Emergency lighting: What’s required, and how it’s designed
- Understand where emergency lighting is required in nonresidential buildings, as required by codes and standards.
- Learn about performance requirements for emergency lighting.
- Comprehend how emergency lighting is implemented, and which devices should be used.
Emergency lighting is required to illuminate building areas when things go wrong—for example, when the normal electrical supply is interrupted by a utility outage or by a fire or failure within the building. In most facilities, the largest part of emergency illumination lights the pathways and exits that lead out of the building—the egress paths. Its intent is to facilitate evacuation of the facility, particularly in the event of a fire, and to reduce the tendency of occupants to panic under stress, and in the dark.
Because the performance of emergency lighting is directly related to life safety, code officials are notoriously demanding of strict compliance in its design and installation. Differing interpretations about emergency lighting requirements easily can lead to a costly delay of occupancy. A clear understanding of the code requirements for emergency lighting, and a clear understanding of code officials’ views of any issues that admit interpretation, will go a long way toward avoiding expensive and embarrassing surprises late in construction.
The term “emergency lighting” appears frequently in the codes, but it is nowhere directly defined. For the purposes of this article, emergency lighting refers to lighting equipment that is specifically identified as such in one of the codes, with limited exception. Certain lighting that must illuminate under emergency conditions in health care facilities, but is not technically defined as emergency lighting, is addressed separately.
These codes are referenced in this article:
- International Building Code (IBC), 2015 edition.
- NFPA 70: National Electrical Code (NEC), 2017 edition.
- NFPA 99: Health Care Facilities Code, 2015 edition.
- NFPA 101: Life Safety Code, 2015 edition.
- NFPA 110: Standard for Emergency and Standby Power Systems, 2016 edition.
- NFPA 111: Standard on Stored Electrical Energy Emergency and Standby Power Systems, 2016 edition.
Code-enforcement agencies may adopt these codes, or other codes, and may enforce other editions. Provisions of the various codes sometimes differ regarding similar sets of requirements. Designers should verify the codes and editions in force, and consult authorities having jurisdiction (AHJ) regarding their interpretations of ambiguous or conflicting requirements, before design commences.
Emergency egress lighting, and other emergency lighting
The existential requirements for emergency lighting appear independently in the IBC and in NFPA 101. IBC Section 1008, Means of Egress Illumination, covers lighting requirements for exit routes. It calls for egress lighting for nearly all occupancies, with limited exceptions for agricultural and livestock buildings, dwelling units in institutional occupancies and most residential occupancies, and aisles in assembly occupancies. Egress lighting must remain active whenever the building is occupied (IBC 1008.2).
Under normal conditions, egress lighting must be served by the building’s primary electrical supply. When that supply fails, an emergency power supply must illuminate specific areas, particularly pathways that lead to exits, the exits themselves, and exit discharges. The IBC allows for a number of options for the form of the emergency power system. It may be an onsite generator, a battery-powered system, or a distributed set of batteries attached to individual luminaires.
NFPA 101 provides a similar set of requirements. Emergency lighting is required for egress in all occupancies addressed by the code, with the exception of one- and two-family dwellings and rooming houses. Overall, NFPA 101 describes emergency lighting requirements more specifically than does the IBC.
The IBC generally applies to new construction and renovation projects. Its provisions are not normally enforced retroactively on existing buildings, except where the AHJ determines that public safety is compromised by existing conditions (IBC 102.6). NFPA 101 is enforceable on existing buildings and includes separate requirements for existing and new facilities for each type of occupancy that it addresses.
For emergency lighting, NFPA 101 requirements for new and existing facilities are substantially identical, with a few exceptions. Certain existing worship venues, for example, are permitted to operate without emergency lighting under NFPA 101, while similar new facilities are required to provide it (NFPA 101 126.96.36.199, 188.8.131.52).
NFPA 101 requires emergency egress lighting in exit accesses, at exits, and at exit discharges. For this purpose, the term “exit access” denotes only designated stairs, corridors, ramps, escalators, and passageways leading to an exit. “Exit discharge” denotes similar designated building components leading to a public way. In a typical design project, these building components are designated by the architect and indicated in the life safety plans. When those plans are not available early in the design process, the designer can get very close to compliant egress lighting by providing emergency lighting in corridors, stairways, at exits, and immediately outside exits.
