Q. What is the most effective way to satisfy the two lamp requirement for emergency lighting for outdoor areas called out in the NEC?

A. The clause you refer to comes from article 700.16 in the NEC. The middle paragraph reads:

“Emergency lighting systems shall be designed and installed so that the failure of any individual element, such as the burning out of a lamp, cannot leave in total darkness any space that requires emergency illumination”.

While a lot of attention has been given to the middle of the sentence, referring to the failure of a lamp, there is much more to this requirement. First, the intent of the NFPA was to address interior spaces with two or more exits that require emergency lighting and where an emergency generator is provided for egress illumination. The goal was to require more than one fixture in that interior space to receive emergency generator power, thus, eliminating the potential to have that space left in total darkness should the luminaire (or lamp) fail. Secondly, the requirement specifically calls out the words “systems” and “total darkness”. These words carry the same, if not more, importance that the burning out of a lamp. The myth that this requires two lamps in the emergency mode is a contradiction to the NEC itself. If we look at section 700.12 (F) Unit Equipment, subsection 3, it reads:

“Provisions for one or more lamps mounted on the equipment, or shall be permitted to have terminals for remote lamps, or both”.

If we are to apply this clause to exterior spaces, it would be most practical to treat your exterior egress lighting just as you would any other interior space. By designing your exterior egress lighting with simple redundancy you satisfy the true intent of the article and should not have to worry about your designed and installed system leaving a space in total darkness.

Q. How can I determine exit sign products that meet the 100 ft spacing requirement in code?

A. Signs that have been determined by UL standard 924 not to meet the 100’ viewing distance are to be labeled with their maximum viewing distance. There are two prescribed visibility testing programs for exit signs in accordance with UL 924; the analytical test method and the observation visibility test. Both tests are unique and offer different sets of criteria to determine a pass/fail but, unfortunately, there are currently no discrete markings required to determine which test method was used during qualification.

The analytical test method is a highly repeatable test. In abbreviated form - A digital camera, connected to a computer, is used to test 20 specific points along the illuminated letters E X I T. These measurements are used to determine maximum and minimum values to calculate averages, max to min ratios and the like. The data is referenced to a minimum average illumination level, in this case no less than 8.57 cd/m² (candelas per meter squared). The non-illuminated background is also measured to calculate contrast characteristics.

The observation visibility test is a bit more subjective and extremely difficult to repeat, especially at the as-installed facility by an inspector. In abbreviated form - Two human subjects from four age groups must be represented, these age groupings are: 18 – 30, 31 – 40, 41 – 50, and 51 – 70. The test subjects are to have visual acuity of 20/40 or corrected to not less than 20/40. The signs are then manipulated to change the appearance of the legend; the E would be taped off at the lower right hand corner to make it look like an F and the X would be taped off to make it look like a Y. The test area is then completely darkened and the test subjects are given five minutes for their eyes to adjust prior to asking them to read the text on the sign. A percentage of correct answers are required for a pass.

Some signs that have been approved using the observation visibility test method have been subjected to the analytical test. The compared data indicates that there are products employed that measure almost 1000 times less bright than those tested purely under the analytical method. Today, the only way to properly determine the test method used is to ask the manufacturer.

Q. Why are there different types of diagnostic circuits available and do some meet the periodic test requirements for life safety products better than others?

A. The periodic testing requirements found in NFPA 101, Life Safety Code and the International Fire Code (IFC) call for no less than a 30-second test every 30 days and a full 90-minute test annually. Both publications also provide an exemption clause to the 30 day test cycle where the allowance for self-testing/diagnostic equipment shall automatically transfer into the emergency mode for no less than the specified amount of time and to perform a diagnostic routine. If the installed equipment meets the test requirements then the facility personnel are only required to perform a visual walk-thru of the facility looking for diagnostic errors with the equipment and to log the walk thru event. The exemption, however, does not apply to the full 90-minute test requirement. Each code publication specifically states that a full 90-minute test shall be performed annually. It is best to educate yourself in what the different manufacturers’ test programs have to offer and how they meet your facility needs as well as the code requirements. It is also beneficial to identify product where a 90-minute test may be manually activated without having to open distribution breakers.