Underground Bacteria Generates H 2 S and Trips Control Panels

The building, having approximate dimensions of 42-m length, 9.7-m width, and 5.2-m height, is constructed of reinforced concrete walls and roof, and is designed to be blast resistant. There are four rooms in the building: the control room, which houses the instrumentation panels; the uninterrupted-power-supply (UPS) room, which houses the UPS equipment; the battery room; and the HVAC room. The panels in the equipment room are mounted on raised access flooring (false floor), having space for cables running underneath. The plan view of the building is shown in Fig. 1. The panels in this building tripped frequently, leading to unplanned plant outages, and thereby posing a risk to overall plant operations and integrity. It was observed that tripping of panels was mainly caused by failure of the electronic cards in the panels. Multiple cards had to be replaced, depending on the failure, and the rate of replacement was once in an approximately 1-month interval. Visual inspection of the cards did not indicate any defect. Site survey observations indicated a mild odor of H2S prevalent in the vicinity of the building and in areas under the false floor, discoloration of soil surrounding the building, high groundwater levels, and damages to building cable-entry sealants. To investigate the root cause and provide remedial measures, a technical study involving several testing techniques was carried out and the root cause was identified. Remedial measures were proposed to overcome the issue and were implemented at site. This paper presents the tests carried out during the study, the test results, and the recommended remedial measures and their implementation and effectiveness, which enabled mitigation of the failure of the control panels.