Oct 2021

Seismic Restraint of Sprinkler Systems – NFPA-13 versus FM Global Standards

Improperly protected sprinkler piping can move violently during an earthquake, resulting not only in extensive water damage to the interior of the building and equipment, but also result in a catastrophic fire due to the impairment of the fire protection system caused by the broken sprinkler piping.

Properly protecting sprinkler systems against damage from earthquakes is covered in NFPA-13, Standard for the Installation of Sprinkler Systems, as well as FM Global Data Sheet 2-8, Earthquake Protection for Water-Based Fire Protection Systems.

The basic concepts and intent of NFPA-13 and FM Global Data Sheet 2-8 are similar and there is considerable agreement between the two standards; however, there are some differences.

Without going into too much detail, below are examples of some of the differences between the two standards:

  • NFPA-13 does not specify when seismic bracing is required, just how to install it when it is required. FM Global specifies seismic bracing be provided when located in 50-year through 500-year earthquake zones, as shown on the maps in FM Global Data Sheet 1-2, Earthquakes.
  • NFPA-13 allows the use of tension-only (i.e. – wire/cable type) braces, where FM only allows the use of tension-only bracing for end of branch line restraint.
  • NFPA-13 does not require lateral bracing on piping when the pipe is supported by short (6 in. or less) rod hangers. FM does not allow this exception.
  • NFPA-13 allows wraparound U-hangers and U-hangers that hold the pipe tight against the underside of a structural member to act as lateral braces on feed mains and cross mains. FM Global does not but does allow U-bolts to be used as lateral braces.
  • In multistory buildings, FM Global requires intermediate 4-way bracing on risers so that bracing is provided at each floor having a supply main.
  • FM Global requires horizontal bracing of manifolds at the base of risers.
  • FM Global requires 4-way bracing at both the top and bottom of vertical feed mains and cross mains 6 ft or longer.
  • FM Global requires lateral and longitudinal braces at changes of direction for horizontal feed mains and cross mains, and longitudinal bracing on branch lines 21⁄2 in. and larger.
  • FM Global limits the l/r ratio for braces used in compression to 200 or less, verses 400 or less for NFPA-13.
  • FM Global does not allow the use of powder-driven fasteners to attach braces to the building structure.

  • FM Global does not allow the attachment of braces to wood members less than 31⁄2 in. unless the member adequacy is confirmed by a Registered Professional Engineer.
  • For FM Global, the sway bracing components need to be FM Approved, whereas NFPA-13 only requires UL listed components.
  • The FM Global data sheet covers seismic protection of foam-water sprinkler systems, fire pumps and suction tanks. These are not addressed in NFPA-13.

Regardless of which standard is utilized, review of the proposed bracing types, locations, load calculations, etc. is best addressed during the design process and reviewed prior to installation via the plan review process.  Post installation field examination is beneficial to confirm the installation matches the design specified on the drawings. Contact Risk Logic to schedule an evaluation of the seismic bracing of your automatic sprinkler system.