How Many Fire Extinguishers Do I Need? A Factory Calculation Method

The method in five steps

Most counting mistakes come from using a rule of thumb copied from another building. A defensible count follows the logic of NFPA 10 (Standard for Portable Fire Extinguishers), which many buyers, insurers and auditors in Bangladesh use as the reference alongside BNBC and Fire Service requirements.

1. Classify the hazard of each area: light, ordinary or extra.
2. Identify the fire classes present in each area (A, B, electrical, cooking oil).
3. Lay out units for travel distance, so nobody has to walk too far to reach one.
4. Check floor area against rating, using the extinguisher's rating on its label and NFPA 10's coverage table for that hazard class.
5. Add units for special hazards, then mount, sign and record them.

Work floor by floor and zone by zone. A five-storey building with the same layout on each floor still needs the full calculation repeated for each floor, because extinguishers on one floor do not protect another.

Step 1 and 2: hazard class and fire classes

NFPA 10 groups occupancies into three hazard levels based on how much combustible material is present and how fast a fire could grow:

Many garments and textile production floors are at least ordinary hazard because of fabric, cartons, lint and dust. Warehouses with high stacks of fabric or finished goods are often treated as extra hazard. If you are unsure between two levels, use the higher one.

Then list the fire classes in each zone. A sewing floor has Class A (fabric, paper) and electrical (machines, DB boxes). A generator room adds Class B (diesel). A canteen adds cooking oil. Each class needs a suitable extinguisher; see fire extinguisher types.

Step 3: travel distance

Travel distance is the actual walking distance from any point on the floor to the nearest suitable extinguisher, measured along the routes people can walk, around machines, racks and partitions. It is not a straight line on the drawing.

For Class A hazards, NFPA 10 sets a maximum travel distance of 75 ft (about 23 m). Practical tips for applying it:

• Draw the walkable aisles on the floor plan first. On a sewing floor, the main aisles and cross aisles between machine lines are the real routes.
• From each candidate extinguisher position, trace 23 m along the aisles. Every work position must fall inside at least one of these walking radii.
• Corners, toilets, store rooms and mezzanines are where gaps usually appear.
• Class B and other special hazards have their own, generally shorter, distance rules in NFPA 10; check the standard for those zones rather than reusing the Class A figure.

Travel distance usually produces sensible positions: near exits, at stair landings, at aisle intersections and next to columns where units are easy to find.

Step 4: floor area and extinguisher rating

Every listed extinguisher carries a rating, such as a number followed by "A" for Class A capacity (for example 2-A or 4-A on UL-listed units). A higher number means the unit can control a larger Class A fire.

NFPA 10 provides a table that, for each hazard level, gives:

• the minimum rating a single extinguisher must have,
• the maximum floor area each unit of A rating may cover, and
• the maximum floor area any single extinguisher may cover.

The check is: total floor area of the zone, divided by the area one of your chosen extinguishers may cover at that hazard level, gives the minimum number of units. Compare that with the number your travel-distance layout produced. Whichever is larger governs.

This is why the rating on the label matters as much as the kilogram size. Low-rated units can require noticeably more extinguishers on a large floor than higher-rated ones. If a supplier cannot tell you the rating of the model offered, or the unit has no rating at all, you cannot complete this step, which is a reason to ask for listed products. Our procurement checklist explains what to request.

Worked example: a garments sewing floor

The floor. A rectangular sewing floor of 60 m × 30 m (1,800 m²), ordinary hazard. Two exit stairs, one at each short end. A central main aisle runs the full 60 m length, with cross aisles every few machine lines. Four DB boxes are grouped in two locations along one long wall. There is a small machine-oil store in one corner.

Travel distance layout. The farthest work positions are at the long walls, about 15 m walk from the main aisle via the cross aisles. That leaves roughly 8 m of the 23 m allowance to travel along the main aisle, so units on the aisle need to be no more than about 16 m apart. Positions at about 8 m, 24 m, 40 m and 56 m along the aisle cover the full length, and placing the two end units close to the stair doors keeps them on the escape route. Result: 4 Class A units on the main aisle.

Area check. Look up the ordinary-hazard row of the NFPA 10 table for the rating of the model you plan to buy, and divide 1,800 m² by the area one unit may cover. If that gives more than 4, add units (for example along the long walls) until both checks are satisfied, or choose a higher-rated model.

Special hazards. Add a CO2 unit at each DB box group (2 units) and a foam or ABC unit at the oil store (1 unit).

Repeat the exercise for every floor, the cutting section, the finishing floor, the warehouse and the canteen. The example is illustrative; your final layout should be checked against current BNBC, Fire Service and buyer or auditor requirements by a competent person.

Mounting height, signage and visibility

• Height: under NFPA 10, typical portable extinguishers are mounted with the top no higher than about 1.5 m (5 ft) above the floor, with heavier units mounted lower. Units should not sit directly on the floor; use a bracket or a stand.
• Visibility: on the escape route, near exits and stair doors, at the same position on every floor. If a unit is not visible from the aisle, add a sign above it.
• No obstruction: keep stacked cartons, trolleys and bundles away. A blocked extinguisher counts as missing in an audit.
• Pair with the right equipment: fire bucket stands, sand buckets and equipment boxes can support portable units in production areas, but they do not replace them.
• Record keeping: number each unit, mark it on the floor plan and keep a monthly check tag.

Browse fire extinguishers and fire safety equipment such as bucket stands and equipment boxes, and see our RMG and textile page for wider factory requirements.

Common counting mistakes

• Measuring travel distance as a straight line across machine rows.
• Counting kilograms instead of ratings in the area check.
• Using powder units in server rooms or water units near DB boxes.
• Forgetting mezzanines, store rooms, stairs, rooftop generator areas and canteens.
• Placing units deep inside the floor instead of on the route towards an exit.
• Buying the count once and never updating it after a layout change.

When your layout is ready, send it through request a quote and we will price the full list, including stands, signs and CO2 or K-type units.

Frequently asked questions

Sources

• National Fire Protection Association (NFPA)
• Fire Service and Civil Defence, Bangladesh