The film dubbing is a long task (5 hours for a 50 minutes film) requiring a sustained attention and excluding the minor lapses (advances or delay of synchronism; intonation...). After about two hours, the lapses are more frequent. The aim of this study is to introduce a 30 minutes break after 150 minutes of dubbing work in order to verify if break is beneficial to work quality and alertness. Prior to study, 9 error types are registred by task analysis. Work time is divided into six thirty minutes periods. During each of them, errors are recorded and alertness is self-esteemed. For every one operator, two conditions are tested in a counterbalanced order: one with break after 150 minutes of work; the other without break. The results show that in condition without break, errors means increase during afternoon (from midday to 2 pm) whereas quality of dubbing is constant during the day with break. Concerning self-esteemed alertness, the same evolution is recorded. Without break, alertness decreases from 10 am to 2 pm whereas, with break, it remains constant and even increases at 2 pm. These results clearly indicate that breaks, even short breaks, may reduce task errors in real work situation and increase alertness. In this study, only 10% of work time spent in break induces 30% error reduction and 50% increase of operator's well being sensation.
