Examples of measurable parameters for antimicrobial devices include temperature, membrane pore size, UV intensity, contact times, and turbidity. In many cases, there may be more than one critical limit to prove the process is in control and effective. For example, the use of chlorine to treat water may warrant not only measuring chlorine concentration on a routine basis, but also pH, as chlorine is heavily reliant on pH for its effectiveness. In addition, the amount of organic matter in water impacts chlorine efficacy; therefore, turbidity measurements could be an important parameter to monitor. In regards to UV light treatment, critical limits may include percent transmittance (UV absorbance), turbidity, and flow rate.
Difference Between Critical and Operating Limits
Meeting critical limits helps growers assure their water treatment method is effective. If a critical limit is not met, corrective actions must be performed as it is assumed there is a significant increased risk in contaminated produce. In order to assure compliance with critical limits, operating limits can offer an extra layer of protection. Operating limits are criteria that are more stringent than a critical limit. Operating limits are beneficial in allowing the detection of a potential problem before a deviation occurs. The process may be adjusted when the operating limit is not met, which avoids violating the critical limit. These actions are termed “process adjustments.” A grower may use these adjustments to avoid loss of control resulting in a deviation and the need to take corrective actions. Additionally, spotting a trend toward loss of control early and acting on it can save time and money by avoiding corrective actions, such as product disposal or recalls. An example of the use of operating limits is given in Figure 1 and illustrates the use of operating limits and process adjustments, as well as critical limits and corrective actions. In this example of chlorination, a critical limit is established at two ppm. The graph indicates that the concentration of free chlorine fell below the established critical at 14:00. Setting an operating limit above the critical limit, in this example at five ppm would have alerted the grower to make a process adjustment to bring the free chlorine concentration back above the operating limit. If an adjustment is made before the concentration drops below the critical limit, no corrective action record is required. However, in this example, an adjustment was not made until after the concentration dropped below the critical limit of two ppm; therefore, appropriate corrective actions must be taken and documented.
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