The certification of training does not expire on a schedule, but OSHA has specifically established the requirements for retraining. Section 1910.147(c)(7)(iii) of OSHA 29 CFR 1910.147 Standard sets standards for employee retraining:
1910.147(c)(7)(iii)(A): Retraining shall be provided for all authorized and affected employees whenever there is a change in their job assignments, a change in machines, equipment or processes that present a new hazard, or when there is a change in the energy control procedures.
1910.147(c)(7)(iii)(B): Additional retraining shall also be conducted whenever a periodic inspection under paragraph (c)(6) of this section reveals, or whenever the employer has reason to believe that there are deviations from or inadequacies in the employee’s knowledge or use of the energy control procedures.