1. Calculation of PFP Thickness
Thursday, 20 April 2017

2. 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

3. SI Units: Imperial (US) Units: Hp/A = M/D = = = A/V = = = W/D = = =
A/P =
Heated Perimeter
metres = =
m-1 or /m
Cross Section Area
metres²
Mass of Section
Kilograms / metre = =
kg/m²
Heated Perimeter
metres
Heated Surface Area
metres² = =
m-1 or /m
Volume of Steel
metres³
Weight of section
Pounds/foot = =
lb/ft/in
Heated Perimeter
inches
Cross Section Area =
Square inches =
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.

4. Cross Sectional Area (A = m²)
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/m Hp/A = 1.905m / m²
Hp/A = 62 m-1
For H120 (400°C):
Chartek 7 = 11 mm
High Hp/A = Thicker PFP
305 x 305 x 97 kg/m Hp/A = 1.789m / m²
Hp/A = 145 m-1
For H120 (400°C):
Chartek 7 = 16 mm

5. 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
4 Sides exposed
Hp/A=
Hp/A = 62 m-1
3 Sides exposed
Hp/A=
Hp/A = 52 m-1
Flange only exposed
Hp/A=
Hp/A = 13 m-1
1.905 m
1.587 m
0.393 m m² m² m²
Note: Cross Sectional Area Remains the same in all cases!

6. How to calculate an Hp/A?
The
Yellow
Book!

7. How to calculate an Hp/A?

8. 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

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

10. What about other section shapes?
Wall, Floor or Deck
Wall, Floor or Deck
Decreasing Hp/A = Lower PFP thickness required