Emergency lighting is intended to provide adequate lighting of escape routes at times when the normal lighting in a building fails, usually during a fire or other emergency. Under these circumstances, the occupants must be able to evacuate the building quickly and safely – often impossible without the aid of emergency lighting.
The National Building Regulations (NBR) includes regulations concerning emergency lighting. A code of practice was subsequently published by the South African Bureau of Standards (SABS 0114-2) to provide consistent recommendations for installers and users of emergency lighting. This document describes in detail what is required of an emergency lighting installation. The Code is the first comprehensive document of its type to have been prepared specifically for South African conditions.
Premises requiring emergency lighting
Emergency lighting is required in premises without natural light or where persons work at night. Those premises which are not habitually occupied at night and where there is sufficient natural light, do not require emergency lighting.
As an example, an open plan office used mainly during the day and seldom at night, will require no emergency lighting in the office space. The area around the core of the building - the lift foyer and emergency stairs, would require it since this is part of the escape route and will not receive adequate natural lighting. The same would apply to any basement parking area.
Types of emergency lighting
It would not be economically viable or desirable to insist on a single standard of bright lighting for all occupancies. It is therefore logical to differentiate between emergencies in diverse premises.
* Escape route lighting
The illumination of escape routes to permit safe and quick evacuation during a fire or an emergency.
* Safety lighting
The illumination of areas where it is necessary to shut down plant during an emergency or to highlight hazardous equipment or processes such as hot metals, chemical vats and rotating machinery, which may endanger evacuees en route to an exit.
* Standby lighting
Required to allow essential services to continue, eg, operating theatres, fire stations etc.
Illuminance levels
The intensity of light required for the various types of emergency lighting is as follows:
* Escape route lighting
Not less than 0,3 lux measured at floor level. This is approximately equivalent to the light output from a full moon at night with no cloud or smog obscuring the sky.
Depending upon the category of the buildings, different minimum illuminance levels of escape route lighting are required:
0,3 lux - in buildings where the majority of the occupants are familiar with the layout of the premises, eg, offices.
1 lux - in public buildings where the majority of occupants are unfamiliar with the building eg hospitals, hotels and places of entertainment.
3 lux - in old age homes and premises catering for the infirm.
* Safety lighting
Not less than 20 lux.
* Standby lighting
Illuminance levels cannot be specified but must be sufficient to allow the essential work to continue.
Duration
Some thought must be given to how long lighting should be expected to perform satisfactorily under its own power.
Safe evacuation is only part of an emergency scenario. If people are trapped, the continued presence of emergency lighting may be the one comforting assurance which prevents panic and loss of life.
There are also occasions when the main power supplies fail. When the power is restored but the system fails again before the batteries have been recharged a reasonable duration is vital.
In the case of self-contained luminaires, the duration deteriorates with age and temperature. A duration of 120 minutes when new, can become 60 minutes when the installation is five years old.
A minimum of 120 minutes for luminaires and 60 minutes for directional signs is therefore accepted.
Uniformity ratio
It is essential to control the relationship between minimum and maximum illuminances otherwise visibility will be impaired. The fairly low light levels of emergency lighting will accentuate any flare or uneven illumination, temporarily blinding people using escape routes. The ratio should consequently not exceed 40:1, ie, escape route lighting at a level of 0,3 lux should not have to compete with bright spots of greater intensity than 12 lux. It is far better to use a larger number of luminaires with a low output than a few with a high light output.
Types of luminaires
Only fixed, permanent installations should be allowed for illuminating areas requiring emergency lighting. Fortunately, virtually any standard type luminaire can be adapted for use as an emergency unit.
The SABS has published tables referring to a variety of popular luminaires giving the maximum spacing at a given mounting height to achieve both the illuminance levels and uniformity ratio.
Portable light sources (eg, torches) should not be considered as emergency lighting because of the following serious disadvantages:
* Workers would have difficulty in locating them in the darkness.
* The torches must still be in the positions designated for them.
* They must still operate (very frequent check would have to be made on them).
* Torches do not satisfy the 40:1 uniformity ratio.
Signs
Any feeder or emergency route in any building should be clearly marked and signposted to indicate the direction of travel during emergencies. 'Exit', 'Uitgang' signs or symbolic pictograms and arrows conforming to SABS 1186, are permitted. Pictograms comprising white figures on a green background and used in conjunction with direction arrows are preferable to signs reading Exit/Uitgang. The interpretation of pictograms is not determined by language standards or reading capabilities.
Two types of signs are recognised:
* Standard box type.
* Diffuser type upon which the same symbols or letters can be stencilled.
Either sign can have symbols or letters 125 mm or 75 mm high. Signs 125 mm high can be spaced up to 36 m apart; those 75 mm high, 18 m apart. Any greater distance requires extra signs to reduce the spacing to these distances.
References
D.N. Lee, Emergency Lighting – a new direction.
Fire Protection, Vol. 12 No. 4 1985.
SABS 0114: Part II 1999 – Code of Practice
For interior lighting. Part II – Emergency Lighting.
Fire Protection Association of Southern Africa.
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