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Design of Automatic Fire Sprinkler System

An Automatic Fire Sprinkler System is designed to contain and control an unfriendly fire allowing your family the precious time needed to escape from danger and decrease the amount of damage to your valuables from heat and smoke. An Automatic Fire Sprinkler System is a network of water-filled pipes which starts at your domestic water service line and ends with strategically spaced fire sprinkler heads located throughout your home. The sprinkler heads are frangible bulbs filled with a liquid that, when heated, expand causing the bulb(s) to break and the system to release water. The water from the sprinkler head will cover the area where the fire is located and will continue to operate until the fire department can fully extinguish the fire.

Almost all newly built commercial or industrial buildings require automatic fire sprinkler systems for life safety, the protection of the property, the safety of the firefighters, and to minimize business interruption.  These systems are designed and installed as prescribed in the National Fire Protection Association (NFPA) Standard for the Installation of Sprinkler Systems or NFPA 13.  In the simplest form, these systems include a series of connected pipes and fittings, with valves, alarm initiating devices, and automatic sprinklers that are supplied by a reliable water supply.

The four primary systems are the wet pipe system, the dry pipe system, the preaction system and the deluge system.

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Wet Pipe System

The wet pipe sprinkler system is, in general, the most cost-effective, the most versatile as far as protection strategies and pipe installation are concerned, and the easiest to maintain.  Its cost effectiveness is based on its having fewer components, requiring less maintenance and testing and having fewer design restrictions than any of the other three types of systems.  Wet pipe systems are installed where temperatures will not fall below 40°F (4°C) and where one of the design objectives is to put water on a relatively small fire as quickly as possible.

In a wet pipe system, components are arranged in such a manner that, as soon as the heat from a fire operates the heat responsive element of an automatic sprinkler, the water is discharged through the sprinkler to the fire.  It is possible to design these systems for fire control – controlling a fire to the room or area of origin until the fire department arrives and extinguishes the fire; fire suppression – actually suppressing the fire; or life safety protection – as in residential occupancies.  The wet pipe system can also include additives such as antifreeze or foam concentrate.

Design issues relative to the wet pipe sprinkler systems would include the following:

  • Is there a possibility or potential for freezing anywhere the water-filled components are installed?

  • Is interior or exterior corrosion a factor to be concerned about?

  • What are the appropriate materials for a wet pipe system?

Dry Pipe System

When sprinkler systems are required in buildings, or areas of buildings, where the ambient temperature will not be maintained above 40°F (4°C) dry pipe systems are an option.  The dry pipe system is more expensive than the wet pipe system; requires more maintenance and testing (weekly, monthly, annually, and over its lifetime); and has additional design requirements beyond those of the basic wet pipe system.

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Preaction System

The preaction system is similar to a dry pipe system. It has a similar valve, and in general the same pipe, fittings, alarm initiating devices, and automatic sprinklers.  In addition to the sprinkler system, however, the preaction system incorporates a detection system.  Preaction systems areusually less cost-effective than the dry pipe systems and require additional maintenance and testing as well as maintenance and testing of the detection system.

There are many types of detectors and detection systems that can be used with the preaction systems.  It is in the system designer’s best interest to work closely with the owner and the architect to utilize the type of detection system that is appropriate for each specific area or system.  An example of such an area is the data or computer room, where the products of combustion can do as much damage to sensitive equipment as the thermal damage from a fire or the resultant application of water.  In these rooms, an air sampling detection system may be more appropriate than smoke detectors.  The air sampling system may detect particles of combustion before the human eye or nose does and can send signals or warnings before there is actual smoke damage or a fire or before water is necessary.

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Deluge System

Deluge systems are similar to preaction systems, in most cases utilizing the same valves, pipe, fittings, alarm initiating devices, automatic sprinklers, and detectors, although all of the sprinklers are open and do not include the heat responsive element.  Spray nozzles can be used in deluge systems instead of the open automatic sprinklers.  The difference between preaction and deluge systems is that with the sprinklers open at all times, neither air nor water can be maintained in the piping.  The deluge system requires a detection system to operate and signal the deluge valve, opening the valve and allowing water to flow through the piping and discharge through all of the sprinklers or nozzles simultaneously.

