In my January article, I reviewed some strobe light requirements and issues that designers and installers should be aware of for a correct visual notification installation. Here are a few more things to consider.
Let’s start with the design considerations. First, determine whether you will be using public or private mode signaling. Public mode is for notifying occupants in an area or the entire building and is most common. Private mode is allowed for certain occupancy classifications and is used for notifying staff to implement emergency procedures. It is commonly used in institutional occupancies like hospitals and nursing homes. If using private mode, there are no location, mounting height or candela ratings required. Strobes are installed where they will be effective for staff notification. This will take some discussion with other stakeholders to determine the best locations.
Designers now have options with the addition of performance-based alternatives. We all know that sometimes it is challenging to install strobe lights in the proper locations required by NFPA 72. Information on performance-based alternatives can be found in 220.127.116.11 (2019 edition). It states “Any design that provides a minimum of 0.0375 lumens/feet2 (0.4036 lumens/m2) of illumination at any point within the covered area at all angles specified by the polar dispersion planes for wall- or ceiling-mounted public mode visual notification appliances.”
To figure out performance-based strobe coverage, the inverse square law is used to calculate the illumination at each of the angles in the horizontal and vertical planes per ANSI/UL 1971, Standard for Signaling Devices for the Hearing Impaired, and the effect of polar distribution is included using the minimum percentages in ANSI/UL 1971 or actual test results recorded by the listing organization. The easiest way to determine this is to use a strobe light manufacturer’s coverage calculator. Then, to determine the lumens per square foot in a given area, simply divide the candela rating of the strobe by the room’s square footage. For example, the square footage of a 20-foot-by-20-foot room is 400 feet. If you are planning to put a 15-candela strobe in the room, divide 15 by 400, which gets 0.0375 lumens/feet2. Remember that shop drawings are now required to show locations and candela ratings for each installed strobe light. This is the designer’s responsibility, not the installer.
When determining visible notification coverage, you need to know how the space will be used to choose locations and proper candela ratings. NPFA 72 allows for breaking up larger spaces into virtual rooms. Knowing how the space will be used and what will be in it makes it easier to decide whether to treat the space as one room or multiple smaller virtual spaces. Remember that you don’t necessarily need to directly see the strobe light, as long as it can be recognized as operating. Additionally, strobe lights are not required in exit stairwells and elevators.
Finally, where do you install strobe lights in sleeping rooms? They must be within 16 feet of the pillow. The candela rating is determined by the distance below the ceiling.
I have had many conversations about whether strobes are required in hotel room bathrooms. Sometimes it may provide better protection installed in the bathroom and sleeping area. The ADA doesn’t require them, but some AHJs do. Be sure to verify this. Remember that code requirements are the minimum.
The requirements for testing strobe lights have changed in recent editions of NFPA 72. On the initial acceptance test, the purpose of testing is to verify the installation meets code and design criteria. This includes verifying the location, mounting height, candela rating and that the unit operates properly. Verification of the correct candela for the strobe lights is not required on periodic tests because it is considered a design function. You simply verify the strobe flashes.
During periodic inspection, it is your responsibility to verify that no changes were made that would affect the system operation. For example, some rooms have strobe lights, but not others, that should raise a flag that the layout might have changed. Was a room or wall added? It is not the inspectors’ responsibility to determine if the strobes are in the correct places, but it is a good practice to know enough to identify problem areas and report them to the owner.
Header Image: shutterstock / pixmeeup