Lehigh Portland Cement Co., Union Bridge, Maryland A comprehensive system of engineered noise controls was installed throughout Lehigh Portland Cement's Union Bridge plant over several years. The system reduces individual noise levels by as much as 20 dB, doubling and tripling permissible employee noise exposure times. Sound level meters with octave band analyzers were used to identify high-noise equipment and prioritize problem areas. Then, controls were engineered and installed. Rubber decks were placed in crushing department screens, reducing noise 5 dB. Noise barriers and sound-absorbing curtains were hung beside raw, finish, and coal mills, reducing noise 10 to 12 dB. Hardware was used that lets curtains hang in place, but swivel or slide out of the way for maintenance access. Compressor rooms were lined with absorbent material to stop noise reflection, and openings were closed with acoustical doors. Silencers were installed in fan-exhaust and HVAC ducts, reducing noise levels 5 to 10 dB. Also, some exhausts were reoriented to direct noise away from buildings and neighbors. Blowers were retrofitted or purchased with inlet and outlet silencers, and others were enclosed in noise barriers, reducing noise levels 14 to 20 dB. High-torque drives were changed to quieter helical offset tooth drives. Scores of bin vibrators were changed to quieter models. Acoustical booths for operators were installed to provide quiet areas in the midst of equipment. In the laboratory, the vacuum unit for the Alpine fineness apparatus and a rotary sample grinder were enclosed in cabinets, reducing noise levels 22 and 15 dB, respectively. Mobile equipment with cab air conditioners also was purchased.