Section 551.431 - Time spent on standby duty or in an on-call status(a)(1) An employee is on duty, and time spent on standby duty is hours of work if, for work-related reasons, the employee is restricted by official order to a designated post of duty and is assigned to be in a state of readiness to perform work with limitations on the employee's activities so substantial that the employee cannot use the time effectively for his or her own purposes. A finding that an employee's activities are substantially limited may not be based on the fact that an employee is subject to restrictions necessary to ensure that the employee will be able to perform his or her duties and responsibilities, such as restrictions on alcohol consumption or use of certain medications.(2) An employee is not considered restricted for "work-related reasons" if, for example, the employee remains at the post of duty voluntarily, or if the restriction is a natural result of geographic isolation or the fact that the employee resides on the agency's premises. For example, in the case of an employee assigned to work in a remote wildland area or on a ship, the fact that the employee has limited mobility when relieved from duty would not be a basis for finding that the employee is restricted for work-related reasons.(b) An employee will be considered off duty and time spent in an on-call status shall not be considered hours of work if:(1) The employee is allowed to leave a telephone number or to carry an electronic device for the purpose of being contacted, even though the employee is required to remain within a reasonable call-back radius; or(2) The employee is allowed to make arrangements such that any work which may arise during the on-call period will be performed by another person.45 FR 85664, Dec. 30, 1980, as amended at 64 FR 69180, Dec. 10, 1999