Shedding Light on Emergency Egress: Exploring Solutions
By Ryan Maroney, PE – As you know, emergency egress lighting codes can be difficult to interpret. In my previous article, we focused on “the why” of code requirements of emergency egress lighting and discussed the purpose behind these requirements. Let’s take this one step further and dive into solutions for implementing emergency egress lighting on your next project.
“Bug-eye” lights used as standalone fixtures can be used to satisfy emergency egress lighting requirements. With this approach, emergency lighting units are provided along the egress path, wired to the unswitched leg of the circuit that feeds the normal lighting fixtures. These bug-eye lights remain off during normal building operation in the presence of utility power, during which time their integral batteries remain fully charged up by the utility power. Upon losing utility power, or if the breaker feeding the lighting trips, the bug-eyes turn on and provide illumination, via their integral batteries. These units are generally small and inexpensive, which can be a plus in a project with a tight budget.
However, it is arguably the least aesthetically pleasing solution available, due to the addition of separate units spaced along the egress path dedicated solely to emergency egress lighting. Maintenance wise, these units can be easily tested and replaced, as they are visible and distinguishable in the space. However, being as they are dispersed, maintenance will require physically reaching each unit, which can be time consuming depending on the size of the building and egress path(s).
Internal Battery Back-up in Select Light Fixtures
The next solution is to utilize batteries that are integral to the normal lighting fixtures. This solution is similar to the first in the use of individual batteries to achieve illumination during a power outage, however, this option conceals the batteries within the construction of the normal lighting fixtures. This makes it a more aesthetically appealing solution, as there are no additional visible units dedicated solely to emergency illumination.
Operationally, upon utility power failure, the luminaire(s) with these integral batteries will remain on to provide emergency illumination, thanks to the battery (although typically at a reduced lumen output). Upfront installation and wiring is fairly simple and straightforward in this option.
Cost-wise, this option is often similar to the previous option, as it does add a fair amount of cost when a general luminaire is ordered with an integral battery backup.
One drawback to this option is it can be more maintenance-intensive to replace the batteries. Depending on how many fixture types are in the building, there could be several different battery types to replace. Also, physically replacing the batteries can be a hassle as they are inside the fixtures, thus requiring opening up the fixtures. Cold temperatures can also be an issue for batteries, making this option tricky for exterior applications.
With this approach, a lighting inverter is used to provide emergency egress lighting. A lighting inverter is basically a large battery (or bank of batteries). However, unlike the first two options, a lighting inverter can be placed in a central location and can be wired to back up many light fixtures. This can be advantageous from a maintenance standpoint, as you can go to one location for testing and replacement of batteries.
Operation-wise, upon power failure, the lights that are wired to the lighting inverter will remain on, to provide emergency lighting, while the other lights not backed-up by the inverter will go dark. The idea is that the inverter comes on whenever the normal lighting circuit in the egress path loses power, whether it is a utility outage or a local breaker tripping.
One drawback to this solution is that lighting control zones and wiring can often be tricky with lighting inverters and will require some planning and forethought.
Instead of using batteries in one form or another, as in the first three options, the last solution is to use a generator to back up the emergency egress lighting. A typical generator is diesel or gas (natural gas or propane) powered, and following a power outage, can usually run well past the 90-minute minimum code requirement for emergency egress lighting, as long as there is fuel available to keep it running. Generators used for emergency lighting must comply with NEC article 700, but we won’t get into the details here (if you’d like more information, see Garth Stevens’ series of articles on this topic). In short, there are many requirements to follow if using a generator for emergency egress lighting, which can add complexity and cost to your power system. However, particularly if you have other uses or needs for a generator, utilizing a generator for emergency egress lighting is a great option. No longer are there batteries to worry about. Rather, in this option, maintenance will consist of testing and maintaining the generator.
Regardless of which option is implemented, each solution will require annual testing of the emergency egress lighting for 90 minutes, and monthly testing for 30 seconds. For a generator, monthly testing of 30 minutes is also required. Proper maintenance and testing are essential in order to ensure that adequate emergency egress lighting is available when a power outage arrives.
There are many important considerations when it comes to deciding how to best tackle emergency egress lighting. For every project, it is essential to weigh the pros and cons for each option prior to finalizing a solution. One project may hold aesthetics as a top priority, while another may be most concerned about maintenance issues or cost. Whatever the case may be, there is a solution for even the most demanding projects.
Ryan Maroney, PE, is an electrical engineer in the Morrison-Maierle Bozeman office. His design work primarily consists of lighting, lighting controls, power, and fire alarm for commercial buildings. In his free time, Ryan can be found in the mountains hunting and hiking with his wife, Katie.
Technical review of this article provided by Garth Stevens, PE.