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Fire Extinguisher Spacing Calculator: NFPA 10 and OSHA 1910.157 Placement

Calculate Extinguisher Count and Grid Spacing by Fire Class and Travel Distance

Free fire extinguisher spacing calculator for facility managers and fire safety officers. Select the fire hazard class and enter your floor area dimensions to get the required number of extinguishers and grid spacing pattern. Uses NFPA 10 maximum travel distances: 75 ft for Class A, 50 ft for Class B, and 30 ft for Class K cooking areas.

The travel distance rule is not a straight-line measurement. It follows the path a person would actually walk around shelving, equipment, and partitions to reach the nearest extinguisher. A 75-foot travel distance translates to roughly a 53-foot grid spacing because you have to account for diagonal paths across the grid. This calculator does that math and tells you how many units you need and where to put them.

Pro Tip: NFPA 10 Section 6.2.1.1 requires Class A extinguishers within 75 ft travel distance, but OSHA 1910.157(d)(2) says the same thing and it is the enforceable standard. For mixed-use spaces with both ordinary combustibles and flammable liquids, the Class B 50-foot rule controls. Put a 2-A:10-B:C rated extinguisher on the grid and you cover Class A, B, and C in one unit. Class K kitchens always need a separate wet-chemical unit within 30 feet of the cooking appliance.

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Fire Extinguisher Spacing Calculator
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How It Works

  1. Select Fire Class

    Choose the fire hazard class for the area: Class A (ordinary combustibles), Class B (flammable liquids), Class C (electrical), Class D (combustible metals), or Class K (cooking oils and fats).

  2. Enter Area Dimensions

    Input the length and width of the space in feet. The calculator determines the number of extinguishers needed so no point exceeds the maximum travel distance.

  3. Calculate Grid Spacing

    The calculator converts maximum travel distance into a grid pattern for rectangular areas, accounting for diagonal travel. Class A uses 75 ft travel (about 53 ft grid), Class B uses 50 ft travel (about 35 ft grid).

  4. Review Placement Plan

    See the minimum number of extinguishers required, recommended grid positions, and the extinguisher size/rating needed for the hazard level. Verify all points are within required travel distance.

  5. Verify Obstructions

    Walk the actual floor and check that travel paths around shelving, equipment, and partitions do not exceed the maximum distance. Add units if any path is blocked or too long.

Built For

  • Facility managers laying out extinguisher placement for a new warehouse before the fire marshal inspection
  • Safety officers recalculating spacing after a plant rearrangement changes walking paths around new equipment
  • General contractors determining extinguisher needs for a construction site per OSHA 1926.150 temporary requirements
  • Restaurant owners confirming Class K wet-chemical extinguisher placement within 30 feet of commercial cooking equipment
  • Property managers documenting NFPA 10 compliance for multi-tenant industrial buildings with mixed hazard classes
  • Insurance auditors verifying extinguisher count and spacing meet the rated class for the occupancy type

Features & Capabilities

Class-Based Travel Distance

Applies correct NFPA 10 travel distance for each fire class: 75 ft (Class A), 50 ft (Class B), 30 ft (Class K), or user-defined for special hazards.

Grid Spacing Conversion

Converts travel distance to rectangular grid spacing using the diagonal factor. A 75 ft travel distance becomes a 53 ft grid (75 / sqrt(2)).

Extinguisher Count Output

Calculates the minimum number of units to cover the area. Shows the layout as a grid with recommended mounting positions.

Rating Recommendations

Suggests minimum extinguisher ratings for light, ordinary, and extra hazard occupancies per NFPA 10 Table 6.2.1.1.

Multi-Class Support

Handles areas with mixed hazards by applying the most restrictive travel distance. Shows when a single ABC-rated unit covers multiple classes.

PDF Export

Export spacing calculations and placement grids as a branded PDF for fire safety plans and inspection documentation.

