NFPA 13 sizes a sprinkler system around the hazard classification of the space it protects, which is why the same square footage can require very different systems depending on what’s inside.
Light Hazard
Spaces with low combustible content and low fire spread potential, such as offices, classrooms, hotel guest rooms, and hospitals. These require the lowest water density and generally the least robust (and least costly) system design.
Ordinary Hazard (Group 1 and 2)
Covers moderate combustible loads, such as retail stores, parking garages, and light manufacturing (Group 1), up to higher-content spaces like libraries and mercantile occupancies with taller storage (Group 2). Water density requirements step up accordingly.
High Hazard
Reserved for occupancies with high fuel loads or fast fire spread potential, such as chemical processing or high-piled storage warehouses. These require the highest water density and often the most complex system design, sometimes including specialized systems beyond standard sprinklers.
Why It Matters for Your Project
Hazard classification, decided early in design, drives pipe sizing, sprinkler spacing, and water supply requirements — which is a major reason two buildings of the same size can have very different sprinkler costs. See our System Design and Code Compliance guides for more, or the Fire Protection Glossary for other terms.