Find how many fire extinguishers each floor needs under NFPA 10: Class A count from hazard, rating and area, a check of the 75 ft (22.9 m) travel distance, and Class B extinguishers for flammable-liquid areas. Works in m² or ft².
Minimum quantities only. Final placement must keep the actual walking distance — around walls, racks and partitions — within the limit, and comply with the adopted edition of NFPA 10 and the local fire authority (e.g. civil defence) requirements.
| Criterion | Light hazard | Ordinary hazard | Extra hazard |
|---|---|---|---|
| Minimum rating per extinguisher | 2-A | 2-A | 4-A |
| Max floor area per unit of A | 3,000 ft² (279 m²) | 1,500 ft² (139 m²) | 1,000 ft² (93 m²) |
| Max floor area per extinguisher | 11,250 ft² (1,045 m²) | 11,250 ft² (1,045 m²) | 11,250 ft² (1,045 m²) |
| Max travel distance | 75 ft (22.9 m) | 75 ft (22.9 m) | 75 ft (22.9 m) |
The count is the larger of two answers: floor area ÷ coverage per extinguisher, and the number needed so nobody walks more than 75 ft to reach one. A bigger rating covers more area, but never more than 11,250 ft² — so in a large open floor, travel distance usually decides the count, not rating.
| Rating | Light hazard | Ordinary hazard | Extra hazard |
|---|---|---|---|
| 2-A | 6,000 ft² (557 m²) | 3,000 ft² (279 m²) | — |
| 3-A | 9,000 ft² (836 m²) | 4,500 ft² (418 m²) | — |
| 4-A | 11,250 ft² (1,045 m²) | 6,000 ft² (557 m²) | 4,000 ft² (372 m²) |
| 6-A | 11,250 ft² (1,045 m²) | 9,000 ft² (836 m²) | 6,000 ft² (557 m²) |
| 10-A | 11,250 ft² (1,045 m²) | 11,250 ft² (1,045 m²) | 10,000 ft² (929 m²) |
| 20-A | 11,250 ft² (1,045 m²) | 11,250 ft² (1,045 m²) | 11,250 ft² (1,045 m²) |
| 30-A | 11,250 ft² (1,045 m²) | 11,250 ft² (1,045 m²) | 11,250 ft² (1,045 m²) |
| 40-A | 11,250 ft² (1,045 m²) | 11,250 ft² (1,045 m²) | 11,250 ft² (1,045 m²) |
Coverage = rating × area per unit of A, capped at 11,250 ft². “—” means the rating is below the minimum for that hazard.
| Hazard | Rating — 30 ft (9.15 m) travel | Rating — 50 ft (15.25 m) travel |
|---|---|---|
| Light | 5-B | 10-B |
| Ordinary | 10-B | 20-B |
| Extra | 40-B | 80-B |
A larger B rating buys a longer travel distance. Class B extinguishers are counted by spacing, so the tool lays a grid over the Class B area at the allowed distance. A multipurpose ABC extinguisher with both ratings can serve both duties.
Travel distance is the actual walking path, not a straight line. As a first estimate, the tool divides the floor into a grid of squares whose centre is no more than 75 ft (straight line) from any corner — squares of about 106 ft (32.3 m) — and places one extinguisher per square. Walls, racking and corridors make real paths longer, so check the final layout on the drawing.
Office floor, light hazard, 2,500 m² (26,910 ft²), 62.5 × 40 m, 4-A extinguishers.
Under NFPA 10 a light-hazard floor needs one 2-A extinguisher per 557 m² (6,000 ft²), and no extinguisher may cover more than 1,045 m² (11,250 ft²). Ordinary hazard halves the area per unit of rating. The 22.9 m (75 ft) travel distance often requires more units than area alone.
75 ft (22.9 m) for Class A hazards. For Class B it is 30 ft or 50 ft depending on the extinguisher's B rating, and 30 ft from cooking appliances for Class K.
Only up to a point. A higher A rating covers more area, but never more than 11,250 ft² per extinguisher, and the 75 ft travel distance still applies. In large open floors the travel distance usually decides the number.
Offices, classrooms, churches and hotel rooms are normally light hazard. Shops, car parks and light manufacturing are ordinary hazard; woodworking, auto repair and high-piled storage are extra hazard.
Yes. Extinguishers are distributed floor by floor; a single floor cannot rely on units on another level. The tool calculates per floor and multiplies by the number of floors.
Found a number that looks wrong, or a case the tool does not cover? Say so here — corrections are welcome and get answered.
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