Calculation of PFP Thickness

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Calculation of PFP Thickness

• Friday, 18 December 2009

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• The thickness of fire protection required is
  determined by
• Duration
• Critical Steel Temperature
• Steel section size and type
• Hp/A ratio
• Thickness stated in the local or international
  approval

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SI Units Hp/A M/D A/V Imperial (US)
Units W/D A/P
metres
Heated Perimeter


m-1 or /m
metres²
Cross Section Area
Kilograms / metre
Mass of Section


kg/m²
metres
Heated Perimeter
Heated Surface Area
metres²


m-1 or /m
metres³
Volume of Steel
Pounds/foot
Weight of section


lb/ft/in
inches
Heated Perimeter
Square inches
Cross Section Area


in2/in
Heated Perimeter
inches
All express the relationship between the amount
of steel capable of absorbing heat to the area of
steel surface exposed to the fire.
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How much PFP do I need?
Hp/A - Section Factors
Heated Perimeter (Hp m)
Cross Sectional Area (A m²)
Low Hp/A Thinner PFP 305 x 305 x 240 kg/mHp/A
1.905m / 0.0305m² Hp/A 62 m-1 For H120
(400C) Chartek 7 11 mm
High Hp/A Thicker PFP 305 x 305 x 97 kg/m Hp/A
1.789m / 0.0123m² Hp/A 145 m-1 For H120
(400C) Chartek 7 16 mm
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How much PFP do I need?
How Hp/A changes with sides exposed to
fire. (Example 305 x 305 x240 Kg/m UC)
Wall, Floor or Deck
Wall, Floor or Deck
Flange only exposed Hp/A Hp/A 13 m-1
3 Sides exposed Hp/A Hp/A 52 m-1
4 Sides exposed Hp/A Hp/A 62 m-1
1.587 m
0.393 m
1.905 m
0.0305 m²
0.0305 m²
0.0305 m²
Note Cross Sectional Area Remains the same in
all cases!
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How to calculate an Hp/A?
The Yellow Book!
www.asfp.org.uk
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How to calculate an Hp/A?
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What do I do with my Hp/A?
Chartek 7 Certificate
Interchar 963 loadings
Example of Certificate of Fire Approval with
table of Hp/A v required PFP thickness
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What do I do with my Hp/A?
Interchar 963 loadings
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What about other section shapes?
Wall, Floor or Deck
Wall, Floor or Deck
Decreasing Hp/A Lower PFP thickness required