STROBE COVERAGE, MORE OR LESS

Q Where is the rule found that allows me to install strobe lights in a hallway following the room spacing rules instead of the corridor rules? A The “Spacing in Corridors” rule found in both the 1999 and 2002 editions of NFPA 72 states that corridors up to 20 ft. in width, must be equipped with strobe lights placed within 15 ft. of each end of a corridor/hallway, spaced not more than 100 ft. apart, and be at least 15 candela. Also, a new corridor begins with any change in elevation or interruption of field of view (fire doors, etc.). It’s a fairly simple rule without many choices involved. However, a new option in the 2002 edition of NFPA 72, allows for the “Spacing in Rooms” rules in 7.5.4.2, to be applied to corridors. The strobe lights shown in the illustrations are all 15 candela, unless marked otherwise. Strobes are manufactured with different visible ratings, and vary between each manufacturer and strobe model. The candela ratings shown below are the minimum ratings allowed. Illustration B. Corridors are required to be treated as rooms when they are over 20 ft. wide. Applying the 1999 edition to example B, you would have to follow both the corridor rules and the room spacing rules together because of the width of the center corridor. In this illustration, even though the areas to be covered are larger, you could install as few as three appliances: two 15 candela strobe lights for the two corridors and one 135 candela strobe to cover the 22 ft. x 60 ft. “room.” You could also cover this space by installing two 34 candela strobes, one at each ‘x’, instead of the one 135 cd. strobe allowed by the “Spacing for Rooms” rule 4-4.4.1.3. Illustration C. Under rule 7.5.4.2.4 of the 2002 edition of NFPA 72, when a corridor is 20 ft. or less in width, you have the option of treating it as either a corridor or a room. The room spacing rules of 7.5.4.1.5 are met by installing two 94 candela strobe lights to cover the two 50 ft. horizontal corridors, while the center corridor meets the rules of 7.5.4.2 for corridor spacing. Illustration D. Illustration D dramatically shows the effect of the rule option allowed in the 2002 edition of NFPA 72, when compared with the less flexible rules of the 1999 edition. Sometimes less is more. There are times when you may install less strobe lights even though the current draw will be more because you are installing fewer, yet higher candela strobes. Usually, in cases of historic preservation or in an aesthetic sensitive application, less will be better. Greg Kessinger, SET, CFPS, president of an alarm installing company since 1981, teaches NICET training classes to fire alarm system designers and installers and continuing education seminars for Ohio’s fire alarm inspectors. You can reach him at 888-910-2272; e-mail: [email protected]; or visit his website at www.FireAlarm.org.