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The Automatic Sprinkler

The Automatic Sprinkler 2 of 11

What are automatic sprinklers? How do they fight fire? Why are they needed? Where should they be located? The more you know about sprinklers and how they operate, the better your chances of avoiding a large loss.

Over the last five years, the average fire loss to an adequately sprinklered FM Global-insured location was less than US$600,000; the average fire loss to locations needing sprinklers was US$3.2 million. A study of these losses has demonstrated that auto-matic sprinkler protection is your best defense against fire.

Having performed consistently for more than 100 years, automatic sprinklers are the most efficient “fire-fighters” in the world. They’re also your first line of defense against fire. Yet, some people fail to understand their importance. Excuses for not installing automatic sprinklers vary. Among the most popular:■ A fire won’t happen here.■ The fire service or brigade

is near.■ Fire protection costs too much.■ Insurance will cover it.

Each excuse gambles that a devastat-ing fire loss will not happen. Or, even if it does, business won’t be affected. In reality, choosing not to install sprinklers where they’re needed cre-ates the potential for disaster.

This brochure is made available for informational purposes only in support of the insurance relationship between FM Global and its clients. This information does not change or supplement policy terms or conditions. The liability of FM Global is limited to that contained in its insurance policies.

Rapid Fire Growth

10 seconds 1 minute, 50 seconds 3 minutes, 30 seconds

These successive photos illustrate how quickly a fire can grow, often faster than it takes personnel to respond. If automatic sprinklers had been available, they would have responded within the first two minutes, before the fire could grow out of control.

Fire Develops FastUsually, a fire starts small and can remain nearly invisible for lengthy periods while it incubates. Once it is large enough to see or trigger an alarm, and starts to grow, the time be-tween a small fire and an inferno can be measured in seconds. As a result, sprinklers are needed to control or suppress the fire before it rages out of control.

When sprinklers operate, water is discharged and an alarm is sounded. The sprinklers concentrate the water directly in the area of the fire without being hindered by heat, smoke or toxic gas, as a firefighter would be. If provided with a strong enough water supply, only sprinklers over the fire and in the immediate area will oper-ate. By operating in the early stages of fire development, sprinklers use less water and control the fire more

effectively than hose streams applied much later. In a building without sprinklers, the fire is uncontrolled. By the time the fire service has been called and arrives on the scene, heat, flames and smoke will be intense and easily could exceed manual firefighting capabilities. FM Global statistics show that fire damage in an unsprinklered building is far more extensive and costly, and business downtime is much longer than when a properly designed sprinkler system is in place.

What Is an Automatic Sprinkler?Automatic sprinklers are installed at regular intervals in an extensive net-work of piping and valves. This sys-tem feeds water to the sprinklers. The sprinklers discharge water as soon as their thermal-sensing elements are heated to their rated temperatures.


Sprinklers are installed in one of three positions: upright, pendent or sidewall. Sidewall sprinklers, depending on the type, can be installed vertically or horizontally.

The three main parts of a sprinkler are the orifice, the deflector and the thermal-sensing element.

The OrificeThe orifice is the opening through which water is discharged. Its size varies, depending on the type of sprinkler. The orifice size determines the sprinkler’s discharge coefficient. Sprinklers may have discharge coeffi-cients of 2.8 (40), 5.6 (80), 8.0 (115), 11.2 (160), 14.0 (200), 16.8 (235), 22.4 (315) and 25.2 (360)

gal./min./psi1/2 (L/min./bar1/2). The flow from a sprinkler is equal to the discharge coefficient multiplied by the square root of the water pressure at the sprinkler.

The DeflectorWith a standard installation, water is discharged uniformly below the plane of the deflector in an umbrella-shaped spray pattern. The design of the deflector determines the shape and characteristics of the spray pattern.

The Thermal-Sensing ElementThe thermal-sensing element oper-ates the sprinkler. There are two types: fusible element (or solder element) and glass bulb.

When the sensing element of the fusible element-type sprinkler reaches its operating temperature, the solder melts, permitting the sprinkler to open. Water under pressure is dis-charged from the sprinkler’s orifice, striking its deflector and spraying downward in an umbrella-like pattern onto the fire.

