Hazardous materials storage is governed by a framework rather than by a single hazard. NFPA 400 sorts materials into physical hazard categories, including flammable and combustible liquids and solids, oxidizers, organic peroxides, pyrophorics, unstable reactives, water-reactives, and cryogenics, and health hazard categories including toxics and corrosives. Each category carries its own maximum allowable quantity per control area, and the whole compliance question begins with classifying accurately.
The control area concept is what makes this framework consequential. A control area is a space within a building bounded by fire-rated construction in which hazardous materials may be stored up to the maximum allowable quantity for each class. Within the limits, ordinary occupancy requirements apply. Above them, the space becomes a high hazard occupancy, which brings construction type, separation, egress, explosion control, and ventilation requirements that reach far beyond fire protection scope and can be extremely expensive to retrofit.
That threshold behavior is why the inventory assessment matters more than the suppression design on these pages. Facilities that accumulate hazardous materials incrementally cross MAQ without a triggering event, and the discovery typically comes during a permit review, an insurance survey, or an AHJ inspection prompted by something unrelated. At that point the options are reducing inventory, adding control areas through rated construction, or accepting an occupancy reclassification, and the cost differential between them is very large.