An 8 in. (200 mm) Schedule 40 steel main is to be supported from a trapeze hanger. The trapeze hanger is to span between two joists which are 7.5 ft…

The minimum size for a trapeze hanger member is determined by the size of the pipe it supports and the span of the trapeze. According to NFPA 13, Table 17.4.4.1.3, for an 8 in. (200 mm) pipe being supported, and a trapeze span of 7.5 ft (2.3 m), the next largest span in the table, 8 ft (2.4 m), must be used. The intersection of the row for an 8 in. supported pipe and the column for an 8 ft span specifies a minimum trapeze member size of 3 in. (80 mm) Schedule 40 steel pipe.

A. 2.5 in. (65 mm) Schedule 40 steel pipe: This size is insufficient. Per the NFPA 13 table, a 2.5 in. trapeze pipe is only adequate for a maximum span of 6 ft (1.8 m) when supporting an 8 in. main.

C. 2.5 in. (65 mm) Schedule 10 steel pipe: This option is incorrect due to both insufficient diameter for the span and the incorrect pipe schedule, which is less robust than the required Schedule 40.

D. 3 in. (80 mm) Schedule 10 steel pipe: While the diameter is correct, the pipe schedule is not. The prescriptive requirements in the NFPA 13 table are based on Schedule 40 pipe, which has a thicker wall than Schedule 10.

1. NFPA 13, Standard for the Installation of Sprinkler Systems, 2022 Edition, Table 17.4.4.1.3, "Trapeze Hanger Sizing for Steel Pipe."

2. NFPA 13, Standard for the Installation of Sprinkler Systems, 2019 Edition, Table 17.4.4.1.3, "Trapeze Hanger Sizing for Steel Pipe."

3. NFPA 13, Handbook for the Standard for the Installation of Sprinkler Systems, 2019 Edition, Chapter 17, Section 17.4.4.1, "The size of the trapeze member is determined from Table 17.4.4.1.3 based on the size of the pipe being supported and the span of the trapeze."