The standard risk assessment practices used in industry since the OSHA 1910.119 regulation was issued, are to conduct Process Hazard Analyses (PHAs) for hazardous and exothermic (or otherwise high risk) processes. During PHAs, the potential consequences of an undesired event are evaluated along with the safeguards that exist to mitigate the consequences or reduce the frequency of the event. If the PHA team determines that the risk is still not tolerable, additional safeguards are recommended to reach a tolerable level of risk. Typically, a Quantitative Risk Assessment can be completed to evaluate the effectiveness of these existing or newly proposed safeguards. Unfortunately, this is a complex and time-consuming, task. The reactively new methodology of Layer of protection analysis (LOPA) allows a PHA team to evaluate the effectiveness of safeguards in reducing risk in an efficient yet semi-quantitative fashion using some basic assumptions and standard lookup tables. The LOPA methodology can be utilized to evaluate the effectiveness of Safety instrument functions (SIF) (e.g., automated critical interlocks and alarms) to achieve a tolerable risk. The LOPA methodology provides consistency in an approach to risk assessments and communications. It can support an effective mechanical integrity or risk-based maintenance system for critical components of an SIF. This article describes LOPA and includes several scenarios that will provide an overview of how the LOPA methodology is used in a multi-batch pharmaceutical facility. (C) 2009 American Institute of Chemical Engineers Process Saf Prog 28: 312-316, 2009