Most MSDSs recommend not to extinguish a hydrogen fire, rather to try to disconnect the hydrogen source. In which cases is extinguishing recommended?

Situations where extinguishing a hydrogen leak prior to stopping flow is safer are rare. Hydrogen releases have a high potential for inadvertent re-ignition and subsequent explosion. Some vent stacks might be equipped with an extinguishing system, but these often can be more hazardous than allowing a properly designed vent stack to continue to burn until the source is isolated.