Layer of protection analysis (LOPA) is a semiqyantitative tool for analyzing and assessing process risk The fool has grown greatly in popularity and ness since The publication of The first CCPS/AIChE guidebooks on the subject, Layer of Protection Analysis; simplified Process Risk Assessment (LORA). This article is a summary, of a new CCPS guideline book that includes the following: Initiating events (IEs). Independent protection layers (IPLs) Criteria for identifying the value of each prospective IE and IPL data. This book is a necessary reference for those applying the LOPA methodology. (C) 2009 American Institute of Chemical Engineers Process Saf Prog 000: 000-000, 2009