Illuminating the means of egress
Differentiating the requirements of egress lighting versus emergency egress lighting requires a close look at several codes and standards
- Understand the code requirements of both egress and emergency lighting.
- Know the four most common alternate power sources for emergency egress lighting fixtures.
- Learn the difference between an automatic load control relay and a branch circuit emergency lighting transfer switch and when each should be used.
Both egress lighting and emergency egress lighting are of the upmost importance to create a safe environment and they share a common purpose. Each has specific needs and requirements when it comes to code.
According to the 2015 edition of the International Building Code, Chapter 10, “the means of egress serving a room or space shall be illuminated at all times that the room or space is occupied.” In other words, this means that whenever a person is in a room within a building, all corridors and vestibules between that room and an outside door of the building, including a path outside of the building to the public way, needs to be illuminated.
There are multiple codes that define egress lighting. The two most common codes are the IBC and NFPA 101: Life Safety Code. It is important to check with the state where the building is located as well as the local authority having jurisdiction to determine which code — and which version of the code — is enforced in the area where the building is located. Most states have adopted the IBC with their own amendments. While most areas have the same general requirements, it is important to know the exact requirements in the area of the building.
The first step in design is to determine the means of egress. To determine this, one needs to understand the definition of the components of the means of egress (see the definitions sidebar).
|Aisle||An unenclosed exit access component that defines and provides a path of egress travel.|
|Exit||That portion of a means of egress system between the exit access and the exit discharge or public way. Exit components include exterior exit doors at the level of exit discharge, interior exit stairways, interior exit ramps, exit passageways, exterior exit stairways and exterior exit ramps and horizontal exits.|
|Exit access||That portion of a means of egress system that leads from any occupied portion of a building or structure to an exit.|
|Exit discharge||That portion of a means of egress system between the termination of an exit and a public way.|
|Means of egress||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 parts: the exit access, the exit and the exit discharge.|
|Public way||A street, alley or other parcel of land open to the outside air leading to a street dedicated or otherwise permanently appropriated to the public for public use and which has a clear width and height of not less than 10 feet.|
Definitions of the components of the means of egress are defined in the 2015 edition of the International Building Code.
The exact means of egress can be difficult to determine in certain spaces. It is important to consult with the architect who is designing or renovating the building and/or the AHJ to determine the exact means of egress. It is often a good idea to ask the architect to identify and mark the means of egress in their documents. This can make design coordination more efficient and make it easier for any review process of design documents.
After the means of egress is determined, it is the necessary to define the lighting requirements. Per 2015 IBC section 1008.2.1, as well as NFPA 101 184.108.40.206, the means of egress illumination level shall be provided at not less than 1 footcandle (11 lux) at the walking surface. Note that this is the minimum of what must be maintained along the entire means of egress when any portion of the building that would be expected to use that portion of the means of egress is occupied. It is not an average level of illumination.
There are exceptions to this for certain areas such as theaters, auditoriums and similar spaces where light levels may be desired to support presentations, the use of certain audiovisual systems or performances. Supplemental code research will provide explanations of any exceptions for these types of spaces in a building.
NFPA 101 also requires that a minimum of 10 footcandles be provided at the walking surface of new stairs. See Figure 1 as an example of the means of egress for a space; the corridor indicated needs to maintain 1 footcandle minimum when the space is in use.
In recent years, energy codes have been adopted that try to reduce the amount of energy used in each building. Portions of these codes have targeted the energy required and used to illuminate buildings. A primary energy reduction measure that has been identified for lighting is a requirement to turn off lighting when spaces are not occupied. The result has created some conflict when newer energy codes and egress lighting requirements do not align. Both codes can be met simultaneously, however it is not as simple as it was in the past, and special care needs to be taken to ensure that requirements in both are adhered to.
For example, the IBC does not allow egress lighting to be shut off or reduced in most cases while the building is occupied. NFPA 101 does, however, allow the use of occupancy sensors in the means of egress with some limitations. Per NFPA 101 220.127.116.11.2:
“Unless prohibited by Chapters 11 through 43, automatic lighting control devices shall be permitted to temporarily turn off the illumination within the means of egress, provided that each lighting control device complies with all of the following:
- In new installations, the lighting control device is listed.
