The role of operator’s performance for continuous, hazard-free and economically viable production in the chemical industry is of paramount importance. Even a minor error may result in a near miss, an abnormal situation, and even a catastrophic accident. This paper analyzes and discusses the role played by distinct training methods performed in an Immersive Virtual Environment (IVE) to form and influence the performance of operators. We designed and conducted an experiment for a specific procedure of a polymerization plant, i.e. catalyst-injector switch, where the operator has to follow a sequence of actions. Two groups of participants (N = 24) were trained within the IVE according to different training methods. The Immersive Observers (IO) group observed a trainer explaining and performing the procedure, while the Immersive Actors (IA) group performed singularly and personally the procedure through a so-called guided-tour. The IO group showed higher accuracy, precision, process understanding, identification skill and lower help requirements than those of IA group, conversely IA group showed better speed when compared with the former. The results lead to the conclusion that IVE are not effective per se and need guidance by a competent trainer when the task is unfamiliar. The impact for future research and practice are discussed.