Retail stores present many challenges for the notification of shoppers and employees when a fire alarm system actuates. One obvious challenge is the high ambient noise levels that the audible notification appli-ances must overcome. Compliance with the Americans with Disabilities Act (ADA) and NFPA 72-2007 for the placement of strobes is another.
“Big box” stores such as Home Depot, Lowes, Target and Wal-Mart offer one of the more difficult retail scenarios. To solve this problem, the NFPA Fire Protection Research Foundation’s Detection and Alarm Research Council initiated a study in July 2005. It iden-tified the need for application guidance of direct visual signaling as a means for occupant notification in large spaces.
The foundation responded to a request from the National Fire Alarm Code (NFPA 72) Technical Committee on Notification Appli-ances for Fire Alarm Systems. The Technical Committee asked for additional data to provide the users of the code with annex material explaining how to address visible signaling in large spaces, such as a big box store.
So what do you do when you win the fire alarm installation contract for a big box store? First, prescriptive code requirements exist for wall and ceiling mounted notification appliances. The wall-mounted requirements are the same as you would follow in your “standard” projects:
“188.8.131.52 Wall-mounted appliances shall be mounted such that the entire lens is not less than 2,030 mm (80 in.) and not greater than 2,440 mm (96 in.) above the finished floor or at the mounting height specified using the performance-based alternative of 184.108.40.206.
“220.127.116.11 Where low ceiling heights do not permit mounting at a minimum of 2,030 mm (80 in.), visible appliances shall be mounted within 150 mm (6 in.) of the ceiling. The room size covered by a strobe of a given value shall be reduced by twice the difference between the minimum mounting height of 2,030 mm (80 in.) and the actual, lower mounting height.” [NFPA 72-2007]
However, big box stores do not have a lot of walls to allow wall-mounting of appliances. And, the mounting strobe lights at a height of 80 to 96 inches along aisles with rack storage subjects the lights to frequent mechanical damage by forklift trucks and stock handling op-erations. The code provides specific tables to assist the contractor in locating appliances. But, as research shows, each store is different. Racks, aisles and ceiling heights change. And, in some of these stores, the very bright ambient light that helps the shopper to view the product makes it difficult to see a flashing visible fire alarm notification appliance (strobe).
For ceilings that exceed 30 feet, the code allows installers to suspend ceiling mounted visible notification appliances at or below 30 feet. They may do this, provided the strobe location does not fall below the viewing plane.
If installers place the ceiling-mounted visible notification appliance at the center of the room, then the installer may use the prescriptive locations in the tables in Chapter 7. If the installer does not locate the ceiling-mounted visible notification appliance at the center of the room, the installer must determine the effective intensity by doubling the distance from the appliance to the farthest wall to obtain the maximum room size.
The annex of the code states the prescriptive requirements of the code assume the use of appliances having very specific characteristics of light color, intensity, distribution and so on. The annex further explains that the code has based the appliance and application require-ments on extensive research. However, that research only included typical residential and commercial applications, such as school class-rooms, offices, hallways and hotel rooms. While these specific appliances and applications will likely work in other spaces, their use might not provide the most effective solution and might not prove as reliable as other visible notification methods.
The researchers did not test the methodology in warehouses or other large, well-lit spaces. Nevertheless, because other codes require strobes in these spaces, authorities having jurisdiction (AHJs) enforce the installation and performance requirements of NFPA 72, despite the lack of any technical foundation for their location. In some cases, authorities impose their own requirements, such as not allowing ceil-ing-mounted appliances. The annex of NFPA 72-2007 states that more efficient methods of visible signaling may exist for large spaces, such as warehouses and distribution centers (“Direct Visual Signaling as a Means for Occupant Notification in Large Spaces,” Robert P. Schifiliti, P.E.).
For example, in large warehouse and distribution spaces, including big box stores, a fire alarm system designer may provide visible signaling using the appliances and applications of Chapter 7 of the code. However, such a design would require a relatively large number of appliances. A designer must carefully engineer alternative applications to ensure reliability and function. Such designs would require permission of the AHJ.
Tests of a system in large warehouse/superstore designed, using the prescriptive approach of the code, showed high ambient light lev-els resulted in both indirect and direct signaling effects. A seriously deficient signal-to-noise ratio produced by the operating visible noti-fication appliances existed in many locations.
However, designers could sometimes achieve indirect and some direct notification with visible notification appliances located over the aisles or unobstructed by stock. Direct notification occurs even when occupants do not look up toward the ceiling-mounted visible notification appliances due to the extended cone of vision shown in the Figure A.7.5.3 (b) from NFPA 72-2007.
The visible notification appliance intensity and spacing resulting from the prescriptive design generally proved sufficient for occupant notification by a combination of direct and indirect signaling. Testing showed visible notification appliances directly over aisles or visible notification appliances in adjacent aisles—not obstructed by stock—achieved the best performance.
The performance-based design method will almost always result in aisles not having a line of visible notification appliances in them because the spacing of visible notification appliances can exceed the spacing of aisles.
Also, the research recognized that stores might relocate aisles after installation of the system. Good design practice places visible noti-fication appliances over aisles, especially those that will likely remain unchanged, such as main aisles and over checkout areas.
Where reorganization of aisles results in visible notification appliances not in or over an aisle, or where such an arrangement provides the base design, occupants must have a clear view from that aisle to a nearby visible notification appliance. See Figure A.7.5.3 (b) from NFPA 72-2007.
Some spaces might have marginal visible notification appliance effect (direct or indirect). However, occupants in these big box stores and large storage occupancies move frequently and place themselves in a position where they receive notification via the visible notifica-tion appliances. In addition, complete synchronization of the visible notification appliances in the space produced a desirable effect. Indi-rect signaling can achieve visible notification. This means the viewer need not actually see the appliance, just the effect of the appliance.
By producing minimum illumination on surfaces near the appliance, such as the floor, walls and desks, indirect signaling can produce proper notification. However, the appliances must produce a sufficient change in illumination before occupants will notice the indirect signaling.
The tables and charts in the code specify a certain candela-effective light intensity for certain size spaces. These were based on extensive research and testing. Appliances do not typically produce the same light intensity when measured off-axis. To ensure the appliance pro-duces the desired illumination, it must have some distribution of light intensity to the areas surrounding the appliance. UL 1971, Standard for Safety Signaling Devices for the Hearing Impaired, specifies the distribution of light shown to provide effective notification by indi-rect visible signaling.
As a result of the research several significant points emerge:
- Strobe lights prove effective for both direct and direct viewing even if not located directly over an aisle, provided sufficient penetration to the aisle occurs.
- A design with strobe lights over every aisle proves more effective than one where strobes serve several aisles.
- Aisles focused the occupant’s vision and improved direct signaling effects.
This information should go a long way in helping the professional contractor with the challenges of visible notification appliance loca-tions when he or she provides a fire alarm system for any of the big box stores or large warehouse spaces.
MOORE, a licensed fire protection engineer, frequent speaker and an expert in the life safety field, is a co-editor of the current National Fire Alarm Code Handbook. Moore is a principal with Hughes Associates Inc. at the Warwick, R.I., office.