An external audit is an independent assessment performed by an accredited certification body to verify a management system's conformity with an ISO standard.
The external (or third-party) audit is conducted by a certification body accredited under ISO/IEC 17021-1. It is divided into two stages: Stage 1 (documentation review and readiness assessment) and Stage 2 (on-site implementation audit). Its result determines whether certification is granted, maintained or withdrawn.
Internal audit is performed by the organization or a hired consultant. External audit is executed by an accredited certification body with authority to grant, maintain or withdraw certification.
It depends on scope, organization size and standard. ISO/IEC 17021-1 and IAF MD documents establish minimum auditor-days. A mid-sized organization may require 4-8 total auditor-days.
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