Introduction: Reducing occupational accidents is of utmost importance. This research investigated how individual and job-related risk factors affect occupational accidents in one of the largest tunnelling companies in Iran. Methods: A descriptive cross-sectional natural experiment utilizing data from 760 employees who consented to participate in the study. 150 individuals had a history of occupational accidents and 610 individuals did not. Information about accidents was extracted from reports, medical records, and interviews. Results: The main causes of accidents were unsafe acts performed by workers. 71% by unsafe acts alone, and another 12% unsafe acts in unsafe conditions. The odds ratio of occupational accidents was significantly higher in workers aged under 30 years (p = 0.016), with a high school diploma or lower educational achievement (p = 0.012), low job satisfaction (p = 0.035), work experience less than 16 years (p = 0.023), as well as lack of regular exercise (p = 0.001). Within the final adjusted logistic model, low levels of education (OR= 5.81; 95% CI, 1.03-9.03) and younger age group (OR= 2.38 95% CI, 0.24 to 8.02) remained significant. Conclusion: Use of young and inexperienced staff, low education, and lack of simple and understandable safety guidelines for workers in the tunnelling industry have led to unsafe acts that can increase the rate of occupational accidents. Changes in working conditions, and unstable job security also contribute to explaining the accident rates in this 12-month period. Managers should pay special attention to these individual-organizational factors to prevent accidents and promote safety.