What will the office of the future look like and how will it affect fire alarm system design? I recently read a prediction by Steelcase, a manufacturer of office equipment, stating what the company foresees: more flexible offices with an increase in shared space to allow more collaboration. However, with many employees now comfortably working from home during the COVID-19 stay-at-home orders, the vision for the future office becomes even murkier and harder to predict.
If the flexible and open office prediction becomes a reality, the layout of the audible and visible notification appliances will present the first challenge to fire alarm system design. Installers would normally place wall-mounted appliances in the hallway or in the walls surrounding a large space. With an open floor plan, you need to ensure the system design remains flexible to meet the customer’s needs.
With an open floor plan, the best design for audible/visible notification appliances means installing the notification appliances on the ceiling. You must follow the ceiling-mount requirements of NFPA 72, National Fire Alarm and Signaling Code. Chapter 18 states: “All notification appliances installed in conformity with Chapter 18 shall be listed for the purpose for which they are used.”
This means the notification appliances you intend to mount on the ceiling bear the listing mark of a nationally recognized testing laboratory acceptable to the authority having jurisdiction. Do not install notification appliances listed for wall mounting on the ceiling.
You will want to provide the most cost-effective design, so locate the audible notification appliances first. The code requirements remain unchanged, for the audible notification appliances “shall produce a sound level at least 15 dB above the reduced average ambient sound level or 5 dB above the maximum sound level having a duration of at least 60 seconds after reduction of the ambient noise level, whichever is greater, measured 5 ft (1.5 m) above the floor in the area required to be served by the system using the A-weighted scale (dBA).”
Can you overdesign for audibility? Will this present a danger to occupants? The code does not presume to know how long a person might remain exposed to an audible notification system.
However, the whole premise of the audibility requirements intend to cause the occupants to evacuate the space. The upper limit of 110 dBA coordinates with the noise limit requirements set by the Occupational Safety and Health Administration. The annex in Chapter 18 describes, “In addition to the danger of exposure to a high sound level, long-term exposure to lower levels may also be a problem when, for example, occupants must traverse long egress paths to exit or technicians test large systems over extended time periods.”
Thus, you must not overdesign the audible notification appliances.
Once you have added these appliances to the design drawings, you can determine the quantity and placement of the visible notification appliances. Again, you should use ceiling-mounted visible appliances.
Some individuals believe the design can simply incorporate combination audible/visible appliances throughout a building. However, to provide a cost-efficient and competitive design for your client—and perhaps, more important, to win the project—then using combination audible/visible units wherever your design requires an audible notification appliance will not meet the design goals.
The room’s physical dimensions determine the number and candela output of the visible notification appliances needed. The code allows one or more visible appliances to provide notification with strict adherence to spacing requirements. Whenever more than one visible appliance operates within the field of view of the occupants, the fire alarm system must synchronize the appliances.
You must use Table 22.214.171.124.1 (b), “Room Spacing for Ceiling-Mounted Visible Appliances,” to determine the appropriate strobe size that matches the room size in the design. For normal ceiling heights up to 20 feet, a single, ceiling-mounted strobe of 75 candela will adequately provide notification for a room size not exceeding 44 feet by 44 feet (1,936 sq.ft.). With a 30-foot ceiling height, the room size covered by that same notification appliance reduces to 30 feet by 30 feet (900 sq.ft.).
Many new collaborative office spaces will still have conference rooms, requiring the appropriate number of visible appliances installed. And, some of these office layouts will include what architects label “private enclaves.” Typically, authorities having jurisdiction do not consider these private enclaves as conference rooms, and such enclaves will not need their own visible appliances.
As you can see, a variety of different performance requirements govern the design of audible and visible notification appliances. Understanding these differences will help you meet customers’ goals, while remaining competitive and making a profit.