A fire is a large uncontrolled flame that spreads more or less quickly and usually causes substantial damage. Its scenario is made up of unexpected elements and events and its characteristics vary according to the location, atmospheric conditions, combustible equipment elements, the means implemented to slow down its propagation, and a heap of other parameters.
However, there are 3 vital elements for a fire to break out that together form the ‘fire triangle’:
In a general manner, the curve above is widely admitted to represent the stages of a fire. During the development phase, the curve shows a relatively slow rise in temperature up to the major event that is known as the flash-over.
This phenomenon generally occurs when the temperature reaches 500 to 600°C, i.e. when the gaseous layers provoked by the fire ignite themselves, provoking the ignition of all combustibles present in the fire. The fire then enters its most intense state and has come to full development.
The test circumstances attempt to reproduce real-life circumstances but without the development phase, so that the elements being tested can be exposed directly during the full intensity of the fire. In order to frame and define the test conditions, nominal curves showing a rise in temperature have been determined, following a curve similar to that of the flashover. During ‘classic’ fire tests, the temperatures are determined by curve ISO 834.
This curve with a very rapid rise in temperature makes it possible to reach 550°C after just 5 minutes of testing.
The doors are tested on both sides, i.e. with the fire located on the side of closure and opening. In other words, the test is carried out with the hinges IN the fire during a first test and OUTSIDE of the fire during the second test. The duration of the test is determined by the resistance class and ranges from 15 to 240 minutes.
The success of fire-resistance tests involves different categories of criteria: integrity (E), radiation (W) and insulation (I).
Flame-tightness or integrity (E) is determined by 3 measurement criteria:
a piece of cotton wool should not catch fire when held very close to the door;
a flame cannot take shape in a continuous way for more than 10 seconds on the protected side of the door;
no opening can be formed through the door that measures over 25 mm in diameter nor may any gap that measures more than 150 mm by 6 mm.
Thermal insulation (I) is a criterion that measures the rise in temperature of the door on the protected side.
To measure this rise in temperature, thermocouples are placed at different standardised points of the door. In addition to the fixed thermocouples, a mobile thermocouple is used to measure points that are likely to exceed the authorised temperatures.
Radiation (W) is a measurement of the radiation flow located on the protected side at 1 m from the tested element and cannot exceed 15 kW/m2.
This criterion (W) is never noted alone, but always together with the airtight criterion (E).
The Netherlands, for example, require EW doors, such as EW30, EW60, EW120, etc.