(a) The frequency of patrolling mains must be determined by the severity of the conditions which could cause failure or leakage, and the consequent hazards to public safety.
(b) Mains in places or on structures where anticipated physical movement or external loading could cause failure or leakage must be patrolled at intervals not exceeding 4 1/2 months, but at least four times each calendar year.
(c) Distribution lines operating at 125 psig (862 kPa) or more in Class 3 and 4 locations must comply with the transmission patrolling requirements in section 255.705 of this Part.