(Yicai Global) Sept. 20 -- Hebei's Tangshan, China's major steelmaking city, has changed its environmental protection policy to liberate less-polluting steel firms from earlier restrictions and allow them to ramp up production. >The city's government will classify local steel companies into four groups based on their emsions, transport of raw materials and products, and added value of products, the policy statement shows. Those put into the least polluting A group will face no suspension in production th autumn and winter.Type B firms must sit idle for 30 percent of the time during the winter heating peak between October and March. Th goes for 50 percent of the time to type C and 70 percent for type D.In recent years, China's government has stepped up measures to control air pollution, which usually peaks during the winter heating season from mid-November to mid-March in northern China. Heavy steel production, which uses coke as its raw material, one of the reasons behind the smog.The earlier restrictions that went across the board were denounced by industry peers. The one-size-fits-all approach dcourages the companies from transforming their product structure and upgrading their equipment to more environmentally friendly versions, Fan Xiaohua, a steel analyst from JLC Network Technology, told Yicai Global.It rumored that five firms in Tangshan can meet the type A requirements, but it will take them about two years to re-vamp their equipment to the ultra-low emsion standard, Fan said. Most firms are types B and C, the analyst added.The city of Linfen required Shanxi Coking, China's major coke producer, to start production limitations early th month, which was one month earlier than last year, the Shanxi province-based firm said last week.