Emergency lighting is like insurance: necessary – even mandatory – and indispensable in the event of accidents. But under normal circumstances, it is a subject that does not arouse much excitement. Emergency lighting must be there, it must work and preferably not cause too much trouble and costs. Because of the latter point, it is wise to pay serious attention to it during construction or replacement.
There are roughly two choices when designing an emergency lighting installation: central or decentralized. It is not a matter of taste, like the choice between Coca Cola or Pepsi. What is the best solution for a building and organization depends on the local situation, cost considerations and preferences of the user or manager of a property. Therefore, it is good to consider the different characteristics of central and decentralized solutions before we discuss functional retention in relation to emergency lighting.
Decentralized emergency lighting
With decentralized emergency lighting, all luminaires, escape route indication and escape route lighting are connected individually to the nearest mains voltage. Each fixture has its own battery and charger. One of the advantages is that the installation and the electrical connection are usually simple. It’s a matter of screwing and connecting. One of the disadvantages is that – due to the limited capacity of the internal battery – only a limited amount of light is available in emergency mode. It can be a challenge when lighting hazardous workplaces in an emergency, where a lot of light is needed to safely switch off e.g. machines. For users, the biggest practical disadvantage is that the batteries have to be replaced every few years. Since the emergency lighting is not always the most accessible place, this is often a tedious and labor-intensive job.
Central emergency lighting
With central emergency lighting, the luminaires are operated and controlled from a common emergency lighting centre. Setting up such an installation requires more planning and preparation, for example because of its cabling. On the other hand, there are the advantages of central emergency lighting: the batteries generally last much longer, maintenance is easier and faster to carry out, higher light levels are possible and the luminaires are much less sensitive to low and high temperatures than ‘loose’, decentralized luminaires with own battery. This makes a central emergency lighting system also suitable for applications at high or low (up to -40 °C) ambient temperatures.
Function retention and fire sections
An important point of attention when installing central emergency lighting is the concept of functional retention. Functional retention means that an installation must continue to operate for a minimum period (usually 30 minutes) after a fire has broken out. However, functional retention is not so much about the room where the fire rages; everyone should be able to get out of there within 30 seconds. This primarily concerns the situation in the other rooms. The power supply and cabling must be robust enough for the installation in the other rooms to continue to function during that time.
NEN 1010 sets requirements for (construction of) cabling of central emergency lighting installations and the building order sets requirements for, among other things, a building’s fire resistance and escape routes. The most important thing is that a fire in one fire section must not affect the emergency lighting in the other sections. Functional retention therefore plays no role in decentralized emergency lighting. These fixtures are not dependent on power from or via another room.
Functional retention in practice
In short, the maxims for central emergency lighting are quite simple in practice. Cable routing through a room requires functional restraint, cables in a room do not. 30 minutes of functional retention is sufficient in most cases, and in rooms with more than one centrally supplied emergency lighting fixture, the fixtures should be alternately connected to at least two separate power circuits.
Function preservation can of course be achieved by using specific cable system solutions. These consist of cables with functional integrity that are mounted on a suitable substrate or carrier using the correct mounting materials. However, it is also often possible, especially in new construction, to achieve functional retention through architectural solutions. If, for example, the cables are mounted in concrete structures in the wall or floor or deep in the ground, you also have the necessary functional retention without the need for a lot of specific mounting material with functional retention.
Furthermore, by making smart choices in the configuration of your central emergency lighting installation, you can greatly reduce the need for functional maintenance by using substations to which the luminaires are connected per room.
It is even possible to completely eliminate cabling while maintaining functionality by using separate, small emergency lighting centers for each room, the so-called Low Power Systems (LPS). In that case, as with decentralized emergency lighting, no functional maintenance is required at all, because the emergency lighting in each room is not dependent on the rest of the building.
Choice of path and consequences
Emergency lighting is not rocket science, but it is important to carefully consider choices and consequences when installing or replacing emergency lighting. What is the best choice for our organization in this situation? Of course, the cost aspect also plays a big role. Therefore also include the costs in the long term, not only purchase and construction, but also maintenance and replacement. One solution is not necessarily better than the other. Sometimes decentralized is simply the best solution, sometimes central.
Edwin de Graaf, product manager Emergency lighting at Eaton (and organizer of Lunch & Learn program)