PASSIVE FIRE CONTROL

INTRODUCTION



Fire safety is a essential part of any building. Fire safety aspects are of two types :


ACTIVE FIRE CONTROL
PASSIVE FIRE CONTROL






Passive fire protection are those measures taken care of during designing of a structure and does not need any energy consumption.
They directly affect the architecture of the building.
Such means device the methods of assembling of components of a building such that spread of fire is limited to barest minimum.



FIRE SAFETY ASPECTS



Following fire safety aspects are taken care of in passive fire protection :
(1)Internal hazards
(2)Personal hazards
(3)Exposure hazards



1) INTERNAL HAZARDS



Internal hazards are hazards related to building itself and the property inside the building .They depend upon :
• Size, shape, and height of the building
• Material and design of construction
• Contents of the building
• Maintenance of the building

Internal hazards can be countered by :
1.)Fire resistance of the structure
2.)Compartmentation
3.)fire and smoke venting



1)FIRE RESISTANCE OF THE STRUCTURE




This aspect depends on the fire rating of different materials used for construction and the general planning of the building. The materials used for construction should have fire rating as specified by the relevant bylaws and IS codes.



The structural members can also be designed to increase fire resistance of the structure . For instance, the depth of slab, columns, and beams can be increased for additional fire protection.


2) COMPARTMENTATION
The aim of compartmentation is to contain the fire within the building.This is done by minimumising possible area by choking the fire and reducing the fuel .
Compartmentation can be studied under :
Integrity of compartment wall (horizontal compartmentation )
Integrity of compartment floor (vertical compartmentation)
Structural integrity and continuity of its fire
resistance (integral compartmentation )

HORIZONTAL COMPARTMENTATION
Normally in all buildings horizontal compartmentation is achieved by formation of rooms but doors are not sufficiently fire resistant .
The fire resistance of timber door is less than that of wall. To overcome this, doors should be made of composite materials .
Fire proof compartment is a enclosure of which all elements ie doors, windows, ventilators and walls have the required fire resistance . Such compartments should be used in places such as godowns, warehouses factories etc.
Fire proof doors shall confirm rigidity to requirements specified in IS 1648 – 1961.

VERTICAL COMPARTMENTATION
Like horizontal compartmentation vertical compartmentation is similarly achieved by floor slabs . Openings to accommodate vertical circulation can be ready means of passage of fire from one storey to another like staircase, lift chamber as also holes and pipes .
Holes and pipes : The same principles and considerations of combustibility applied to groups of pipe and services both vertically and horizontally .It has been a general rule, for many years, to use a 6 inch non combustible cast iron pipe through a wall for preventing any fire hazards.


STAIRCASE AND LIFTS
It is vitally important that staircases and lifts have the same standards of fire resistance as that of rest of the building .( or at least half hour) for this:
Stairs shall be constructed of non-combustible materials throughout .
Interior of the staircase should have at least one side adjacent wall and shall be completely enclosed.
A staircase shall not be be arranged around a lift shaft unless the later is entirely enclosed by a material of fire-resistance rating as that of the type of the construction itself.
Hollow combustible construction should be avoided.

3) SMOKE AND HEAT VENTING
Smoke and heat venting can be effectively used in structures with
Undivided floor areas with ceiling heights such that in case of fire smoke layer is developed at least 4.5 m above floor level such
conditions are frequently encountered in large industrial and
storage buildings.
The design of fire venting should take care of two cases
The first has to do with limited growth fires ie fires which are not expected to growth beyond a predictable heat release ,
Second type of fire is the one which, if unchecked, will continue to grow to unknown size

In buildings such as factories and ware houses fire curtains are provided at relevant intervals and automatic or manually operated vents are provided .


PRINCIPLES OF VENTING
Hot gases rise vertically from the fire and then flow horizontally below the roof untill blocked by a vertical barrier (ie curtain),thus initiating a layer of hot gases below the roof .
The volume and temperature of gases to be vented depend upon heat release of the fire and the amount of air supply to it .
The depth of layer of hot gases increases , the fire incontinues to grow, and the layer temperature continues to rise untill vents operate .
Operation of vents within a curtained area will unable some of the unable some of the upper layer of hot gases to escape, and slow the rate of deepening of the layer of hot gases. With sufficient venting area,the rate of deepening of layer can be arreste for even reversed .


