Fire

Building Protection System: Fire Alarm and Suppression System Overview

OBJECTIVES

Upon completion of this lesson you will be able to:

  • Describe fire alarm and detection system and its components.
  • Enlist types of detectors & fire alarm control panel and also explain them.
  • Describe fire suppression system and its types.
  • Explain working principles and use of suppression systems.

A fire alarm panel with pull station

1 Fire Alarm and Detection Systems

Fire detection and fire alarm components are integrated into a single system. It recognizes, when a fire is occurring and activates the fire alarm system, which alerts the building occupants and, in some cases, the fire department. Some fire detection systems also automatically activate fire suppression systems to control or extinguish the fire.

2 Fire Alarm System Components

A fire alarm system has three basic components;

  • Alarm Initiation Device
  • Alarm Notification Devices
  • Fire alarm control Panel

2.1 Alarm Initiation Device

The alarm initiation device is either an automatic or manually operated device that, when activated, causes the system to indicate an alarm. Manual initiation devices require human activation while automatic devices function without human intervention.

2.1.1 Manual Initiation Devices

Manual initiation devices are designed so that building occupants can activate the fire alarm system on their own if they discover a fire in the building i.e. manual pull station, break glass etc.

2.1.2 Automatic Initiation Devices

Designed to function without human intervention and will activate the alarm system when they detect evidence of a fire. These systems can be programmed to transmit the alarm to fire department, even if the building is unoccupied, and to perform other functions when a detector is activated. These devices can use any of several types of detectors which are given below.

2.1.2.1 Smoke Detectors

A sensing device that is part of a fire alarm system and designed to sense the presence of smoke and available in a variety of designs/styles. Smoke detectors also have a visual indicator, such as steady or flashing light, that indicates when the devices has been activated. Two types of smoke detectors i.e. ionization and photoelectric are commonly available.

2.1.2.2 Heat Detectors

These devices can provide property protection but cannot provide reliable life safety protection because they do not react quickly enough to incipient fires. They are generally used in situation where smoke alarm cannot be used. Heat detectors are often installed in unheated areas, such as attics and storage rooms, as well as in boiler rooms and manufacturing areas. Several types of heat detectors are available, each of which is designed for specific situation and applications i.e. fixed temperature heat detectors, rate of rise heat detectors etc.

2.1.2.3 Flame Detectors

Specialized device that detect the electromagnetic light waves produced by a flame. These devices can quickly recognize even a very small fire and used to protect the aircraft hangers or specialized industrial setting in which early detection and rapid reaction to fire are critical. Such detectors are also used in explosion suppression system, where they detect and suppress an explosion as it is occurring.

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2.1.2.4 Alarm Initiation by Fire Suppression Systems

Automatic sprinkler system is usually connected to fire alarm system and will activate alarm if a water flow occurs. Such a system not only alerts the building occupants and the fire departments to possible fire but also ensures that someone is made aware that water is flowing, in case of accidental discharge.

2.2 Alarm Notification Device

The alarm notification device is generally an audible device, often accompanied by a visual device that alerts the building occupants when the system is activated. Audible and visual alarm notification devices such as bells/horns produces an audible signal when alarm is activated. Visual notification devices such as high intensity strobe lights or other types of flashing lights as well as audio devices.

2.3 Fire Alarm Control Panel

The control panel links the initiation device to the notification device and performs other essential function. The control panel manages and monitors the proper operation of the system. It can indicate the source of an alarm, so that responding fire personnel will know what activated the alarm and where the initial activation occurred.

Most fire alarm systems in buildings other than single residential units have several alarm initiation devices in different areas and use both audible and visible devices to notify the occupants of an alarm. The fire alarm control panel serves as the “brain” of the system, linking the initiation devices to the notification device.

2.4 Fire Alarm Annunciation Systems

Some fire alarm system gives little information at the alarm control panel. Others specify exactly which initiation device activated the fire alarm. The systems can be further sub-divided based on whether they are zoned are coded system;

2.4.1 Noncoded alarm system

In this system, the control panel does not provide any information indicating where in the building the fire alarm was activated. The alarm typically sounds a bell or horn. The fire department personal must than search the entire building to find which initiation device was activated. This type of system is generally found only in older, small buildings.

2.4.2 Zoned Noncoded alarm system

Most common type found in newer buildings. The building is divided into multiple zones, often by floor or by wing. The alarm control panel indicates in which zone the activated device is located and some times which type of device was activated. Responding personal can go directly go that part of the building to search for the problem and check the activated device. Hospitals often used this type of system, because it is not possible to evacuate all staff and patients for every fire alarm. A code list tells building personal which zone is in and alarm condition and which areas must be evacuated.

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3 False, Unwanted and Nuisance Alarms

This term is generally used by the public to describe all fire alarms activation that are not associated with a true emergency.

  • False alarm occurs when individuals deliberately activate a fire alarm when there is no fire, causing a disturbance.
  • Unwanted alarm occurs when an alarm system is activated by a condition that is not really an emergency i.e. a smoke alarm too close to a kitchen may be triggered by normal cooking activities.
  • Caused by improper functioning of an alarm system or one of its components. A feature that automatically provides a backup method for air to be supplied to regulator of an SCBA if the primary passage malfunctions.

