Section 4.3.1/Hazard Classification
NFPA 13 Section 4.3 classifies occupancies as Light Hazard, Ordinary Hazard (Group 1 or 2), or Extra Hazard (Group 1 or 2), determining sprinkler spacing, density, and water supply requirements.
Every area protected by a sprinkler system must be classified by occupancy hazard. Light Hazard (Section 4.3.1) includes occupancies where the quantity and combustibility of contents are low, such as offices, churches, hospitals, and educational facilities. Ordinary Hazard Group 1 (Section 4.3.2) includes occupancies where combustibility is low and stockpiles do not exceed 8 feet, such as parking garages, laundries, and restaurant service areas. Ordinary Hazard Group 2 (Section 4.3.3) includes occupancies where the quantity and combustibility of contents are moderate and stockpiles do not exceed 12 feet, such as mercantile, manufacturing, and library stack rooms. Extra Hazard Group 1 (Section 4.3.4) includes occupancies with high combustibility and little or no flammable liquids, and Extra Hazard Group 2 (Section 4.3.5) includes occupancies with moderate to substantial amounts of flammable liquids or extensive shielding. The hazard classification directly determines the sprinkler spacing, design area and density, and pipe sizing calculations.
Why this section exists
The hazard classification is the foundation of sprinkler system design. A system designed for light hazard delivers water at a lower density over a smaller design area, while an extra hazard system requires a much higher density over a larger area. Getting the classification wrong means the sprinkler system may be fundamentally undersized for the actual fire risk. The classification system provides a standardized framework that accounts for fuel load quantity, combustibility, expected fire growth rate, and storage heights. Mixed-use buildings require the highest applicable classification for each area, or hydraulically separated zones.
What plan reviewers look for
Plan reviewers check that the hazard classification is stated on the sprinkler drawings for every protected area. They verify the classification matches the actual use of each space by comparing it to the occupancy descriptions in Sections 4.3.1 through 4.3.5. For buildings with multiple hazard classifications, they check that each zone is identified on the floor plans and that the hydraulic calculations use the correct classification for the most demanding area. They also verify that storage areas above 12 feet are not classified under the occupancy hazard approach and instead use the commodity storage chapters (Chapters 12 through 20).