Some process accidents and the actions needed to prevent them occurring again are described. They illustrate the following points: . Some investigators are too eager to recommend changes in instructions or better observation of them than to look for ways of removing hazards or for changes in design that will make an accident less likely. . Some people fail to calculate the effects of changes or the time required for them to take place. . Facts that are well known in one industry or company may be unknown in another. The incidents have been chosen because of their value as learning experiences. (C) 2004 Elsevier B.V. All rights reserved.