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A study to gain insight into the way “process-alarm systems” are actually used and evaluated in practice, and to know how busy the human operator is in dealing with the system is presented. Observations and interviews were carried out with eight experienced control room operators from a fertilizer plant. For 63 h all the warning signals of the conventional system were recorded and rated by the operators. The method of observation is briefly described. The actual ratings were compared with those assumed in advance. The results indicated that in the fertilizer plant the process-alarm system was mainly used as a monitoring tool and not as an alarm system requiring action. Therefore “annunciator system” would be a better term. The number of warning signals recorded was surprisingly high. Suggestions are given to reduce this number; e.g., annunciator systems can be improved by reducing the number of irrelevant cluster and oscillation signals. In interviews outside the control room favorable and less favorable aspects of the system were discussed with the operators and critical incidents (human errors) were analyzed. Five incidents are briefly described. On the basis of this study, the various functions of the annunciator system are discussed. A plea is made for further research in the laboratory, so as to tackle some of the “interface” problems that were found.