The cartilage rings are C-shaped because the back of the trachea presses against the esophagus. The cartilage opens at the esophagus and is replaced by connective tissue and muscle. This gives the esophagus space to allow food to be swallowed easily. The rings of the trachea are stacked one on top of the other, with a small space between them.
In 2014, a survey of the Australian working population revealed that the most common carcinogenic exposures in the workplace were solar ultraviolet radiation, diesel engine exhaust, environmental tobacco (second-hand) smoke, benzene, lead and silica.
It is estimated that 558,000 workers are potentially exposed to Cr(VI) in the United States. Workers in a variety of occupations are potentially exposed to Cr(VI). Workplace exposures occur mainly in the following areas: Welding and other types of hot work on stainless steel and other metals that contain chromium.