Finding the causes of an accident or operating problem and deciding what actions to take to prevent it happening again is rather like dismantling a set of Russian dolls (Fig. 1). Each time we ask "why?" (or a similar searching question) we find another cause besides the ones we have found already and another action (or set of actions) we can take to prevent similar accidents occurring again. Many investigators stop too soon. This occurred at Flixborough, at Bhopal and in the investigation of many lesser-known accidents. We are more likely to find the deeper causes and the more original actions if groups of people with wide interests and experience are able to take part in the investigations or discuss the investigation reports. We should never look at an accident report as "closing out" a problem. As we read it, we should ask ourselves, "what else could be done?" (c) 2005 Elsevier B.V. All rights reserved.