How much fire water does a given building need? FM Global DS 3-26 (Fire Protection for Nonstorage Occupancies, April 2019, Interim Revision April 2025) places nonstorage occupancies in three hazard categories (HC-1, HC-2, HC-3) and gives each a design density and demand area by ceiling height and system type. Incidental and low-piled storage are also covered; higher storage goes to DS 8-9 (Section 1.0).
Hazard Category (Table 2.2.2 and Appendix C)
The category follows the predominant occupancy per Table 2.2.2, with examples in Appendix C Tables C-1 and C-2. Higher-hazard areas within a site, such as plating lines with plastic tanks, are protected at the higher category.
| Occupancy (Appendix C examples) | Category |
|---|---|
| Offices, hotels, residential and apartments, hospitals and hospital laboratories, schools, dormitories, museums, libraries, restaurant seating areas, airport terminals | HC-1 |
| Shopping malls and retail areas, supermarkets, theatres, sport arenas, metal-working and machine shops, electronics assembly, food production, woodworking and furniture, textiles, IT facilities and electrical rooms, hospital utility plants | HC-2 |
| Parking garages and car parks, vehicle repair and assembly, truck loading docks, plastic injection moulding (PP/PE/PS), plastics manufacturing, coating and printing in paper plants, film and TV studios, exhibition halls, pharmacies with storage | HC-3 |
Design (Table 2.3.1.10, p. 6)
| Category | Ceiling to 9 m, wet / dry | To 13.5 m, wet / dry | To 18 m, wet / dry | To 30 m, wet |
|---|---|---|---|---|
| HC-1 | 4 mm/min × 140 m² / 4 × 140 | 8 × 230 / 8 × 330 | 8 × 230 / 8 × 330 | 24 × 110 |
| HC-2 | 8 × 230 / 8 × 330 | 8 × 230 / 8 × 330 | 8 × 230 / 8 × 330 | 24 × 110 |
| HC-3 | 12 × 230 / 12 × 330 | 12 × 340 / 12 × 430 | 20 × 280 / 20 × 370 | 24 × 110 |
- The 30 m designs are limited to K14.0 (K200) and larger sprinklers, and no dry-system design is given at that height (2.3.1.10.1).
- Note 1: for dormitory, residential and dwelling areas with at least one-hour compartmentation, the demand area may be the largest room, but not less than four sprinklers, with corridors treated as rooms.
- Note 2: for wet HC-2 and HC-3 areas under 9 m, 160°F (70°C) K11.2EC (K160EC) upright sprinklers may use 12 mm/min over 140 m² (minimum 6 sprinklers) and K14.0EC (K200EC) upright sprinklers 12 mm/min over 90 m² (minimum 4).
- At least 0.5 bar at the most remote sprinkler in all cases (2.3.1.11); hose allowance 950 L/min for HC-1 and HC-2 and 1,900 L/min for HC-3 (2.3.1.12); 60 minutes duration for all categories (2.3.1.13).
- Manufacture of large contiguous components such as aircraft, boats and wind turbine blades exceeds typical HC-2/HC-3: use Table 2.3.1.10 below 18 m and K25.2 (K360) sprinklers at 12 sprinklers × 3.5 bar above it (2.3.1.14).
- The table does not apply to ignitable liquids beyond incidental quantities, dust or lint on horizontal surfaces, plastic construction elements, combustible concealed spaces, or storage beyond incidental amounts (2.3.1.10).
Total Demand and Volume
Density × demand area is a lower bound for the sprinkler flow; the actual flow comes from the hydraulic calculation per DS 3-0. Lower bounds for wet systems under ceilings up to 9 m:
| Category | Sprinklers (minimum) | Hose | Total | 60-minute volume (minimum) |
|---|---|---|---|---|
| HC-1 | 4 × 140 = 560 L/min | 950 L/min | 1,510 L/min | 90.6 m³ |
| HC-2 | 8 × 230 = 1,840 L/min | 950 L/min | 2,790 L/min | 167.4 m³ |
| HC-3 | 12 × 230 = 2,760 L/min | 1,900 L/min | 4,660 L/min | 279.6 m³ |
The hose allowance is deducted from the water supply curve at the base of the riser (DS 3-0 2.1.2.4.4). See the DS 3-0 most demanding area article for a worked design area.
System and Sprinkler Selection (2.3.1.4–2.3.1.8)
- Wet, dry, preaction or antifreeze systems may be used; wet systems unless the area is refrigerated or unheated and can fall below 4°C (2.3.1.4–2.3.1.5).
- Wet systems use 70°C sprinklers, or 100°C where the ambient exceeds 38°C; no standard-response sprinklers above 18 m ceilings; sidewall sprinklers in HC-1 and HC-2 (K14EC sidewall also in HC-3) (2.3.1.5).
- Dry systems use upright or dry pendent sprinklers at 140°C (70°C acceptable in HC-1 and HC-2), standard coverage; water delivery 60 s to the single most remote sprinkler or 40 s to four sprinklers on two lines (2.3.1.6).
- Single-interlocked preaction systems are treated as wet or dry, non-interlocked and double-interlocked as dry; antifreeze systems as wet (2.3.1.7–2.3.1.8).
Quick Checklist
- Hazard category from Table 2.2.2 and Appendix C; higher-hazard areas assessed separately
- Design from Table 2.3.1.10 by ceiling height and system type
- At least 0.5 bar at the most remote sprinkler
- Hose allowance of 950 or 1,900 L/min; 60 minutes duration
- Incidental storage limits (3 m and 20 m² for Class 1–3; 1.8 m and 6 m² for plastics) respected
- Excluded conditions (ignitable liquids, dust, plastic construction, concealed spaces) checked
Frequently Asked Questions
How is the FM hazard category assigned?
By the predominant occupancy per FM DS 3-26 Table 2.2.2, using the examples in Appendix C. Offices, hotels, hospitals and schools are HC-1; shopping malls, metal-working, food production and woodworking HC-2; car parks, vehicle repair, plastic injection moulding and exhibition halls HC-3. Higher-hazard areas within a site are protected at their own category.
How is fire water volume estimated for a nonstorage building?
Density × demand area from DS 3-26 Table 2.3.1.10 gives a lower bound for the sprinkler flow; add the hose allowance (950 L/min for HC-1 and HC-2, 1,900 L/min for HC-3) and multiply by 60 minutes, which applies to all categories. For a wet HC-2 area under 9 m the minimum is (1,840 + 950) × 60 = 167.4 m³; the hydraulic calculation gives the actual figure.
Why does the hose stream allowance matter so much?
It is a real part of the demand, not a margin: DS 3-26 2.3.1.13 requires the water supply to provide the sprinkler flow plus the hose allowance for 60 minutes. For HC-1 the 950 L/min hose allowance exceeds the minimum sprinkler flow of 560 L/min, so sizing a tank on the sprinklers alone would leave it well short.
How does FM DS 3-26 relate to NFPA 13?
Both assign occupancies to a density and area, but the categories and values differ; FM uses HC-1 to HC-3 with the designs, hose allowances and 60-minute duration of DS 3-26, and a single value per category rather than a curve. A project should follow one framework consistently rather than mixing density from one with hose allowance or duration from the other.
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Download MEP Calc on the App StoreFM Global Property Loss Prevention Data Sheet DS 3-26, Fire Protection for Nonstorage Occupancies, April 2019, Interim Revision April 2025 (1.0, 2.2, Table 2.2.2, 2.3.1, Table 2.3.1.10, 2.3.2, Appendix C Tables C-1 and C-2); related data sheets DS 2-0, DS 3-0, DS 3-2, DS 8-9 and DS 7-15.