From OSHA’s final rule for electric power generation, transmission and distribution

Before each job:
(i) In assigning an employee or a group of employees to perform a job, the employer shall provide the employee in charge of the job with all available information that relates to the determination of existing characteristics and conditions required by paragraph (a)(4) of this section.
(ii) The employer shall ensure that the employee in charge conducts a job briefing that meets paragraphs (c)(2), (c)(3), and (c)(4) of this section with the employees involved before they start each job.

Subjects to be covered:
The briefing shall cover at least the following subjects: hazards associated with the job, work procedures involved, special precautions, energy-source controls, and personal protective equipment requirements.

 Number of briefings:
(i) If the work or operations to be performed during the work day or shift are repetitive and similar, at
least one job briefing shall be conducted before the start of the first job of each day or shift.
(ii) Additional job briefings shall be held if significant changes, which might affect the safety of the employees, occur during the course of the work.
Extent of briefing:
(i) A brief discussion is satisfactory if the work involved is routine and if the employees, by virtue of
training and experience, can reasonably be expected to recognize and avoid the hazards involved in the job.
(ii) A more extensive discussion shall be conducted:
     (A) If the work is complicated or particularly hazardous, or
     (B) If the employee cannot be expected to recognize and avoid the hazards involved in the job.