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Frequently Asked Questions

What is a Harmonic Mean (such as Harmonic Mean Fit Factor aka HMFF) and why does it keep showing up?

The harmonic mean of a set of numbers is the reciprocal of the arithmetic mean of the reciprocals of the numbers in the set. In excel, you can get it by typing "=HARMEAN(" and selecting your set of individual exercise fit factors. Here are some reasons HM shows up so often.

Mathematical - The harmonic mean is mathematically appropriate for averaging rates or ratios. In fit testing, the fit factor represents a ratio of ambient particle concentration to particle concentration inside the respirator, making the harmonic mean a natural choice for averaging these ratios while maintaining mathematical coherence.


Statistical Robustness - The harmonic mean is less sensitive to extreme values compared to other means like the arithmetic mean. In fit testing, where fit factors can vary widely between individuals and testing conditions, the harmonic mean provides a more robust measure of central tendency, reducing the impact of outliers on the overall fit factor calculation.


Compatibility with Worst-Case Scenario - Fit testing aims to assess the worst-case scenario in terms of respirator fit, ensuring adequate protection for respirator users in a variety of conditions. The harmonic mean, by giving more weight to lower fit factor values, reflects this worst-case scenario more effectively than other means, aligning with the conservative approach to respiratory protection.


Conservative Estimation - The harmonic mean tends to be smaller than the arithmetic mean, especially when there are large discrepancies between values. In fit testing, this conservative estimation helps ensure that the calculated fit factor represents a more stringent assessment of respirator performance. 

What are resilience tests?

Resilience Tests or ResTests ests are protocols(such as Ground Truth, Crown Jewel, Extended Tests, Crash2.5, Warhammer) that have an emphasis on longer duration test sessions or longer duration tests. It is more relevant to disposable masks as these are more likely to have structural changes throughout their lifetime, which is often a work day. See the Protocols tab in the main FTtP.xlsx file.

What is the ResTestThePlanet initiative?

ResTestThePlanet is an initiative to crowdsource comparative resilience tests and sets of conventional 8 exercise OSHA tests on a broad range of respirators in a hypothesis-free approach. It is primarily aimed at identifying disposable respirator models that are able to withstand measured and repeatable jaw motion on the largest proportion of the general public. It is therefore intentionally not constrained by specific size requirements on either the tester or the mask - anybody of any size can test on any respirator as long as it is in the default configuration in which it is found in the package, aside from nosewire adjustment. If multiple respirator sizes are available, contributors are encouraged to test every single size. Contributor size data is stored, but does not drive the selection process of which mask to test. The resulting dataset, when collected at scale, could be useful for selection of initial candidate respirators for QNFT. Results on modified respirators are also collected, although flagged with a different analysis code. This can be used for R&D in emerging niches but doesn't affect the main histograms.

Why is there so much emphasis on disposable masks compared to PAPRs and elastomerics?

Disposable respirator designs are advancing faster than elastomerics and PAPRs.

I have a Portacount or other CPC machine. How can I contribute to the dataset?

Email the above sentence to and we'll send a box with a standard set of controls!

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