NFPA 72 (National Fire Alarm and Signaling Code) defines spacing requirements for visible notification appliances (strobes) in Chapter 18, Notification Appliances. Tables 220.127.116.11.1 (a) states wall mount visible notification requirements based on size of the room and number of strobes (1 or 4). Table 18.104.22.168.1(b) states ceiling mount visible notification requirements based on size of room and mounting height of the strobe.
The tables provide an easy way to determine visible notification requirements for rooms by simply reading the appropriate table. The tables are based on square rooms, but many rooms are not actually square. NFPA 72 allows a square that encompasses the entire room to be used as the basis for visible notification requirement or allows the room to be subdivided into multiple squares for notification purposes.
Corridors, which tend to be long, rectangular spaces are also permitted to use room spacing room. However, consider a corridor that is 10 feet wide and 100 feet long. Since the example corridor is rectangular, we can use a square that encompasses the entire room when using the tables (a 100’ x 100’ room). If wall mount strobes are used, Table 22.214.171.124.1(a) calls for 1 – 375cd strobe, or 4 – 95cd strobes. The ceiling mount table, Table 126.96.36.199.1(b) only covers room up to 70’ x 70’ (185cd strobe required). The corridor “room: could be subdivided into two 50’ x 50’ room for spacing, which would require 2 95cd strobes (either wall or ceiling mounted) located 25’ from each end of the corridor.
188.8.131.52 presents spacing rules for corridors that allow an alternative method of locating and space strobes other than the room spacing tables. 184.108.40.206.1 allows corridors 20 feet or less wide to use room spacing or corridor spacing rules. Because occupants of corridors are usually moving and alert, NFPA 72 allows the less stringent requirements of 220.127.116.11 to be used.
Applying the corridor spacing rules of 18.104.22.168, strobes in corridors shall not be less than 15cd. Strobes shall be located not more than 15 feet from the end of the corridor with a separation of not more than 100 feet between appliances, and the strobes may be mounted on either side of the corridor. The intent of the code is to have strobes near every exit of the corridor.
However, any interruption of the viewing path to the strobe — such as a door, elevation change or other obstruction — requires that the area be treated as a separate corridor. The diagrams below illustrate corridor spacing and adjustments based on obstructed viewing paths.