FM Global DS 2-0: Sprinkler Pipe and Hanger Systems in Detail

Pipe and hanger arrangement is covered in FM Global DS 2-0 Section 2.4 (Sprinkler System Piping, pp. 32–42): 2.4.1 pipe, 2.4.2 connections and 2.4.3 hangers and supports. Additional rules for earthquake zones are in DS 2-8. Clause and page numbers in this article refer to DS 2-0, October 2021, Interim Revision April 2025.

Pipe Material and Wall Thickness

• Minimum size: 1 in. (25 mm) for sprinkler piping; every size chosen must be proven by hydraulic calculation to meet the design in the occupancy-specific data sheet (2.4.1.1.1.1–2.4.1.1.1.2).
• Wet and deluge systems: black steel, or steel pipe resistant to internal oxidation (2.4.1.1.2.2).
• Dry, preaction and other systems: steel pipe resistant to internal oxidation, or black steel where the gaseous medium complies with 2.2.1.10 (an inert gas such as nitrogen, or air with a regenerative dryer) (2.4.1.1.2.3).
• Internally galvanized pipe: not in wet systems, and not where the ambient temperature can exceed 130°F (54°C) unless specifically FM Approved for it (2.4.1.1.2.4). See DS 2-1 for corrosion.
• Water-sensitive occupancies (data centres, museums, semiconductor fabs): minimum wall thickness per Table 2.4.1.1.2.1(b) is 3.2 mm for DN25–40, 3.6 mm for DN50–65, 4.0 mm for DN80, 4.5 mm for DN100 and 5.0 mm for DN125–150.
• Nonmetallic pipe (CPVC etc.): nonstorage occupancies only, shielded by a non-removable barrier rated at least 15 minutes (2.4.1.3.2–2.4.1.3.3). Exposed pipe needs all of the following: pipe FM Approved specifically as exposed pipe, an HC-1 occupancy per DS 3-26, a ceiling no higher than 9.1 m, a wet system, quick-response ceiling sprinklers and metallic vertical sections (2.4.1.3.4). Systems with rigid thermoplastic pipe are tested with water, never pneumatically (2.7.3.2.9).

Connections (2.4.2)

• Two pipe sizes are joined with one-piece FM Approved reducing fittings; connections such as mechanical tees must not project into the flow path (2.4.2.1).
• Minimum wall thickness, Table 2.4.2.2.1(2): welded or roll-grooved pipe 2.6 mm for DN25–65, 2.9 mm for DN80, 3.2 mm for DN100, 4.0 mm for DN150; threaded or cut-grooved pipe 3.2 mm for DN25–40, 3.6 mm for DN50–65, 4.0 mm for DN80, 4.5 mm for DN100, 5.0 mm for DN150. Roll-grooved pipe may go down to 1.7 mm with couplings listed in the Approval Guide for that thickness.
• Threaded: sealant on the male threads only, without preventing full thread engagement (2.4.2.2.2.2).
• Grooved: groove dimensions to the coupling manufacturer’s requirements; roll grooves formed before galvanizing or painting (2.4.2.2.3).
• Welded: FM Approved welded connections; welder qualification to ANSI/AWS B2.1 or EN ISO 9606-1; removal of all cut coupons documented (2.4.2.2.4).
• Plain-end connections: pipe thinner than 0.133 in. (3.38 mm) must be FM Approved pipe specifically listed with FM Approved plain-end connections (2.4.2.3.1).

Hanger Spacing (Table 2.4.3.3.1.1)

Nominal size	Wall thinner than Table 2.4.3.1.1(1)	Wall equal to or thicker than Table 2.4.3.1.1(1)
DN25–32	3.7 m	3.7 m
DN40–80	3.7 m	4.6 m
Above DN80	Not applicable; use the table wall thickness	4.6 m

The threshold wall thicknesses in Table 2.4.3.1.1(1) are 2.7 mm for DN25–50, 2.9 mm for DN65–100, 3.3 mm for DN125–150 and 4.6 mm for DN200–300. Where a pipe has its own listing in the Approval Guide, that listing governs (2.4.3.3.1.1).