Deluge systems can be installed in warm or cold very high hazard areas and the primary objective is to put as much water on a fire as is required to contain or control a severe fire hazard as quickly as possible.  These systems are utilized where a large amount of water is necessary quickly such as in flammable and combustible dispensing operations, aircraft hangars, and transformers.  The deluge systems frequently include foam concentrates.

Design issues relative to the deluge system would include:

  • What is the appropriate detection system?

  • Is the water supply adequate and appropriate for all sprinklers flowing?

  • Where will the discharged water run to and does it require containment?

deluge system.jpg

Sprinkler System Design Issues

As indicated above there are some design issues that are specific to the different types of systems.  However, there are design issues or considerations that apply to all sprinkler systems.  Some of these are as follows:

  • Is the water supply adequate?

  • What are the insurance requirements and will they impact the system design?

  • Will the system be designed with the minimum code compliance or will it be designed for what is best for the client to exceed the minimum requirements?

  • Has the proper hazard analysis been undertaken and have all of the hazards been identified properly and evaluated?

  • Have the automatic sprinklers that are appropriate for the hazards as well as the system been selected?

The type of sprinkler system must be determined early in the design process. That decision in turn has implications on the remainder of the system design, from hydraulic criteria to water supply and system components.  The owner’s or client’s operations, processes, and overall needs must be included in determining the type of system for a specific project.

Finally, long-term effects such as the cost of inspection, testing, and maintenance of the sprinkler and detection systems, as well as life expectancy of the pipe, fittings, and other components must be included in the overall evaluation.

Looped Sprinkler System

A sprinkler system in which multiple cross mains are tied together so as to provide more than one path for water to flow to an operating sprinkler and branch lines are not tied together.

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Gridded Sprinkler System

A sprinkler system in which parallel cross mains are connected by multiple branch lines. An operating sprinkler will receive water from both ends of its branch lines while other branch lines help transfer water between cross mains.

Gridded System.png

Classification of Occupancies

Select the hazard type according to NFPA-13 (refer to attached).

Light Hazard Occupancies: where the quantity and / or combustibility of contents I slow and fires with relatively low rates of heat release are expected. Examples: Educational, Hospitals, Institutional, Museums, Residential, restaurant seating areas etc.

Ordinary Hazard (Group 1): where combustibility is low, quantity of combustibles is moderate, stockpiles of combustibles do not exceed 8 ft (2.4m), and fires with moderate rates of heat release are expected. Examples: Automobile parking and showrooms, bakeries, glass manufacturing, laundries, restaurant service areas etc.

Ordinary Hazard (Group 2): where combustibility and quantity of combustibles is moderate to high, stockpiles of content with moderate rates of heat release do not exceed 12 ft (3.66m) and stockpiles of contents with high rates of heat release do not exceed 8 ft (2.4 m) . Examples: Leather good manufacturing, Chemical plants, cereal mills, dry cleaners, Libraries -large stack rooms areas, machine shops, paper and pulp mills, repair garages, tire manufacturing, etc.

Extra Hazard (Group 1) : where the quantity and combustibility of contents are every high and dust, lint or other materials are present. Examples: Aircraft hangers, combustible hydraulic fluid, printing, rubber reclaiming etc

Extra Hazard (Group 2): where moderate to substantial amounts of flammable or combustible liquids are present. Examples: Flammable liquids spraying, open oil quenching, plastic manufacturing, varnish and paint dipping etc.

System Component Definitions

Branch Lines: The pipes supplying sprinkler, either directly or through or through springs, drops, return bends, or arm-overs.

Arm - Over: A horizontal pipe that extends from the branch line to a single sprinkler or a sprinkler above and below a ceiling.

Cross Mains: The pipes supplying the branch lines, either directly or through risers.

Feed Mains: The pipes supplying cross mains, either directly or through risers.

Riser Nipple : Vertical piece of pipe between the main and branch line.

Risers: The vertical supply pipes in a sprinkler system.

Sprig: A pipe that rises vertically and supplies a single sprinkler. 


