Respirator Protection Factor Calculator

Work out respirator protection factor instantly with clear inputs, formula shown and shareable results.

About Respirator Protection Factor Calculator

The hazard ratio, ambient concentration divided by the exposure limit, is the minimum protection factor a respirator must provide. Assigned protection factors are 10 for a half mask, 50 for a full face with particulate filters, and 1000 or more for a powered or supplied air hood. The concentration inside the facepiece is ambient divided by the assigned factor.

Formulas

Required protection

Required APF = ambient concentration / exposure limit

Inside concentration

Inside = ambient / assigned protection factor

Worked example

With the default values below, Respirator Protection Factor Calculator returns Protection factor required of 25.00. Change any input above and every figure here is recalculated in your browser.

Inputs used

Ambient concentrationminimum 0 ppm: 250 ppm
Exposure limitminimum 0.001 ppm: 10 ppm
Assigned protection factor of the respiratorminimum 1: 10

Results

Protection factor required: 25.00
Concentration inside the facepiece: 25.000 ppm
Provided over required protection: 0.400
Adequacy: Insufficient — select a higher assigned protection factor

Step by step

1Values used
2Required protection
3Inside concentration
4Protection factor required= 25.00
5Concentration inside the facepiece= 25.000 ppm
6Provided over required protection= 0.400
7Adequacy= Insufficient — select a higher assigned protection factor

Assumptions and limits

The result is derived only from the 3 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to 3 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
Preliminary estimate only. Respiratory protection must be selected under a written programme with fit testing, medical clearance and cartridge change schedules as required by your regulator.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Preliminary estimate only. Respiratory protection must be selected under a written programme with fit testing, medical clearance and cartridge change schedules as required by your regulator.

Frequently Asked Questions

How is the Respirator Protection Factor figure worked out?

Required APF = ambient concentration / exposure limit. The hazard ratio, ambient concentration divided by the exposure limit, is the minimum protection factor a respirator must provide.

Does a higher APF always solve the problem?

No. Above the immediately dangerous to life or health level, or in oxygen deficiency, no air purifying respirator is acceptable regardless of its factor: supplied air or self-contained breathing apparatus is required.

What values do I need to enter?

This calculator takes 3 inputs: Ambient concentration, Exposure limit, Assigned protection factor of the respirator. The pre-filled defaults are a realistic worked example — replace them with your own site or project figures.