Zhejiang Shuangyang Fan (浙江双阳风机股份) manufactures fans, dampers and silencers across four lines — building services, metro and tunnel, nuclear and industrial — from three plants in Shangyu District, Shaoxing. Its fire and smoke dampers are UL Listed under file R39146 in category EMME, the classification covering dampers for fire barrier and smoke applications tested to ANSI/UL 555 and UL 555S. The company reports more than three hundred and thirty fan and damper product types and over fifty patents, with reference projects across airports, hospitals, utility tunnels and metro systems.