IACS: Interpretation on ship noise measurement (MSC.337(91))

The International Association of Classification Societies (IACS) has published Unified Interpretation SC304 which provides guidelines for the calibration and use of sound measuring instruments on ships in accordance with the MSC.337(91) Code on noise levels.

Equipment Specifications:

Sound Level Meters: The document specifies that sound pressure levels should be measured using precision integrating sound level meters. These meters must meet the technical standards of IEC 61672-1 (2002-05), Type/Class 1. This standard ensures that sound level meters are capable of providing high-precision measurements of sound pressure levels.

An exception was made for older models of sound level meters manufactured according to IEC 651/IEC 804 standards, which were permitted for use until July 1, 2016. After this date, all meters should comply with the updated IEC 61672-1 standard or its equivalent as deemed acceptable by the relevant administration or authority.

Calibration and Verification:

Calibration of Sound Meters: The sound calibrators used to adjust or verify sound level meters must comply with the IEC 60942 (2003-01) standard and be approved by the manufacturer of the sound level meter. This ensures compatibility and accuracy in sound measurements.

Regular Verification: Both the calibrator and the sound level meter need to be verified for accuracy at least every two years by a laboratory that is accredited according to ISO 17025 (2005). This accreditation ensures that the laboratory meets international standards for technical competence in calibration testing.

Interpretation and Implementation:

Calibration Standards: Calibration should be conducted in accordance with IEC 61672-3 for sound level meters and IEC 60942 Appendix B for field calibrators. It is important that the calibration edition corresponds with the edition of the manufacturing standard that the instruments were built to meet.
Documentation Requirements: The company conducting the sound measurement must provide documentation that verifies which standard was met during calibration. This information should be clearly marked on the instrument or in accompanying paperwork. Additionally, the documentation should include the results of periodic tests and clarify the performance class that the instrument meets after calibration.

Implementation Timeline:

Uniform Implementation: The IACS (International Association of Classification Societies) requires that this interpretation be uniformly applied by its member societies from the next calibration date on or after July 1, 2026. This ensures that all equipment used for noise measurement on ships will be calibrated to consistent standards across the industry.