The IBC specifically requires emergency lighting in certain spaces not used for egress: electrical rooms, fire command centers, fire pump rooms, and generator rooms. No special performance characteristics are specified for these areas. A minimal interpretation would be that these areas require egress illumination. That solution might be suitable for utility spaces, where emergency light would provide wayfinding and be supplemented by portable battery-powered lamps. However, egress-level lighting would certainly be inadequate for a fire command center. A conservative approach for a fire command center might be to provide adequate lighting on each of the normal and emergency power systems, to ensure that the failure of one of those systems won’t leave the center in darkness. Given the IBC’s ambiguity about emergency illumination in these areas, it is worthwhile to verify the AHJ’s interpretation of the code during design.
Exit signs are required along the egress path, at doorways leading to an egress path, and at exits, placed to ensure that an exit sign is visible from no more than 100 ft or the listed viewing distance of the exit sign (IBC 1013.1). This requirement is echoed in NFPA 101 (184.108.40.206.1).
NFPA 110 7.3 requires battery-powered emergency lighting with an average illumination at floor level of 3 fc at generator sets and at generator paralleling gear (NFPA 110 7.3). This requirement also is in NFPA 99.
NFPA 99 calls for battery-powered lighting in locations where deep sedation or general anesthesia is used, with lighting levels sufficient to terminate procedures in the room. These battery lighting units are required to operate for at least 30 minutes (NFPA 99 220.127.116.11.11). The purpose of these battery-powered lights is to ensure that a surgeon wielding a scalpel will not be left in total darkness should normal power fail during a procedure, and to provide minimal lighting for terminating a procedure should the standby lighting also fail.
Technically, these lights are not emergency lights, as there is no emergency electrical system defined for health care facilities. The NEC allows these lighting units to be connected to the critical branch rather than the life safety branch.
General performance requirements for emergency egress illumination are shown in IBC 1008.3.4 and 1008.3.5 and in NFPA 101 7.9.2. Illumination requirements are identical in these two codes. The egress path must be illuminated at an average level of 1 fc, with a minimum level of 0.1 fc; the maximum-to-minimum illumination level ratio must be 40:1 or less. Emergency lighting must remain illuminated for at least 90 minutes. Illumination levels are allowed to decline to an average of 0.6 fc, with a 0.06-fc minimum, at the end of the 90-minute period.
NFPA 101 18.104.22.168 requires that new emergency lighting power systems be at least Type 10, Class 1.5, Level 1 systems, as defined in NFPA 110. That requirement translates to restoration of power to emergency lighting within 10 seconds after loss of normal power, for a duration of 1.5 hours, for a system of adequate reliability for application where its failure could result in loss of life or serious injury, as described in NFPA 110 4.4.1 and in NFPA 111 4.5.1.
Emergency illumination requirements for stairways are subject to interpretation under NFPA 101. Section 7.9 contains detailed requirements for illumination of the egress path, but it does not contain any specific requirements for stairways. Section 7.8, Illumination of Means of Egress, requires that new stairs be illuminated at 10 fc “during conditions of stair use.” Analysis of requirements in 7.8 shows that its requirements are considerably more stringent than those covering emergency lighting in 7.9.
For example, 7.9 allows for a minimum illumination of 0.1 fc while 7.8 requires a minimum of 1 fc along the egress path. A reasonable interpretation, then, is that Section 7.8 covers requirements under normal conditions while 7.9 covers emergency illumination requirements.
However, some AHJs have enforced the 10-fc rule on emergency lighting in stairways. Facilities using generators for the emergency power source have little difficulty meeting this requirement, as emergency lights operate at full illumination. Facilities relying on unit equipment, though, will require prodigious batteries or numerous lighting units to maintain this illumination level.
Testing requirements for emergency lighting appear in NFPA 101 7.9.3. Lamps and power sources must be periodically tested to verify that they continue to function in accordance with code requirements. All emergency lighting systems, regardless of their power source, must be tested monthly for a period of at least 30 seconds. For unit equipment, monthly testing typically consists of a short test of the battery and lamp, implemented by a test switch on the luminaire.
