Question: Visible notification (strobes) are being provided in a warehouse application with high-rack storage. The racks isles are less than 20’ feet wide, 100 feet long, and the ceilings are 40’ high. Can the corridor spacing rules of NFPA 72, Chapter 18 be used for strobe location and spacing?
Answer: Corridor spacing requirements of NFPA 72, Chapter 18 would not apply in this application because isles between racks are not considered corridors. Why not?
NFPA 72, Chapter 3, contains definitions that are used within NFPA 72. Chapter 3 contains terms that have specific meanings within NFPA 72. Chapter 3 also states that if a term does not have a definition within NFPA 72 that Merriam-Webster’s Collegiate Dictionary ordinary accepted meaning shall be used.
Webster’s definition of a corridor is “a passageway (as in a hotel or office building) into which compartments or rooms open.” Based on this definition, the isles between high-rack storage would not qualify as a “corridor.”
Visible notification in the isles between the racks would be determined by the spacing tables in NFPA 72, specifically Table 18.5.5.4.1(a) (wall mount) and Table 18.5.5.4.1(b) (ceiling mount). While either wall mount or ceiling mount visible notification would be acceptable in this application, both present potential advantages and disadvantages.
Consider wall mount notification appliances. Wall mount visible notification appliances are permitted to be mounted between 80 and 96 inches AFF. Since this application involves storage racks, there is an increased chance of damage to the appliances as material is moved in and out of the racks.
Consider ceiling mount appliances. Ceiling mount visible appliances may be mounted on ceilings up to 30 feet high. Ceilings above 30 feet require the appliances to be suspended at or below 30 feet. The ceiling in this application is 40 feet high, so ceiling strobes would need to be suspended to a minimum 30 feet above the floor.
The isles between the racks are rectangular (20’ x 100’), and the spacing tables in NFPA 72 are square. NFPA 72 permits the designer two options: use a square that encompasses the entire space or break the room into smaller squares for squares for determining notification coverage.
Using the first solution, the 20’ x 100’ isle would utilize spacing based on a 100’ x 100’ room. Table 18.5.5.4.1(a) (wall mount) requires a single 375cd strobe (not a commonly available intensity) or four 95cd strobes. Table 18.5.5.4.1(b) (ceiling mount) only covers rooms up to 70’ x 70’.
Using the second solution, 20’ x 100’ could be broken into multiple squares. If we broke the isle into five 20’ x 20’ squares, the wall mount table would allow one 15cd strobe in each location, requiring 5 strobes to cover the isle. Since NFPA 72 does not limit the size of the square used to encompass an area, the 50’ x 50’ row which allows a single 94cd strobe could be used to reduce the number of appliances required for each isle to 2.
The multiple square strategy could also be applied to ceiling mount strobes. If five 20’ x 20’ squares are used five 55cd strobes suspended to 30 feet above the floor would be required to cover each isle. If two 50’ x 50’ squares are used, the isle can be covered with two 95cd strobes suspended to 30 feet above the floor.