4 Fire Suppression System

It Include automatic sprinkler system standpipe systems, and specialized extinguishing systems. Most newly constructed commercial buildings incorporate at least one of these systems. Understanding how these system works is important because they can affect fire behavior. In addition, fire fighters should know how to interface with these systems and how to shut down a system to prevent unnecessary damage.

4.1 Automatic Fire Sprinkler Systems

It is the common type of fire suppression system. Automatic sprinklers are reliable and effective with a history of more than 100 years of successfully controlling fires. When properly installed and maintained, these systems can help control fires and protect lives and property. In most automatic sprinkler system, one sprinkler head is opened at a time as they are heated to their operating temperature.

  • A system of water pipes is installed throughout a building to deliver water to every area.
  • These pipes may be placed above or below the ceiling.
  • Each sprinkler head covers a particular floor area.
  • A fire in that area will activate the sprinkler head which then discharges water on the fire.
  • This kind of system is analogous to having a fire fighter in every room with a charged hose line, just waiting for a fire.

One of the major advantages of a sprinkler system is that it can function as both a fire detection system and a fire suppression system.

4.1.1 Automatic Sprinkler System Components:

Heads, Piping, Control valves, Water supply and Fire pump (Optional)

4.1.2 Mounting Position:

Sprinkler heads with different mounting positions are not interchangeable because each mounting position has deflectors specifically designed to produce an effective water stream down or out toward fire. Each automatic sprinkler head is designed to be mounted in one of three position.

  • Designed to be mounted on the underside of the sprinkler piping, hanging down toward the room i.e. pendant sprinkler head.
  • Designed to be mounted on top of the supply piping i.e. upright sprinkler heads.
  • Designed for horizontal mounting projecting out from a wall i.e. sidewall sprinkler heads.

4.2 Standpipe System

4.2.1 Class-I standpipe

A class standpipe is designed for use by fire department personnel only. Each outlet has a 2 ½ inch (64-mm) male coupling and a valve to open the water supply after the attack line is connected. A class-1 standpipe system must be able to supply an adequate volume of water with sufficient pressure to operate fire department attack lines.

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4.2.2 Class-II Standpipe

May be useful at facilities such as refineries and military bases, where workers are trained as an in-house fire brigade. The outlets are generally equipped with a length of 1 ½ inch single jacket hose preconnected to the system. Class-II standpipe outlets are frequently connected to the domestic water piping system in the building rather than an outside main or a separate system.

4.2.3 Class-III Standpipe

This kind of system has 2.5-inch outlets for fire department use as well as smaller outlets with attached hoses for occupant use. The occupant hoses may have been removed either intentionally or by vandalism so the system basically becomes a Class I system. Fire fighters should use only the 2.5-inch outlets and 1.5-inch outlets may have pressure-reducing devices for use by untrained civilians.

4.3 Specialized Extinguishing Systems

Automatic sprinkler systems are used to protect whole buildings, or at least major sections of buildings. Nevertheless, in certain situations, more specialized extinguishing systems are needed. These kinds of systems are often used in areas where water would not be an acceptable extinguishing agent. There are three types of these specialized extinguishing systems which are as;

  1. Dry-Chemical Extinguishing Systems
  2. Wet-Chemical Extinguishing Systems
  3. Clean Agent Extinguishing Systems
  4. Carbon Dioxide Extinguishing Systems

Dry-Chemical Extinguishing Systems

This system uses same types of finely powdered agents as drychemical fire extinguishers. The agent is kept in self-pressurized tanks or in tanks with an external cartridge of carbon dioxide or nitrogen that provides pressure when the system is activated. Some gas stations have dry-chemical systems that protect the supply areas. These systems are also installed inside buildings to protect storage of flammable liquids.

4.3.1 Wet-Chemical Extinguishing Systems

This system used in most new commercial kitchens to protect the cooking area and exhaust systems. It uses a liquid extinguishing agent, which is much more effective on vegetable oils than are the dry chemicals used in older kitchen systems. Wet chemical systems are also easier to clean up after a discharge so the kitchen can resume operations more quickly after the system has discharged.

4.3.2 Clean Agent Extinguishing Systems

Operate by discharging a gaseous agent into the atmosphere at a concentration that will extinguish a fire. Detectors are installed in these areas to activate the system, although a manual discharge button is also provided with most installations. Discharge is usually delayed 30 to 60 seconds after the detector is activated to allow workers to evacuate the area.

Used to protect computers or sensitive electronic equipment or where valuable documents are stored. Agents of these systems are nonconductive and leave no residue. Extinguish a fire without causing significant damage to the contents of a room.

4.3.3 Carbon Dioxide Extinguishing Systems:

Similar in design to clean agent systems and extinguish a fire by displacing the oxygen. Large quantities of Co2 are required for totally flooding to extinguish a fire and may designed to protect either a single room or a series of rooms. They usually have the same series of prealarms and abort buttons because the activation of such a system is immediately dangerous to life

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