The glass bulb-type sprinkler head consists of a bulb filled with liquid. As the liquid expands from the heat of the fire, pressure in the bulb builds until the bulb bursts, permitting the sprinkler to open.

Orifice

Thermal-sensing element

Deflector


Where Are Sprinklers Needed?Sprinklers are needed wherever combustible construction material or occupancies exist; wherever any activity might fuel, ignite or spread a fire; wherever something might be damaged by fire or products of combustion. Few places exist where sprinklers are not needed.

How Do Sprinklers Fight Fires?Alarm ResponseA sprinkler system sounds an alarm whenever water is discharged from one or more sprinklers. Specifically, the local alarm—the bell outside the building—sounds, alerting anyone in the area to the discharge. At the same time, depending on the system, an alarm also may sound at an on-site monitoring/supervisory station or an off-site central station alarm facility or municipal dispatcher. Of course, personnel should call the local public fire service at the first alarm or sight-ing of fire.

Sprinkler ResponseControl and suppress. These two key words best describe how sprin-klers respond to fire. Control-mode sprinklers control the fire. Water discharged from control-mode sprin-klers wets burning surfaces to a lim-ited degree, but, more importantly, wets unburned surfaces imme-diately beyond the fire area, reducing fire intensity and preventing further fire spread.

In addition, the sprinkler discharge cools the area near the roof or ceil-ing, preventing structural damage as well as preventing sprinklers far from the fire area from operating need-lessly.

Suppression-mode sprinklers work by applying water at high momentum directly into the fire plume while it is still small, effectively stopping the fire before it really gets started. As a result of this fast response and lim-ited fire growth, fewer sprinklers will operate and the amount of fire, water and smoke damage may be reduced.

Types of Sprinkler Systems AvailableInside a sprinklered building, the piping system may comprise one or more of the following types:

Wet PipeThe wet-pipe system is the most common. All piping is filled with wa-ter under pressure. When one or more

sprinklers operate, water is immedi-ately discharged out of each opened sprinkler and continues flowing until a control valve is shut off after the fire has been extinguished.

Dry PipeThe dry-pipe system is used in unheated buildings or other areas where water could freeze in the pip-ing. Piping contains air or nitrogen under enough pressure to hold water back at a valve located in a heated area or enclosure. When a sprinkler operates and begins releasing air, the drop in air pressure automatically opens the valve. Water then flows into the piping to the sprinklers.

The time lag between sprinkler operation and water discharge makes dry-pipe systems somewhat less efficient than wet-pipe systems. A quick opening device can help reduce this time. The device can be an exhauster, which helps remove the air, or an accelerator, which enables the dry-pipe valve to open faster.

Potential Results of a Fire

Without Sprinklers■ Hose streams may not be able to reach the fire.■ There may be delay in attacking the fire; partitions may block access.■ Heat and smoke may keep firefighters out.■ Building structural integrity may be compromised resulting in collapse.

With Sprinklers■ Sprinklers protect all areas.■ Sprinklers promptly attack fire anywhere.■ Sprinklers work in conditions where humans cannot.■ Sprinklers help maintain structural building integrity.


PreactionLike a dry system, the preaction system contains no water; water will not enter the piping until an accept-able automatic detection system acti-vates within the protected area. When the detector activates, an automatic water-control valve releases water into the piping, allowing it to flow from any sprinkler that subsequently opens. The detection system provides an early alarm before any sprinkler operates.

DelugeThe deluge system is used to pro-tect hazards when water must be discharged immediately over a large area. Like the preaction system, it

In any well-protected property, sprinklers are needed:

Over:■ Processing operations■ Combustible storage■ Combustible conveyors■ Grouped cable■ Steelwork supporting process equipment exposed to fire

Inside:■ Concealed or vacant spaces in combustible construction

(such as attics, crawl spaces)■ Dryers, ovens and ducts where combustible material is present■ Elevator shafts and stairwells (only when combustible)■ Any areas where combustible interior finish, furniture and records

storage are present ■ Areas where: – Combustible storage or new combustible construction is added – Building construction and contents are combustible

uses a detec-tion system considered acceptable for the hazard being protected. When the automatic water control valve actuates, water enters the piping and discharges from open nozzles, wetting the entire protected area.

