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What Is a Confined Space? Definitions and Characteristics

A valve vault is a classic confined space — accessible through a narrow manhole, large enough to work inside, but not built for regular occupancy [S6].
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A valve vault is a classic confined space — accessible through a narrow manhole, large enough to work inside, but not built for regular occupancy [S6].
CRITICAL: Never assume a confined space is safe based on past experience or appearance alone. A worker in Montana died after entering a valve vault that 'always had normal air' — without testing the atmosphere first. The vault was oxygen-deficient. Always evaluate every entry independently [S2].
Use a decision-tree approach when evaluating any space: First, does it meet all three confined space criteria? If yes, then assess for PRCS hazards (atmosphere, engulfment, configuration, or other serious hazards). Document your findings — OSHA requires employers to evaluate workplaces and inform employees of permit space existence, location, and hazards [S5][S6].
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