Three numbers with different meanings
The APF belongs to a respirator type or class within a particular selection framework. A fit factor comes from a test of the seal between a facepiece and an individual. Filter efficiency describes another property: retention of the contaminant for which the filter was tested. A high number in one of these assessments does not replace the other checks or establish that the complete equipment is suitable.
Match protection to the exposure
Selection begins with the contaminants, their physical forms and foreseeable concentrations. The relationship between outside exposure and the applicable criterion helps identify the required protection within the relevant selection rules. Choosing the largest number in a catalogue is insufficient. Respiratory protection must also suit the task, duration, environment and other equipment worn by the worker, as well as the individual’s ability to use it correctly.
Why the reference country matters
APF tables are not universal. HSE describes the United Kingdom framework, while OSHA specifies values for the United States. Before adopting a value, check the applicable technical or regulatory reference and the complete respirator configuration. An APF from one table should not be combined with a class from another and accessories not approved by the manufacturer as a complete assembly. Record the basis used for selection.
Conditions behind the expected protection
An APF assumes appropriate selection, training, maintenance and correct use. Individual fit is essential where protection depends on a tight facial seal. Damaged straps, defective valves or an incompatible filter cannot be compensated for by a high factor on a product sheet. Observed defects require correction before use and should inform the respiratory protection programme. Reliable protection depends on the working system, not just the purchased device.
Limits the number cannot remove
An APF does not permit an air-purifying respirator in oxygen-deficient conditions or beyond its use limitations. Immediately dangerous atmospheres require specific selection criteria. Nor does the APF determine gas-cartridge service life. Retain the exposure assumptions, chosen reference, complete equipment specification and reasons for selection, so the decision can be reviewed when the substance, task or environmental conditions change. These checks complement measures to control contamination at source.
Equipment substitutions also need review. Replacing a half mask with a similar-looking model does not ensure the same assigned factor, filter compatibility or fit. The complete assembly should match the documentation used for selection and the equipment actually issued to each worker, including any accessories needed for the particular task.
