Safety Column
In metrology an unbroken chain of comparisons refers to the path of comparisons from the international prototype kilogram to any properly calibrated standard in the field. This “chain” can also be seen as a Chain of Custody for samples taken or work performed in the field by inspectors. The paperwork that states, Who, What, When, Where, and Why. It can show the path of every place and/or person the sample took until it was tested and reported. It may also provide a look at the process an inspector made during an inspection and how his equipment is calibrated and appropriate for the work performed. If any link in this chain is missing, an expert may invalidate your work or data. A calibration program for standards and equipment requires that a program is set up and organized for specific regulatory actions. Does your state have statutes or regulations saying they will test fuel devices and if so, how often? What rules and regulations are in place to allow your inspectors to go into a place of business and check pumps or scales for accuracy? What rules apply to your inspector’s testing equipment? What handbooks or standard operating procedures are followed to give every business equal treatment under the regulations? Having definitive answers to these questions in statutes, codes, and regulations form the base of how programs should be set up to check devices in the field. These answers also provide safeguards for when questions arise regarding inspections and regulatory actions. Documented measurement uncertainty is a look at the possible doubt in a measurement. A good example from a metrology perspective is different employees calibrating the same weight on a particular scale. Most times 2 different people won’t get the exact same result, but we can say they will be close plus or minus some amount. Field staff also have uncertainty applied to their equipment. Multiple variables affect the results of field work, such as, leveling, temperature, weather conditions, using the same procedure every time, etcetera. Minimizing these factors helps to prevent uncertainty in the field. Documenting issues encountered in the field also helps to minimize or improve this uncertainty. How many times have we asked, “Did you follow the SOP?” Documented and validated procedures are sometimes dictated in an official operating manual, or it can be an administrative procedure created by your own program managers. Documenting a procedure helps with multiple issues. It can assist in training new inspectors. It helps with succession training to avoid the loss of institutional knowledge. It allows all inspectors within your state to follow the same standard operating procedure for every test to obtain measurements that are repeatable and objective.
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