Fire resistance

What is fire resistance?

The objective of determining fire resistance is to assess the behaviour of a specimen of a building element when subjected to defined heating, pressure and – if relevant – loading conditions. The experimental methods provide a means of quantifying the ability of an element to withstand exposure to such stresses. More precisely, the issue is to quantify the separating and/or loadbearing capacity of a building element in order to ensure the separating function and/or structural stability of a building.

A representative sample (called "test specimen") of the building element is exposed to a specified scheme of heating and – where relevant – of loading. The tests are carried out on specimens in full size or on small-scale models for elements exceeding the dimensions of the furnaces.

The performances of the test specimen are determined by assessing criteria described in test methods. Fire resistance of the test specimen is expressed as the times for which the appropriate criteria have been satisfied. The times so obtained are a measure of the adequacy of the construction in a fire, but they have no direct relationship with the duration time of a real fire.

Fire resistance of building elements shall be assessed using one or several levels of thermal attack. Test standards identify which attack(s) shall be used depending on the type of test specimen. These various levels of thermal action reflect different fire scenarios.

Performances et criteria

The test methods describe some failure criteria to assess. The time, in minutes, during which each criterion was satisfied represents a test result. For one test, there are thus as many test results as criteria to assess.

From there, test methods define some performances. Each of them is determined by the combination of several criteria and is expressed as the time, in minutes, during which the appropriate criteria have been satisfied simultaneously.

The main fire resistance performances are the following ones.

 

Loadbearing capacity (classification R)

This is the ability of an element of construction to withstand fire exposure under specified mechanical actions, on one or more faces, for a period of time, without any loss of structural stability.

 

 

Integrity (classification E)

This is the ability of an element of construction that has a separating function to withstand fire exposure on one side only by preventing the passage of flames and hot gases through and to prevent the occurrence of flames on the unexposed side.

 

 

Insulation (classification I)

This is the ability of an element of construction that has a separating function to withstand fire exposure on one side only by restricting the temperature rise of the unexposed face to below specified levels.

 

 

Radiation (classification W)

This is the ability of an element of construction that has a separating function to withstand fire exposure on one side only so as to reduce the probability of the transmission of fire as a result of significant radiated heat, either through the element, or from its unexposed surface, to adjacent materials.

The criteria for insulation and integrity performances shall automatically be assumed not to be satisfied when the loadbearing capacity performance ceases to be satisfied.

The criteria for insulation performance shall automatically be assumed not to be satisfied when the integrity performance ceases to be satisfied.