Created by: Glen Zhu | Updated Date: September 9th, 2023
Technical fire protection equipment and especially fire alarm systems are considered to be of great importance. They enable modern buildings with elaborate architecture and both a complex infrastructure and purpose to easily meet today’s fire protection and safety requirements. The systems are used for fire detection, alarming and evacuation and thus serve the protection of people and material assets.
A further critical task as a superordinate system element is to take over the central function of the control systems of other safety-related systems and equipment in the event of fire. Satisfactory fulfilment of these demanding requirements means that a detailed synchronisation of all parties involved, coordination of the interfaces and appropriate documentation of all measures are essential.
The fire detection and alarm concept must concretely define such things as the protection objectives of the operator as well as possible requirements under building law which, for example, can result from a special building regulation, a building permit or a required fire protection strategy. It describes the necessary requirements and brings them in line with the normative specifications and generally accepted engineering practices.
It thus contributes to the safe planning, execution and subsequent operation of the systems. Insurance regulations that require compliance with the current VdS (German Property Insurance Association) inspection agency guidelines under contract law should also be taken into account.
It thus contributes to the safe planning, execution and subsequent operation of the systems. Insurance regulations that require compliance with the current VdS (German Property Insurance Association) inspection agency guidelines under contract law should also be taken into account.
Since safety technology protects people and material assets, it must be guarded especially well against failure due to lightning and surges. This also prevents false alarms which are problematic in a number of respects:
However, the failure of fire protection equipment in the event of a direct lightning strike is particularly critical because, in this case, the probability of a fire breaking out is significantly increased.
Precautions should be taken to avoid false alarms or even the possible destruction of the fire alarm system due to atmospheric surges and the effects of thunderstorms. In many countries building codes or other regulations insist on FAS for specific building types or building occupancies.
Minimum measures for buildings without external lightning protection systems have been defined by IEC 60364-4-44 since October 2016. This standard describes mandatory measures for the power supply lines leading into a building. IEC 60364-4-44 recommends rather than requires surge protection measures for Internet, telephone and broadband cable lines.
According to VdS 2833 (see also DIN VDE 0845-1), shielding and earthing measures for alarm systems should be carried out as well. Clarification is also necessary as to whether surge arresters are required based on the indicators listed in the VdS 2833 guideline. If this is the case, the operator of the alarm system must be informed of the need to implement the protective measures. If lightning protection is not prescribed by legal or official regulations, a risk analysis can help to clarify the need for and the protection class of a lightning protection system designed to avert potential hazards with possibly devastating effects.
If surge arresters are used in buildings with external lightning protection systems, VdS 2833 stipulates that they must be installed at the corresponding transitions between the respective lightning protection zones.
Fire alarm systems should protect people and animals as well as facilities and buildings against fire and smoke. This also includes rapid alerting of the fire brigade and localization of hazard zones as well as swift evacuation. In accordance with these protection objectives, a fire alarm system takes over the reception, processing and display of fire and fault messages as well as control of alarm, transmission and fire-protection systems.
To address all these issues, a system is equipped with the following functional components:
The heart of the fire alarm system is the Fire Alarm Control Panel (FACP). Here, all incoming information is monitored, checked, evaluated and processed up to and including the automatic initiation of necessary measures.
Depending on the size of the fire alarm system, either freely configurable devices or ready-made compact control panels are used.
Figure 1 – Installation zones for lightning and surge arresters according to VdS 2833
Based on the Lightning Protection Zone (LPZ) concept according to IEC 62305-4, the building is divided into what are known as installation zones in accordance with the guideline VdS 2833. Appropriate SPDs (Surge Protective Devices) are then employed at the transitions between zones to achieve the protection objectives for the system. In order to meet the requirement for high availability for a fire alarm control panel, the control panel itself is assigned a separate zone (usually LPZ 2) (Figure 1). This means that all lines to and from the control panel must be protected by surge arresters.
Figure 2 – A corresponding protection concept for all components of a fire alarm system
In case of an emergency, the fire brigade peripheral devices should quickly and reliably inform the fire brigade about the location of the fire as well as access and escape routes.
In addition, peripheral fire brigade devices make it possible to enter the building without force in case of an emergency. One of these is the fire brigade key depot (figure: FSD), a lock box for keeping the key to the building located at the entrance. In the event of a fire alarm for the fire brigade, the key depot is unlocked to provide the emergency services a means of non-forced entry into the building for the purpose of firefighting. Fire brigade key depot, key depot columns and release elements must be connected to the building’s equipotential bonding with a cross-section of at least 4 mm2.
If the key depot / key depot column is located in the area of LPZ 0A prone to lightning strikes, the devices must be connected directly to the equipotential bonding/earthing system with a copper conductor of at least 16 mm2 capable of sustaining lightning current.
All conductors must be protected with surge protective devices in dependence on the location of the key depot / key depot column. A surge protection concept for a fire brigade key depot can be found in Figure 3.
Figure 3 – Lightning and surge protection concept for the fire brigade key depot (FSD)
In addition to correct selection of the surge protection devices, safe and functional wiring and line installation as well as prop- er connection of the shield and the drain wires are important and should not be neglected.
Usually, drain wires are earthed directly at the FACP (Fire Alarm Control Panel) or are already earthed via the module. This means that the shield does not have to be earthed additionally at the FACP. In its further course, it must not be connected directly to earth potential in order to avoid fault messages or problems on the signal / ring conductors. Consequently, indirect shield earthing is required for lightning equipotential bonding. This can be accomplished, for example, using appropriate SPD’s equipped via so called gas discharge tubes.
Another aspect of indirect shield earthing is the avoidance of equalizing currents caused by two separate earthing systems. To prevent equalizing currents via equipotential bonding, only one end of the shield must be connected directly to earth potential (Figure 4: Building A). The other end is earthed indirectly by means of a gas discharge tube (Figure 4: Building B).
Figure 4 – SPD direct or indirect shield earthing for cables across several buildings with different earth potentials
Despite well-executed equipotential bonding, incorrect cable routing can lead to an impairment of the protective effect or even damage to the end device. If strict spatial separation or shielding of an unprotected line upstream of the SPD and a protected line downstream of the SPD is not observed, the electromagnetic interference field can cause interference impulse to be coupled into the protected side of the cable.
IEC 60364-4-44 describes various installation instructions for cable installation, such as avoiding the formation of loops, separate routing of power supply and information technology cables as well as the separation of protected and unprotected cables. Figure 5 further illustrates this installation information.
Fire alarm systems report the occurrence of hazardous situations in the area being monitored. As safety devices, high demands are placed on the technology with respect to safe operation and the prevention of false alarms. The described protective measures against overvoltage caused by lightning strikes and switching operations contribute to achieving this objective.
Forced by regulations and authorities in many countries appropriate protection is required. Optimal protection against the damaging effects of lightning and surges is achieved through coordinated measures of external and internal lightning protection and suitable approved SPDs.
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