In the post that I present today, I am going to show the basic concepts about Resistance to Fire.
Aim of Resistance to Fire
The mission of Resistance to Fire is to determine the time that an element or constructive system is able to maintain the characteristics related to its bearing capacity and / or integrity and / or thermal insulation when is exposed to temperatures similar to those that can be found in a fire fully developed (close to 1000ºC). It is also possible to evaluate other characteristics such as radiation or smoke leakage.
Due to the specimens tested in resistance to fire are complete construction systems, the tests are carried out in special test furnaces.
In order to reach the temperatures that simulate the conditions of the fires, the heating curves are used. There are different types of curves that will depending on the fire scenario that is taken as reference.
The type of curve to be followed during a test shall be described in the reference standard applicable to the construction system.
Some examples of heating curves are:
- Standard temperature/ time curve
- Slow heating curve
- Semi-natural fire
- External fire exposure curve
- Constant temperature attack
Performance characteristics
The characteristics that are included in a classification of Resistance of Fire and that are obtained from the tests are the following:
R- Loadbearing capacity
Is the ability of the construction element to withstand for a period of time and without loss of structural stability, exposure to fire on one or more faces, under defined mechanical actions.
The criteria provided for evaluating an imminent collapse will vary depending on the type of loadbearing element.
E: Integrity
Is the ability of the construction element with a separating function, to withstand exposure to fire only on one face, with no transmission of fire to the unexposed face as result the passage of flames or hot gases. This may cause ignition of the unexposed surface or any material adjacent to that surface.
The evaluation of the integrity of an element is carried out by the following observations:
– Cracks or openings that exceed the established dimensions.
– Ignition of a cotton pad.
– Sustained flaming on the unexposed face.
I: Thermal insulation
Is the ability of the construction element to withstand exposure to fire on one side only, without the transmission of the fire due to a significant heat transfer from the exposed side to the unexposed side. The transmission shall be limited in such a way that no ignition of the unexposed surface or any material close of that surface is ignited. The element should also constitute a barrier to heat, sufficient to protect the people close to it. To evaluate this characteristic, there are two general criteria that must be met:
– Average temperature on the unexposed face.
– Maximum temperature.
Optional performance characteristics
In addition to the commented above, in some elements or construction systems may require additional performance parameters or extend the classification with other performance parameters.
W: Radiation, is the ability of the construction element to withstand one side fire exposure so as to reduce the possibility of fire transmission due to significant heat radiation through the element or from the unexposed side to adjacent materials. In the tests, where the radiation characteristic is required, the maximum radiation value shall not exceed 15 kW/m2
M: Mechanical Action, is the ability of the element to withstand impacts, and represents the case in which a structural failure of another component in a fire causes an impact on the element considered. The element is subjected to the impact of a predefined force shortly after the time for the desired classification R, E and / or I. In order to have its classification supplemented with M, the element must resist the impact without prejudice to the performance R, E or I.
C: Self-closing, is the ability of an open door or window to close completely on its frame and engage any latching device that may be fitted, without human intervention, by store energy, or be mains power backed up by stored energy in case of power failure. It applies to elements that are normally kept closed and must be automatically closed after each opening. It also applies to elements that are normally kept open and to be closed in the event of fire, and to mechanically operated elements which must also be closed in the event of fire. The test must be pass / fail. The test requirements are specified in EN 14600.
S: Smoke leakage, is the ability of an element to reduce or eliminate the passage of gases or smoke from one side to another side of the element. There are two types of smoke leakage depending on the temperature. Sa is associated with ambient temperature and Sm considers the leakage at ambient temperature at 200 °C.
G: Soot fire resistance, is the ability to withstand this type of fire. This classification is used in chimneys and their associated products.
K: Fire protection capability, is the ability of a wall or ceiling covering to provide protection against ignition, carbonization and other damage to the material behind the covering for a specified period of time. Depending on the classification period, we can have K1 for classification periods of 10 min or K2 for classification periods of 10 min, 20 min or 30 min.
Classification periods
Resistance to fire tests measure the time that the element or system is able to guarantee the characteristics related to its bearing capacity and/or integrity and/or insulation. Therefore, the results of the tests are always associated with time periods (in minutes). The available time periods are: 10, 15, 20, 30, 45, 60, 90, 120, 180, 240 or 360.
Bibliography
EN 13501-2:2007 + A1:2009. «Fire classification of construction products and building elements – Part 2: Classification using data from fire resistance tests, excluding ventilation services”.
EN 13501-3: 2005 + A1: 2009 “Fire classification of construction products and building elements – Part 3: Classification using data from fire resistance tests on products and elements used in building service installations: fire resisting ducts and fire dampers”.
EN 13501-4:2007+A1:2009 “Fire classification of construction products and building elements – Part 4: Classification using data from fire resistance tests on components of smoke control systems”.