For AODA: There is no specific requirement for how frequently employees must be retrained on AODA. Organizations are required to train existing and new people at the organization as soon as practicable, and on an on-going basis for anyone who is new. You also need to provide training whenever changes to your accessibility policies are made and, possibly if someone changes their job duties.   For WHMIS 2015: At least once a year, the employer must review the training and instruction provided to workers, in consultation with the joint health and safety committee or health and safety representative of the workplace. Again, there is no specific requirement for how often employees must be retrained on WHMIS in Ontario. However, the CCOHS recommends that employees be retrained at least every three years, or whenever there is a significant change in the workplace that could affect their safety. For Workplace Violence and Harassment: the program can be reviewed as often as necessary, but at least annually, to ensure that it adequately implements the policy with respect to workplace harassment and violence.  Health and Safety Awareness: All employers must ensure workers and supervisors complete, or have completed, an awareness training program that meets the regulatory requirements. This is mandatory whether they work on a construction project, in a retail store or factory, hospital or long-term care facility, mine or mining plant, or farming operation, etc.