#101Wednesdays - Shedding Some Light on Emergency Lighting
In this week's edition of #101Wednesdays, I'll take a look at what I think is one of the Life Safety Code's most widely misunderstood requirements: emergency lighting.
We take for granted that when we're in a public building, if the lights go out, emergency lights will kick on to illuminate the path of egress in the event of an emergency. In many, but not all, cases this is true. Emergency lighting is required by the Code where specified by the applicable occupancy chapter. In some cases, emergency lighting is always required (e.g., health care occupancies). In other cases, it depends on the number of stories in height and occupant load (e.g., business occupancies). To determine whether emergency lighting is required for a specific occupancy, go to the X.2.9 subsection of the applicable occupancy chapter, where X is the chapter number (e.g., 38.2.9 for emergency lighting requirements in new business occupancies).
Where emergency lighting is required, the performance requirements are specified in Section 7.9, which prescribes such criteria as illumination levels (average of 1 ft-candle at the floor level – 7.9.2.1.1) and maximum delay from the time the normal illumination source fails (10 seconds – 7.9.1.3). These criteria are widely understood and implemented. What are not widely understood and implemented, in my experience, are the conditions under which emergency lighting must be provided, as specified in 7.9.2.3:
7.9.2.3* The emergency lighting system shall be arranged to provide the required illumination automatically in the event of any interruption of normal lighting due to any of the following:
(1) Failure of a public utility or other outside electrical power supply
(2) Opening of a circuit breaker or fuse
(3) Manual act(s), including accidental opening of a switch controlling normal lighting facilities
Let's take a look at each of the three scenarios described in 7.9.2.3 and the means by which emergency lighting might be provided.
Item (1) describes a condition where the building loses its normal, incoming power supply from the grid (e.g., lightning strikes a pole and takes out a transformer; the neighborhood is in the dark). If emergency lighting is provided by battery-operated unit lights, the units will sense the loss of power to the lighting circuit and activate, illuminating the egress path. (It's important to ensure that the unit is wired or plugged into a lighting circuit, and not a power circuit. The unit needs to activate when the lighting circuit loses power, not a power circuit.) If emergency lighting is powered by an emergency generator (emergency and standby power system), then likewise, the system will recognize the loss of power to the building, the emergency generator will start, and subsequently power the emergency lighting circuits. In most cases, compliance with Item (1) isn't a problem.
Item (2) describes a condition where a circuit breaker or fuse, located anywhere in the building, opens, resulting in loss of the normal means of egress illumination. This could be a breaker in a distribution panel on, say, the 8th floor of the building. If such a breaker protecting a lighting circuit trips, again, battery-operated unit lights on that circuit will activate and provide the required illumination. But what about systems powered by a generator? We wouldn't expect the generator to come online when a breaker in a distribution panel trips. So how will emergency lighting be provided in this case? Hold that thought.
Item (3) describes a condition where someone accidentally flips a light switch and the required means of egress illumination goes dark. Battery-operated unit lights won't activate because the circuit still has power; power has just been interrupted from the switch to the luminaire (that's code-speak for light fixture). Likewise, we would hope the emergency generator won't start every time someone turns out the lights (and it doesn't). So how can we possibly meet the emergency lighting performance criteria for the scenario described in Item (3)?
It's important to note that the Code does NOT tell the designer how to arrange the lighting circuits; it only specifies the required performance criteria. I can describe one means to meet the performance requirements of 7.9.2.3, but keep in mind, it's not necessarily the only means: arrange the lighting circuits so that no area required to be provided with emergency lighting is normally illuminated by fewer than two separate lighting circuits, one of which is an emergency lighting circuit where an emergency generator is employed. Here's how it works:
Scenario (1): Building loses power; all lighting circuits are de-energized; battery-operated unit lights activate, or generator comes online, transfer switch energizes emergency lighting circuit; good to go.
Scenario (2): Distribution panel breaker trips; regardless of which lighting circuit loses power, the other circuit in the same area will still be energized. As long as an average of 1 ft-candle is initially provided along the designated egress path, the emergency lighting performance criteria have been met without necessarily activating any battery-operated unit light or the emergency generator; again, good to go.
Scenario (3): Someone accidentally opens a switch controlling the normal lighting; like Scenario (2) above, the other circuit will provide the needed average 1 ft-candle. Using this arrangement, the NFPA 101 emergency lighting performance criteria are met for all three conditions.
When I describe how 7.9.2.3 works in NFPA's three-day Life Safety Code Essentials seminar, I usually see some jaws hit the table (figuratively), which indicates, to me, that these provisions are, perhaps, not being widely implemented, or enforced. It's the Code's intent to provide emergency lighting for any condition that causes the normal illumination source to lose power, not just failure of the building's normal power supply.
I'm hopeful that this installment of #101Wednesdays has illuminated some of you.
Since NFPA will be closed December 24 through January 2, this will be the final installment of #101Wednesdays until 2017. I'd like to wish everyone a very happy holiday season, and I look forward to posting lots more topics next year. Until then, stay safe!
Got an idea for a topic for a future #101Wednesdays? Post it in the comments below – I'd love to hear your suggestions!
Did you know NFPA 101 is available to review online for free? Head over to www.nfpa.org/101 and click on “Free access to the 2015 edition of NFPA 101.”