Sprinkler Discharge Characteristics Identification

Refer to Table for Sprinkler Discharge Characteristics Identification

Table Sprinkler DIscharge Charac

Sprinkler Temperature Ratings, Classifications and Color Coding's of sprinklers

Refer to Table for Sprinkler Temperature Ratings, Classifications and Color Coding's of Sprinklers

Table Temperature Ratings, Class

Pipe Material Specifications

Piping above ground for size upto 4 inches (100 mm) shall be Galvanized Iron, Seamless, Class’s’, Heavy duty - BS 1387 or according to Table Pipe above 4” (100 mm) shall be Black Steel, Wrought Steel, Sch 40, Seamless or according to table

Table Pipe or Tube Material and Dimensions

Table 6.4.1 Fittings Materials and Dimensions

System Protection Area Limitations

The maximum floor area on any floor to be protected by sprinklers supplied by any one sprinkler system riser or combined system riser shall be as follows:

Protection Area limitations.png

Protection Areas per Sprinkler

The protection area of coverage of the sprinkler shall be established by multiplying the S dimension by the L dimension, as follows: As = S x L

S Dimension.png
S Dimension.png
A = SXL_Page_1.png

Protection Area of Coverage and Maximum Spacing between Sprinklers

The maximum allowable protection area of coverage for sprinklers (As) shall be in accordance with value indicated in 

Table for Light Hazard occupancies, Table for Ordinary Hazard occupancies, Table for Extra Hazard occupancies, Table for High- Piled Storage.

Table Light Hazard Coverage
Table Ordinary Hazard Cover
Table Extra Hazard Coverage
Table High-piled

Maximum Distance from Walls

The distance from the sprinklers to wall shall not exceed on-half of the allowable maximum distance between sprinklers. The distance from the wall to the sprinkler shall be measured perpendicular to the wall.


Minimum Distance from Walls

Sprinklers shall be located a minimum of 4 inch (102 mm) from the wall


Minimum Distances between Sprinklers

Sprinklers shall be placed not less than 6 ft (1.8 m) on centre.

In-rack sprinklers shall be permitted to be placed less than 6 ft (1.8 m) on centre.

Distance below Ceilings

Under unobstructed construction, the distance between the sprinkler deflector and ceiling shall be minimum of 1 inch (25.4 mm) and maximum of 12 inch (305 mm) throughout the area of coverage of the sprinkler.

Under obstructed construction, the sprinkler deflector shall be located in accordance to below figure

Figure Vertical Changes in C

Sprinkler under Peak of roofs and Ceiling

Sprinkler under peak of roofs and ceiling shall be in accordance with below Figure (a) and Figure (b).

Figure (a).png
Figure (b).png
Table Sprinkler under roof.png

Protection Area of Coverage and Maximum Spacing for Side Wall Sprinklers.

The maximum allowable protection area of coverage for sprinklers and maximum distance between them shall be in accordance with value indicated in Table

Table Protection and Maximum S

Extended Coverage Upright and Pendent Spray Sprinklers - Protection Areas and Maximum Spacing. Table

Table Extended Coverage Sprink

Protection Areas and Maximum Spacing for CMSA (Control Mode Specific Application) Sprinklers. Table Large Drop Sprinklers.png

Protection Areas and Maximum Spacing for ESFR (Early Suppression Fast-Response) Sprinklers. Table

Table Protection Areas and Ma

Sprinklers in Electrical Room

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Rated Pressure

System components shall be rated for the maximum system working pressure to which they are exposed but shall not be rated at less than 175 psi (12.1 bar) for components installed above ground and 150 psi (10.4 bar) for components installed underground.

Pressure Reducing Valves

If water pressure in excess of 175 psi (12.1 bar), a listed pressure reducing valve shall be installed and set for an outlet pressure not exceeding 165 psi (11.2 bar) at the maximum inlet pressure. 

Pressure gauges shall be led on the inlet and outlet sides of each pressure reducing valves.

A relief valve of not less than 13 mm in size shall be provided on the discharge side of the PRV to set to operate at a pressure not exceeding 175 psi (12.1 bar).


Calculating Pipe Sizes

Pipe sizes shall be in accordance with Table for Light Hazard Pipe Schedules, Table 22,5,3,4 for Ordinary Hazard Pipe Schedule, Table for Upright Sprinklers Above and Pendent Sprinklers below a Ceiling and pipe sizes for extra hazard shall be hydraulically calculated (Table A.22.5.4 for reference purpose only).

Table Light Hazard Pipe Sched
Table Ordinary Hazard Pipe Sche
Table Number of Sprinklers Abov
Table A.22.5.4 Extra Hazard Pipe Schedul

Sprinkler Discharge Patter (Figure A.

