An emergency lighting system is used to help the occupants of a building exit safely during an emergency. It is comprised of a number of different fixture types, including exit signs, egress lighting and anti-panic fixtures. In the United States, emergency lighting requirements are set by local building codes, which are often based on standards developed by the National Fire Protection Agency (NFPA). NFPA Standard 101 addresses life safety issues, including emergency and egress lighting.
Performance
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According to NFPA 101 Section 7.9.2.1, emergency lighting must be designed to illuminate the area for at least 90 minutes after the main power supply is disrupted. The initial level of lighting during this 90-minute period must be at least 10.8 lux (1 ft-candle) on average. This illumination rating should be measured at the floor level along the exit routes.
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Automatic Operation
Emergency lighting must be designed to automatically illuminate exit routes in the event of an emergency. Per NFPA 101, Section 7.9.2.2, an emergency is defined as failure of the main power supply or the opening of a fuse on the electrical panel. It may also be defined as any manual act which directly or indirectly effects normal light levels. These emergency lighting systems must be in continuous operation, or should be able to operate automatically in separate occurrences with no need for a manual reset.
Backup Power
All emergency lighting must be placed on either a generator or battery-based backup supply. According to NFPA 101 7.9.2.3, any generator used to back up power for emergency lighting must be operated and maintained according to NFPA Standard 110. Standard 110 specifies generator requirements and testing procedures. In NFPA 101 Section 7.9.2.4, standards for battery backup are addressed. Under this standard, only reliable and rechargeable batteries may be used, and any batteries used must comply with the National Electrical Code.
Testing
NFPA 101 Section 7.9.3.1 states that all emergency lighting components must be tested according to one of three specified methods. The first method is a test lasting at least 30 seconds, which must be performed every 30 days. The second method may be used on battery powered systems, and must be performed annually for at least 90 minutes. The third testing option allows special diagnostic equipment to be used to test the system every 30 days. All testing and inspection records should be maintained by the owner for review upon request by the local fire marshal.
Exit Signs
Exit sign requirements are outlined in NFPA 101 Section 7.10. According to this standard, all exit signs must have the word "Exit" displayed in letters at least 6 inches tall. The sign must be continuously illuminated at all times that the building is occupied. Exit sign lighting must provide at least 5-foot candles of luminance, which can be provided from either external or internal light sources. These signs should be placed at all egress doors and stairwells, and should be equipped with arrows in the event that the exit path is unclear.