IEA_AARST_Radon_Reporter_JUNE_2024

20 | June 2024 RESEARCH Pressure Field Extension Testing Brittney Christie and Gunnar Barr, Obar Systems, Inc. Abstract The most important step in a Sub-Slab Depressurization System (SSDS) design process is Pressure Field Extension (PFE) testing. This paper explores the importance of performing PFE testing prior to the design and installation of a SSDS. Introduction Why Diagnostics? Sub-Slab Depressurization Systems (SSDS) are designed to continuously apply vacuum to the soil beneath the slab thus creating a negative pressure field beneath the building. Vacuum is applied through a network of pipes and an externally mounted fan; the soil gasses are exhausted above the roofline. The primary goal of PFE testing is to determine the radius of influence produced at a given applied vacuum and resulting airflow yield. It is critical to understand the soil permeability and have knowledge of the aforementioned goals prior to the design and installation in order to maximize the efficiency of the SSDS. Experimental Pressure Field Extension Testing Process The Pressure Field Extension (PFE) testing process consists of installing diagnostic suction points strategically located throughout the building at locations best suited for full-scale suction points to be installed as part of a mitigation system. The flow and vacuum characteristics of the soil beneath the slab are defined through various vacuum levels applied to the sub-slab material through the suction holes. Pressure differential measurements are recorded at a series of smaller diagnostic test holes drilled at various distances from the suction point(s). These measurements are taken at multiple levels of applied vacuum. The measurements taken along with the data collected throughout this process determine the Radius of Influence (ROI). Using the ROI and other data gathered during PFE testing, the number and location of suction points, pipe diameters, and fan type needed to mitigate the building can be determined. Pressure Field Extension Testing Equipment A fan capable of applying multiple levels of applied vacuum that covers a range of commercially available mitigation blowers is used by the technician performing the PFE testing. Vacuum and airflow are measured as close to the slab as possible. Carbon filtration is used on the exhaust if it is not practical to rout the fan discharge outside the building.