- The lighting control device is equipped to automatically energize the controlled lights upon loss of normal power and is evaluated for this purpose.
- Illumination timers are provided and are set for a minimum 15-minute duration.
- The lighting control device is activated by any occupant movement in the area served by the lighting units.
- In new installations, the lighting control device is activated by activation of the building fire alarm system, if provided.
- The lighting control device does not turn off any lights relied upon for activation of photoluminescent exit signs or path markers.
- The lighting control device does not turn off any battery-equipped emergency luminaires, unit equipment or exit signs.”
Emergency egress lighting
The means of egress also needs to be illuminated during an emergency situation. When this emergency situation includes a building power outage, the emergency egress lighting is used to illuminate this egress path during this emergency situation. To be able to describe and explain the different requirements of emergency egress lighting, it is important to differentiate between the requirements associated with egress lighting and those associated with emergency egress lighting.
IBC 1008.3.5 and NFPA 101 18.104.22.168 share several base requirements for illumination during an emergency situation. First, the illumination level measured at the walking surface shall not be less than 0.1 footcandle (minimum illuminance, not average). Second the illumination level shall not have less than a 1 footcandle average over the means of egress. Finally, even illumination with a maximum to minimum ratio of not more than 40:1 needs to be provided. See Figure 2 for an example of a lighting calculation indicating emergency illuminance in the means of egress.
IBC 1008.3.1, 10008.3.2 and 1008.3.3 indicate exact areas that require emergency egress illumination. Emergency illumination is not required but may be provided in other areas of a building, however the following are the areas required to have emergency egress illumination:
- Aisles, corridors, exit stairways and ramps in rooms or spaces that require two or more means of egress.
- Interior and exterior exit stairways and ramps, exit passageways, vestibules, exit discharge areas and exterior landings in buildings that require two or more means of egress.
- Electrical equipment rooms, fire command centers, fire pump rooms, generator rooms and public restrooms greater than 300 square feet.
An example of a space where emergency lighting may be provided even though it is not required by code would be a large mechanical room where a worker could find themselves in the middle of a lot of equipment and parts and would have a difficult time exiting the space during a power outage without emergency illumination.
The IBC and NFPA 101 define emergency egress lighting requirements. Engineers and designers also need to understand the installation and power source requirements. These requirements are defined in NFPA 70 (2017 edition): National Electrical Code Article 700. The NEC is updated on a regular three-year cycle and each state adopts this code along different schedules, so it is important to confirm the applicable version of the code with the state and AHJ for the area where the building is located.
The first thing to define when deciding how to power emergency egress lighting fixtures is the alternate source of power that is to be used. The four types of most commonly used alternate power sources in the majority of commercial buildings are: individual batteries, central lighting inverter, mini-inverters distributed throughout the building or a central emergency generator. All four have their positives and negatives, which need to be weighed on an individual case-by-case basis (see Table 1).
NEC Article 700.16 indicates that “emergency illumination shall include means of egress lighting, illuminated exit signs and all other luminaires specified as necessary to provide required illumination. Emergency lighting systems shall be designed and installed so that the failure of any individual lighting element, such as the burning out of a lamp, cannot leave in total darkness any space that requires emergency illumination.”
Therefore, care needs to be taken during design to ensure that the failure of any single LED driver or the burning out of any single LED board does not leave an area in total darkness. There are lighting fixtures that can be ordered with multiple LED drivers and multiple LED boards. This would meet the requirements of the section.
Another option is to provide multiple lighting fixtures in an area that are powered by an emergency power source. Typically, this is not to too difficult to achieve in interior spaces. In the past, it was common for a typical lighting design serving an exit discharge area to consist of a single luminaire. This is no longer a code-compliant solution unless this single fixture has redundant components as described previously.
When individual battery units or mini-lighting inverters are used, the installation is fairly straightforward. The battery in the luminaire is wired to the normal circuit such that the battery is being charged when normal power exists. When normal power fails, the luminaire is then powered from the associated battery. This provided two separate sources of power for the fixture and meets code requirements.
