Distribution systems: Patrolling.

(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—#

(1)In business districts, at intervals not exceeding 4 1/2 months, but at least four times each calendar year; and#

(2)Outside business districts, at intervals not exceeding 7 1/2 months, but at least twice each calendar year.#