The discharge pattern for most sprinklers is fully developed at about a four foot distance below the sprinkler. ... A small portion of the discharge wets the wall behind the sprinkler. The discharge from sidewall sprinklers is less effective compared to upright and pendent sprinklers.

Figure A. Sprinkler Discharge Pat

Floor Control Valve Stations (also called Zone Control Valve Assembly)

Zone Control Valve is a system designed to separate the area in case of maintenance and to get the indication of fire zone on a combination of Butterfly valve, Flow Switch, Pressure Gauge and Test & Drain Valves.

Its main purpose it to regulate water flow in the designated “zones” or areas and in some buildings, by floors / levels, thus named zone control valve.

Figure A. Examples of Accept
Table (b) Maximum Distance Betwe
Figure A. Distance from sprinkler
Table Hanger Rod Sizes.png
Figure A. (a) Distance from Sprin
Table Minimum Bolt Size for C

Branch Pipe shall not exceed 8 Sprinklers.

On a branch pipe we can only install maximum up to 08 Nos. of sprinklers according to KFD regulations

Maximum 08 sprinkler on a branch lines_P

Sprinkler Head installation without false ceiling:
Distance between slab and sprinkler shall be minimum 1" (25 mm) and maximum 12" (300 mm)

Upright Sprinklers.png

Pendent sprinkler heads installation when false ceiling height is less than 80 cm.

Pendent sprinkler installation less than

 Two layer sprinkler heads when false ceiling height is more than 80 cm.

Typical two layer sprinkler installation

Install one sprinkler below any duct or cable tray when width is more than 80 cm below.

Typical Sprinkler installation below duc

Installation Control Valve (Also called Alarm Check Valve)

An alarm check valve is basically a check valve with an alarm port. The main purpose of the alarm check valve is to ring a mechanical bell called a water motor gong. The valve should, (if properly maintained), help hold the system pressure steady and reduce the possibility of false alarms.

The alarm check valve is a water flow alarm device designed for vertical installation in the main supply to a wet pipe sprinkler system. When a flow of water from the system equals or exceeds that of a single sprinkler, the valve is to actuate a fire alarm.

Local alarms shall be provided on all sprinklers system having more than 20 sprinklers.

Alarm Check Valve 2.png

Fire Department Connection

A fire department connection shall be provided as described in accordance with Figure Pipe size shall be a minimum 4 in (100 mm) for fire engine connections and 6 in 9150 mm ) for fire boat connections.

The FDC shall be on the system side of the water supply check valve.

The FDC shall be on the street side of the building. A listed check valve shall be installed in each fire department connection.

There shall be no shut-off valve in the FDC piping.


Sprinklers shall be installed beneath all stairways of combustible construction.

One sprinkler shall be installed at the top of the vertical shaft.

Sidewall sprinklers shall be installed at the bottom of each elevator hoisting not more than 2 ft (0.61 m) above the floor of the pit.

Upright and pendent sprinklers shall be installed at the top of the elevator hoist ways.

Open grid ceiling shall not be installed beneath sprinklers.


System Main Drain

Auxiliary drains shall be provided where there is change in piping direction prevents drainage of system piping through the main drain valve.

Provision for flushing:

All sprinkler systems shall be arranged for flushing. Readily removable fittings shall be provided at the end of all cross mains. All cross main shall terminate in 31.8 mm or larger. All branch lines or gridded system shall be arranged to facilitate flushing.

Table Drain Size.png

Automatic Sprinklers shall be installed in:

A) Basement used as a car parks or storage occupancy if the area exceed 200 m2.

B) Multilevel basements. 

C) Any room or other compartment of a building exceeding 1125 m2 in area.

D) Departmental stores or shops, if the aggregate covered area exceed 500 m2.

E) All non-domestic floors of mixed occupancy which constitute a hazard and are not provided with staircase independent of the remainder of the buildings.

F) Godowns and warehouses as considered necessary.

International Experience:

A) 55% of fires were extinguished by the operation of two or less sprinkler heads.

B) 80% of fires were extinguished by the operation of eight or less sprinklers.

C) 90% of fires were extinguished by the operation of 18 or less sprinkler heads.
D) Sprinkler coverage for the fire protection of occupancies has full legislative as well as insurance supports.

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