From the Chief’s Corner: Public Safety Grid Testing: What’s in a Grid...

Posted on July 24, 2019

In recent conversations with Safer Buildings Coalition members, the topic of grid testing, and more specifically the interpretation of what size the grid should be, has come up. So, this month I will try to shed some light on this important issue as it relates to public safety in-building communications systems. 

The answers can be found in the 2019 Edition of NFPA 1221;  specifically, in sections 11.3.9 and 11.3.9.1, as well as Annex A. 

To get started you must first go to section 9.6.4 Testing Requirements. This section will send you to 11.3.9 and 11.3.9.1, which read as follows:

11.3.9* Test and Inspection of In-Building Two-Way Radio Enhancement Systems. Where two-way radio communications enhancement systems are installed, a system test shall be conducted, documented, and signed by a person approved by the AHJ upon system acceptance and once every 12 months.
11.3.9.1 Initial Acceptance Test Requirements.
11.3.9.1.1 All new systems shall be initially acceptance tested to verify that the system as installed meets the performance requirements of Section 9.6.
11.3.9.1.2 Qualifications of testing personnel shall be submitted to the AHJ for approval and acceptance.
11.3.9.1.3 All systems initial acceptance testing documentation shall include a listing of the following:
(1) All system equipment utilized
(2) Manufacturer’s data sheets
(3) Installation, testing, and maintenance documentation
(4) As-built drawings showing all equipment locations
(5) Written documentation acceptable to the AHJ of the initial system testing, including the DAQ measured at all locations in the building or areas covered by the installed system
(6) Secondary power calculations
(7) List of assigned frequencies

To find specific information about grid size requirements, we must look at Annex A, as denoted by the asterisk next to the “11.3.9” listing. 

Annex A, Section A.11.3.9 Test Procedures states that “The test plan should ensure testing throughout the building. Test procedures should be as directed by the AHJ.”  Next are the grid size dimensions that are most often utilized for system testing.  The recommendation is to divide a floor area into 20 grids. Minimum and maximum sizes are identified at 20 feet and 80 feet, respectively. Additionally, a maximum floor size of 128,000 square feet is recommended, which would allow grids of 80’ x 80’ to be utilized.  Where a floor size exceeds 128,000 square feet the floor area should be subdivided into sectors each having an area less than or equal to 128,000 square feet.

In conclusion, how testing is to be done is as directed by the AHJ.  As each buildings size and shape will vary, the information in Annex A is intended to serve as a guideline for determining actual grid sizes. Another best practice to utilize during testing is to treat each critical area which requires 99% coverage as its own grid.  Remember, the ultimate goal of grids and testing is to simply have a process for ensuring that all areas of the building have been tested so that we know that when first responders need communications, they will have it.