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TECHNICAL ADVISORY DOCUMENT TAD0023
Passive Fire Protection of Steel
Introduction
When exposed to fire steel gets hot and beyond a certain limiting temperature, elements within a steel structure will start to lose strength and may no longer support the load for which they were designed.
This limiting temperature will depend on the specific steel section used and on the imposed load.
Passive Fire Protection (PFP) is designed to provide insulation to these steel elements. By reducing the rate of heat transfer and thereby extending the time taken to reach the critical limiting temperature. Which extends the time taken to reach structural collapse and allows people time to evacuate the structure safely.
It is obvious that a large, heavy steel section will heat up more slowly than a thin, lightweight steel section.
Thus it is reasonable to expect that a heavy steel section will require less insulation (in the form of PFP) than will a lightweight steel section.
Heavy section will take longer to heat up in a fire. Thus for a given period of fire resistance less fire protection would be required on the heavier section.
This relationship depends on the mass of the steel section and the surface area exposed to the fire.
In the USA it is referred to as W/D and in Europe as Hp/A (or A/V).
The concept is of great important for intumescent PFP as it allows for less material to be used on heavy sections (thus saving cost) whilst ensuring that sufficient material thickness is applied for lighter steel sections (thus ensuring safety).
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