29 C.F.R. § 553.230 – Maximum hours standards for work periods of 7 to 28 days—section 7(k).

(a) For those employees engaged in fire protection activities who have a work period of at least 7 but less than 28 consecutive days, no overtime compensation is required under section 7(k) until the number of hours worked exceeds the number of hours which bears the same relationship to 212 as the number of days in the work period bears to 28.
(b) For those employees engaged in law enforcement activities (including security personnel in correctional institutions) who have a work period of at least 7 but less than 28 consecutive days, no overtime compensation is required under section 7(k) until the number of hours worked exceeds the number of hours which bears the same relationship to 171 as the number of days in the work period bears to 28.

(c) The ratio of 212 hours to 28 days for employees engaged in fire protection activities is 7.57 hours per day (rounded) and the ratio of 171 hours to 28 days for employees engaged in law enforcement activities is 6.11 hours per day (rounded). Accordingly, overtime compensation (in premium pay or compensatory time) is required for all hours worked in excess of the following maximum hours standards (rounded to the nearest whole hour):

Work period (days)	Maximum hours standards
Fire protection	Law enforcement
28	212	171
27	204	165
26	197	159
25	189	153
24	182	147
23	174	141
22	167	134
21	159	128
20	151	122
19	144	116
18	136	110
17	129	104
16	121	98
15	114	92
14	106	86
13	98	79
12	91	73
11	83	67
10	76	61
9	68	55
8	61	49
7	53	43