S 1.9 Fire sealing of trays

Initiation responsibility: Building Services Manager, Fire Safety Engineer

Implementation responsibility: Fire Safety Engineer, Building Services

Electrical and IT cables are usually concentrated in installation trays. Trays are often found along escape and rescue routes, going through underground car parks, warehouses, workshops, or are used as transit trays to go through areas used for other purposes.

In buildings with several fire zones, the routing of electrical and IT cables is subject to fire protection regulations. This applies especially to cables crossing through fire zones, walls, or ceilings, or traffic routes. Additional requirements for maintaining the functionality of electrical cables in case of fire must be met, especially when the trays are used for emergency lighting or fire alarm, burglar alarm, or extinguishing systems. For this reason, the fire safety engineer should be consulted whenever planning the trays. The trays must provide fire protection as well as protection against sabotage. Both can be achieved through proper sealing of the trays.

When electrical cables are tightly packed in a separate cable channel with fire protection, large increases in temperature can arise. This can lead to an increase in the electrical resistance of the wiring with the accompanying additional heat. This problem can be alleviated either by reducing the number of cables or by providing sufficient ventilation. For this reason, the guidelines in DIN VDE 0100-520 "Erection of low-voltage installations - Part 5: Selection and erection of electrical equipment - Chapter 52: Wiring systems" the German version of IEC 60364-5-52 IEC 60364-5-52 must be followed depending on how the cables are laid. This is the responsibility of the electrical planner.

The commonly used ventilation methods and techniques, for example using ventilation bricks, have the disadvantage that they do not provide sufficient protection against acts of sabotage. This means that lines requiring high or very high levels of protection which are routed through unprotected areas such as underground car parks are barely protected against deliberate acts when these methods are used. Custom planning measures are required in this case. This can mean using sufficiently large channels, making ventilation of the channel in risky areas unnecessary, or using a special ventilation concept that is designed to meet the specific security requirements.

Openings through walls and ceilings must be sealed to conform to the fire resistance class of the wall or ceiling after the lines have been laid. To make it easier to install additional cables later on, suitable materials such as soft firestops or fire protection cushions can be used as a temporary measure. The corresponding standards and guidelines, such as DIN 4102 "Fire behaviour of building materials and elements", must be followed. Cable trays expand when heated, e.g. due to a fire, and can destroy a soft firestop or a fire protection cushion when the tray goes through a wall.

For this reason, trays should not be routed through the fire protection element, but should end at least 10cm before the wall on both sides. This also makes it easier to fan out the lines and cables, which now must be routed individually and not as a bundle through the fire protection.

Often a variety of cables, e.g. telephone, LAN, and building services cables, are conveyed in a single tray. If any changes need to be made to the cabling, it should already be clarified in the planning phase whether any other cable systems are scheduled for replacement in the foreseeable future. Combining projects correspondingly minimises downtime and can save additional costs entailed by repeated fire sealing.

If the route planned is not possible due to fire protection regulations, then an alternative route must be investigated. Furthermore, the fire seals should be inspected at regular intervals, for example annually, after the installation work is completed.

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