An audit must have a defined structure, an understood purpose, and enough details to assure completeness. It should be divided into discrete levels with specific topics so that the auditor can fully identify and understand the degree to which each facility or company complies with the requirements. Each of these levels should also be designed to abalyze different types of information, implementaiton actions, and infrastructure. This article proposes and discusses a four-level approach to conduct a comprehensive and complete audit. The four levels are as follow: Recognition and acknowledgement of the need to comply with a specific set of rules or regulations, An implementation strategy and infrastructure, Evidence of compliance, and Quality assessments The content and purpose of each level as well as the interaction between levels is discussed and explained in this article .(C) 2009 American Institute of Chemical Engineers Process Saf Prog 28: 343-346, 2009