Manufacture Of Gas; Distribution Of Gaseous Fuels Through Mains ISIC Code 3520. This class includes the manufacture of gas and the distribution of natural or synthetic gas to the consumer through a system of mains. Gas marketers or brokers, which arrange the sale of natural gas over distribution systems operated by others, are included. The separate operation of gas pipelines, typically done over long distances, connecting producers with distributors of gas, or between urban centers, are excluded from this class and classified with other pipeline transport activities. This class includes the production of gas for the purpose of gas supply by carbonation of coal, from by-products of agriculture, or from waste, manufacture of gaseous fuels with a specified calorific value, by purification, blending, and other processes from gases of various types including natural gas, transportation, distribution, and supply of gaseous fuels of all kinds through a system of mains, sale of gas to the user through mains, activities of gas brokers or agents that arrange the sale of gas over gas distribution systems operated by others, commodity and transport capacity exchanges for gaseous fuels, remodeling or renovating existing residential structures.