Fire safety in buildings
Fire regulations define the means to be used in the design of a building to protect its occupants. These means can be active (detectors, sprinklers, etc.) or passive (structural materials, fireproof coatings, façade products, etc.).
Fire safety in the façade
The building code defines fire performance requirements for the safety of physical persons and for emergency action, described in IT249.
IT 249 (Technical Instruction)
The outbreak of a fire on one floor of a building creates a risk of propagation to the upper floors or laterally through the facades. The purpose of Technical Instruction 249 for façades is to:
Define the provisions relating to facades and their junction with floors that do not require experimental verification by means of the LEPIR2 test, defined by the decree of 10 Sept. 1970, for the evaluation of the C+D and the fire behaviour of the attachment of facades to floors.
Define the provisions to avoid the rapid passage of flames or hot gases from one floor to another, whether the application of the C+D rule is required or not.
Specify the conditions of application of the regulatory requirements (C+D; MCM; ...)
The C+D is used to calculate the configuration of the building (positioning of openings, presence of balconies)
C+D = Distance preventing the propagation of a fire between 2 openings on 2 superimposed floors.
C= vertical distance
D= horizontal distance. This distance is not to be taken into account
0.15 m (considered as D=0)
Mobilisable Combustible Mass
The mobilisable combustible mass depends on the nature of all the materials in the façade. Imposed according to the C+D and the nature of the building.
It is the quotient of the quantity of heat likely to be released by all the combustible materials located in a given reference area.
The calculation of the MCM is to be carried out on the most unfavourable area of the building.
The MCM is expressed in Mega Joules/m².
Sum of the combustible masses of the different materials
materials making up the wall X S ITE / S ref
S ref : reference surface
S ITE : MCM of the insulation
S opening : surface of the opening
Fire regulations for load-bearing walls
Mechanical fire resistance (R)
In the case of load-bearing facade walls, the mechanical fire resistance (R) is the main performance of the wall
- The values for airtightness and insulation are not relevant, as the side opposite the fire (outside) should not be protected.
- The values of E and I will only be used if the brick is used in internal partition walls between dwellings.
The concept of "duration
- The duration requirement is established according to the nature of the structure (it is quicker to evacuate a single-family house than an R+6).
- It is a given in the regulations. It varies according to the type of structure: from 15 minutes (a single-family home) to 90 minutes (a 7-storey building).
The concept of "wall load-bearing capacity"
- The load that the wall must support varies according to the structural design of the structure.
- Nevertheless, it can be assumed, by way of approximation, that one level of elevation results in a load drop of approximately 5 t/ml on the load-bearing wall below the level: ➡ 1 level = about 5 t/ml.
- It is of course possible to reduce this load by creating concrete columns, for example. Thus a 4 storey building theoretically supports 4 x 5 = 20 t/ml on the ground floor on the brick. If the designer decides to lower the load via columns, he can quite successfully reduce this load to 10 t/ml by positioning stiffeners using our angles and double seismic table.
- The load drops at the head of load-bearing walls can be calculated according to DTU20.1 or Eurocode 6. Important: It is not allowed to mix the two dimensioning methods.
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