Lights Out--Battery Power for Exit Signs & Emergency Lights
When the lights go out, emergency lighting systems step in to provide light and a safe way out. These systems vary in the type of light used, source, and necessary battery. Be prepared the next time there is a power outage.
Functioning emergency lights are required to comply with state building and fire codes, insurance standards, and even OSHA standards.
An emergency light is a battery-backed lighting device that switches on automatically when a building experiences a power outage. Emergency lights are standard in new commercial and high occupancy residential buildings, such as college dormitories. Most building codes require that they be installed in older buildings as well.
For large commercial or industrial facilities that may not have windows or those that continue operations during the night shift, a power outage can create a kind of panic that feeds on itself and intensifies when a large crowd experiences sudden darkness — at times prompting serious injuries or even fatalities. With emergency lighting, occupants would have to navigate great distances through rooms filled with obstacles, darkened hallways, and stairs to reach safety.
Backup batteries for emergency lighting systems or EXIT signs function much like automobile batteries do. They are continually discharged and recharged during normal operation. Proper testing schedules can extend the battery life for this backup power source. A maintenance-free rechargeable sealed lead-acid battery will power the system when the power goes out.
These batteries do still have a limited service life and many factors can affect battery life (e.g. changing temperatures). Therefore, there is not a strict rule for how long a specific battery should last. Testing of battery function should take place every three months. The two most commonly used battery types for emergency lighting are lead acid and nickel cadmium.
Safety requires installed emergency lighting throughout the path of any egress, stairs, aisles, corridors, ramps, escalators, and passageways leading to safety. These locations must be continually illuminated for a minimum of 90 min.
Transfer of emergency lighting must be automatic, within 10 seconds, of the loss of normal lighting power. The emergency lighting unit must provide initial illumination that's no less than an average of 1 footcandle (fc), or 10 lux, and a minimum at any point of 0.1 fc, or 1 lux measured along the path of egress at floor level.
Because batteries can be fairly expensive, it's worthwhile to reuse them where possible. The maximum usable life is between three and five years. If they have been dated, you can discard the old ones by taking them to a certified recycler. If the outer case appears warped, then they have been overheated and some of the plates are too close inside. Swollen batteries need to be replaced. With age batteries become sulfated, and an insulating coat builds up on the internal plates, therefore increasing the internal impedance. Otherwise, put them in a dedicated test unit for about 24 hours and see if they take a charge, in which case they are the batteries that have come out of units with bad chargers, so they can be reused.
Consider having a calendared maintenance schedule for replacing your important backup batteries.