After moving people to a safe location, if it safe to do so, isolate the source of hydrogen feeding the fire. Burns and explosions are hazards when exposed to a hydrogen fire. For more best laboratory preventative safety practices as well as first responder response to a hydrogen incident See both CHS training resources: 

• https://www.aiche.org/ili/academy/courses/ela210/hydrogen-laboratory-safety
• https://www.aiche.org/ili/academy/courses/ela253/introduction-hydrogen-safety-first-responders    

AICHE ELA253 CHS ” Introduction to Hydrogen Safety for First Responders” is a good reference and discusses both LH2 and GH2. LH2 fires are very unusual. LH2 releases usually are GH2 so the fires at either ambient for low flow or the GH2 is a cryo temperature for high flow. Fires from LH2 tanks ignite less frequently than GH2 high-velocity releases. The colder the gas the less potential for ignition. The guidelines for managing a hydrogen fire is to eliminate the source of the fire before putting
the fire out while keeping equipment exposed to higher temperatures cool.