FIRE SPREAD

Types of fire spread Internal fire spread Surface fire spread• The lining of walls and ceilings are important factor in spread of fire and its

gaining hold . This particularly dangerous in circulation areas where it prevent people escaping.

• Two factors relating to property of material need to be taken care are:• -Resistance to flame spread over the surface• -Rate of heat release once ignited

Structure fire spreadThere are three factors need to be consider under this:

-Fire resistance and structural stability

-Compartmentation within buildings

-Fire and smoke in concealed spaces

External fire spread

The spread of fire from one building to another is prevented by the fire resistance qualities of external wall and roofs . Roofs should be fire resistant from outside and should also resist surface flame spread . Different roof coverings but sheet metal flat roof covering perform the best. While various bitumen felt roof covering depend on the types of layers, under layers and supporting structure.

FIRE DETECTION AND

ALARM SYSTEM

Block diagram of FDA system

Input Devices

OutputDevices

Control Panel

Input Devices Fire Box (Manual Pull Station)

When shorted trips an alarm (usually fire) Installed in the normal exit path

Types of Fire BoxSingle Action

Pull handle onceGlass Break

Glass rod or plate is brokenDouble Action

Lifting of a cover or opening a door

Heat detectors 1. fixed temp type heat detector2. rate-of-rise type heat detector

Smoke detectors3. Photoelectric4. Ionization

Flame detectors1. Ultraviolet light (UV)2. Infrared (IR)

Fire-gas detectors

FIRE DETECTORS

Heat Detectors

Smoke Detector

Flame Detector

Fire-gas Detector

Fixed temp. heat detectors

Detect heat by one or more of 3 primary principles of physics:

Expansion of heated material

Melting of heated material

Changes in resistance of heated material

Rate-of-rise heat detectors

Operate on the principle that the temperature in a room will increase faster from fire than from atmospheric temperature

Will initiate an alarm when the rise in temp. exceeds 12-15F (7-8C) per minuteAlarm can be initiated at a temp. far below that required for a fixed-temp. device

◦Reliable devices, not subject to false activations◦But if not properly installed, they can be activated under non fire conditions (eg. detector located

too close to doorway and subject to extreme fluctuations in temperatures)

Pneumatic rate-of-rise spot detector

Pneumatic rate-of-rise line detector

Thermoelectric detector

Photoelectric smoke detector Uses a photocell coupled with a specific light source. Basically smoke entering the smoke detector chamber disrupts the

light beam causing an alarm signal to be initiated More sensitive to smoldering fires

1: optical chamber2: cover3: case molding4: Photodiode (detector)5: infrared LED

Ionization smoke detector

Invisible products of combustion enter the chamber decreasing the

current between the –ve & +ve plates, thereby initiating an alarm

signal. Generally responds faster to flaming fires versus smoldering fires Automatically resets when the atmosphere clears

Fire-gas Detectors

• Monitors levels of carbon dioxide and carbon

monoxide (common to all fires)

• More discriminating than other detectors – can

be designed to be sensitive only to gases

produced by specific types of hostile fires and

ignores gases produced by friendly fires

• Not many in use – very specialized applications

SMOKE AND HEAT VENTING SYSTEMSmoke and heat venting system comprises of one or more of following elements:--Smoke ventsThe main function is to create and maintain smoke free zones in which people can escape from fire. It also provides better protection from fire damage.-Heat ventsThe task of heat vent is to conduct away hot burning gases during the development of fire. -Mechanical smoke extractorsIt perform the same task as smoke vents but use forced ventilation to achieve the extraction of smoke. These are useful where smoke vents are neither appropriate nor feasible for technical reasons.

The working principle of smoke and heat venting system lies in the property of hot gases to rise. The effectiveness of the system depends on :

-the aerodynamic efficiency of the air venting

-the effect of wind

-the size of air vents

-the activation of air vents

-the location of the installation relative to the general arrangement and size of the building

Sprinkler system-Wet sprinkler system are system in which the pipe line network behind the wet alarm wall station is permanently filled with water .

-Whereas, in dry sprinkler the pipe line behind the dry sprinkler wall station is filled with compressed air which prevents water from flowing into the sprinkler network.

-Normal sprinkler system deliver a spherical water distribution system towards the ceiling and the floor

-Umbrella sprinkler falls in the parabolic pattern towards the floor.

-The spacing between the sprinkler must be atleast 1.5m.

SPRINKLER SYSTEM

OPEN NOZZLE SYSTEMSprinkler system with open nozzle are water distribution system with fixed pipelines to which open nozzles are attached at regular intervals when on standby the pipe network is not filled with water.

Fire Extinguisher Classification

• Through the classification system, extinguishing agents matched to fire hazards

• Classification designated with letters

• Class A fires: ordinary combustibles• Class B fires. flammable and combustible liquids and gases• Class C fires: energized electrical equipment• Class D fires: combustible metals• Class K fires: cooking media

-Interior stair shall be constructed of non combustile material throughout.

-the staircase shall not be arranged around a lift shaft unless it is entirely enclosed by a material of fire resistance.

-the width of staircase should not be less than 75cm.

-the escape stairs shall have straight flights with 25cm treads and riser not more than 19cm

-handrails shall be provided with the minimum height of 90cm.

-the internal enclosing walls of staircase shall be of brick or RCC having fire resistance of not less than 2hours

STAIRWAYS