identification and analysis of human errors by phea technique in isomax unit of an oil refinery

according to industrial accident’s investigation 60 to 90% of all accidents have directly been caused by human error. in this study , which has been done in the isomax unit of an oil refinery , totally 25 existing occupational tasks were  reviewed by aid of the results produced from interviewing the workers , discussing with supervisors & line managers and considering all the past accident’s reports .from all 25 , 10 tasks were selected as susceptible and critical to human error occurrences .all selected tasks were analyzed by hierarchal task analysis.in the second stage , phea( predictive human error analysis) technique was used for predicting and extraction of human errors in the selected tasks .apart from determination of identified error’s type (action, checking , retrieval , selection, sequence and communication error), description of errors , the consequences of their occurrence and proper solutions for prevention and recovering from errors were developed and entered into phea worksheet . the performed phea technique was identified totally 161 errors in all 10 tasks .the type of identified errors were different and their number were, according to the sequence written in the pervious paragraph , 108 , 12 , 24 , 4 , 5 , and 8 respectively. some important of these errors which have had , according to the accidents occurring the past , high frequencies were : the task was not done , too much done , too early or too late was done , has been done in different sequence  and … .finally for preventing and recovering from the identified errors some proper solutions, particularly in the area of hardware change in equipment design , have been proposed : labeling of equipments , making the colure pumps or switches  different with each other , installing acoustic telephone booths in the site  and … .