Summary A number of studies have shown that limited work experience, which is often characteristic of very young workers, is associated with an increased risk of occupational injury. The young workers most likely to sustain injuries on the job are those who have left school without obtaining a secondary school diploma, who hold manual jobs, or who have objectively identified learning difficulties. In 2007-2008, Québec’s Ministère de l’Éducation, du Loisir et du Sport (MELS) launched its Training for a Semiskilled Trade (TST) program (known in French as Formation menant à l’exercice d’un métier semi-spécialisé, or FMS) designed specifically for these young people, who are regarded as being at greater risk of occupational injury. During this training, students aged 15 to 17 complete a workplace apprenticeship of 375 hours spread over one school year. In Québec, the Act respecting Industrial Accidents and Occupational Diseases defines an industrial accident as “a sudden and unforeseen event, attributable to any cause, which happens to a person, arising out of or in the course of his work and resulting in an employment injury to him.” This study focused on unforeseen events encountered by TST students during their workplace apprenticeships. The events could be either totally new to the apprentices or familiar to them, but in all cases their occurrence was unforeseeable. An unforeseen event disrupts the apprentice’s normal work process and may, in certain circumstances, result in an incident or even an industrial accident. The unforeseen event may intrinsically pose a risk to the apprentice’s health and safety, as, for example, when a dishwasher trainee in a restaurant injures his hand on a glass that breaks while he is washing it. Or again, it may be the variations in the apprentice’s activity caused by the unforeseen event that pose risks, as for example, when a printer’s helper apprentice burns himself while trying to restart a plastic film sealing machine that has broken down shortly before. To handle unforeseen events, apprentices develop strategies that may be more or less adapted, depending on their experience with the situation at hand. The aims of this study were to identify and classify the types of unforeseen events that occur, their immediate causes, and the observed strategies (whether individual or collective) used to handle such situations, as well as to document the consequences of the work activity, such as loss of time and risk of injury. To achieve these aims, video-sequence observation data collected during a prior study of nine TST apprentices over two apprenticeship days (T1 and T2) were analyzed. The nine apprentices were working in a variety of activity sectors: wholesale and retail trade, manufacturing, and food services. The conceptual framework used for these analyses was the model of the work situation, focusing on the individual at work, used in ergonomics. The results showed that the nine apprentices encountered different types of unforeseen events related to the activity sector involved and to the type of task performed during observation. The events occurred in relatively similar proportions at the beginning (T1) and end of the apprenticeship (T2). The students encountered a total of 554 events over the two days. Nearly 10% of the events resulted in loss of work time while approximately 19% of them posed occupational health and safety risks for the apprentices. Over half of the events likely to cause an accident were associated with specific work contexts of three apprentices: a woodworker, a stock handler in a household appliance/electronics store, and a butcher’s helper. The results indicated that these three students had to perform heavy material handling tasks. Of all the types of unforeseen events observed, material handling tasks ranked fourth in terms of overall unforeseen events encountered, but first among unforeseen events associated with a risk of accidents. Moreover, the apprentice’s work actions or techniques often caused the unforeseen events associated with a material handling activity. This seems to confirm the positive influence of the know-how and tacit knowledge developed by many expert material handlers, as demonstrated in several previous studies. To handle these unforeseen events, the students adopted individual strategies only, collective strategies only, or both. In most cases, however, they took the initiative of developing individual strategies, trying to find adequate ways of doing things on their own rather than asking for help. In other words, they tried to solve the problems caused by the unforeseen events and performed additional tasks to rectify errors. Only the three students (printer’s assistant, butcher’s helper, and cook’s helper) who benefited from a richer social environment utilized proportionately more collective strategies than the other students. These collective strategies were mostly initiated by their co-workers, who provided them with in situ training after the unforeseen event to help them perform the task. The event’s occurrence thus served as a learning opportunity. Based on the results of this study, a number of suggestions can be made for organizations: Analyze certain categories of unforeseen events that pose accident risks in order to propose appropriate prevention mechanisms; Provide apprentices with learning opportunities by ensuring gradual increments in level of task complexity and sources of constraints; Enhance workplace training by replicating unforeseen or sudden situations that are also credible in the work context, in order to provide opportunities for students to develop adapted strategies while under supervision and receiving feedback; In particular, analyze the material handling tasks that apprentices will be asked to perform and adopt training strategies; Assess the importance of the motor aspect of learning during training, and provide mechanisms for encouraging the transfer of knowledge that is useful for learning trade skills and efficient work methods; Pay particular attention to the human resources in the workplace who could pass on their occupational knowledge and skills and help foster the development of reflective competencies. The results of this study will be integrated into a project aimed at introducing support tools to foster occupational health and safety learning among students in the TST program. These tools will be coupled with training materials for the teachers responsible for using them, the students involved, and the businesses that agree to take and train these students.