Filtration Efficiency Claims: Misleading?
By Reinhard Schuetz, P. Eng.
February 2020

Simply put... a substantial number of published efficiency claims related to mechanical/fibrous filtration technologies (eg: HEPA filters) seem to be ‘misleading’, ‘inconsistent’ and/or ‘irrelevant’ compared to actual long-term filter effectiveness.
Manufacturers undoubtedly try adhering to regulatory (eg: ASHRAE - American Society of Heating, Refrigerating and Air-Conditioning Engineers) stipulated test specifications, such as requiring HEPA (High Efficiency Particle Air) filters to achieve 99.97% particle capture down to 0.3μm (PM 0.3). Yet, there is also no guarantee some fiber spacings don’t actually exceed 0.3 μm.

Noticeably, in addition to vendors focusing their advertising on 99.97% ‘laboratory’ efficiency rating, they quite often also claim mitigation of harmful organisms and toxic chemicals. This leaves the general public, as well as various institutional users (eg: Health Care Systems; Travel Industries; etc.) with the likely impression that such filters can eliminate ‘all contaminants, all the time’ with 99.97% efficiency.
This is potentially very ‘misleading’, as well as ‘inconsistent’ with published academic studies and regulatory agency reports, since viruses and chemicals can respectively be up to about 50x and 3,000x smaller compared to expected 0.3μm fiber spacings.

Filter Research Findings
In comparing HEPA filter advertised efficiency claims to independent research and regulatory documents, a ‘disturbing eye-opening’ pattern becomes evident – essentially that the presented, or sometimes even ‘absent’, marketing information is ‘misleading’ in relation to actual day-by-day and/or long-term operational effectiveness of the device.

  • According to a Clemson University (2002) report, “As most testing is performed in a laboratory with synthetic dust, the classification does not always provide a reliable basis for the estimation of a filter’s life or its performance in actual applications.” Also, “extensive field-testing and real-life tests ... show that laboratory tests do not predict the performance of filters over their whole service life.”
  • In addition, the Clemson study also stated that “test dust used in the ASHRAE 52.1 test standard is of an entirely different nature from atmospheric dust, the dust that a filter would normally be exposed to in real-life situations. The ASHRAE dust is made up of much larger particles than those present in the atmosphere;”
                                                                             
Another factor taken into consideration in the Clemson study is that “test conditions in the laboratory are controlled and are conducted for a reasonably short period of time. They (filters) are not subjected to the environmental and temporal conditions that a filter would be subjected to in actual testing conditions.”

ASHRAE Research Project RP-1649 (2019) found that, based on MERV 8-14 filters, “The same (type of) filter performed very differently in different homes...”
The ASHRAE Research Project also explained that “specifying a filter with a certain efficiency from a laboratory test is not a guarantee that you will actually get that performance when the filter is installed ...” and thus, filter “performance can’t be extrapolated from laboratory tests alone.”

In addition, the ASHRAE Research Project noted that “Efficiency is important, but what we really care about is the overall performance of the filter” and “One way of measuring performance is to consider the effectiveness of the filter.” Median effectiveness for the filters tested over the project period amounted to 30%.

ASHRAE Position Document (2018) outlines numerous features of  ‘mechanical’ and ‘sorbent’ filters related to ‘capturing’ contaminants:
  • Particle filtration systems, using mechanical filters, can reduce indoor air-bone concentrations of particles by removing them from the airstream but not by inactivating infectious species;
  • Model assumptions and inputs have a high level of uncertainty; 
  • There are no strong studies empirically documenting that filtration reduces respiratory infections;
  • Sorbent filters typically entail either physisorption (adsorption) or chemisorption (absorption) methods to capture gases, but they  not capture all contaminants equally;
  • Due to weak sorbent forces of attraction, gases once ‘adsorbed’ can later desorb back into the airstream (ie:              creating atmospheric contamination);
  • Chemicals added to ‘absorption’ filters need to be more or less specific for individual contaminants;
  • At present, almost no empirical data are available to enable drawing conclusions about the health benefits of using sorbents, based on long-term effectiveness related to mixtures of contaminants at low level concentrations;
  • Nearly no documents exist regulating and necessitating examination of long-term performance of filtration and air cleaning devices.
The Research Council of Norway(1995) found that the filter “efficiency of electrostatically charged synthetic media fell significantly right from the start and did not improve much with service. From this work it can be stated that lifetime and in situ testing of filters clearly point out the fact that the challenge dust and testing conditions must correlate more closely to the environment to which the filters would be exposed in actual use.”
  • FAA’s Civil Aerospace Medical Institute (2015) specifically states that “HEPA filters, by definition, are designed to capture particles but not gases and vapors, which pass directly through...”. “Aerosols collected via HEPA filters include dusts, fibers, bacterial cells, fungal spores, and pollen grains.”
  • In addition, the Medical Institute clarifies that “Viruses are among the smallest of microorganisms, ranging in size from 0.02 to 0.3 μm in diameter and are thus too small to be captured by HEPA filters. Likewise, fumes are generally less than 0.05 μm in diameter (Hinds, 1999) which are also too small to be captured via filtration.”

CONCLUSION
Existing mechanical and sorbent filter advertisements are typically ‘remiss’ in providing information related to how 99.97% particle capture efficiency is actually achieved. Offering filter marketing claims, either through data ‘unrelated’ to real-life operating conditions or via ‘absence’ of relevant critical test details, leaves consumers without proper evaluation criteria to make an informed decision regarding overall long-term filter effectiveness.

SUMMARY
With respect to unfiltered jet engine ‘bleed air’, or regular outside air, entering an airplane, other prior studies reported evidence of finding related particulate matter and toxic contaminants on interior ventilation duct and fuselage surfaces. This would imply that ‘human lungs’, not mechanical devices, are the main critical ‘first line of defense’ against harmful contamination on airplanes! Variations of upgraded HEPA filters have been used for recirculated air on airplanes for decades; however, ‘fume events’ and ‘health issues’ have remained a regular occurrence.

In addition to the aforementioned studies and reports considering mechanical and sorbent filtration devices to be only somewhat effective at trapping harmful contaminants, filtration of re-circulated mixed bleed and/or outside contaminated air can thus only be expected to provide minimal improvement of overall air quality within occupied airplane compartments. Yet, patented alternative pollution control technology, capable of simultaneously destroying air-borne harmful organisms and toxic chemicals, is presently available.

More articles by Reinhard Schuetz/Eng.  HERE

©2020-Author:
Reinhard Schuetz, P. Eng.
Calgary, Alberta,
Canada