Sport Science

FACEMASK TESTING

           We have invented a new way to measure the penetration efficiency of a (respirator or surgical) face mask.  It has a number of advantages over the currently used measurement systems in which a stationary mask is impacted with a moving aerosol during which the upstream and downstream particle concentrations are compared.  The equivalent system described here instead moves a mask through a stationary aerosol in a closed chamber and compares the particle concentrations before and after the movement of the mask.  Other things (such as particle size and concentration) being equal, moving a mask through an aerosol chamber at a given speed is physically equivalent to moving the aerosol onto the mask at the same speed, and the mask efficiency measured either way will be exactly the same.  This system provides many advantages, including greater simplicity, greater accuracy, an exact constant aerosol flow speed through a mask, more easily made concentration measurements, more realistic impacts, more controlled averaging, the absence of the need for preliminary impacts during flow stabilization, and a much lower cost.  A prototype of the system has been fabricated and the data obtained from this prototype were analyzed and used to demonstrate the consistency and repeatability of thesystem.

          The current mask testing standards (ASTM F2299, CDC-NIOSH 42 CFR 84) and the most popular testing system (TSI Model 8130, with a 245-page operating manual) are extremely complicated, and we have not seen any independentinvestigation of how accurate or repeatable the testing is.  We believed that it was unnecessarily difficult to test masks by forcing a moving aerosol onto them and that it would be much easier and more controllable to instead test a mask by moving it through a stationary aerosol, so we proceeded to design a new measurement system based on that idea.  We quickly obtained a patent (US 11,215,548) and had a prototype of the system designed and fabricated by our partner LexDesigns.  The penetration measurements we made using this device were very encouraging and so we proceeded to design and construct a more compact automated version.  This portable device will be sufficiently inexpensive and easy to operate that it could be used almost anywhere to ensure that available masks are effective in reducing the inhalation of airborne pathogens. 

          There is a need for such a compact device because it is currently extremely difficult for the user of a face mask to know for certain if that mask is actually effective in providing protection from the inhalation of airborne pathogens present in his local environment.  It has been widely reported that many commercially-available N95, KN95, and surgical masks are in fact almost-useless fraudulent products, even if the mask carries a label from a reputable US manufacturer.  Masks can be evaluated using the current technology only by a limited number of laboratories, and the testing is expensive and it can take weeks to receive test results.  Our greatly simplified testing technology will solve this problem by enabling the placement of highly accurate, portable, inexpensive testing devices in any location with accessible electrical power.  These devices will be simple to operate and can be used by almost anyone to determine if an available mask is sufficiently protective.  The currently available testing devices are much too large, expensive, and difficult to operate and maintain for such widespread use. 

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In the existing testing protocols, efficiency is evaluated by impacting the mask or material with an aerosol containing colloidal particles that are carried in air onto the mask material at a specific airflow velocity, and measuring the particle concentration upstream from the material (before) and also downstream (after). The penetration ratio R (the ratio of the downstream concentration to the upstream concentration) determines the filtration efficiency E = (1 – R)·100%.  To effectively determine and compare efficiencies, the moving particle concentration and the upstream and downstream airflow velocities must be accurately measured and maintained, and the upstream and downstream particle counters must be carefully coordinated and must be able to function accurately in a moving air stream.  This requires the incorporation of sophisticated and expensive laboratory equipment, including compressors, pumps, condensers, pressure reducers, flow valves, and flowmeters.  (See Figure 1 in the ASTM F2299 Standard.)  Apart from the specific issues described below, the extreme complexity of this measurement system alone gives rise to many possible sources of error.  Our alternative measurement system is much simpler, and potentially more effective and accurate, than those currently in use.  The system has  many other advantages, including the following:

 1.     The speed of a moving mask holder is easy to precisely set and maintain (e.g., by using an electric motor) and can be sustained with great accuracy.  Measuring and maintaining an aerosol flow speed is, on the contrary, much more difficult, requiring pumps, control valves, flowmeters, etc.  And even when using all this equipment a speed variation of ±2.5% is allowed.

2.     In a moving aerosol, particle concentration and stability are difficult to maintain, requiring specialized valves and regulators.  Constant concentration is automatic in a stationary aerosol.

3.     Only one particle counter is required.  The moving aerosol systems require two. 

4.     It is easier and more accurate to measure the particle concentration in a stationary aerosol than in a moving one.

5.     The current systems simultaneously compare the impacting particle count (measured upstream of the mask) with the penetration particle count (measured downstream of the mask) even though the penetration particle volume came from a previously encountered impacting volume.  In the new system the impacting particle count and the penetration particle count are made on the same chamber volume.

6.     The current systems require that, before penetration data are taken, the mask material be impacted during a preparation time in order for the aerosol concentration to stabilize.  This means that the testing does not measure the efficiency of a new mask but rather one that has been exposed for a period of time to a steady stream of particles.  In the alternative system new mask material can be impacted immediately after the material is installed. 

7.     The current systems are expensive to purchase and maintain.  The new system will be significantly less expensive and require only routine maintenance.

