)
Class 2 / Flammable Gas / ERG 115
PPE: Level B minimum with cryogenic-rated gloves and face shield; SCBA required; protect skin from cryogenic burns
ISOLATION: ERG 115: isolate 800m all directions; evacuate 1600m downwind if tank/rail car involved in fire
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 1966 — Hydrogen, refrigerated liquid (cryogenic liquid)
Class: 2 | Placard: Flammable Gas | ERG Guide: 115
Appearance: Colorless, odorless cryogenic liquid stored at extremely low temperature (-253°C). Boils rapidly at ambient temperature, producing large volumes of flammable gas.
Water Reactivity: No significant reaction with water, but rapid vaporization and extreme cold hazard on contact
Extinguishing: Do not use water or foam; use dry chemical, CO2, or allow to burn under controlled conditions
PPE: Level B minimum with cryogenic-rated gloves and face shield; SCBA required; protect skin from cryogenic burns
Isolation: ERG 115: isolate 800m all directions; evacuate 1600m downwind if tank/rail car involved in fire
— Key Hazards —
• EXTREMELY FLAMMABLE.
• Will be easily ignited by heat, sparks or flames.
• Will form explosive mixtures with air.
— 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/1966 | Always use current ERG + SOP/SOGIC BRIEFING
Use for: Incident command briefing, staging area whiteboard, or pre-entry team brief. Full chemical + response details.
UN1966 Hydrogen, refrigerated liquid (cryogenic liquid) Cls2 ERG115 | allfirefighter.com/hazmat/un/1966SMS / 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/1966
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FAQ
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.
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 cryogenic-rated gloves and face shield; SCBA required; protect skin from cryogenic burns
No. This is a training/quick-reference aid only. Always consult the current ERG Guide 115 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.