For storage-battery and generator systems, testing is typically accomplished by de-energizing the normal power source serving emergency lighting and observing that the lamps illuminate. Generator systems must be tested monthly by initiation at a transfer switch and run under load for at least 30 minutes (NFPA 110 8.4.2). Emergency lighting tests are normally performed in conjunction with monthly standby power system tests.
For coordination with emergency lighting tests, it would be convenient to initiate monthly generator tests from the emergency system’s transfer switch; however, NFPA 110 requires that the transfer switch initiating the test be rotated among switches from one month to another (22.214.171.124). Where multiple transfer switches exist, the normal power supply to emergency lighting equipment must be intentionally de-energized to observe its operation from the emergency supply.
Storage-battery systems are required to be tested in accordance with their manufacturer’s recommendations, rather than in accordance with a code-mandated schedule (NFPA 111 8.4.1). For these systems, it may not be possible to coordinate periodic battery system tests with tests of emergency lighting. Nevertheless, emergency lighting must be tested monthly.
Storage-battery systems and unit equipment must be tested annually for 90 minutes.
The installation requirements for power systems serving emergency loads, including emergency lighting, appear in NEC Article 700, Emergency Systems. The power sources permitted under the IBC-storage-battery systems, onsite generators, and unit equipment-also are permitted under Article 700, along with fuel cell systems per 700.12(A), (B), (C) and (D). A separate utility service may serve as the alternate source, where its reliability is acceptable to the AHJ as per 700.12(D). The AHJ should be consulted in advance of construction where a fuel cell system or alternative service is contemplated as the emergency supply.
The electrical supply must provide power within 10 seconds of the loss of normal power (700.12), echoing the response requirements of NFPA 101 and the IBC. Surge-protection devices are required on all emergency system switchboards and panelboards (700.8).
Article 700 requires strict separation of the emergency system wiring from all other wiring, beginning at a separate vertical switchboard section or disconnect switch connected to the emergency supply (700.10(B)(5)(c)). Lighting and power circuits that serve anything other than required emergency loads may not be served from the emergency system (700.15). If standby power is required for other purposes, it must be served from a separate vertical section, panelboard, or disconnect switch, through a separate transfer switch. The system capacity must be adequate to serve all the loads connected to the system simultaneously, or a load-shed system must be provided to maintain service to emergency loads by selectively disconnecting other loads (700.4(B)).
Overcurrent devices on the emergency power system must be selectively coordinated with all upstream devices. The definition of “selective coordination” in the NEC is quite strict, requiring coordination for the “full range” of overcurrent settings and device operating times. Achieving selective coordination with circuit breakers will require careful device selection; otherwise, fuses must be used.
Emergency system feeders and generator control circuits must be protected from fire by one of several methods. Equipment serving emergency feeders must be protected by either an automatic fire-suppression system or a 2-hour-rated enclosure.
Special occupancies: health care
NFPA 99 and NEC Article 517 modify certain requirements for emergency systems in health care facilities. Those documents do not define an emergency electrical system; instead, they define an essential electrical system consisting of a life safety branch, critical branch, and equipment branch. Emergency egress lighting is served by the life safety branch (517.33(A)) and other lighting that must remain operative to provide patient care and support necessary for hospital functions served by the critical branch (517.34(A)). The life safety branch must comply with the requirements of NEC Article 700 for emergency systems, except where specifically modified in Article 517 (517.26).
Article 517 abrogates the standby system capacity requirement of Article 700, allowing the system to be sized for the maximum demand that the load is likely to produce (517.30(D)). Selective coordination requirements are limited to faults that persist for more than 0.1 second, as per 517.30(G) as well as NFPA 99 (126.96.36.199.2.1).
The applicability of fire-rating requirements for health care facilities is open to interpretation. NFPA 99 specifically exempts the life safety branch from compliance with the fire-rating requirements of Article 700.10(D) under 188.8.131.52.1.6 and 184.108.40.206.1.5. However, no such exemption appears in NEC Article 517. Fire ratings can be expensive and difficult to apply after construction, so the wise course is to get clarity from the AHJ about whether fire-rating requirements will be enforced during design.
Hardware: internally illuminated exit signs
NFPA 101 and the IBC permit the use of internally illuminated exit signs, provided that they are listed for the purpose and approved by the AHJ. The two most common technologies used in internally illuminated signs are photoluminescence and radioluminescence. Both of these technologies provide the significant advantages of obviating annual battery-duration testing and periodic battery replacement, and both have disadvantages.
