Emergency lighting that provides occupants with a clear path of egress is a code requirement in most commercial and institutional buildings.
Emergency lighting can consist of dedicated emergency fixtures including combo exit/emergency units mounted on walls or ceilings. Another option is fluorescent fixtures that include both standard ballasts for normal operation and a battery operated emergency ballast that converts the fixture to emergency mode during a power outage.
Numerous codes can apply including International Building Code (IBC), NFPA 101: Life Safety Code, NFPA 70: National Electrical Code, NFPA 110: Standard for Emergency and Standby Power Systems, NFPA 111: Standard on Stored Electrical Energy Emergency and Standby Power Systems, and NFPA 99: Health Care Facilities Code.
While consistency between these various codes has improved in the last few years, there will be differences between jurisdictions on code application depending on when codes were adopted and how they are interpreted.
Before proceeding with an emergency lighting design or retrofit, it’s important to check with local code officials to confirm existing requirements.
Emergency Lighting Code Requirements
The key parameters for emergency lighting as defined in NFPA 101 are the requirements for stairs to have a minimum of 10 fc (108 lux) measured at the walking surface, and a minimum of 1.0 fc (10.8 lux) for floors and walking surfaces with an exception for assembly occupancies of 0.2 fc (2.2 lux) during periods of performances or projections involving directed light (a movie theater).
In the event of a power outage, the emergency lighting must become available within 10 seconds. Additionally, battery-powered emergency lighting shall be continuously available for 90 minutes after the power outage.
The emergency illumination shall be spaced to provide initial illumination along the defined path of egress of not less than an average of 1.0 fc (10.8 lux) and not less than 0.1 fc (1.1 lux) at the floor of the egress path.
Different illumination levels may be required for stairs and other building components along the path of egress.
How Emergency Ballasts Work With Existing Fluorescent Fixtures
While dedicated emergency fixtures are one option, this post will focus on converting standard fluorescent fixtures so they do double duty as both conventional lighting fixtures and emergency lighting when necessary.
Fluorescent emergency ballast/battery packs are now common units that convert standard fluorescent fixtures into emergency lights. The emergency ballast operates the same fluorescent lamp (or lamps) as the fixture, so there's no exposed equipment to detract from the ceiling or wall appearance. This type of emergency lighting application is useful in commercial offices and public buildings, institutional, and health care facilities.
Most of these emergency ballasts are available as dual-voltage models. You can retrofit them in the field or order them as part of the fluorescent fixture for new installations.
When there is a power outage, the emergency ballast / battery backup takes over to provide a minimum of 90 minutes of illumination meeting the code requirements listed above.
When AC power returns after a power outage, the emergency ballast automatically switches to the charging mode and fully recharges the NiCad battery in 24 hrs.
Generally, power units for emergency lighting systems have built-in test equipment, or procedures, that regularly exercise the unit to ensure proper operation. Failure to successfully complete a test will activate a trouble light.
One way to manually check the unit for proper operation is with a test switch usually included when you purchase the emergency ballast. Some emergency ballasts can be ordered with a handheld remote control transmitter that will eliminate the need for a ladder when testing the unit.
With the increasing use of LED fixtures in buildings, emergency driver / ballast units are now available to accomplish the same battery backup illumination available with fluorescent fixtures. LED fixtures can function normally, but will automatically switch to code-compliant emergency mode when necessary.
Also available are dedicated emergency LED fixtures that can replace traditional incandescent or halogen emergency units.
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