General Note:
Design of the system, NFPA Code 2001, "Standard on Clean Agent Fire Extinguishing Systems" is followed for calculation
Objective:
Objective is to calculate FM 200 weight and number of nozzles required for both IP units and SI units
Fire hazard classes
First of all we have to understand fire hazard classes. There are 3 types of fire hazard classes mentioned below:
- Class A includes (Fire in ordinary combustible materials such as wood, cloth, paper, rubber & plastics)
- Class B includes (Fire in flammable liquids like oil, grease, tars, oil based paints, flammable gases)
- Class C includes (Fire that involves energized electrical equipment)
Design concentration
Now let's talk about design concentration for fire hazard classes which is important for FM200 system design calculation
- Design concentration for Class A (6.70)
- Design concentration for Class B (8.97)
- Design concentration for Class C (7.20)
Safety factors for design concentration
Also we have to define safety factors for design concentration for fire hazard classes
- Safety factor for Class A (1.2)
- Safety factor for Class B (1.3)
- Safety factor for Class C (1.2)
Amount of FM-200 required to achieve the design concentration at a specific temperature can
be calculated from the following formula
Calculations for IP units
W =V/S (C/100-C)
Where:
W = FM 200 weight in lbs
V = Protected space volume in cubic feet
C = FM-200 Agent volumetric design concentration, percent by volume
S = Specific vapor volume in cubic feet/pounds
S = 1.885 + (0.0046 x T)
where T minimum anticipated temperature of protected volume in °F
V = Net Volume of protected area
V = L x W x H
V = 33.28 x 26.24 x 13.12
V = 11457 ft3
Fire hazard classification is C type
So C = Design concentration = 7.20
Safety factor = 1.2
C = Final design concentration = design concentration x safety factor
C = 7.2 x 1.2 = 8.64
T = Minimum Temperature for area = 70 °F
S = Specific vapor volume = 1.885 + (0.0046 x T)
S = 1.885 + (0.0046 x 70)
S = 2.21 ft3/lb
Now we have all the values and we can calculate W (FM 200 weight)
W =V/S (C/100-C)
W = 11457/2.21 x (8.64/100-8.64)
W = 491 lbs
Now we have to calculate no of nozzles
Protected Area = L x W
Protected Area = 33 x 26 = 858 ft2
Coverage area per nozzle (90 deg corner nozzle) = 1024 ft2
Coverage area per nozzle (180 deg corner nozzle) = 2048 ft2
Coverage area per nozzle (360 deg corner nozzle) = 4096 ft2
Since we selected 90 deg corner nozzle so
No of nozzles = Protected area / Coverage area per nozzle
No of nozzles = 858 / 2048
No of nozzles = 1
Now let's do same calculations for SI units
Calculations for SI units
W =V/S (C/100-C)
Where:
W = FM 200 weight in kgs
V = Protected space volume in cubic meter
C = FM-200 Agent volumetric design concentration, percent by volume
S = Specific vapor volume in meter/kg
S = 0.1269 + (0.0005 x T)
where T minimum anticipated temperature of protected volume in °C
V = Net Volume of protected area
V = L x W x H
V = 10 x 8 x 4
V = 320 m3
Fire hazard classification is C type
So C = Design concentration = 7.20
Safety factor = 1.2
C = Final design concentration = design concentration x safety factor
C = 7.2 x 1.2 = 8.64
T = Minimum Temperature for area = 21 °C
S = Specific vapor volume = 0.1269 + (0.0005 x T)
S = 0.1269 + (0.0005 x 21)
S = 0.1374 m3/kg
Now we have all the values and we can calculate W (FM 200 weight)
W =V/S (C/100-C)
W = 320/0.1374 x (8.64/100-8.64)
W = 203.62 lbs
Now we have to calculate no of nozzles
Protected Area = L x W
Protected Area = 10 x 8 = 80 ft2
Coverage area per nozzle (90 deg corner nozzle) = 95 ft2
Coverage area per nozzle (180 deg corner nozzle) = 190 ft2
Coverage area per nozzle (360 deg corner nozzle) = 380 ft2
Since we selected 90 deg corner nozzle so
No of nozzles = Protected area / Coverage area per nozzle
No of nozzles = 80 / 95
No of nozzles = 1
So this is how you can design FM 200 Clean agent fire extinguishing system. For more details you can watch my tutorials below. Let me know if you have any questions. Thank you
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