Calculation of PFP ThicknessSaturday, April 22, 2023

The thickness of fire protection required is determined by:

1. Duration

2. Critical Steel Temperature

3. Steel section size and type

Hp/A ratio

4. Thickness stated in the local or international approval

SI Units:

Hp/A =

M/D =

A/V =

Imperial (US) Units:

W/D =

A/P =

Heated Perimeter

Cross Section Area=

metres

metres²= m-1 or /m

Heated Perimeter

Weight of section= inches

Pounds/foot= lb/ft/in

Heated Perimeter =Square inches =Cross Section Area

in2/ininches

All 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=

metres²

metres³= m-1 or /m

Volume of Steel

Mass of Section

Heated Perimeter=

Kilograms / metre

metres= kg/m²

How much PFP do I need?

Hp/A - Section Factors

Cross Sectional

Area (A = m²)

Heated Perimeter (Hp = m)

Low Hp/A = Thinner PFP305 x 305 x 240 kg/m

Hp/A = 1.905m / 0.0305m²Hp/A = 62 m-1

For H120 (400°C): Chartek 7 = 11 mm

High Hp/A = Thicker PFP305 x 305 x 97 kg/m

Hp/A = 1.789m / 0.0123m²Hp/A = 145 m-1

For H120 (400°C): 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 Deck Wall, Floor or Deck

4 Sides exposed

Hp/A=

Hp/A = 62 m-1

0.0305 m²

1.905 m

3 Sides exposed

Hp/A=

Hp/A = 52 m-1

0.0305 m²

1.587 m

Flange only exposed

Hp/A=

Hp/A = 13 m-1

0.0305 m²

0.393 m

How to calculate an Hp/A?

www.asfp.org.uk

TheYellowBook!

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 thickness

Chartek 7 Certificate Interchar 963 loadings

What do I do with my Hp/A?

Interchar 963 loadings

What about other section shapes?

Wall, Floor or Deck Wall, Floor or Deck

Decreasing Hp/A = Lower PFP thickness required