SGM-SF_2017with 12/20 Revisions

5 SGM-SF SGM-SF Discussion CG SECTION 6: ASD SYSTEMS Safety Advisory— Post-tension slab construction is common for certain larger slab-on-grade buildings. Do NOT cut into a post-tensioned slab if there is a chance you will rupture a cable. Cables can burst out of the concrete taking life and limb. Before any slab work begins, have a competent or qualified person identify the cable locations. CG 6.1 ASD Suction Points 6.1.1 Suction pits 6.1.2 Sumps 6.1.3 Sub-membrane suction point s 6.1.4 Non-habitable air spaces The term “Non-habitable air spaces” encompasses depressurization of a wide range of airspace configurations. These depressurization systems require special care to design and implement air barrier isolation of the airspace. (See Section 8.9 Sealed isolation assembly.) Advisory —Adverse effects for inadequate isolation can include failed systems, excessive energy penalties and flue spillage from atmospherically vented combustion appliances. Advisory— A Sealed isolation assembly can sometimes require creating access ports and extensive efforts for sealing the structural assembly. 6.1.5 Block walls Advisory— When Block Wall Depressurization is applied directly to a wall, suction point considerations include the degree to which a complete air barrier can be established between soil gas within the blocks and indoor air. CG 6.2 ASD Piping 6.2.1 Air and water tight 6.2.2 Slope required Advisory— The constructed piping must be glued or sealed in a manner that does not leak water and be configured to drain water so that water droplets that naturally and persistently form within pipes do not collect to obstruct airflow. The goal: An ASD system that continuously controls the destination of soil gas with an appropriate degree of care to not compromise other building systems and health of occupants. General: Inducing a negative pressure difference of about 1 pascal (4/1000 inch water column) within soil gas relative to indoor air is commonly witnessed to successfully reduce radon entry for most, if not all of the year. This is partly because even zero pressure difference reduces soil gas entry. However, the season when these measurements are conducted is a critical consideration. Cold weather example: During coldest weather, even barely detectable PFE sometimes witnessed in challenging structures does not usually need additional protective buffer if success is confirmed by indoor measurements. This is because PFE will often be stronger in mild weather. Cold weather example of concern: If during cold weather a strong vacuum such as 5 pascal (20/1000 inch water column) is applied, PFE vacuums are expected to increase in mild weather. With studies showing that about 40-50% of ASD exhaust air is often coming fromwithin the building, high vacuumASD systems with robust airflows increase the likelihood of unnecessary energy penalties and compromised building systems such as inducing flue gas spillage at combustion appliances. Mild weather concerns: When PFE measurements are made in mild weather, the extent that negative pressure will increase within a building during cold weather is an unknown commodity. If negative pressure internal to the building during cold weather increases to overwhelm PFE witnessed, the system or portion of the system will temporarily cease to stop soil gas entry. As a protective buffer for this situation, seasoned professionals often seek to achieve about 2.5 pascal (10/1000 inch water column) pressure difference in mild weather, whenever possible. Verification: Actual confirmation of adequacy would require testing under varied seasonal conditions.