Hyperbaric oxygen is useful in -
The Undersea and Hyperbaric Medical Society (UHMS) currently recognizes hyperbaric oxygen therapy (HBO) as an approved therapy for 13 pathologic entities. These are conditions for which HBO has substantial scientific support demonstrating therapeutic benefit.
Hyperbaric oxygen is currently considered a primary treatment modality for

carbon monoxide poisoning, cerebral arterial gas embolism, osteoradionecrosis, decompression sickness, and clostridial gas gangrene.

It is also considered an adjunctive therapy for 

acute exceptional blood loss anemia, acute thermal burns, compromised skin grafts or skin flaps, crush injury, compartment syndrome, necrotizing soft-tissue infections, non-clostridial gas gangrene, radiation tissue damage, refractory osteomyelitis, selected problem wounds, and intracranial abscesses.

Treatment of frostbite injuries with HBO is considered experimental.

The treatment protocol for frostbite includes rapid rewarming, close observation, elevation and splinting daily hydrotherapy, and serial debridements.- Schwartz 9/e p409
Tetanus
Gas gangrene
Frostbite
Vincent's angina