7.3 Calculation of PFP Thickness

Calculation of PFP Thickness*

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The thickness of fire protection required is determined by:

DurationCritical Steel TemperatureSteel section size and typeHp/A ratioThickness stated in the local or international approval


SI Units:

Hp/A =

M/D =

A/V =

Imperial (US) Units:

W/D =

A/P = Heated PerimeterCross Section Area=metresmetres=m-1 or /mHeated PerimeterWeight of section=inchesPounds/foot=lb/ft/inHeated Perimeter=Square inches=Cross Section Areain2/ininchesAll express the relationship between the amount of steel capable of absorbing heat to the area of steel surface exposed to the fire.Heated Surface Area=metresmetres=m-1 or /mVolume of SteelMass of SectionHeated Perimeter=Kilograms / metremetres=kg/m


How much PFP do I need?Hp/A - Section FactorsCross Sectional Area (A = m)Heated Perimeter (Hp = m)Low Hp/A = Thinner PFP305 x 305 x 240 kg/m Hp/A = 1.905m / 0.0305mHp/A = 62 m-1For H120 (400C): Chartek 7 = 11 mm High Hp/A = Thicker PFP305 x 305 x 97 kg/m Hp/A = 1.789m / 0.0123mHp/A = 145 m-1For H120 (400C): Chartek 7 = 16 mm


How much PFP do I need?How Hp/A changes with sides exposed to fire.(Example 305 x 305 x240 Kg/m UC)Note: Cross Sectional Area Remains the same in all cases!Wall, Floor or DeckWall, Floor or Deck

4 Sides exposed

Hp/A=

Hp/A = 62 m-10.0305 m1.905 m3 Sides exposed

Hp/A=

Hp/A = 52 m-10.0305 m1.587 mFlange only exposed

Hp/A=

Hp/A = 13 m-10.0305 m0.393 m


How to calculate an Hp/A?www.asfp.org.ukTheYellowBook!


How to calculate an Hp/A?


What do I do with my Hp/A?Example of Certificate of Fire Approval with table of Hp/A v required PFP thicknessChartek 7 CertificateInterchar 963 loadings


What do I do with my Hp/A?Interchar 963 loadings


What about other section shapes?Wall, Floor or DeckWall, Floor or DeckDecreasing Hp/A = Lower PFP thickness required


7.3 Calculation of PFP Thickness

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