29 CFR § 553.213 - Public agency employees engaged in both fire protection and law enforcement activities.
(a) Some public agencies have employees (often called “public safety officers”) who engage in both fire protection and law enforcement activities, depending on the agency needs at the time. This dual assignment would not defeat either the section 13(b)(20) or 7(k) exemption, provided that each of the activities performed meets the appropriate tests set forth in §§ 553.210 and 553.211. This is so regardless of how the employee's time is divided between the two activities. However, all time spent in nonexempt activities by public safety officers within the work period, whether performed in connection with fire protection or law enforcement functions, or with neither, must be combined for purposes of the 20 percent limitation on nonexempt work discussed in § 553.212.
(b) As specified in § 553.230, the maximum hours standards under section 7(k) are different for employees engaged in fire protection and for employees engaged in law enforcement. For those employees who perform both fire protection and law enforcement activities, the applicable standard is the one which applies to the activity in which the employee spends the majority of work time during the work period.