Accredited testing laboratories: the role and limits of conformity assessment

DIN EN ISO/IEC 17025 defines the general requirements for the competence of testing and calibration laboratories. The following focuses on the work of an accredited testing laboratory as a conformity assessment body.

The laboratory’s core competence is testing: determining characteristics of an object of conformity assessment using defined procedures. The scope of accreditation is determined by the test methods and procedures listed in the accreditation certificate. The accreditation body has confirmed the laboratory’s competence for these methods and procedures.

Test results are documented in a test report, for which the standard specifies minimum requirements.

Test report and certificate: terminology and distinctions

In the context of statements of conformity, a distinction is often made between a test report and a certificate. There is no strictly standardised distinction. However, analysis of the relevant standards suggests the following practical differentiation:

• Test report (DIN EN ISO/IEC 17025): in its simplest form, contains only test results, without a normative basis for evaluation or an explicit statement of conformity.
• Certificate (DIN EN 10204 – “Types of inspection documents”): supplements the test results with a normative basis for evaluation and a statement of conformity, such as “fulfilled” or “not fulfilled”.

In the following, the term “test report” is used consistently, in line with DIN EN ISO/IEC 17000 and 17025.

Content and significance of the test report

The test report is a testing laboratory’s central document. It confirms the conformity of a test item with defined requirements (test characteristics). Typical contents include:

• procedures for selecting samples and determining properties,
• presentation and evaluation of test results, taking measurement uncertainties into account where applicable,
• a decision on conformity.

In practice, review and decision often fall within the responsibility of the same person.

Opinions and interpretations

Test reports may also contain opinions and interpretations. DIN EN ISO/IEC 17025 sets out clear requirements for these:

• they must be clearly identified as such in the test report;
• they must not be confused with inspections or product certifications;
• they should only be provided by personnel with broader system knowledge that typically goes well beyond laboratory staff’s technical expertise. This includes knowledge of manufacturing processes, application conditions, typical defect patterns, normative requirements and relevant legal frameworks.

 

Accreditation and requirements for testing laboratories

Unlike DIN EN ISO/IEC 17000, DIN EN ISO/IEC 17025 does not distinguish between first-, second- and third-party conformity assessment bodies. What matters is that accredited testing laboratories fulfil defined minimum requirements, particularly concerning quality management, technical capabilities and competence:

Quality management

The requirements are largely based on DIN EN ISO 9001. Accredited testing laboratories fulfil its principles but are not automatically ISO 9001 certified.

Technical capabilities and competence

• technical competence and qualifications of personnel,
• selection and validation of suitable testing and sampling procedures, for example in non-destructive testing,
• recording test and measurement results, including testing equipment and environmental conditions,
• evaluation of results taking measurement uncertainties into account,
• traceability of measurement results, for example through calibration and reference materials,
• assurance of the quality of results, for example through proficiency testing,
• presentation of test and measurement results in the test report in accordance with the relevant standards.

Alongside quality management, structured handling of test and measurement data – their recording, safeguarding, traceability and presentation – is particularly important.

Context: the role and limits of the testing laboratory

A testing laboratory accredited to DIN EN ISO/IEC 17025 focuses on:

• testing the properties of a specific test item in accordance with standards using accredited procedures,
• preparing test reports that document the results for that particular item and point in time.

The statement of conformity in a test report relates exclusively to the tested sample or the production or delivery batch it represents. It may not be extended to other samples, batches or future points in time (“extrapolation”).

A typical practical question

A typical question for an accredited testing laboratory is: “Does the strength of this component meet the requirements of standard N123?”

The testing laboratory provides a reliable, methodologically substantiated answer within the clearly defined scope of its accreditation.

***

Further information: Part 4 of the series “Conformity assessments in materials testing”: “Inspection as conformity assessment: role, responsibilities and distinctions”.(opens in new tab) (opens in new tab)