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NFPA 13
Validated against the standard.
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$2.99 Pro
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How it works
Enter your values
Type in your inputs — the app fills code tables and constants for you, so there's nothing to look up.
Get a code-checked result
Instant answer with a clear PASS / FAIL and the exact NFPA 13 reference behind every number.
Save & export
Keep a history of calculations and export a clean PDF report to share or attach to a permit (Pro).
What this calculator does
The occupancy hazard classification drives the entire sprinkler design — the required density, the design area, and the spacing. This app helps you assign the correct NFPA 13 hazard class and returns the matching density/area design point.
The NFPA 13 hazard classes
- Light hazard — offices, schools, churches; low combustible load.
- Ordinary hazard (Group 1 and Group 2) — most commercial and light manufacturing.
- Extra hazard (Group 1 and Group 2) — high combustible or flammable-liquid processes.
Each class maps to a density (gpm/ft²) over a design area (ft²) on the NFPA 13 density/area curves.
Worked example
A light-hazard office is commonly designed around 0.10 gpm/ft² over a 1,500 ft² area; an ordinary hazard space calls for a higher density over a similar or larger area — the values the hydraulic calc then uses.
Related calculators
Feed the density into the sprinkler hydraulic calculator and place extinguishers with the extinguisher calculator.
Hazard classification FAQ
Why does hazard class matter so much?
It sets the required water density and design area in NFPA 13, which in turn drives pipe sizes, the hydraulic demand, and the water supply the system needs.
What are the main classes?
Light hazard, Ordinary hazard Groups 1 and 2, and Extra hazard Groups 1 and 2, ranging from low to high combustible loading.
Does it give the density and area?
Yes. For the selected class it returns the density/area design point used as the input to the hydraulic calculation.
Does it work offline?
Yes, it runs 100% offline with no account. Free with rewarded ads; a one-time $2.99 Pro unlock adds PDF export and saved history.
Get Hazard Class on your phone
Free with rewarded ads · $2.99 lifetime Pro · iOS & Android. Works 100% offline on the job site.