28.3 The sample is to be dropped a minimum of one time. However, if only one drop test is performed, it shall not be a flat drop. If one drop test is a flat drop, then at least one other test shall be performed that is not a flat drop.28.4 The concrete surface is to be at least 76-mm (3-in) thick and the concrete or metal drop surface shall be large enough in area to cover the DUT.28.5 After the drop,if the DUT is operational it shall be subjected to a discharge and charging cycle in accordance with the manufacturer’s specifications. An observation period per 6.5 is then conducted.28.6 At the conclusion of the observation period, an ″as received″ dielectric voltage withstand test in accordance with Section 18. The DUT shall be examined for signs of rupture and evidence of leakage.28.7 A spark ignition source or gas monitoring as outlined in Section 7 shall be used to detect the presence of flammable concentrations of gases within the sample immediately after the drop and repeated in the instance of increasing temperatures.