confined space

OCCUPATIONAL MEDICINE, PUBLIC HEALTH

Definition An occupational health term of art for a vertically or horizontally limited access space in which an employee carries out a specified task.

Examples, confined spaces Boilers, furnaces, manholes, pipelines, pits, vessels, sewers, silos, storage tanks, and utility vaults.

Half of confined space deaths—hundreds of workers die/year in the US—occur in would-be rescuers; because of the risks associated with working in confined spaces, OSHA has proposed regulations (29 CFR 1910.146)  governing how employees should work in such spaces.   

Reference http://en.wikipedia.org/wiki/Confined_space