What level of oxygen deficiency is considered to be below normal?

Oxygen levels in the atmosphere typically hover around 20.9%. A level considered below normal would generally be recognized at anything below that baseline. Specifically, 19.5% oxygen concentration is the threshold often used in safety regulations and guidelines. Below this level, individuals may experience physiological effects due to oxygen deficiency, which can impair cognitive functions and physical performance.

In many occupational and safety contexts, 19.5% is the point at which precautions become necessary to ensure the health and safety of workers potentially exposed to low oxygen environments, such as confined spaces. Therefore, selecting 19.5% appropriately identifies it as the level indicating a concern for oxygen deficiency, aligning with established standards and safety protocols in various industries related to CAL FIRE's operations.