TYPES OF VENTS
Actually any opening in a roof,over a fire will relieve some heat and smoke , however the casual inclusions of skylights, windows are not reliable.
Vents may be a single unit (entire unit opens fully with a single sensor) or multiple units in rows are, clusters or groups.
If the hazard is localized (solvent storage,dip tank, etc)it is preferable that the vents be located directly above such hazards .
vents should preferably be automatic in operation ie connected in circuit with smoke detectors . However all automatic vents should also be designed to open by manual means.


PERSONAL HAZARDS
The extent of personal hazards depends upon the occupant characteristics or the conditions of occupants in the building which refers to:
Wakefullness of the occupants
Familiarity with building layout
Mobility


ESCAPE ROUTES
Escape routes play a key roll in minimizing personal hazards.
It consists of three distinct parts :
Exit access : the horizontal path from any upper floor starting from any occupied room and leading to the emergency staircase .
Intermediate exits: the vertical path that is staircase or lifts
Exit discharge : the horizontal path from the escape staircase to the final exit in the open area .

DESIGN OF EMERGENCY STAIRCASE
The following requirement should be taken care of the design of emergency staircase :
Fire escapes shall not be taken into account in calculating evacuation time of the building .
Al fire escapes shall be directly connected to the ground .
Entrance to fire escapes shall be separate and remote from the internal staircase .
Fire escape routes shall be free of obstructions at all times.
Fire shall be constructed of non combustible materials .
Fire escape steps shall have straight flight not less than 75 cm wide with 15 cm treads and risers not more than 19 cm . The number of risers shall be limited to 16 per flight .

DESIGN FOR RAMPS
The following requirements should be taken care while designing the ramps :
Ramps with slope of not more than 1 to 10 may be substituted for and shall comply with all this applicable requirements of required stairways as to enclosure, capacity and limited dimensions. Ramps shall be surfaced with approved non-slipping material . Provided that in the case of public offices , hospitals , assembly halls etc. the slope of the ramp shall not be more than 1 to 12.
The minimum width of the ramps in hospitals shall be 2.25 m
Handrails shall be provided on both sides of the ramp.
Ramps shalll lead directly to the outside open space at ground level or courtyards or safe place.


DESIGN FOR LIFTS
The following requirements should be taken care while designing the lift :
All the floors shall be accessible for 24 hours by the lifts . The lifts provided in the building shall not be considered as a means of escape in case of emergency.
Grounding switch at ground floor level to enable the fire service to ground the lifts cars in an emergency shall also be provided.
The lift machine room shall separate and other machinery shall be installed therin .


3)EXPOSURE HAZARDS
Exposure hazards can be resisted by:
a)Isolation from neighborhood structures
b)Access for outside emergency services
c) Proper site planning

a)ISOLATION FROM NEIGHBOURHOOD STRUCTURES
For controlling exposure hazards the distance between buildings play an important role.
The factors which govern the distances are :
occupancy and corresponding fire load ;
Type of construction , which shall be correctly related to the first load and/or the occupancy ;
Height ;
Location ,(i.e. residential or industrial estate )
Front wall facing a road way , street or similar throughout fare;
Back wall , that is , the wall farthest away from the front , and facing the rear space


A)ISOLATION FROM NEIGHBOURHOO STRUCTURES
All the buildings, excluding those with abnormal fire loads having ground or ground and first floor , of construction .
distance between front walls of opposing buildings 9m min
Distance between back walls of opposing buildings 6m min
Sides between back walls of opposing buildings 6 m min


b)ACCESS FOR OUTSIDE EMERGENCY SERVICES
Following points must be taken care of while planning access ways :
The access for fire brigades .
The facades which may be accessible from these roads depending on the number of occupants in the buildings
The height of the building ( less or more than 8m )
The use to which the building is put
Its interior design ( compartmented or in zones )

c)SITE PLANNING
In the site planning , following work station should be kept in isolation with respect to main structure as they involves special fire risk .
Garage areas .
Loading bays
Waste disposal areas
Areas containing central heating plant
Fuel stores
Areas containing refrigeration plant other than small units and display cabinets .
Medium and height voltage transformers.
Ventilation plant rooms .

THE END