Leakage surveys of a transmission line must be conducted at intervals not exceeding 15 months, but at least once each calendar year. However, in the case of a transmission line which transports gas in conformity with Sec. 192.625 without an odor or odorant, leakage surveys using leak detector equipment must be conducted--
(a) In Class 3 locations, at intervals not exceeding 7\1/2\ months, but at least twice each calendar year; and
(b) In Class 4 locations, at intervals not exceeding 4\1/2\ months, but at least four times each calendar year. [Amdt. 192-21, 40 FR 20283, May 9, 1975, as amended by Amdt. 192-43, 47 FR 46851, Oct. 21, 1982; Amdt. 192-71, 59 FR 6585, Feb. 11, 1994]