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•~ <br />`+ 7.2 INSTRIIMENTATION MALFIINCTION <br />Ii Correct functioning of the following instruments is critical <br />to the safe operation of the pH Adjustment System: <br />AE/AT 435 pH probe in pH Adjustment Tank discharge <br />AE/AT 405 pH probe in Fume Scrubber <br />AE/AT 900/10 HCN detector in scrubber stack <br />Failure of either of the pH meters will result in loss of <br />control of the process. Allowing the probes to dry out will <br />cause failure. Although the probes are normally immersed <br />in solution or slurry, they will be exposed whin the plant <br />is shut down. If a protracted shutdown is expected, the pH <br />probes should be removed and immersed in water. <br />Failure of the stack HCN detector will prevent the operator <br />from diagnosing faults in the operation of the scrubbing <br />system. <br />~ ~.3 <br />1 <br />OPERATOR ERROR <br />Operator errors leading to potentially hazardous situations <br />include the following: <br />^ Bypassing interlocks in the control system so that the <br />fail-safe design of the system is negated. <br />^ Opening of access hatches or inspection ports during <br />operation, allowing possible escape of HCN. <br />Other operator errors, which may cause shutdown of the <br />system, but which do not create a hazardous situation, <br />include: <br />^ Closing manual valves in the sodium hydroxide delivery <br />line. This will eventually result in a decrease in the <br />scrubber solution pH to the low-low level, shutting <br />down the Sulfuric Acid Metering Pump. <br />^ Closing manual valves in the process water line to the <br />scrubber solution reservoir. The solution level will <br />eventually fall to the low-low point, shutting down the <br />Sulfuric Acid Metering Pump. <br />^ Closing manual valves in the sulfuric acid delivery .~ <br />line to the pH Adjustment Tank. The pH will increase, <br />and slurry will be discharged to tY~e tailings <br />impoundment with higher than normal levels of cyanide. <br />pj/1504rp 012591 7-3 <br />