Refrigerated AreaThe refrigerated area system, also similar to the preaction system, is intended for use in freezers where water entering piping as a result of a false operation of a detector or valve would freeze, necessitating the removal of piping for thawing. In these systems, both a detector and a sprinkler must operate before water enters piping in the refrigerated area.

What Rating is Right for You?Understanding sprinkler temperature ratings is essential when selecting a sprinkler for a particular application. Sprinklers are available in several nominal operating temperature ratings. The proper rating provides a safety factor designed to prevent sprinklers from operating premature-ly. More specifics about temperature ratings can be found in the Approval Guide, a publication of FM Approvals.

Selecting a temperature rating depends on the hazard the sprinklers are expected to protect and the ambi-ent temperature of the room or space where sprinklers will be installed. Many other variables come into play as well. Refer to the FM Global Property Loss Prevention Data Sheet that pertains to the specific occupan-cy being protected for guidance.

Suppression-mode sprinklers require additional considerations. Their design combines the low or ordinary temperature rating with a much more sensitive element and more effective water distribution and penetration to suppress a fire quickly. Remember, only a few suppression-mode sprin-klers are needed to suppress the fire. Suppression-mode sprinkler selection and installation guidelines should be strictly followed.

Refer to FM Global Property Loss Prevention Data Sheet 2-2, Instal-lation Rules for Suppression-Mode Automatic Sprinklers, for further guidance.


Ensuring a Sufficient Water SupplySprinklers must have water to oper-ate. Additionally, they need enough water at sufficient flow rate and pres

sure to operate over a predetermined time.Water feeds the automatic sprin-kler system from several possible sources: the public water supply, a suction tank and fire pump, a gravity tank, a natural body of water, or a combination of any of these sources. Pumper connections for the fire service normally are provided outside the building to enable firefighters to hook up and boost the pressure and sometimes supplement the flow rate of water being fed to the sprinkler system.

But, if you fail to inspect and moni-tor all valves that control sprinklers, your fire protection could become impaired. Sprinkler-control valves

are installed so parts of the system can be shut down to make a repair or replace a sprinkler after a fire. If the valves are closed and forgotten, however, the system is inoperable. If a fire starts, the property is without protection. It only takes one shut valve to render a sprinkler system useless.

When you close valves, tag them to remind personnel to open them imme-diately after repairs are complete. Following FM Global’s Red Tag Permit System, described

step-by-step in the publication FM Global’s Red Tag Permit System Could Save Your Business (P9006), will help you manage such impair-ments safely and effectively.

An adequate monitoring and main-tenance program, supported by management, should include weekly, recorded inspections of each control valve to make sure it is open and ready for fire. For guidelines on valve inspections, review the FM Global publication Controlling the Shut-Valve Hazard (P7133).

Pendent Upright control-mode sprinkler Pendent suppression-mode sprinkler

Sidewall pendent Painted pendent Sidewall horizontal pendent


Automatic sprinklers are more than just nozzles extending from the ceiling. They form a whole system vital to workplace loss prevention. Each sprinkler must be able to discharge water into a fire at a mo-ment’s notice Also, because the selection of an appropriate sprinkler system is complex and critical to providing adequate protection, it’s important you utilize available resources to help make educated de-cisions. Contacting your FM Global engineer for more guidance and reviewing our applicable Property Loss Prevention Data Sheets are always good places to start.

■ Controlling the Shut-Valve Hazard (P7133)

■ FM Global’s Red Tag Permit System Could Save Your Business (P9006)

■ Inspecting Fire Protection Valves*

■ Managing Impairments Using FM Global’s Red Tag Permit System*

Helpful FM Global publications and online training courses

* Online training course available to FM Global's clients only at http://training.fmglobal.com


Anatomy of a Wet Automatic Sprinkler System

Main drain

Local alarm

Alarm valve

Gate valve to control water supply to system

Water supply

Bulk main (riser)

Cross main

Inspector’s test connection

Branch lines

Fire service connection

(Diagram courtesy of Grinnell Fire Protection Systems Co.)

