ENAC Accreditation, Uncertainty & Metrological Traceability in 3 Seconds.

ISO 17025:2017 and ISO 9001:2015 are complementary standards with different scopes. ISO 9001 defines the requirements for a generic quality management system applicable to any organisation. ISO 17025 is designed specifically for testing and calibration laboratories, and incorporates additional technical requirements that do not exist in ISO 9001: personnel technical competence, validation of testing and calibration methods, measurement uncertainty calculation (clause 7.6), metrological traceability (clause 6.5) and assurance of the validity of results (clause 7.7). A laboratory certified to ISO 9001 is NOT accredited to issue results with recognised metrological validity. ISO 17025 accreditation by ENAC in Spain does confer that recognition.

ENAC (Entidad Nacional de Acreditación) evaluates compliance with ISO 17025:2017 through a process that includes: formal application with description of the accreditation scope, documentary review of the management system (quality manual, test procedures, calibration records), on-site assessment by technical assessors specialised in the laboratory field, demonstration of personnel technical competence (clause 6.2), verification of metrological traceability of principal equipment (clause 6.5) and participation in proficiency testing or interlaboratory comparisons (clause 7.7.2). The typical timeframe from application to accreditation ranges from 12 to 24 months. Maintenance requires annual surveillance assessments and a full reassessment every 4 years.

Measurement uncertainty calculation follows the GUM guide (JCGM 100:2008, Guide to the Expression of Uncertainty in Measurement). The process consists of: (1) identifying the measurand and the mathematical model of the measurement; (2) identifying all sources of uncertainty (instrumental, repeatability, reproducibility, temperature, purity of standards, etc.); (3) quantifying each component as Type A standard uncertainty (statistical evaluation) or Type B (other information: calibration certificates, manufacturer specifications, literature); (4) combining components using the law of propagation of uncertainty; (5) calculating the expanded uncertainty U = k · uc with coverage factor k=2 for a confidence level of ~95%. ISO 17025:2017 clause 7.6 requires laboratories to identify the contributions to uncertainty and to report them in test reports when relevant.

Metrological traceability (ISO 17025:2017 clause 6.5) is the property of a measurement result whereby the result can be related to a reference through an unbroken and documented chain of comparisons, each with its associated uncertainty. In practice, it means that every measuring instrument in the laboratory must be calibrated by an accredited laboratory that in turn uses standards traceable to national standards (CEM in Spain, PTB, NPL) or international standards (BIPM). Traceability is demonstrated through: valid calibration certificates for each instrument, a calibration programme with defined intervals, records of intermediate checks between calibrations and an equipment management procedure identifying those that affect test results. ENAC verifies the traceability chain as a central part of the assessment.

ISO 17025:2017 distinguishes between verification and validation of methods (clause 7.2). Verification applies to standardised methods (ISO, EN, ASTM, etc.) and consists of confirming that the laboratory can meet the requirements of the method under its local conditions. Validation applies to non-standardised methods, laboratory-developed methods, or standardised methods used outside their intended scope. Parameters to be validated include: accuracy (bias), precision (repeatability, reproducibility), limit of detection (LOD), limit of quantification (LOQ), linearity, working range, selectivity and specificity, robustness, and measurement uncertainty. Validation records are mandatory documented information and are audited by ENAC assessors to verify that the method is fit for purpose.

ISO 17025:2017 clauses 6.4 (equipment) and 6.5 (traceability) establish the requirements for equipment management. The laboratory must: maintain an inventory of all equipment that affects laboratory results, assign unique identification to each item, define a calibration and maintenance programme with intervals based on use, manufacturer specifications and method requirements, perform intermediate checks between calibrations for critical equipment, have procedures for dealing with out-of-specification equipment (including retrospective assessment of impact on previous results), and retain historical calibration records for the period defined in the management system. Equipment with defects or out of service must be labelled and identified to prevent use. Software that forms part of equipment or that processes test data is also subject to validation requirements (clause 6.4.7).