How to Design a Fire Sprinkler System

Fire sprinkler system is an essential part of the fire suppression system for controlling fire at its incipient stage. The system design and installation is handle by versatile mechanical building services engineers or sometimes by specialized fire-fighting professionals.

The Fire sprinkler system is based on the sprinkler head, which should not be too close to obstacles nor each other, the control station, and an accurately sized pipe to avoid fire spread.

Building services Professionals thus outline the following five steps in achieving an efficient fire sprinkler system:

  • Determination of the building hazard classification
  • Determination of the head spacing requirement
  • Selection of a piping configuration 
  • Selection of a pipe sizing method

Building Hazard Classification

Building Hazard Classification

Ever since time, building services professionals do classify every building project into a category to provide related services to every building as required. On this note, fire-fighting engineers classified every building project into three, based on the degree of fire effect.

This category includes

  • Light hazard occupancies
  • Ordinary hazard occupancies
  • Extra hazard occupancies

Having gotten the category the building you are to design falls; we now proceed to the second stage of the design process

Sprinkler Head Spacing

Sprinkler head spacing is a factor of the head type, installation type, and the building hazard classification.

The head type varies from a standard type sprinkler head to an extended type sprinkler head.

The Standard sprinkler head has a maximum coverage area of 15m2 while the Extended spray sprinkler head has a maximum coverage area of 18m2.

The installation types also determine the spray of the sprinkler head, which NFPA has rules for. The Wall type sprinkler, for example, has an average of 4.2m straight throw from the centerline with extensive coverage of 70’. On this note, building services professionals do recommend a spacing of 3.7m between two heads.

Ordinarily, NFPA recommends the standard spacing for each sprinkler head according to the hazard classification to achieve an efficient fire sprinkler system. The summary is as shown below.

Sprinkler Head Spacing

NFPA also recommends an average of the recommended spacing as the maximum between sprinkler and wall or obstruction deeper than 350mm, while special considerations should be given to custom ceilings.

Sprinklers are required in every building spaces other than the following as specified by NFPA

  • Bathrooms lesser than 5.1m2
  • Closets, pantries and other non-dwelling spaces lesser than 2.2m2
  • Wall or ceiling surfaced with non-combustible material.
  • Staircases, shafts, balconies, and other open building spaces.

The Sprinkler Piping Configuration

Like the water supply system, sprinkler pipes can be configured in three ways 

  • Tree piping layout
  • Loop piping layout
  • Grid piping layout

The Grid piping layout is sometimes prohibited in some jurisdictions because of its difficult flexibility.

Firefighting professionals are required to select the most efficient system based on the building configuration.

Sprinkler Pipe Sizing

Sprinkler pipe sizing is a factor of empirical considerations on the pipe types, pressure requirement, and hazard classifications. The two primary method used in the industry in sizing sprinkler pipes are:

  • The pipe schedule method 
  • The hydraulic calculation method               

The Pipe schedule method is mostly used for residential apartments or projects lesser than 465m2 area. The sprinkler pipes are always 25mm diameter. The pipe schedule method thus involves computing each sprinkler pipe to the range pipe using the sprinkler schedule table below and eventually to the sprinkler main. This process computation is also based on the NFPA 13 standard, while different schedules were specified for different sprinkler pipes.

sprinkler pipe schedule

With my experience in the industry, the table above has always worked efficiently for different project types and pipe types.

The hydraulic calculation method is an elaborated method based on the density level by using mathematical analysis of pipes’ capacity.

Designers also employ dedicated software such as Elite fire pro for the system that requires the use of pumps.

The use of AutoCAD line can do the system drafting, pipes in AutoCAD MEP, Revit MEP sprinkler system, Sprinkler pipes in Autofluid, or other AutoCAD pipe design plugins. A good recommendation plugin for AutoCAD users is the Tharwart fire plugin.


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