• Every section of pipe longer than 1.8 m has at least one hanger (2.4.3.3.1.2).
• Main hangers within 0.9 m of the last branch line and within 0.6 m of any connection to vertical pipe (2.4.3.3.1.4–2.4.3.3.1.5).
• Branch line hangers: within 0.3 m of the main where the main hanger is more than 1.8 m from the branch connection; within 0.3 m of a horizontal change of direction; 0.3–0.9 m from the last sprinkler on single-path lines (2.4.3.3.1.6–2.4.3.3.1.8).
• Main hanger spacing may increase by 1.5 m when branch line hangers meet 2.4.3.3.1.3; for DN65 and larger, up to 8 m with paired hangers no more than 0.9 m apart either side of the coupling (2.4.3.3.1.9).
• Hangers at least 75 mm horizontally from upright sprinklers in nonstorage occupancies and at least 300 mm in storage (2.4.3.3.1.11).
• Vertical pipe supported at least every 3.6 m; additional support for vertical pipe 1.2 m or longer with an upright or pendent sprinkler attached directly (2.4.3.3.2.2–2.4.3.3.2.4).
• Minimum rod diameter (Table 2.4.3.1.3): 10 mm for DN25–100, 12 mm for DN125–200, 16 mm for DN250–300.
• No hangers attached directly to roof decking; attachment to steel deck is limited to branch lines up to DN80 under the conditions of 2.4.3.2.2.2. Supporting members must carry the hanger loads plus a single additional 250 lb (113 kg) point load at the most critical hanger (2.4.3.2.1.2).
• Nothing, including conduit, cable trays, air piping, speakers or signs, is hung from sprinkler pipe (2.4.1.1.5.4).

Additional Rules in Earthquake Zones (DS 2-8)

DS 2-8 applies in FM 50-year to 500-year earthquake zones as defined in DS 1-2 (DS 2-0 Section 2.1.5). The main additions:

• A four-way brace within 0.6 m of the top of every riser (2.2.1.1.2.1).
• Feed and cross mains are braced regardless of size: on straight runs, lateral braces at no more than 12.2 m and longitudinal braces at no more than 24.4 m (2.2.1.1.4.4).
• Lateral bracing on branch lines is needed from DN65 upwards (2.2.1.1.5.1); smaller dead-end branch lines get a short hanger or lateral restraint within 1.8 m of the end (2.2.1.1.6).
• Diagonal brace members on horizontal pipe at least 30° from vertical, preferably at least 45° (2.2.1.3.5.2).
• No powder-driven fasteners for hangers (2.2.1.8.1.1); no two-piece plain-end couplings without torque indication (2.2.1.7.2); no nonmetallic pipe above ground (2.2.1.9.2).

See the DS 2-8 earthquake protection article for details.

Quick Checklist

• Pipe type suits the system type; no internally galvanized pipe on wet systems
• Wall thickness checked against Table 2.4.2.2.1(2) for the joining method
• Nonmetallic pipe only in nonstorage areas and under the conditions of 2.4.1.3
• Hanger spacing from Table 2.4.3.3.1.1 and the wall thickness threshold
• Hanger distances at the last branch line, vertical connections and last sprinkler met
• In earthquake zones, DS 2-8 bracing, flexibility and clearances applied

Frequently Asked Questions

Where can CPVC (nonmetallic) pipe be used?

Under FM DS 2-0 Section 2.4.1.3, nonmetallic pipe is limited to nonstorage occupancies and is normally shielded by a fixed barrier rated at least 15 minutes. Exposed pipe needs a product FM Approved specifically as exposed pipe, an HC-1 occupancy, a ceiling no higher than 9.1 m, a wet system, quick-response ceiling sprinklers and metallic vertical sections. In earthquake zones DS 2-8 does not allow nonmetallic pipe above ground.

Can a DN50 pipe have hangers 4 m apart?

Yes, if the wall is thick enough. Under DS 2-0 Table 2.4.3.3.1.1, DN50 steel pipe with a wall at or above the 2.7 mm value of Table 2.4.3.1.1(1) may have hangers up to 4.6 m apart; thinner pipe is limited to 3.7 m. On mains the spacing can increase by 1.5 m under the conditions of 2.4.3.3.1.3.

Does FM DS 2-0 set a pipe velocity limit?

No. DS 2-0 gives no limit on water velocity in the pipe. Under 2.4.1.1.1.2 each pipe size must be proven by hydraulic calculation to meet the design in the occupancy-specific data sheet; the calculation method is in DS 3-0.

What pipe should be used on a dry system?

DS 2-0 2.4.1.1.2.3 calls for steel pipe resistant to internal oxidation, or black steel where the system is pressurised with a gaseous medium meeting 2.2.1.10, such as nitrogen or air with a regenerative dryer. Internally galvanized pipe is acceptable on dry systems but not on wet systems (2.4.1.1.2.4); see DS 2-1 for corrosion.

Does a vertical drop to a sprinkler need extra support?

Yes. DS 2-0 2.4.3.3.2.3 and 2.4.3.3.2.4 call for additional support on vertical pipe 1.2 m or longer with an upright or pendent sprinkler attached directly. Where a pendent sprinkler is secured to a supported structure such as a suspended ceiling, that length may increase to 3.6 m (2.4.3.3.2.5).

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