from FireMedic8:

HOW TO PROTECT YOURSELF & FAMILY FROM HARMFUL EMS COVID POLICIES

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CDC is a Public-Private Partnership
https://www.cdc.gov/partners/pdf/P3_External_Fact_Sheet.pdf

OSHA Definition;

Oxygen deficiency means that concentration of oxygen by volume below which atmosphere supplying respiratory protection must be provided. It exists in atmospheres where the percentage of oxygen by volume is less than 19.5 percent oxygen. Oxygen deficiency means that concentration of oxygen by volume below which atmosphere supplying respiratory protection must be provided. It exists in atmospheres where the percentage of oxygen by volume is less than 19.5 percent oxygen.

1910.134(i)(1)(ii)(A)
Oxygen content (v/v) of 19.5-23.5%
1910.134(i)(1)(ii)(D)
Carbon dioxide content of 1,000 ppm or less