Calibration: The comparison of a measurement instrument or system of unverified accuracy to a measurement instrument or system of known accuracy to detect any variation from the required performance specification.
–American Society for Quality
It is absolutely essential that calibration be an integral part of a food or ingredient processor’s quality and safety program. Almost all regulations and management standards that address food quality and safety include language that stresses the importance of calibration. The low-acid canned food regulations found in the U.S. Code of Federal Regulations 21 CFR Part 113 reference the need for calibration:
“Each thermometer should have a tag, seal or other means of identity that includes the date on which it was last tested for accuracy.”
As does the Hazard Analysis and Critical Control Points (HACCP) regulations that are mandated for meat and poultry, seafood and juice:
“Records that document the calibration of process monitoring instruments.”
And, finally, ISO 22000, the food safety management system’s requirements for any organization in the food chain, states in Section 8.3:
“The organization shall provide evidence that the specified monitoring and measuring methods and equipment are adequate to ensure the performance of the monitoring and measuring procedures.”
The bottom line is that all instruments used for ensuring quality, safety, sanitation and legal compliance must be calibrated. In addition, if there are monitoring devices that are necessary to ensure worker safety and/or safe operation of equipment, they must be included in the calibration program. An example of such a device would be a pop-off valve on a pressure vessel.
To achieve this goal, processors need to perform the following:
• Develop effective procedures for calibration;
• Document those procedures;
• Maintain records of calibration activities, including corrective actions;
• Review records to ensure that procedures are being followed;
• Observe the employees doing the calibration procedure to ensure they are following the procedures; or, audit third parties contracted to do similar work.
It is also important to assign someone to manage the calibration program to ensure that it is properly designed, implemented and maintained.
Who Manages the Program?
So, who should manage the calibration program? This depends on each and every company. What happens frequently is that processors do not assign an individual to manage the calibration program, but allow it to be done by different operating groups. The production people might be responsible for unit operations such as metal detectors or magnets, whereas engineering takes responsibility for temperature-indicating devices (TIDs) and pressure gages. The quality manager or laboratory supervisor will ensure that the instruments in the laboratory are properly calibrated. There may be other groups that get involved. For example, the warehouse people might be responsible for looking after refrigerators, freezers and relative humidity controls.
What can happen in a situation like this is that there are many different calibration programs that use different forms and procedures. In addition, there may be critical instruments that “fall through the cracks” and are either not being calibrated or not being calibrated frequently enough to adequately ensure safety or quality. It is okay to have different persons responsible for their areas, but one person needs to manage the entire program. His or her role is to ensure that there is a consistent program that addresses all calibration activities that need to be done to ensure product quality and safety. The calibration manager needs to work with his group to establish a standard format for procedures. The manager must also evaluate all monitoring instruments in the plant and determine not only whether calibration is necessary, but how often this should be done. By conducting a risk assessment, they can determine not only which devices are essential for the production of safe, wholesome and high-quality products, but also whether the procedures are being employed properly.
The job description of the manager responsible for calibration should clearly state that this individual is responsible for managing the program. He or she must accept their job description, acknowledging responsibility. Among their duties will be to ensure that the program remains on schedule, that it is audited per established schedules and that calibration records are being reviewed per established schedules. In addition, the calibration manager must ensure that all persons responsible for calibrating instruments or ensuring that they are calibrated have been trained on the procedures and/or work instructions required to do the work and that records of these sessions are maintained.
Developing and Documenting Procedures
It is absolutely imperative that all procedures involved in the calibration program be documented. There should be a general protocol that describes how the calibration program will be developed and implemented, plus work instructions that describe how each instrument or class of instruments should be calibrated.
The general protocol should include the following elements:
• Objective of the program
• Responsibility
• Calibration procedures
• Documentation responsibilities
• Corrective actions
Each work instruction should include step-by-step procedures on how the calibration should be done, the standards that will be employed, the tolerances and how the results shall be reported. If the instrument is out of calibration, the procedures must not only describe what will be done with the instrument, but more importantly, it must address what to do with any product that might be affected. Most operations “tag” their instruments after calibration. The calibration tag may include who did the work, the date the work was done and the date of the next scheduled calibration. These tags should be made of materials that are water- and oil-resistant so they will survive the rigors of production, including cleaning. Additionally, if tagging is part of the program, removal of outdated tags and replacement with new ones should be included in the procedures.
With instruments such as pressure gages or TIDs, it is best to calibrate the unit at three points that bracket the normal operating parameters. The risk assessment exercise should be used to help establish how to calibrate the instrument.
There is a difference between calibration and verification. Perhaps the best example to use when differentiating the two is a scale. Scales are usually calibrated one or two times per year by a regulatory agency or a licensed calibration organization. These groups test the units against known standards and adjust them as needed. Many operations routinely verify their scales. To do this, they routinely check performance using standard weights.
Calibration procedures must address instruments used for monitoring process operations and performing quality tests, and any standards used in-house. Processors must send standard thermometers (National Institute of Standards and Technology or American Society for Testing and Materials), weights and other devices to an outside agency for calibration at regular intervals.
Procedures for sending instruments out must also be documented. If a state agency comes into your facility once a year to calibrate scales, load cells and other devices, procedures describing how this is done, who is responsible and what needs to be done if the instrument is found to be out-of-calibration are necessary.
One of the most valuable tools for documenting and organizing a calibration program is a master calibration schedule (Table 1). Rolling all instruments that require calibration into this master list allows a processor to easily monitor the program and makes life much easier for auditors. The whole program is summarized in one document. Of course, hard copy records of calibration records must be available for review and to verify that the work was not only done, but done properly.
Records and Corrective Actions
Records of all calibration activities must be maintained either as hard copies or electronically. Many processors roll their process instrument calibration into a maintenance management software program. These systems are available commercially or can be developed internally using programs such as Excel™ or Access™. If your company decides to purchase or build an electronic system to maintain and monitor a calibration program, consider incorporating the following features: