Respiratory Protection for Oxygen Deficient Atmospheres

This article describes several aspects of oxygen (O₂) deficiency with an emphasis on respirator programs and respirator selection. The Occupational Safety and Health Administration's (OSHA) 29 CFR 1910.134 and ANSI/ASSE Z88.2-2015 (Z88.2) have much in common. However, their exposure criteria and terminology used for describing levels of O₂-deficiency and the approaches to assessing O₂-deficiency differ. These differences can have a significant impact on an employer's respirator program and respirator selections for workplaces at altitudes above sea level. Under certain circumstances, Z88.2 leads to a more conservative respirator selection than OSHA because its O₂-deficiency criteria and hazard assessment approach relies directly on partial pressure of oxygen (PO₂) at all altitudes. Z88.2 defines an O₂-deficient atmosphere as either immediately dangerous to life or health (IDLH), or non-IDLH based on the atmosphere's PO₂ and defines respirator selection for these two O₂-deficient atmospheres. Unlike Z88.2, OSHA does not directly access the biologically significant aspect of an atmosphere's PO₂ in its hazard assessment. OSHA defines an O₂-deficient atmosphere based upon a percentage of oxygen. OSHA does not use the term "O₂-deficient IDLH"; however, OSHA considers any atmosphere with less than 19.5% O₂ as IDLH and defines respirator selection for IDLH atmospheres. Although OSHA does not use the term "PO₂" in their respirator standard, OSHA's exceptions to O₂-deficient IDLH respirator selection policy are based on PO₂ altitude-adjusted, O₂ percentage criteria. This article provides descriptions of OSHA and Z88.2 requirements to evaluate workplace oxygen deficiency, their approaches to O₂-deficiency hazard assessment, and describes their significance on respirator programs and selections. Alternative solutions to wearing respirators for protection against O₂-deficiency resulting solely from high altitudes are also discussed. Selection and implementation of alternative solutions by the employer and their Physician or other Licensed Health Care Professional (PLHCP) are not covered by either respirator standard. Appendix A provides information about the physiological effect of wearing respirators and the mechanics of respiration, which is an important consideration in lower O₂ atmospheres.