Photoluminescent materials absorb energy from incident light and slowly release that energy as visible light. Energy is stored in the electron clouds surrounding the individual atoms of the photoluminescent material, in that incident light knocks electrons into elevated energy states. As those electrons return to lower-energy states, they release their stored energy as visible light.
On the macroscopic scale, these materials behave as light batteries, charged by incident light and discharged into darker environments. These materials are applied as the letters in exit signs, where they glow to mark the egress path in low illumination.
Photoluminescent exit signs have long usable life and require little maintenance. Units are typically warranted for 15 to 25 years. The primary maintenance method is to clean the face of the sign, as obscuration of the face will directly reduce the light output, which will reduce the charging effectiveness.
Photoluminescent exit signs must be continuously illuminated to a minimum level under normal conditions—typically 5 fcs—to remain charged. As energy codes become more restrictive, requiring occupant sensing, daylight controls, and control of egress lighting, the application of photoluminescent lighting becomes more challenging.
Photoluminescent materials are generally charged by light in the upper end of the visible light spectrum and the low end of the ultraviolet region. They charge well under fluorescent and metal-halide lamps, which produce a fair amount of blue and ultraviolet light. LEDs produce substantially less high-energy light and are less effective at charging photoluminescent exit signs than older lighting technologies. Photoluminescent signs to be charged by LED luminaires must be marked for compatibility with LED illumination (NFPA 101 220.127.116.11).
Radioluminescent exit signs contain a small amount of radioactive material-typically tritium, a radioactive isotope of hydrogen. Tritium decays by emitting high-speed electrons that impinge on a specially selected phosphor, which glows visibly in response. Tritium, a gas, is typically enclosed in a phosphor-coated glass tube, and the tube is encased in a block of clear plastic to minimize the likelihood that the tritium will be released into the environment. The usable life of radioluminescent exit signs is limited by tritium decay and by degradation of the phosphor. The half-life of tritium is about 12 years.
Use of radioluminescent exit signs triggers additional compliance and record-keeping requirements. The presence of radioactive materials in these signs necessitates proper disposal, with attendant costs and records. With its low level of radioactivity and long half-life, tritium illumination is not believed to pose a significant health hazard.
The illumination level of self-illuminated exit signs is not specified in the codes. Instead, these signs are listed and labeled with a maximum viewing distance. Signs must be placed to ensure that an exit sign is visible within the listed viewing distance at all points on the egress path.
Hardware: unit equipment
“Unit equipment” is an electrical term used to describe battery-powered lighting units. It’s described in NEC 700.12(F)(1) and 701.12(F)(1) as consisting of a rechargeable battery, a battery charger, provisions for connecting attached or remote lamps, and means of powering lamps from the battery when the normal supply is unavailable. The term covers both illumination fixtures and exit signs. Unit equipment may illuminate with the facility’s normal lighting and switch to battery power under emergency conditions, or it may operate only when the normal supply fails.
Installation and performance requirements are described in 700.12(F)(2) and again in 701.12(F)(2). In particular, unit equipment must be powered from the same lighting circuit that supplies normal lighting in its area. Battery-powered lighting can’t distinguish between the failure of a branch circuit and general failure of the normal supply. Under circuit-failure conditions, it will illuminate until its batteries fail. Normal lighting attached to the same circuit will immediately extinguish. The purpose of that requirement is to ensure that the failure of the circuit serving emergency lighting is obvious, and maybe even inconvenient, to the building occupants.
Unit equipment must be permanently installed while specifically permitting flexible cord-and-plug connections of 3 ft or less. Cord-and-plug installations should be designed with care, if at all, because NEC 400.12 specifically prohibits flexible cords that penetrate ceilings or floors or are concealed above ceilings.
Performance requirements for unit equipment, as described in NEC 700.12, are identical to those described for emergency lighting in the IBC and NFPA 101: At least 60% of initial illumination must be maintained for 90 minutes. NEC 700 includes an additional requirement that the battery voltage remains at no less than 87.5% of its nominal voltage during the entire 90-minute period. Presumably, the maximum-discharge voltage requirement is intended to ensure that batteries are not damaged by repeated deep-discharge cycles during annual exposure.