Assumptions

  • Maximum travel distances per NFPA 10: 75 ft for Class A, 50 ft for Class B, 30 ft for Class K cooking hazards
  • Grid spacing derived from travel distance using diagonal factor: grid spacing = travel distance / sqrt(2)
  • Travel distance measured along the actual walking path, not a straight-line distance, per NFPA 10 Section 6.2
  • Extinguisher mounting height follows NFPA 10 and OSHA: top of unit not more than 5 ft above floor (3.5 ft for units over 40 lbs)
  • Minimum ratings per NFPA 10 Table 6.2.1.1: 2-A for light hazard, 2-A:10-B:C for ordinary hazard, 4-A:40-B:C for extra hazard
  • Open rectangular floor plan assumed — obstructions, partitions, and dead-end corridors require additional units beyond the grid calculation

Limitations

  • Does not account for physical obstructions (shelving, machinery, partition walls) that increase actual walking paths beyond grid spacing
  • Class D (combustible metals) extinguisher spacing requires site-specific engineering based on the specific metal hazard — not covered by this grid method
  • Mixed-occupancy buildings may have different hazard classes on different floors or zones — each zone must be calculated separately
  • Does not evaluate extinguisher visibility, signage, or cabinet recessing requirements per NFPA 10 Section 6.1
  • Construction-phase temporary extinguisher requirements per OSHA 1926.150 may differ from permanent placement per NFPA 10
  • Clean agent, CO2, and specialty extinguisher sizing for server rooms, labs, and clean rooms is beyond the scope of grid-based placement

References

  • NFPA 10 — Standard for Portable Fire Extinguishers (placement, spacing, maintenance, and inspection)
  • OSHA 29 CFR 1910.157 — Portable Fire Extinguishers (workplace requirements, training, and inspection)
  • OSHA 29 CFR 1926.150 — Fire Protection in Construction (temporary fire extinguisher requirements)
  • NFPA 10 Table 6.2.1.1 — Extinguisher Size and Placement for Class A Hazards by Occupancy
  • NFPA 10 Table 6.3.1.1 — Extinguisher Size and Placement for Class B Hazards
  • NFPA 96 — Standard for Ventilation Control and Fire Protection of Commercial Cooking Operations (Class K requirements)

Frequently Asked Questions

NFPA 10 and OSHA specify maximum travel distances by fire class: Class A ordinary combustibles require 75 feet maximum travel distance, Class B flammable liquids require 50 feet, and Class K commercial cooking equipment requires 30 feet. Travel distance is measured along the actual path a person would walk, not a straight line, accounting for obstacles, aisles, and doorways.
NFPA 10 requires a minimum 2-A rated extinguisher for light (low) hazard occupancies, 2-A:10-B:C for ordinary hazard, and 4-A:40-B:C for extra (high) hazard. The letter rating indicates the fire class, and the number indicates the relative extinguishing capacity. A 2-A extinguisher can handle approximately 25 square feet of Class A fire.
No. Class C fires are energized electrical equipment fires. Once the power is disconnected, they become Class A or Class B fires. NFPA 10 requires that extinguishers for Class C hazards be rated for both the electrical hazard (C) and the underlying fuel class (A or B). A 2-A:10-B:C extinguisher covers all three classes.
OSHA 29 CFR 1910.157 sets minimum workplace requirements that largely reference NFPA 10. Key OSHA additions include mandatory annual maintenance, monthly visual inspections, and employee training on extinguisher use. OSHA allows employers to establish a written fire safety policy and evacuate rather than fight fires, but extinguishers must still be provided unless the employer has an emergency action plan meeting OSHA requirements.
OSHA requires monthly visual inspections (checking accessibility, charge gauge, physical condition) and annual maintenance by a qualified person. Hydrostatic testing is required every 5 or 12 years depending on the extinguisher type. All inspections must be documented with a tag or label showing the date and inspector's initials.
Disclaimer: Spacing calculations are based on rectangular open-floor geometry. Actual placement must account for obstructions, aisle widths, and AHJ (Authority Having Jurisdiction) requirements. Not a substitute for a fire protection engineering review or fire marshal approval.

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