Perforated Yellow Gas Ducting Coils Available In 60mm , 100mm & 160mm x 50m coil lengths. Both the National Grid and Wales & West Utilities Specify that ducting for gas main service pipes MUST be ” Yellow Perforated Ducting ” and conform to BS 4962 ( complies with TRANSCO Specifications ) This Allows For the gas to vent safely in the event of a leak . From The Southern Distribution Depot