FM Global High-Rise Sprinkler Design: DS 3-7, DS 3-11 and DS 2-0

FM Global does not have a separate high-rise section in DS 2-0; Section 2.6 of DS 2-0 is plan review. Vertical zoning and pump arrangement are covered in DS 3-7 Section 2.2.2 (Fire Protection Pumps, April 2012, Interim Revision April 2025, pp. 6–7), pressure-reducing valves (PRVs) in DS 3-11 (October 2021, Interim Revision January 2023), sprinkler selection in DS 3-26 and riser details in earthquake zones in DS 2-8. The DS 3-7 glossary defines a high-rise building as one more than 23 m in height. FM's dedicated high-rise data sheet, DS 1-3 (High-Rise Buildings), is not among the sources used for this article.

Vertical Zones and Pumps (DS 3-7 Section 2.2.2)

• All fire pumps on the first floor or a basement level with direct access from the street; consider flood exposure below grade (2.2.2.1).
• Fire pumps are not installed in series (2.2.2.2). The reasoning in 3.1.2 (p. 23): with an approximately 3% failure-to-start rate for electric-motor-driven pumps, the reliability of the third zone in a three-zone series arrangement falls from 97% to 91%.
• Sprinklers are supplied directly from fire pumps, from a gravity tank of sufficient capacity and height, or from a combination; the gravity tank filling pump should refill the tank in 8 hours or less (2.2.2.4).
• Zones are limited to 85 m vertically, each with its own fire pump and independent fire service connections (2.2.2.5).
• For zones above 85 m, pipe and fittings at the pump discharge and lower elevations are rated for at least the pump churn pressure plus the maximum static suction pressure.
• Where electric pumps are used and the building is beyond the pumping capability of the fire service, a reliable emergency power source is provided (DS 5-23).
• Where more than one pump in parallel is needed to meet the demand, the pumps do not start simultaneously, and failure of one to start does not prevent the next from starting (2.4.8.1, p. 15).

Pressure-Reducing Valves (DS 3-7 2.2.2.3 and DS 3-11)

• Design the system so that PRVs are not needed; where unavoidable, use FM Approved valves installed per DS 3-11 (DS 3-7 2.2.2.3).
• No PRVs where the static inlet pressure is 175 psi (12.1 bar) or less; no PRVs in storage and manufacturing occupancies; minimise their use elsewhere. DS 3-11 uses the high-rise as its example: lower floors may need a PRV, upper floors where the pressure is 12.1 bar or less do not, and additional fire pumps can reduce the number of PRVs (DS 3-11 2.3.2.1–2.3.2.3, p. 4).
• No pilot-operated PRVs downstream of a dry-pipe or preaction valve (2.3.2.5).
• PRVs in sprinkler systems are arranged per Figure 2.3.5.1-1, with inlet and outlet gauges, a relief valve on the outlet and the ability to full-flow test at the highest system demand (2.3.5, p. 6).
• Each valve carries a permanent placard with its set pressure, the flow and inlet pressure used for setting, and the design flow and pressure at the outlet (2.3.1.1).
• Inspection and testing (Table 2.4.1.2-1, p. 8): quarterly visual inspection, annual partial-flow test and five-yearly full-flow test. In high-rise buildings the drain riser must be able to take the test flow.
• Automatic breach containment valves (ABCVs) are not installed in fire protection systems, and existing ones are removed (2.3.3.1).
• DS 3-7 3.1.11 lists reducing the number of PRVs in high-rise buildings among the suitable applications for variable speed pumps; see DS 3-7 variable speed fire pumps and DS 3-11 pressure-reducing valves.

Sprinkler Selection (DS 3-26)

• Offices, hotels, residential and hospitals are typically HC-1 (Table 2.2.2 and Appendix C); the wet-system design under ceilings up to 9 m is 4 mm/min over 140 m² (Table 2.3.1.10).
• Residential occupancies are treated as HC-1 and use FM Approved residential sprinklers or FM Approved quick-response nonstorage sprinklers; residential sprinklers are not spaced closer than 2.4 m (2.3.6.1–2.3.6.4, p. 10).
• For dormitory, residential and dwelling-type 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 (Table 2.3.1.10 Note 1).
• Wet systems use 160°F (70°C) sprinklers, 212°F (100°C) where the ambient exceeds 100°F (38°C); standard-response sprinklers are not used under ceilings higher than 18 m (2.3.1.5).
• Car parks, stores and other occupancies are protected per their own data sheets (DS 8-9 for storage).

Risers in Earthquake Zones (DS 2-8)

• In multistorey buildings, a four-way brace on the riser within 0.6 m of each floor level, with intermediate bracing at no more than 7.6 m (2.2.1.1.2.2–2.2.1.1.2.3).
• Flexible couplings and clearance where risers pass through floors; without clearance, flexible couplings within 0.3 m both above and below the floor (2.2.1.4.3.3, 2.2.1.5.1).

Quick Checklist

• Zones no taller than 85 m, each with its own pump and fire service connection
• No pumps in series; parallel pumps start in sequence
• PRV-free design attempted; PRVs only above 12.1 bar static inlet and outside storage and manufacturing
• PRVs FM Approved, placarded and full-flow testable
• PRV inspections recorded at quarterly, annual and five-yearly intervals
• Sprinkler selection per DS 3-26 (FM Approved residential or quick-response sprinklers in residential areas)
• Riser bracing and flexible couplings per DS 2-8 in earthquake zones

Frequently Asked Questions

How does FM limit zone height in a high-rise building?

FM DS 3-7 2.2.2.5 limits fire protection zones in high-rise buildings to a maximum of 85 m vertically. Each zone has its own fire pump and independent fire service connections, and the lower piping serving zones above 85 m must be rated for the pump churn pressure plus the maximum static suction pressure.

When is a pressure-reducing valve acceptable?

FM DS 3-7 2.2.2.3 calls for systems designed so that PRVs are not needed. Under DS 3-11, no PRV is installed where the static inlet pressure is 12.1 bar or less, none in storage and manufacturing occupancies, and their use is minimised elsewhere. Where used, the valve is FM Approved and installed with a placard, relief valve and full-flow test arrangement per DS 3-11.

Can fire pumps be arranged in series in a tall building?

No. FM DS 3-7 2.2.2.2 does not allow fire pumps in series. Section 3.1.2 explains that with a roughly 3% failure-to-start rate for electric-motor-driven pumps, the reliability of the top zone of a three-zone series arrangement drops from 97% to 91%, because one pump failing to start cuts off water to the zones above it.

Can residential sprinklers be used in hotel bedrooms?

Yes. FM DS 3-26 Section 2.3.6 treats residential occupancies as HC-1 and allows FM Approved residential sprinklers or FM Approved quick-response nonstorage sprinklers, spaced no closer than 2.4 m. With at least one-hour compartmentation, the demand area for dwelling-type rooms may be based on the largest room (Table 2.3.1.10 Note 1).

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