Portable Fire Extinguisher Coverage (NFPA 10)

Two limits that turn out to be one. NFPA 10 caps travel distance to a Class A extinguisher at 75 ft and caps coverage at 11,250 sq ft per unit -- and those are not independent numbers: on a clear floor with units on a square grid the worst point is the centre of a square, so spacing can be d x sqrt(2) and area per unit is 2 d^2, and 2 x 75^2 is exactly 11,250. The area ceiling IS the geometry of the travel distance, which tells you it already assumes a perfectly open floor. Class K at 30 ft covers only 1,800 sq ft, so travel distance governs by a mile. The caveat that outranks the arithmetic: travel distance is measured along the PATH, not straight-line, so this count is a FLOOR -- walk the routes. Extinguisher RATING is a separate table and is not shipped.

grid spacing = travel distance x sqrt(2); area per extinguisher = 2 x travel^2 (the worst-case point on a square grid sits at the centre of a square, sqrt(2)/2 of the spacing away); count by travel = ceil(floor area / area per extinguisher); count by the area ceiling = ceil(floor area / cap); required = the larger of the two.

NFPA 10 - a maximum travel distance to a Class A extinguisher of 75 ft at all hazard levels, 30 ft for Class K, and 30 or 50 ft for Class B depending on the extinguisher's B rating and the hazard level; and the 6.1.3.3 ceiling of 11,250 sq ft of coverage per extinguisher. The square-grid relation is geometry, not a code value.

The travel distances and the area ceiling are widely quoted figures. NFPA 10's maximum-area-per-unit-of-A table by hazard classification is NOT reproduced, and Class D travel distances are not shipped.

Estimate. AHJ and licensed professional govern.

Field names used by the API: floor_area_sf, hazard_class, area_cap_sf, travel_used_ft, grid_spacing_ft, area_per_unit_sf, by_travel, by_area_cap, required_extinguishers

• Class A travel 75 ft at all hazard levelsNFPA 10
• Class K travel 30 ft to a wet-chemical unit, in addition to the room's Class A coverageNFPA 10
• Class B travel 30 or 50 ft by B rating and hazard level - entered, not assumedNFPA 10
• Area ceiling 11,250 sq ft per extinguisher, which equals 2 x 75^2NFPA 10 6.1.3.3 plus square-grid geometry
• Path of travel measured along the walking route, so the grid count is an open-floor FLOORNFPA 10 measurement rule
• Rating not determined the maximum-area-per-unit-of-A table by hazard class is separate and not reproducedstated scope limit