Decentralised systems are the number one choice

• When function preservation cannot be guaranteed due to architectural conservation requirements.
• Compromises have to be made in wiring (obstruction of other contract work)
• The obligations of the operating company to perform checks are not met or are neglected.
• The system used is defective or poorly maintained.
• Malfunctions are not rectified immediately.

• If the operating company is not adequately informed about its duties, nobody feels responsible for safety lighting.
• Lack of acceptance of safety lighting often leads to statements such as: “Safety lighting just costs money” or “I’ve known every corner of the building for 30 years now. I don’t need safety lighting.”
• If the emergency lighting concept is bad, projects with several hundred, sometimes several thousand self-contained luminaires, or centralised emergency lighting concepts in which over a thousand and more lightpoints are supplied by one system, conflict with a sensible safety concept.

State-of-the-art, centralised power supply systems with power limits are designed for the decentralised supply of individual fire compartments. Thanks to the limitation of the maximum fire compartment size to 1,600 square meters and the use of LED luminaires, small, inexpensive devices can be used.

The advantages of the decentralised system concept become particularly clear when compared to a centralised system concept. Figs. 1 and 2 show a centralised system concept using a central power system (CPS) in a multi-storey building. Storeys and the necessary staircases are each defined as separate fire compartments. On account of the centralised supply of the fire compartments by the CPS, the wiring system as far as the fire compartment to be supplied must be designed for function preservation in accordance with (M)LAR.

The CPS device is housed in a separate room with function preservation. A major disadvantage of this concept: if there is a break in the E-30 cable at any point, the security lighting fails completely in all downstream areas. This is a disadvantage which can be compensated for or restricted by routing the circuits individually into the fire compartments in question (Fig. 2) or the sub-units are supplied by the CPS in a star-shaped configuration. However, both result in considerably greater expense for function preservation. In the selection of the wiring size, it is also important to note that through the increase in the specific electrical resistance in the event of a fire, a significantly larger wiring size should be chosen than for wiring without the necessary function preservation.

The decentralised system concept centres on the autonomous consideration of the fire compartments: the entire safety lighting system is supplied only within the fire compartment in question.

As a result, no function preservation is required and the complex planning of cables with function preservation can be dispensed with – which also cuts costs. The possibility of doing without function preservation can make itself felt, particularly in listed and historic buildings. However, the biggest advantage is a significantly higher level of safety.

Thanks to the independent supply of the individual fire compartments, the failure of a device would be limited to the fire compartment in question, so that a high level of availability of the safety lighting system would be guaranteed.

If you plan to supply staircases with current using autonomous devices, it makes sense to clarify matters concerning their installation with the fire protection or electrical experts, as special requirements (vandalism, smoke, technical defects) may apply.

With the help of a clever circuit concept, it is often possible to dispense completely with autonomous devices and thus with solutions for their installation. Fig. 4 shows a solution that has frequently proved successful in practice: from each device, a circuit is routed into the staircase to supply one luminaire each in the storey above and the storey below. If a device fails, only two luminaires are affected in one staircase. By supplying the other luminaires from separate devices in the other storeys, the function of the safety lighting is still guaranteed.

Instead of static emergency exit luminaires, dynamic emergency exit luminaires are used; under normal circumstances, these mark the escape doors like a static emergency exit luminaire. If smoke spreads within the staircase, access is marked as blocked by a flashing red cross. The alternative escape route into the second staircase can also be indicated by a flashing green arrow. This prevents people from fleeing into a smoke-filled area. A possible failure of the circuits in the staircases would not adversely affect the safety lighting in the individual storeys, since these are supplied with power from separate circuits.

• No function preservation required
• No additional fire load in the staircase
• High level of safety through multiple, autonomous devices
• High level of safety in the staircase through more than the two circuits required by the standard

• No violation of the protection objective
• Greater planning certainty through area planning and fire compartment planning
• Fire and smoke hazards are taken into account

For a long time now, individual luminaire monitoring (Fig. 5) has proved to be the state of the art, and is an important safety factor in the planning of safety lighting.

The increasing use of LED technology brings not only benefits: in the past, the failure of a fluorescent lamp led, as a rule, to the upstream ballasts being shut down and hence to an error message in the safety lighting system; with LEDs, however, this cannot necessarily be taken for granted. Significantly less than 3% of LEDs fail because of open circuits, and would thus result in a clear fault message. With more than 97% of LEDs, a short-circuit is the cause of failure (Fig. 6). If several LEDs are connected in series, or if there is a combination of a series and a parallel connection of LED lines, the short circuit even of several LEDs does not attract attention, since enough power still flows at the output of the ballast and the still intact LEDs visually compensate for the failed ones through increased brightness. With the help of tried and tested measuring methods, ballasts optimised for LED safety and emergency exit luminaires can detect failures caused by short circuits or open circuits and immediately signal a luminaire failure.

Photometrically optimised, asymmetrical LED optical systems allow the illumination of narrow emergency escape routes with luminaires with only one LED, which allows luminaire spacing of about 35 metres. It seems to be an advantage that, as a result, the required number of safety luminaires can be reduced, but the consequence is also a significantly lower safety level: if one luminaire fails over a distance of up to 70 metres, there is no illumination, or only severely reduced illumination, of the emergency escape route. For such luminaires, an individual LED monitoring system is of particular importance. For safety reasons, the spacing of safety luminaires should not exceed a maximum of twelve metres.

The heart of every safety lighting system is the battery. If it fails, emergency lighting is no longer possible. Annual maintenance and the inspection of the required rated operating time are obligatory, but defective batteries are only seldom detected between the maintenance intervals. The consequence may be a battery like the one shown in Fig. 8.

The solution to the problem could be battery control systems which detect, report and document faulty batteries through permanent monitoring and evaluation of the individual block voltages and temperatures (Fig. 9). This allows rapid rectification of malfunctions and restoration of the safety level. In order to avoid possible hazards due to defective batteries, charging can be adjusted or even shut down.

There are many ways to enhance the security level of a safety lighting system significantly: innovative technologies, emergency lighting and system concepts. In the selection and development of these, planning laws, labour protection laws and normative requirements have to be taken into account. The focus should always be on a critical appraisal based on common sense, compared to a purely pragmatic assessment.

Which system is used depends, among other things, on the type and size of the building, its use, the structural preconditions as well as economic aspects. A sense of proportion is called for in the evaluation of these criteria, taking account of the protection objective to be reached. In any case, all parties involved in the project should be integrated in the creation of the concept in order to achieve a sustainable result.