Human problems with computer control in process plants

The application of computer control continue to grow. If lessons can be learnt from the incidents that have occurred, they may be prevented from happening again. This paper describes some incidents that have occurred in computer-controlled process plants. The errors are, of course, human errors, failures to foresee or allow for equipment failures or failures to foresee how operators will respond to the equipment. The computers provided new and easier opportunities for making old errors.     

Searchlights from the past

"Modern man", wrote the historian, E.H. Carr, "peers eagerly back into the twilight from which he has come, in the hope that its faint beams will illuminate the obscurity into which he is going ...". Carr is wrong. For those who are willing to look, searchlights, not faint beams, shine out from the past and show us the pits into which we will fall if we do not look where we are going. Some of these searchlights illuminate specific technical risks while others remind us of general principles. In an age of rapid change people are particularly prone to ignore the past, but while technology changes, people do not.     

Mining the past

Whenever we hear of an accident elsewhere we are eager to learn what happened and what recommendations have been made to prevent it happening again. However, we can learn as much from past accidents that have been forgotten or were never widely reported. Some such accidents are described, including entry to confined spaces, the collapse of a gasholder and the collapse of a tank for an unusual reason.     

Accident investigation: keep asking "why?"

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?"     

Some fires and explosions in liquids of high flash point

Many fires and explosions have occurred because of a failure to realise that heavy oils, once they are hot, catch fire or explode as easily as petrol.Some incidents are described, together with the precautions necessary to prevent them happening again.The incidents described are: an explosion in a distillation column; several explosions while demolishing storage tanks; a fire while demolishing an old pipeline; a plant destroyed when a spillage of solvent caught fire; an explosion in a lorry wheel; an explosion in a cargo of bananas; a fire while filling a road tank wagon.     

Some myths on hazardous materials

This paper describes some myths about hazardous materials, that is, deeply ingrained beliefs that are not wholly true. Thus many people believe that ex     

Hazop-past and future

This paper outlines the history of Hazop, looks at future developments in its application to computer-controlled systems and suggests ways of using computers to increase the effectiveness of Hazops.     

Learning from experience

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.