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The importance of data integrity in air sampling calibration     

By Aaron Apostolico, CIH, CSP, CIEC

Third-party traceability
    Third-party traceability is an essential component of reliable calibration. It ensures that the measurements obtained from calibrated equipment are traceable to a recognized standard. National Metrological Institutes (NMIs) such as the National Institute of Standards and Technology (NIST) in the USA play a crucial role in establishing and maintaining measurement standards. Calibration reports from accredited laboratories and reference standards from NMIs ensure international comparability of measurement results.

ISO/IEC 17025 accreditation
    ISO/IEC 17025 is the primary standard used by testing and calibration laboratories to demonstrate technical competence. Laboratories must hold accreditation to this standard to be considered technically proficient. ISO/IEC 17025 ensures that the calibration process follows accepted procedures, resulting in traceable and reliable measurement results. Compliance with this standard is often a requirement for regulatory authorities and acceptance of test or calibration results.

Accuracy
    Accuracy is a fundamental aspect of calibration. It ensures that the calibrated equipment performs as expected and delivers predictable results as measured against a traceable master device. The accuracy of a calibrator should exceed that of the equipment being calibrated, with a recommended minimum of two to four times greater accuracy. Calibration certificates should reference the NIST-traceable master device, providing a clear chain of traceability to recognized standards.

Precision
    Precision complements accuracy and refers to the consistency and repeatability of measurement results. A precise measurement shows minimal deviation between successive results. It is important to distinguish between accuracy and precision, as precision alone does not guarantee accuracy. Factors such as equipment bias, sampling train, calibrator performance, and environmental influences can introduce bias and affect precision.

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Stability
    Stability is a critical consideration during air sampling, particularly when striving for consistent airflow. Stable readings, with a deviation no greater than 5%, ensure accurate calculation of volume over the sampling period. Pulsation caused by pump action and back pressure artifacts can affect stability. Piston style calibrators that create pulsation or instabilities in flow should be carefully evaluated to ensure accurate and reliable measurements are collected.

Recordkeeping and documentation
    Maintaining comprehensive records and documentation is vital in the calibration process. Proper recordkeeping ensures sample integrity, supports report preparation, and assists in legal depositions. Each calibration log has specific details that should be captured as it relates to each pump and sample during calibration. These Calibration Log details generally include: Date and time of Calibration, Pump Model, Pump Serial Number, User Name, Unique Sample ID, Calibrator ID, Date of Last Calibration, Ambient Temperature, Ambient Pressure, Number of Samples or Time in Averaged Sample Set, Flow Average (Volumetric) and when applicable a corrected Flow Average (STP). The calibration logs are crucial elements of support documentation in air sampling. These records provide a transparent and traceable history of the calibration process.

Conclusion
    Calibration is essential for maintaining accurate and reliable measurement results. Third-party traceability, accuracy, precision, and stability are key factors that contribute to the reliability of calibration. By adhering to recognized standards, such as ISO/IEC 17025, organizations can ensure the technical competence of calibration laboratories. Furthermore, maintaining accurate records and documentation is critical for preserving sample integrity and supporting legal requirements. Understanding and implementing these principles of calibration will help organizations meet industry standards and ensure the accuracy and reliability of their measurement equipment.