29 CFR 1910.146 Paragraph (d)(2)(iii) of the Respiratory Protection Standard

“Human beings must breathe oxygen . . . to survive, and begin to suffer adverse health effects when the oxygen level of their breathing air drops below [19.5 percent oxygen]. Below 19.5 percent oxygen . . . , air is considered oxygen-deficient. At concentrations of 16 to 19.5 percent, workers engaged in any form of exertion can rapidly become symptomatic as their tissues fail to obtain the oxygen necessary to function properly (Rom, W., Environmental and Occupational Medicine, 2nd ed.; Little, Brown; Boston, 1992). Increased breathing rates, accelerated heartbeat, and impaired thinking or coordination occur more quickly in an oxygen-deficient environment. Even a momentary loss of coordination may be devastating to a worker if it occurs while the worker is performing a potentially dangerous activity, such as climbing a ladder. Concentrations of 12 to 16 percent oxygen cause tachypnea (increased breathing rates), tachycardia (accelerated heartbeat), and impaired attention, thinking, and coordination (e.g., Ex. 25-4), even in people who are resting.

At oxygen levels of 10 to 14 percent, faulty judgment, intermittent respiration, and exhaustion can be expected even with minimal exertion (Exs. 25-4 and 150). Breathing air containing 6 to 10 percent oxygen results in nausea, vomiting, lethargic movements, and perhaps unconsciousness. Breathing air containing less than 6 percent oxygen produces convulsions, then apnea (cessation of breathing), followed by cardiac standstill. These symptoms occur immediately. Even if a worker survives the hypoxic insult, organs may show evidence of hypoxic damage, which may be irreversible (Exs. 25-4 and 150; also reported in Rom, W. [see reference in previous paragraph]).

OSHA further states the following:

“In some cases, respirator use itself can cause illness and injury to employees. There are a number of physiological burdens that are associated with the use of certain types of respirators. The weight of the respirator, breathing resistances during both normal operation and if the air-purifying element is overloaded, and rebreathing exhaled air from respirator "dead space" can all increase the physiologic burden of respirator use (Exs. 113, 22-1, 64-427). Job and workplace conditions, such as the length of time a respirator must be worn, the level of physical exertion required of a respirator user, and environmental conditions, can also affect the physiological burden (Exs. 113, 64-363). In addition, workers who wear glasses or hearing aids may have problems achieving appropriate fit with some respirator face pieces.”

Atmospheric air contains 20.95% oxygen. OSHA has provided regulations when wearing a respirator and state when the oxygen content drops below 19.5%, it is harmful to the human body. A 19.5% oxygen content is only a 1.45% drop in oxygen from atmospheric O2 content. Again, OSHA states:

“. . . rebreathing exhaled air from respirator "dead space" can all increase the physiologic burden of respirator use (Exs. 113, 22-1, 64-427).”

Human exhale contains 84 percent non-breathable gases. How much exhale is trapped in the dead space of a face mask that is breathed back into the lungs and the effects of its physiologic burden? It’s deleterious extent? Duration?

Thanks for this info!

And you can tell it affects oxygen levels five minutes after you put a mask on.