Section 2(1)(r) in The Petroleum and Natural Gas Regulatory Board (Technical Standards and Specifications including Safety Standards for City or Local Natural Gas Distribution Networks) Regulations, 2008
(r)"tertiary network" means a part of CGD network that operates at pressure less than 1.5 psig(100 mbar) and pipelines forming part of this network to service Pressure Distribution Mains shall be designed to ensure uninterrupted gas supply to service lines;