Respirator Selection Calculator

Hazard ratio measures how many times the Airborne concentration exceeds the OEL for a specific chemical hazard, which is entirely independent of atmospheric oxygen content -- Oxygen level instead triggers a separate override that requires at minimum a supplied-air respirator whenever oxygen drops below 19.5%, regardless of what the Hazard ratio calculation shows.

OSHA's Table 1 assigns the same numeric Assigned Protection Factor to several different respirator classes -- for example, a half-mask air-purifying respirator and a supplied-air respirator in demand mode both carry an APF of 10 -- so this calculator names one verified example per required tier rather than listing every type that happens to share that APF.

When Airborne concentration reaches or exceeds the IDLH concentration you enter, this calculator overrides whatever the Hazard ratio and Required APF calculation would otherwise suggest and requires full-facepiece pressure-demand SCBA, because IDLH atmospheres pose an immediate threat to life and only that respirator class is rated for entry under OSHA's standard.

Maximum Use Concentration (MUC) is the Required APF multiplied by the OEL -- theoretically the highest concentration the selected respirator can protect against -- but this calculator caps Effective MUC at the IDLH concentration whenever one is entered, because a respirator should never be relied on above the concentration considered immediately dangerous to life or health, even if the APF math alone would suggest it's adequate.

It doesn't verify respirator fit testing, medical clearance, or training compliance, doesn't account for multiple simultaneous contaminants or their combined effects, and doesn't replace the qualitative and quantitative exposure assessment a qualified industrial hygienist performs under a full written respiratory protection program as required by 29 CFR 1910.134.