Personnel with cryogenic liquids

As with other cryogenic liquids, cryogenic hydrogen is not to be used or handled by any personnel unless they are familiar with its properties and skilled in the procedures necessary for its safe use. Cryogenic liquids other than oxygen which vaporize in enclosed areas may reduce the oxygen content in the atmosphere below the level necessary... 

Basically, we must not permit the cryogenic fluids and their vapors to contact any part of the body. The eyes and face are particularly vulnerable. Accordingly, all operations must be conducted with adequate eye and face protection. All personnel who work with low-temperature systems should wear safety glasses at all times. Further, where there is a possibility of face contact with cold vapors or liquid, a full face shield or perhaps a face shield and hood should be worn. Care must be taken not to permit rising vapors from lighter-than-air gases to enter the shield. As noted in the previous section, only inert hoods such as those made of Teflon or KelF should be worn to avoid skin contact with fluorine. 

---