What safety rules or guidelines should be followed when working with liquefied hydrogen?

Example safety guidelines are listed below but may not be all-inclusive (e.g., they do not cover general practices such as lockout/tagout, management of change, job safety analysis), and most are the same as for gaseous hydrogen. Also reference NFPA 2 and CGA documents such as H-3, H-5, and H-7. Additional safety training material can also be found on the following link to courses and information offered by the AIChE Center for Hydrogen Safety.

Fundamental Hydrogen Safety Credential

1. Wear proper personal protective clothing (fire-resistant clothing, safety shoes, hard hat, safety glasses). Due to potential cold injury, insulated gloves and a full-face shield are also recommended when handling liquid hydrogen.
2. Carry an operating personal flammable gas monitor. 
3. Purge piping of hydrogen when opening to the atmosphere and purge the air from the piping after completing maintenance. Purge gases, warm or cold, should always be an inert, non-flammable gas.
4. Purge with helium gas for cold liquid piping or vessels at or below the freezing temperature of nitrogen (~-320 F). It is recommended that helium be used for any temperatures below -250 F. All purge gases except helium will solidify at LH2 temperatures. Vacuum-jacketed pipe can remain cold for days since they are insulated to minimize heat transfer. LH2 tanks can remain cold for a week or more and may contain residual LH2 that is difficult to drain.
5. Pressure test/leak test before introducing hydrogen back into the piping or vessel.
6. Check the operation of all safety instrumentation at startup and at least annually thereafter.
7.  Check vent stacks for condensate by opening the drain valves (preferably spring-return automatic closing valve).
8. Check the vent stack supports with emphasis on damage, corrosion, or loosening of supports (e.g., guy wire).
9. If the LH2 tank supports are greater than 18  ”, they must be fireproofed (per NFPA 2). Improperly sealed fireproofing can lead to corrosion that is difficult to find. Check the sealing of the fireproofing and check for corrosion on the steel underneath.
10. Liquid hydrogen may create liquefied air on the exterior of uninsulated process and vent piping. Personnel must take care to avoid contact with cold piping and liquefied air due to potential for cryogenic burns. The liquefied air should also not be allowed to contact flammable materials since it will be oxygen-enriched.
11. Keep hot work at least 50 ft from the hydrogen system. Use a job safety analysis and hot work permit system if the work must be closer to assure safety is addressed by developing safe procedures and processes.