Fire Load Calculation
All
occupancies/buildings, etc. can be graded according to their fire hazard and
are to be provided for with suitable fire precautions on the basis of the fire
load.
The formula for
calculating the fire load is as stated.
-----------------------------------------------------
Floor area in
square meters
The
calculation of the fire load is the basis for determining the
classification of the occupancies for the fire grading of buildings.
- Structural the element of buildings are graded according to the time factor which is nearly equal to but does not exceed the test period which the element fulfills its specified requirements.
- Accordingly, all structural elements have been graded under the following five categories depending upon their five resistance, viz.,
Grade 1…………………… 6
hours
Grade 2…………………… 4
hours
Grade 3…………………… 2
hours
Grade 4…………………… 1
hours
Grade 5……………………
0.5 hours
Classification
of Occupancies:
Occupancies
of low fire load:
Ordinary buildings
for residential purposes, hotels, offices, schools, etc, or occupancies having
a fire load not exceeding 2,75,000 kcal/sq.mtr of the net floor area of any
compartment, nor exceeding an average of550,000 kcal/sq.mtr on a limited
isolated area. (for reference, the maximum for this type in F.P.S. system is
1,00,000 B.Th.U/sq.ft)
Occupancies of moderate low fire load:
Retail shops,
bazaars, stalls, factories, etc. hence the fire load exceeds, 2,75,000
kcal/sq.mtr, and is up to 550,000 kcal/sq.mtr. This is equivalent to the fire
load of 2,75,000 kcal/sq.mtr, not exceeding an average of 1,100,000 kcal/sq.meter
on the limited isolated area as per relevant I.S. specifications. Occupancies of
this type should have a fire resistance of two hours.
Occupancies of high low fire load:
Godowns,
warehouses, etc. this category as per I.S. specifications exceeds the fire load
by 550,000 kcal/sq. meter, but does not
exceed an average of 1,100,000 kcal/sq.mtr of floor area. A fire-resistance of
4 hours for these types of occupancies are considered sufficient.
(for reference,
the maximum for this type in the F.P.S. system is 4,00,000 B.Th.U/sq.ft exceeding
an average of 2,00,000 B.Th.U/sq.ft).
The manufacturing
process industry uses the following
material. Calculate the Fire load by using the following data:
Fire load = (combustibles in kg) x calorific
value in kcal/kg
---------------------------------------------
Floor area in
square meters
Fire load (paper) = 1000 x 3732.05 = 373205.74 kcal/sq.mt
--------------------
10
Fire
load (wood) = 20000 x 4186.602 = 418602 kcal/sq.mt
--------------------
20
Fire
load (coal) = 100,000 x 4784.688 =
9569377.99 kcal/sq.mt
---------------------
50
--------------------Fire
load (rubber) = 5000 x 9569.37 =
1913874 kcal/sq.mt
25
Fire load (Petroleum products) = 50,000 x 10287.081 = 17145135.57 kcal/sq.mt ------------------
30
Total fire load =
29420195.3 kcal/sq.mt
The result indicates
that the occupancy has a High fire load. So fire resistance should be of 4 hours.
Installation of fire extinguishers:
Example:
(1) Determine the
number of fire extinguishers required to give adequate protection for a given
property.
Risk: Light
engineering workshop (Light hazard)
Area: 315m x 112
m. i.e. 35,280 sq. meter.
Type of hazard:
Class ‘A’ fire due
to normal combustibles.
As per IS 2190
this is Light Hazard so one 9 ltr water expelling extinguisher for every 600
sq.mtr of the floor area should be installed.
Extinguisher
should be available within 25 meter
radius.
So
no. of extinguisher = 35,280 sq.mt . =
58.8
-----------
600
so no. of extinguisher required is 59.
(2) Determine the
number of fire extinguishers required to give adequate protection for a given
property.
Risk: Petroleum
processing units (High hazard)
Area: 300m x 150
m. i.e. 45000 sq. meter.
Type of hazard:
Class ‘B’ fire due
to petroleum products.
As per IS
2190 this is High Hazard so two 9 liter
foam chemical/mechanical type; or 5 kg capacity dry powder extinguisher for
every 600 sq.metr with a minimum of four extinguishers per compartment shall be
installed.
Extinguisher
should be available within 15 meter
radius.
Here Total area is
45000 sq.mt.
So
no. of extinguisher = 45000 sq.mt . = 75
---------------
600
so no. of extinguisher required is 75.
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