P7.1.1.12 For information on causes of pH too high and preventive measures, see Guide P8.1. See the Appendix for a graph showing how the effectiveness of chlorine as a pH too high disinfectant decreases as the pH increases. (resulting in a lower percentage of the FAC existing in its more powerful disinfecting form). Preventive measures Checking preventive measures Corrective Causes action What to check Signs that action is needed Event: TOO MUCH FREE AVAILABLE CHLORINE Possible hazards: Chlorine; possibly high levels of trihalomethanes, haloacetic acids, chloral hydrate and chlorate (hypochlorite chlorination); possible heavy metals (from corroded fittings). Level of risk: Low–moderate3 P7.1.2.1 Routine maintenance FAC. FAC Identify of dose controller and concentration is cause of Dosing Examination of dosing pumps. more than 50% fault and malfunction maintenance of its MAV.4 rectify. (see Guide Replacement of log. P10). controller if suspect. Maintenance log Replace shows frequent controller Install an system maintenance with new to indicate when FAC needed. unit. concentration is outside designated Maintenance log limits. not signed off. P7.1.2.2 Regular manual FAC. FAC Recalibrate checks on calibration concentration is controller. Dose Calibration of FAC controller. more than 50% controller schedule. Decrease of its MAV. incorrectly chlorine calibrated. Calibration dose rate schedule not signed off. P7.1.2.3 Periodic manual FAC. FAC Adjust checks on FAC concentration is controller Dose Dose flow concentration, more than 50% set-point. controller rates and dose especially during of its MAV. calculations. Recalculate periods of water incorrect, or Frequent dose rates quality variability. incorrect dose calculation and change calculation. Independent on errors found by settings. calculations checks. Train staff in (especially after a Calculation making dose system change when checks not calculations. expected dose rates signed off. are uncertain). Flow rates Install visual flow above expected indicators to allow values. flow to be checked by eye.
P7.1.1.12 pH too high (resulting in a lower percentage of the FAC existing in its more powerful disinfecting form). For information on causes of pH too high and preventive measures, see Guide P8.1. See the Appendix for a graph showing how the effectiveness of chlorine as a disinfectant decreases as the pH increases. Causes Preventive measures Checking preventive measures Corrective action What to check Signs that action is needed Event: TOO MUCH FREE AVAILABLE CHLORINE Possible hazards: Chlorine; possibly high levels of trihalomethanes, haloacetic acids, chloral hydrate and chlorate (hypochlorite chlorination); possible heavy metals (from corroded fittings). Level of risk: Low–moderate3 P7.1.2.1 Dosing malfunction (see Guide P10). Routine maintenance of dose controller and dosing pumps. Replacement of controller if suspect. Install an system to indicate when FAC concentration is outside designated limits. FAC. Examination of maintenance log. FAC concentration is more than 50% of its MAV.4 Maintenance log shows frequent maintenance needed. Maintenance log not signed off. Identify cause of fault and rectify. Replace controller with new unit. P7.1.2.2 Dose controller incorrectly calibrated. Regular manual checks on calibration of FAC controller. FAC. Calibration schedule. FAC concentration is more than 50% of its MAV. Calibration schedule not signed off. Recalibrate controller. Decrease chlorine dose rate P7.1.2.3 Dose controller incorrect, or incorrect dose calculation. Periodic manual checks on FAC concentration, especially during periods of water quality variability. Independent on calculations (especially after a system change when expected dose rates are uncertain). Install visual flow indicators to allow flow to be checked by eye. FAC. Dose flow rates and dose calculations. FAC concentration is more than 50% of its MAV. Frequent calculation errors found by checks. Calculation checks not signed off. Flow rates above expected values. Adjust controller set-point. Recalculate dose rates and change settings. Train staff in making dose calculations.
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