Proposals & Comments


Direct Visual Signaling as a Means for Occupant Notification in Large Spaces

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9.             Proposals and Comments to NFPA 72

During testing in a large warehouse store in 2004, it was noticed that where indirect signaling was marginal or non-existent, there often was sufficient direct viewing of strobes to provide occupant notification.  As a result of that test, a proposal was submitted to the NFPA 72 Technical Committee on Notification Appliances for Fire Alarm Systems to add text to the Annex explaining possible direct signaling effects in large spaces.  The following text and figure was accepted by the committee for inclusion in the existing Annex section A.7.5.3:

 

Tests of a system in a large warehouse/super store designed using the prescriptive approach of 7.5.4.3 showed that high ambient light levels resulted in little or no indirect signaling effect. The signal-to-noise ratio produced by the operating strobes was too low. However, with strobes located over the aisles or unobstructed by stock, direct signaling was achieved. This occurs even when occupants do not look up towards the ceiling mounted strobes due to the extended cone of vision shown in Figure A.7.5.3. The strobe intensity and spacing resulting from the prescriptive design is sufficient for occupant notification by direct signaling.

 

 

 

The committee accepted the proposal but requested that additional data be gathered and added in the form of a Comment on the Report on Proposals.  That request spawned this research project and report.  As a direct result of this project, in October of 2005 the Technical Committee on Notification Appliances submitted a Committee Comment revising the above text and adding a second figure as follows:

 

Tests of systems in large warehouse/super stores designed using the prescriptive approach of 7.5.4.3 showed that high ambient light levels resulted in both indirect and direct signaling effects. The signal-to-noise ratio produced by the operating visible notification appliances was low in many locations. However, with visible notification appliances located over the aisles or unobstructed by stock, indirect and some direct notification was sometimes achieved. Direct notification occurs even when occupants do not look up towards the ceiling-mounted visible notification appliances due to the extended cone of vision shown in Figure A.7.5.3(a). The visible notification appliance intensity and spacing resulting from the prescriptive design was generally sufficient for occupant notification by a combination of direct and indirect signaling. Testing showed that the best performance was achieved where visible notification appliances were directly over aisles or where visible notification appliances in adjacent aisles were not obstructed by stock. The performance-based design method will almost always result in aisles not having a line of visible notification appliances in them since the spacing of visible notification appliances can be greater than the spacing of aisles. Also, it is recognized that aisles may be relocated after installation of the system. Good design practice is to place visible notification appliances over aisles, especially those that are likely to 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 that is the base design, it is important to have a clear view from that aisle to a nearby visible notification appliance. See Figure A.7.5.3(b). Some spaces may have marginal visible notification appliance effect (direct or indirect). However occupants in these large stores and storage occupancies move frequently and place themselves in a position where they receive notification via the visible notification appliances. In addition, complete synchronization of the visible notification appliances in the space produced a desirable effect.

 

Figure 17 - New Figure A.7.5.3(b)

 

 


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Last updated: 01/13/17.