Fire and life safety: Emergency lighting
Emergency lighting is just one component of the means-of-egress, and part of a building’s life safety system. In the event of a power outage, a backup lighting system may be the occupants’ only guide to a safe exit.
By Dale Wilson, AIA, Aon Fire Protection Engineering Corp., Glenview, Ill.
Everywhere, people eat, work, and shop in abundantly illuminated public facilities. But, what if that light so many of us take for granted suddenly ceased to exist, especially in an unfamiliar space, during an emergency? People may become frightened, anxious, uncertain, or disoriented. Coupled with the smell of smoke or another impending emergency, people may even panic. Fortunately, most public facilities are mandated by code to be equipped with emergency lighting that is required to automatically activate in the event of a power failure.
Fire protection engineering and life safety consulting involve a large array of specialty services. One responsibility is to assist architects, engineers, and owners in determining if their buildings include the proper fire protection and life safety amenities that help protect the building’s occupants during an emergency. One important life safety amenity includes the design and installation of the emergency lighting system. Fire protection engineers work in conjunction with architects and electrical engineers to ensure that emergency lighting is properly specified and located in the required means-of-egress pathways in a manner consistent with the applicable building codes.
Emergency lighting is one component of the means-of-egress illumination and is part of a building’s life safety systems. Emergency lighting can be described as any approved illuminating device and appurtenance designed to automatically turn on when the primary power goes out. Exit signs are used in combination with emergency lighting to provide means of egress lighting. Emergency lighting and exit signs are regulated differently but share some requirements, like the requisite to be connected to an emergency backup or 60-sec power system.
From the viewpoint of the various national building codes, emergency lighting is a backup lighting system that illuminates a building or portion thereof. More specifically, the purpose of emergency lighting is to provide a minimum level of visibility of exits or escape routes to help direct occupants safely out of the building in the event of loss of primary power. Emergency lighting is also used to help building occupants, essential personnel, and emergency responders locate firefighting and safety equipment, to perform necessary safety functions, or to shut down equipment and operations that might become hazardous if abandoned. It may seem practical that all buildings should have emergency lights, but not all facilities or occupancies require emergency lighting, and the requirements for installation can also vary from facility to facility.
The need for emergency lighting became imminent almost immediately after the invention of the light bulb. Requirements for emergency lighting can be found in national building codes as far back as the 1920s, and likely earlier. The National Fire Protection Assn. (NFPA) 1927 Building Exits Code says:
The lighting source shall be arranged to assure continued illumination of exit-ways in cases of emergency caused by failure of the principle lighting of the building. Where electric current is the source of the lighting of buildings used for public assembly or congregation, the emergency lighting shall be from a source independent of that for the general lighting or shall be controlled by an automatic device which will operate reliably to switch the circuit to an independent secondary source in the event of failure of the primary source of current.
The general purpose and intent of emergency lighting has essentially remained unchanged over the years, despite changes in technology and more detailed building code language. Changes have been made as to where emergency lighting is required, what is required of the system components, how the system is installed, and when it is to be tested.
There are numerous versions of building codes and various editions of these building codes in use around the country. The most widely used codes in effect today are NFPA 101: Life Safety Code (LSC); and ICC: International Building Code (IBC).
Like code requirements themselves, the language from one code to another and from edition to edition can vary, even though the general intent is the same. Language from state to state or even city to city can also vary. For example, New York City explicitly prohibits the use of batteries independent of conductors as a primary use for emergency lights. Emergency lights must be encased in steel housing; all corridors and possible exits must be accommodated, not just those corridors that are part of the exit plan; and lighting must provide a minimum of 2 fc measured at the floor level, which is a higher illumination level than the nationally recognized code requirement. In the City of Chicago, the requirement for emergency lights to operate is also more restrictive. In lieu of emergency lighting operating in a blackout condition, the City of Chicago requires emergency lighting to activate in brownout conditions, which is defined as an electrical voltage drop of more than 10%. These differences mean that emergency lighting devices used in one part of the country may not be suitable for use in other parts of the country. It is important to verify the requirements for each project location.
Occupancy: Of all the requirements associated with emergency lighting, the type of occupancy is one of the more difficult to navigate. Although it would be good practice to install emergency lighting in all spaces of all buildings, there are exceptions. Exceptions depend on whether the building is public or private and if the building is used as an assembly space, a residential space, a business operation, a storage facility, or one of the other occupancy types specified in the code. Even the size of the structure (area, height, stories, etc.), applications within the building (equipment or materials employed), or whether the structure is new or existing can determine if emergency lighting is required. For example, NFPA 101 does not require emergency lighting in board and care occupancies, where each sleeping room has a direct exit to the exterior at grade level. To simplify the process, it should be common practice to include emergency lighting throughout the building. Besides, the value and benefits of added safety are immeasurable.
Locations: In general, illumination is required along exit access pathways leading to exits, exit stairs, aisles, corridors, ramps, and at the exit discharge pathways that lead to a public way. Some authorities having jurisdiction (AHJs) do not consider luminance or illuminance levels, but instead require specific spacing or locations within buildings. Designing the emergency lighting system involves strategically locating fixtures to assure that minimum levels of lighting and the maximum levels of contrast are not exceeded. Emergency lighting is typically located along the walls in compact units or integrated into the general overhead lighting system. The lighting layout can be challenging in irregularly shaped rooms or in spaces with large quantities of furnishings, which can block the light source from reaching the designated surface and create dark spots.
