Oxygen deficiency is defined as an oxygen level less than what percentage by volume?

Oxygen deficiency is defined as an oxygen level below 19.5% by volume. This threshold is significant in various safety and health regulations, including those set by organizations like the Occupational Safety and Health Administration (OSHA). Human beings generally require an oxygen concentration of about 19.5% to maintain normal physiological function, and levels below this can lead to symptoms of hypoxia, where the body's tissues do not receive sufficient oxygen.

At concentrations below 19.5%, individuals may begin to experience impaired cognitive and physical abilities, which can pose serious risks in environments where oxygen levels can fluctuate. This definition helps identify conditions that might require precautionary measures, such as the use of breathing apparatus or other safety equipment in confined or poorly ventilated spaces.

The other options, while related to oxygen levels, do not represent the recognized threshold for oxygen deficiency. Hence, 19.5% is a vital figure to understand in terms of workplace safety and health standards regarding oxygen levels.