One of the objectives of process automation is to improve the safety of plant operations. Manual operation, it is often argued, provides too many opportunities for operator error. By this argument, process automation should decrease the risk of accidents caused by operator error. However, some accident theorists have argued that while automation may eliminate some types of operator error, it may create new varieties of error. In this paper we present six case studies of explosions involving operator error in an automated process facility. Taken together, these accidents resulted in six fatalities, 30 injuries and hundreds of millions of dollars in property damage. The case studies are divided into two categories: low and high automation complexity (three case studies each). The nature of the operator error was dependent on the level of automation complexity. For each case study, we also consider the contribution of the existing engineering controls such as safety instrumented systems (SIS) or safety critical devices (SCID) and explore why they were insufficient to prevent, or mitigate, the severity of the explosion. (C) 2008 Elsevier B.V. All rights reserved.