This SOP establishes procedures for documenting and investigating calibration failures as required by 21 CFR 111.

Because calibration failures can be quite expensive and time consuming to investigate, and because calibration failures may severely compromise product quality and necessitate extreme measures such as destruction or significant reprocessing of product or even a product recall, the author strongly encourages companies to verify the proper function of critical processing equipment at frequent intervals (e.g. daily, at the beginning of each shift, or after each break). This would include scales used in dispensing of ingredients and product filling; temperature gages for microbial reduction steps; metal detectors; and any other equipment which is key to product quality or safety, especially if the failure to function properly would not be readily noticed and would not be controlled through subsequent processing or testing steps. 

Note that “verification of proper function” does not necessarily mean a formal calibration is required; the verification may be as simple as placing an object of known, constant weight on a scale to confirm that the reading is consistent with historical ones.

In order for calibration failures to be properly identified, calibration personnel should collect and record as-found as well as as-left data. In other words, the calibration process should begin with an evaluation of the equipment’s function (the as-found condition), and end with post-calibration confirmation of the equipment’s function (the as-left condition). Without the as-found data it may be impossible to recognize that a calibration failure occurred.