Illumination levels: The level of illumination and quality and consistency of emergency illumination are important for the building occupants’ safety. Good emergency lighting depends on more than just the levels of illumination. The direction, distribution, and quality of light all contribute to better visibility and a successful emergency lighting design. Effective lighting starts with illuminance, which is the level of light falling on a surface. Emergency lighting illuminance is measured along the path of egress at the floor level. General overhead illumination for emergency lighting is typically dispersed from larger fixtures and in a more vertical, wider pattern, which is less likely affected by contents in the building. Wall-mounted fixtures, which have narrow or smaller lenses, tend to disperse light in a slightly more horizontal fashion and are more easily affected by building contents like partitions, furniture, and other obstructions.
The Illuminating Engineering Society (IES) publishes a table of general illuminance recommendations. Selected portions of this are shown in Table 1.
The two most commonly used building codes (NFPA 101, Section 18.104.22.168, and IBC, Section 1006.4) require that emergency lighting provide a minimum average of one fc for a period 1.5 hours with a minimum of 0.1 fc at any point and a maximum fc level that cannot exceed 40 times the minimum. The minimum- to maximum-level relationship is required to avoid bright to dark patches that could make emergency egress more visually challenging in an already stressful situation. Compared to the IES recommendations for general lighting, the level of illumination required for emergency lighting is relatively minimal. The minimum fc level for emergency lighting is actually below the recommendation for public spaces with dark surroundings; however, the higher end of the spectrum for emergency lighting of 40 fc is more comparable to that suggested for performance tasks.
Public spaces with dark surroundings
Simple orientation for short temporary visits
Working spaces where visual tasks are only occasionally performed
Performance of visual tasks of high contrast or large size
Performance of visual tasks of medium contrast or small size
Performance of visual tasks of low contrast or very small size
Performance of visual tasks of low contrast or very small size over a prolonged period
Performance of very prolonged and exacting visual tasks
Performance of very special visual tasks of extremely low contrast
*A-C for illuminances over a large area
D-F for localized tasks
G-I for extremely difficult visual tasks
Power: Emergency lighting is one of several building life safety features required to be connected to a secondary power source (i.e. batteries or generators). Other systems include exit signage, fire pumps, alarm system, elevators, smoke control systems, and specialty buildings such as airport traffic control towers and buildings containing toxic materials.
Emergency lighting is required to be equipped with at least two sources of functional power so that in the event one source fails, it does not affect the capability of the second source. In the event of power failure, the second source is required to activate within 10 sec. Once activated, the second source of power is required to maintain the minimum illumination levels for a minimum of 90 minutes. The second power source may be in the form of a generator, secondary electrical service, batteries, or any other power source approved by the AHJ capable of meeting the minimum duration and illumination criteria. The secondary power source is activated by a series of control devices including voltage-sensing relays, frequency-sensing relays, time-delay relays, and the like. An automatic transfer switch automatically transfers the electrical load from normal power to an alternate secondary power, should the normal power fail upon loss of emergency power.
Testing is critical for a successful emergency lighting installation. No matter how accurately an engineer designs a system, or how precisely a contractor installs the specified devices, invariably, the building users will locate furnishings, fixtures, and other contents in places that can affect the performance of the emergency lighting system. Unanticipated obstructions can easily change the design characteristics, so in addition to testing the system when installed to ensure it is functioning properly, it is important to incorporate a post-occupancy inspection and test into the project. By adding this last measure, the design engineer and contractors can make the necessary adjustments to ensure optimum performance. Once the engineers and contractors leave the construction site, regular testing becomes the responsibility of the building owner.
Regular testing and maintenance is required of all emergency lighting systems. Ensuring the systems are routinely inspected and tested is tedious, but important nonetheless. Testing may be required more frequently, especially in occupancies with higher tenant turnover. After a change in tenant, a building alteration, or an interior remodel is a good time to conduct a more comprehensive test using light meters to ensure the minimum and maximum lighting values are maintained.
Testing and maintenance requirements for emergency lighting can be found in NFPA 101, Section 7.9.3. In general, a monthly visual inspection and a monthly functional test of the devices for a 30-sec interval are expected, and a complete system test should be conducted annually for not less than a 1.5-hour duration. The annual test requires the actual power to the emergency lighting system be cut, by unplugging the unit, tripping a breaker, or by another approved, safe method. If the devices do not function, the lights are dim, or the system fails to function for the full duration of the test, the owner is responsible to make sure the unit is repaired or replaced. Records of each test should be maintained by the owner for review by the AHJ. The records should include system identification, test dates, test times, tester’s name, results, comments or action items, and a confirmation that any service repair or replacement was conducted.
Although the fire protection engineer is not always the primary consultant to design or specify an emergency lighting system, he or she often works closely with architects and electrical engineers to ensure the system is adequately distributed and located in places that will help occupants safely evacuate a building during an emergency. Emergency lighting is an important component of a building’s emergency systems. Emergency lighting luminaries are often the last thought in the lighting design. This can create problems with the placement of fixtures as they relate to the surrounding room and egress environment.
The applicable building codes that define emergency lighting can vary significantly from place to place, so it is important to conduct the necessary code research prior to designing the emergency lighting system. Although it may be possible to design, locate, and simulate the effects of emergency lighting in a particular design, best practices should always include testing the systems prior to allowing occupancy of a structure. Post-occupancy testing should be routine. The testing should be conducted after the tenant moves in and sets up its furnishings, fixtures, and finishes. Furniture and other fixtures may obscure the illumination levels and result in areas not properly illuminated. In this way, the placement of the fixtures can be adjusted to ensure complete coverage of the areas, and that the tenant’s amenities have not obstructed visibility or created undesirable shadows.
Public facilities and workplaces should be provided with emergency lighting, even where the building codes do not require these systems. Do not take lighting for granted.
Wilson holds a bachelor’s degree in architecture and a master's degree in public service/public administration. He is a registered architect, project manager, and healthcare practice group director for Aon Fire Protection Engineering with over 25 years of experience providing life safety and code consulting services.
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