However, when a central system is used, there are additional code requirements that need to be met, mostly to do with distribution equipment and branch circuit wiring. NEC Article 700.17 addresses emergency branch circuit wiring and states:
“Branch circuits that supply emergency lighting shall be installed to provide service from a source complying with Article 700.12 when the normal supply for lighting is interrupted. Such installations shall provide either of the following:
- An emergency lighting supply, independent of the normal lighting supply, with provisions for automatically transferring the emergency lights upon the event of failure of the normal lighting branch circuit.
- Two or more branch circuits supplied from separate and complete systems with independent power sources. One of the two power sources and systems shall be part of the emergency system and the other shall be permitted to be part of the normal power source and system. Each system shall provide sufficient power for emergency lighting purposes.
“Unless both systems are used for regular lighting purposes and are both kept lighted, means shall be provided for automatically energizing either system upon failure of the other. Either or both systems shall be permitted to be a part of the general lighting of the protected occupancy if circuits supplying lights for emergency illumination are installed in accordance with other sections of this article.”
NEC Article 700.17(1) indicates that if a building has a normal and an emergency distribution system (for example a generator/automatic transfer switch or a central inverter), a single branch circuit can be brought to a lighting fixture as long as it ultimately has both normal and emergency source and means to automatically transfer between the two sources. This requires the use of a branch circuit emergency lighting transfer switch to sense the loss of the normal power branch circuit and transfer to the emergency power branch circuit. BCELTS are covered in NEC Article 700.25 and must carry a UL 1008 listing.
NEC Article 700.17(2) indicates that a space can be served from two separate circuits — as long as one of the sources is part of the emergency system — without the requirement to transfer between the two. This can be accomplished with one of two methods. The first method is to circuit luminaires that have any type of on/off controls to the normal power circuit and have noncontrolled luminaires (night lights) connected to the emergency circuit. This, however, if often in conflict with portions of the newer energy codes.
The second method is to provide an automatic load control relay. By providing an ALCR, there is now the ability to control the on/off functions of the emergency fixtures along with the normal fixtures in the space as the ALCR will automatically illuminate the emergency fixtures upon loss of normal power. ALCRs are covered in NEC Article 700.25 and must carry a UL 924 listing.
ALCRs are smaller and more cost-effective devices than BCELTS and can be used in the majority of applications. One instance where an ALCR would not meet code requirements would be in a situation where there is only a single light fixture in a space that requires emergency egress illumination, assuming that the fixture has multiple drivers and LED boards to meet the “failure of any individual lighting element” requirements.
When an ALCR is used, the luminaire is powered from the emergency lighting circuit and is only sensing the normal lighting circuit to know whether the fixture should be on or off. This then means that if the emergency lighting circuit failed, there will not be any illumination in the space unless the two separate LED drivers and boards are independently circuited and controlled, which is not a common occurrence. Therefore, for this application a BCELTS device could be used.
Building lighting system design can be complicated with a wide variety of “moving parts.” At the onset of a design, there are multiple options available to the designer. The required steps to take are:
- Define the means of egress, using architectural partners or the AHJ as appropriate.
- Develop the method to provide egress lighting in the means of egress that is illuminated any time a space being served by the means of egress is occupied, while also considering applicable energy codes.
- Determine which method of emergency illumination is to be used to provide emergency egress lighting.
If unit batteries or mini-inverters are selected as an emergency source, wiring methods are fairly cut and dry, so the final step is to perform emergency egress lighting calculations to determine where fixtures need to be located. However, if a central emergency system is to be used, there are a few more steps involved in the design:
- Select the type of central system to be used, taking into account space requirements, fuel supply restrictions, potential battery placement with weight and ventilation restrictions, etc.
- Determine on a space-by-space basis how many and which fixtures are required to provide emergency illumination.
- Determine if emergency fixtures will be used as night lighting (depending on compliance with local energy codes) or whether a BCELTS or ALCR device will need to be used. Additionally, the failure of a single element must be taken into account when emergency fixtures are selected.