Some of the physical activities performed by Structure Maintainers - Group B and environmental conditions they experience are: crouching while working in confined spaces; walking along subway tracks, stepping over rails (including live third rails); ascending and descending from trains and catwalks to roadbeds; working on scaffolds and lifts; responding to audible signals such as alarms bells, train whistles, horns and radio conversation; responding to visual signals including distinguishing colored lights; using hand tools; lifting and carrying heavy tools and equipment; and working outdoors in all weather conditions. They install and repair cinder and cement blocks, and ceramic tile; install cement sidewalks and floors; install and repair gratings, ducts, manholes, drains and sewers; mix mortar and concrete, and pour concrete; load, unload and drive motor vehicles; walk and work along tracks and perform flagging duties; and perform related work.