Ever wonder how the sprinkler system works? That complex network of piping and valves is actually quite simple. The water for the system originates at a variety of sources and enters the system through the bulk main (or riser). A gate valve is placed in the riser to isolate the system from the supply in case repairs to the system are required. (Note: It is vital the valve be opened as soon as any repairs to the sprinkler system are completed.) An alarm valve is placed after the gate valve. The purpose of the alarm valve is to send water to activate the local alarm and, possibly, an electronic signal to an alarm station.

From the alarm valve, the water travels through the bulk main to the ceiling, where it feeds into the cross main.

The cross main distributes the water into the individual branch lines. The sprinklers are installed into the branch lines at the proper spacing for the occupancy. An inspec-tor’s test connection, which, when opened, simulates the flow of water through one sprinkler, is provided at the most remote branch line in order to verify the sprinkler system remains functional.



Sprinkler Type Description

Control-mode Provides control of a fire by keeping ceiling temperature relatively cool and

pre-wetting surrounding combustible material to prevent horizontal fire spread

Cooling tower Designed to protect fill areas of crossflow water-cooling towers

Corrosion-resistant Have a protective coating or are manufactured from a corrosion-resistant

material; selected for environment compatibility

Dry Usually installed in unheated areas; extend into the unheated area from

the piping system in the main heated area

Extended-coverage, extra-hazard (ECEH)

A control-mode sprinkler with spacing up to 14 x 14 ft. (4.2 x 4.2 m) intended for the protection of occupancies having high heat-release type fires

Extended-coverage, ordinary-hazard (ECOH)

A control-mode sprinkler with spacing up to 20 x 20 ft. (6 x 6 m) intended for the protection of occupancies having moderate heat-release type fires

Extended-coverage, light-hazard (ECLH)

A control-mode sprinkler with spacing up to 20 x 20 ft. (6 x 6 m) intended for the protection of occupancies having low heat-release type fires

Flushed, recessed, concealed

Sprinklers installed in suspended ceilings for aesthetic purposes; flush – the only exposed part of the sprinkler is the operating element; recessed – the discharge orifice is above the plane of the ceiling; concealed – cover plate concealing the sprinkler releases prior to the sprinkler operating

Control-mode Sprinklers


Pendent Suppression-mode Sprinklers

Sprinkler Type Description

Quick-response The thermal element of these types of sprinklers is more sensitive than the

thermal element of standard-response sprinklers

Pendent Sprinkler is attached to the underside of piping; the deflector is below the

orifice; piping cannot be completely drained in a cold-weather emergency; sediment can collect in sprinklers

Rack storage Sprinkler with integral water shield intended for use within storage racks

Residential Sprinkler intended for life-safety applications, not property protection;

designed to hold fire in check long enough for occupants to escape

Sidewall Installed on the wall, near the junction of the ceiling and wall; satisfactory

for light hazards

Suppression-mode Provides suppression of a fire by operating in the early stages of a fire

and applying a significant volume of water to all vertical burning surfaces

Upright Installed on top of the attached pipe; the deflector is above the orifice

Window and cornice Installed outside a building to protect windows and building cornices

from exterior fire; actuated by a manual or thermosensitive valve

P6924 © 2015 FM Global (Rev. 08/2016) All rights reserved. fmglobal.com

FM Insurance Company Limited1 Windsor Dials, Windsor, Berkshire, SL4 1RSAuthorized by the Prudential Regulation Authority and regulated by the Financial Conduct Authority and the Prudential Regulation Authority.

Contact Us: To report an impairment or to find an FM Global office nearest you, visit fmglobal.com/contact.

Report A Loss: Dial (1)877 NEW LOSS (639 5677)* to report a property or cargo loss 24 hours a day, seven days a week. Or, to contact your client service team or designated claims office directly, go to fmglobal.com/claims or affiliatedfm.com/claims for location and contact information.

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