Fire design for escape routes

Fire design is crucial and can be difficult to perform considering the complexity of buildings such as hospitals, offices or hotels. These structures all require escape routes that present a need for a RSET (Required Safe Escape Time - time it takes people to safely get away to the safe place) which, for strategic buildings, is generally higher than for other construction. This is mainly because hotels, hospitals and offices have a large amount of people to be evacuated and often a low flow capacity. In this case, the correct design of the escape routes is an important element to allow users to evacuate and the security teams to operate during and after the fire.

In the design phase, we tend to see that a lot of attention is paid to the design of structures, compartments, fire dampers and active protection systems. However, little attention is paid to the correct design of the support systems in the event of a fire and, above all, to the design of their fixings.

Typically a lot of attention is given to the compartments but the points of relevance are:

• the operation of the safety systems during a fire
• the resistance of the compartments that can be damaged by the failure of the systems.

The few existing regulatory guidelines, such as European Assessment Documents (EAD), focus on how long overhead installations must maintain their structural integrity when faced with intense heat. Currently, two harmonised European standards – EN 13501, which is a classification of materials’ reaction to fire, and EN 1366-1:2104, which describes fire resistance tests for service installations – are among the most important sources of design guidance for fire-resistant ventilation ducts and smoke control.

In addition to these Europe-wide standards, the German MLAR directive also explains the importance of fire safety for ventilation systems, escape routes and suspended ceilings:

Ventilation systems

• Section 5.2.2 refers to ventilation ductwork, which needs to be fire resistant.
• Section 5.2.4 refers to ventilation ductwork above suspended ceilings, which needs to be fixed in such a way that it won't collapse in the event of fire.

Escape routes

• How to keep escape routes free and for how long in the event of a fire.

Suspended ceilings

• For fire-rated suspended ceilings, the required fire resistance must be guaranteed in the event of a fire coming both from above and below the ceiling.
• Special requirements must be observed for modular support systems when they are installed between the structural ceiling and a suspended ceiling.

Collapsing suspended ceilings, blocked escape routes and damaged indoor or outdoor stairways are to blame for many casualties in the instance of a fire. When pipe and service installations are not designed with fire safety in mind, they can turn into hazards extremely quickly after a blaze breaks out. The thousands of unseen pipes, ducts, cables and strut channels suspended from the ceiling disintegrate in the presence of heat, ultimately crashing to the ground and blocking escape routes.

The crucial point in this case is the excessive deformation of the fastening elements which, due to high temperatures, could damage the false ceilings. Consequently, considering the deformation of the systems and supports at high temperatures, this can influence the positioning of the false ceilings. In fact, it is crucial to define the distance between the extrados of the false ceiling from the system and to assess whether after deformation, the system or the fixture interfere with the false ceiling, in which case this would completely lose its REI characteristics, where REI refers to the fire resistance characteristics.

The key is indeed the correct design of the systems to avoid interruption of the safety systems or damage to the false ceilings due to excessive deformations. For this reason the EOTA (European Organisation for Technical Assessment), released the EAD-280016-00-062 (where EAD means European Assessment Document) in February 2018 entitled "Products Related to installation systems supporting technical equipment for building services such as pipes, conduits, ducts and cables ".

The EAD for the first time explains several points including:

• How manufacturers should conduct a test
• Calculation methods and procedures
• The design methods to ensure the operation of the system in the event of a fire
• Methods for determining the load-strain curve

Discover more about the EAD and the configurations that are contained.

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