By: Osama Alsheikh, Meinhardt (UK)
Causes of fire safety issues vary largely according to the building size, design, and use. The most relevant issue for the façade design is the use of combustible material in the external walls and the correct specification and the construction of cavity barriers and firestopping.
As façade engineers we want to make sure materials and cavity barriers in the façade are specified and constructed in line with the applicable building regulations in the UK and any detailed recommendations from the appointed fire engineer. If we are able to interpret and apply the guidance correctly and detail the façade in a way to meet these requirements, we can help to reduce the fire risks in the building.
If I understand this correctly you are referring to the regulations and standards that are used in the design and construction of fire-safe buildings. In England, these are stipulated in the UK building regulations and the building safety act. “Approved Document B: Fire Safety” is the main document that provides guidance and requirements for achieving fire safety standards in buildings. Recently in the UK, a new piece of legislation called “The Building Safety Act” was introduced to further improve the fire safety of buildings. The act introduces measures and processes that need to be implemented by building professionals and building owners to ensure that building occupants are safe in the event of a fire.
There are a number of key aspects that need to be considered in the design and the construction of the façade to ensure we can contribute to, in the façade and the fenestration industry to fire-safe buildings:
In relation to the façade design, I believe you would consider all the processes and actions taken during the façade design and construction within the “passive fire protection”. I think the main difference between passive and active methods is that passive methods are built in the building façade and structure, and they do not require “activation” like fire alarms, or sprinkler systems which are classified as “active” systems.
“Reaction to fire” refers to the response of the material to a heat source in terms of combustibility, spread of flame, and release of heat. Materials are classified as shown below. In addition to the above classes, two other letters are added to the classification: “S” which refers to smoke production, and “D” which refers to flaming droplets.
The reaction to fire classification is normally based on small-scale tests and is relevant when the combustibility of façade material is being specified. In the UK, the type and the height of the building will determine the minimum reaction to fire classification to be achieved. On the other hand, “Fire resistance” refers to the ability of the façade to resist a fully developed fire. For a non-loadbearing façade, there are two criteria that need to be achieved when specifying these systems; Insulation (prevent transfer of heat), and Integrity (prevent passage of flame and smoke).
Fire resistance of the façade is relevant when an external wall specified by the fire engineer needs to restrict fire spread between buildings or protect escape routes. Fire resistance is usually determined by large scale laboratory tests.
Internal fire coming from the building can break through the openings in the façade and ignite combustible façade materials and then spread further inside façade cavities if there are no cavity barriers provided around openings and at compartmentation lines. This can lead to horizontal and vertical fire spread within the façade, potentially causing additional internal fires in other parts of the building. Fire can also spread internally through the junction (the gap) between the façade and the building structure (floor slab or compartment wall).
Again, controlling fire spread in the façade requires careful selection and detailing of the materials of the façade, considering the combustibility of the façade materials and the construction, and fixing of cavity barriers and fire stopping.
As mentioned earlier, fire-stopping detailing at the junction between the façade and floor slab is extremely important to maintain the fire resistance at the compartmentation and prevent fire spread internally through the façade. Firestopping is usually required to have the same fire resistance as the floor slab (or the structure at the junction for example shear wall).
However, the fire engineer should always be consulted for these requirements.
In order to ensure fire stop contributes to the fire safety of the building and its occupants, it needs to be correctly tested to BS EN 1364-4 and classified in accordance with BS EN 13501-2.
The choice of materials will be determined by the regulations and guidance regarding the fire safety of façades. However, insurers and warranty providers may have additional requirements that will influence the selection of the façade materials. Early conversations with the client, the architect, and the fire consultant are always key for the successful selection of façade materials.
I think one of the important issues with regard to façade design around openings is the fitting of the cavity barriers. Incorrect detailing, specification, or installation of these will increase the risk of fire spread. Façade designers need to consider how cavity barriers can be mechanically fixed and how they are detailed and interact around metal rail framing and other elements in the build-up of the façade.
Also, consideration should always be given to any gaps that can result from tolerances and might be left without adequate fire sealing. Robust quality control on the construction sites and engagement with the cavity barrier product manufacturers are the main keys to a successful installation.
I think that historically ambiguous building regulations and a lack of industry guidance led to misunderstandings and misinterpretations regarding the fire performance requirements for façades in the construction industry. However, in recent years, fire safety regulations have undergone significant developments, including the introduction of a ban on the use of combustible materials in high-rise buildings. Currently, there is ample guidance available from organisations such as the Centre for Window and Cladding Technology (CWCT) and the Society of Façade Engineering (SFE) regarding the fire performance of façades and the considerations of façade design that help façade engineers make informed design decisions.