High-hazard Group H occupancy includes, among other things, the use of a building or structure, or a portion thereof, that involves the manufacturing, processing, generation, or storage of materials that constitute a physical or health hazard.
Hazardous occupancies are classified in Groups H-1, H-2, H-3, H-4 and H-5.
High-hazard Group H-1 buildings and structures that contain materials that pose a detonation (explosion) hazard.
High-hazard Group H-2 buildings and structures contain materials that pose a deflagration or accelerated burning hazard.
High-hazard Group H-3 buildings and structures that contain materials that readily support combustion or pose a physical hazard.
High-hazard Group H-4 buildings and structures which contain materials that are health hazards.
High-hazard Group H-5 semiconductor fabrication facilities and comparable research and development areas in which hazardous production materials (HPM) are used and the aggregate quantity of materials is in excess of those listed in Tables 5003.1.1.(1) and 5003.1.1(2).
Here is a summary of the requirements and their code citations: