The basics of emergency illumination
Engineers should get involved early in the selection of the optimal power system for emergency lighting systems.
- Know the key considerations of emergency lighting design, which involves lighting levels, means of egress, codes, and the AHJ.
- Understand when and where an emergency lighting system is required, what the applicable code is, how it must perform, how it will be powered, and what the typical emergency lighting options are.
- Understand the emergency lighting system in the context and as an integral component of a building’s life safety strategies and technologies.
Through the last several years, challenges associated with emergency lighting have diminished due to comprehensive code development. Cross references between multiple building codes have been refined to minimize contradictions and subjective interpretations. Nevertheless, it behooves the engineer to be involved early with development of conceptual lighting schemes, determination of appropriate codes, and selection of the optimal power system for emergency lighting, not least of which is seeking the input of the authority having jurisdiction (AHJ) prior to submission of the permitting plans for approval. The AHJ interpretation of a specific code application ultimately trumps the professional engineer’s understanding.
Code requirements, applications
The primary codes used to determine proper application of emergency lighting systems include: 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. Determining which year a specific code or standard has been adopted by the jurisdiction where the given building project is located is critical prior to proceeding with emergency lighting design, as not all jurisdictions are enforcing the most current code or standard.
The engineer’s traditional responsibility for illuminating egress paths has been somewhat subordinated by the architect, who is responsible for the building design and determining building type. Further, the architect, in most jurisdictions, generally is responsible for defining the means of egress via the exiting plans. Typically, these exiting plans are subject to approval of the AHJ prior to issuance of a building permit and definitely are required prior to a building occupancy permit. The key stipulation for adequate egress lighting falls under the engineer’s purview once the official egress pathway has been defined.
The prime directive of IBC Section 1006.1 stipulates the means of egress shall be illuminated at all times the building space served by the mean of egress is occupied. By definition, egress is a “continuous and unobstructed path of vertical and horizontal egress travel from any occupied portion of a building or structure to a public way. A means of egress consists of three separate and distinct components: the exit access, the exit, and the exit discharge.” A number of jurisdictions include after-hours cleaning crews in consideration of a building being occupied, so lighting controls for means of egress must function automatically whenever the building is occupied.
NFPA 101: Life Safety Code takes all of the ambiguity out of emergency lighting process and provides clear expectations of the outcomes. Consequently, the initial code source for determining the proper application of emergency lighting is located in NFPA 101 Chapter 7. Emergency illumination is required for buildings as stipulated in Chapters 11 through 43 of this code. Section 126.96.36.199 clarifies that emergency lighting is only required for the purpose of exit access, which includes only designated stairs, aisles, corridors, ramps, and escalators to a defined public way. Obviously, these spaces must clearly be annunciated early in the design process in order to provide an emergency lighting system that can comply with the following performance requirements as specified in sections 188.8.131.52, 184.108.40.206, 220.127.116.11, 18.104.22.168, and 22.214.171.124.
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 be transferred to its alternate source within 10 sec. Additionally, battery-powered emergency lighting shall be continuously available for 1.5 hours 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 defined pathway. At the end of 1.5 hours, the illumination levels are permitted to decline along the path of egress as the emergency power source discharges to an average of 0.6 fc (6.5 lux) but not less than 0.06 fc (0.65 lux). In order to provide sufficient contrast and subsequent visual acuity, the maximum to minimum illumination uniformity ratio shall be no greater than 40:1.
Interestingly, the IBC 2012 is somewhat contrary to NFPA 101, stipulating in IBC 1006.2 the following: “The means of egress illumination shall not be less than 1 fc (11 lux) at the walking surface.” Note that this stipulation does not say “average” nor does it imply an average number; it is clearly the minimum requirement for emergency egress lighting, and is required by some AHJs. The exception to this applies to certain assembly occupancies. Fortunately, the performance of the emergency lighting system is the same in both the IBC and NFPA 101. Ultimately, the challenge presented is getting the AHJ to accede to the NFPA 101 requirements in lieu of IBC 1006.2, which certainly offers more specific parameters than can readily be achieved.
Completing a comprehensive code analysis is necessary to address specific emergency lighting applications for a given building type and jurisdictional requirements. For example, in addition to IBC building general type classifications, the IBC Type I-2 for hospitals have additional emergency lighting requirements as outlined in NFPA 99, NFPA 110, and NFPA 70 Article 517.63, which require supplemental battery-powered emergency lighting for anesthetizing locations. Further supplementary battery-powered emergency lighting is required for both normal main power and emergency main power switchboards. This requirement is codified in NFPA Article 110-7.3. The minimum horizontal footcandles shall be 3.0 fc (32.3 lux) at the floor level.
NFPA 101 Article 7.9.3 requires emergency lighting systems to have periodic functional tests. The functional testing is to be conducted monthly for a minimum of 30 sec, with an annual functional test of 1.5 hours required for battery-powered systems. The key constituent of this requirement is the maintenance of written documentation confirming the mandated monthly and annual functional testing visual inspections. NFPA 101 also allows self-testing and self-diagnosis as long as the self-testing is compliant with the manual requirements. For emergency lighting systems where self-testing is computer-based, a computer-generated report detailing the history of the tests is adequate for AHJ review.
Exit signage is required by NFPA 101 Article 7.10. The two approved types of exit signs are internally illuminated and externally illuminated. We will discuss exclusively internally illuminated exit signs. The exit signs shall not be spaced more than 100 ft apart and must be readily visible in all directions from the exit access. Exit signs with internal battery-powered sources are to be periodically tested in accordance with Article 7.9.3 and are to conform to UL 924. An exit sign’s illumination level is permitted to decline to 60% after 1.5 hours of operation. Floor proximity egress path marking exit signs are required within 18 in. of the floor for various occupancies as detailed in NFPA 101 Chapters 11 through 43. The exit signs must comply with UL 1994: Luminous Egress Path Marking Systems and be approved for delineation of egress pathways. The system must operate continuously anytime the building fire alarm system is activated. Obviously, the intent is to provide a clearly identifiable path of egress if the pathway is filled with stratified smoke and the only viable means out is very low to the floor.
In consideration of energy codes and emergency lighting—and unless specifically prohibited—NFPA 101-126.96.36.199.2 and 3 will allow lighting controls in areas of means of egress. The switch controllers must be listed and have a fail-safe feature, the “on” function must provide a minimum of 15 minutes of illumination, the motion sensor must be activated by occupant movement, and the controller must be activated by the building fire alarm system, if provided. The energy-saving control devices shall not compromise the integrity of the emergency illumination system. Thorough review of proposed lighting control solutions along with the emergency lighting egress plans with the AHJ should preclude any undesirable project outcomes.