8.     Current systems require the continuous introduction of salt particles during each test, whereas the new system requires only a one-time introduction of salt particles into the closed chamber.  Only 0.01g of NaCl in 100ml of H2O will be sufficient for about 500 tests.  

9.     Current systems provide outputs, typically stated as a three-digit percentage (for example, 95.3%), obtained by averaging a sequence of measurements, with no indication of the spread of the individual measurements (standard deviation) or of the (systematic) accuracy errors. (Random uncorrelated errors are reduced by averaging but systematic errors are not.  The accuracy claimed by particle counters alone is ±5%.) Taking these spreads and inaccuracies into account, the scientifically appropriate way to present an output would include an error range (for example, 95% ± 7%).  The new system’s outputs will be in this scientifically correct form, if desired, but with smaller spreads because of increased accuracy. 

10.  With current systems, efficiency measurements are made on a mask exposed to a moving aerosol at a sequence of increasing times, and the average of these measurements is presented as the efficiency value.  However, a measurement made at a later time will obviously take place after the mask has been exposed for a longer period of time, during which the mask will have absorbed additional particles, possibly changing (usually increasing) the efficiency value.  This can introduce a systematic error into the measurements (made at different times) that cannot be reduced by averaging.  This type of error is not present in the new system, and if averaging is used as an option to reduce random errors, the average is taken over measurements made on the same aerosol volume remaining after the movement of the mask.

          An example of the proposed system consists of a closed (say) horizontal cylindrical aerosol chamber within which is a concentric cylindrical shuttle that is effectively sealed but can slide back and forth.  The shuttle has an open central cavity across which the mask material to be tested is attached, and has a low-friction coating, such as Teflon, as it’s outer surface.  The shuttle is propelled by an electric motor that rotates a horizontal threaded rod that engages a matching threaded hole in the shuttle.  When the motor is engaged, the rotation of the attached rod causes the shuttle to move forward in the horizontal direction at a chosen speed.  An aerosol generator and a particle counter are connected to the chamber.  The system is illustrated schematically in Figure 1, and a prototype of the system, designed and fabricated by LexDesigns, is illustrated in Figure 2.

          Using the prototype, we have tested a large number of mask materials in order to provide a proof-of-concept and to demonstrate the viability of the testing system described herein.  The values of the measured mask efficiencies demonstrate that the concepts introduced are effective in providing a mask testing system that is simpler to use and maintain then the systems currently in use.  The acquired data confirm that the new testing system provides consistent and repeatable results, and has all of the advantages listed above. 

Given the well-documented widespread presence of poorly performing face masks on the market, often falsely labeled as being 95% efficient, the utility of an accurate and low-cost testing device cannot be overstated.    The system described above is very inexpensive and simple to use, so that a compact version of it would be suitable for on-premise testing.  These portable devices could be widely deployed almost anywhere.  A prototype of a such a compact version of our system has been designed and fabricated by LexDesigns.  Any mask material can be easily tested by this fully automated device by placing it within a simple holder, screwing the holder together, inserting the holder unit into the device, and pushing a start button on an attached touch screen.  The penetration efficiency of the mask as a percentage will then be displayed on the touch screen within a few minutes.

SANITIZER CONTENT TESTING

We have invented a simple and inexpensive device that measures the relative percentages of two ingredients of different densities combined in a liquid. (For example, measuring the alcohol or hydrogen peroxide content of a hand sanitizer.)  The measurement proceeds by pouring a volume of the liquid into a specialized tubular container in the device, after which the percentage of an ingredient is digitally evaluated and displayed. 

            Products are sold that are a mixture of several simple substances.  Typically, such products often define the percentage of each substance within the mixture.  Further, in order for some mixtures to be effective, the concentration of one of the substances within the mixture may need to be at least a certain percentage in order to achieve the proper level of efficacy.  One such example is hand sanitizer, wherein the concentration of alcohol within the hand sanitizer needs to be at least a certain percentage in order for the hand sanitizer to be effective.  Unfortunately, there really is currently no simple way of quickly determining such concentrations within a mixture, as specialized and/or expensive equipment often needs to be utilized.

Our invented device solves this problem.  The composite liquid is poured into a vessel with a specialized cap.  The vessel is then inserted into the device and the percentage of the relevant ingredient is immediately displayed on a digital screen.  The current prototype is designed to measure concentrations of either Ethanol Alcohol, Isopropyl Alcohol, or Hydrogen Peroxide. 

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Consider a mixture of two liquids (or granular solids) of unequal densities d1 and d2.  The fractions f1 and f2 = 1 - f1 of each liquid in a given volume V of the mixture can be determined by measuring the weight W of the mixture.  The volumes V1 and V2 = V – V1 of the liquids in the mixture satisfy f1 = V1/V and f2 = V2/V and are related to W by

                                    W = d1V1 + d2V2 = d1V1 + d2(V – V1)

so that

                                    W/V = d1f1 + d2(1 – f1).

Solving for f1 gives the formula for f1 as a function of the measured weight W for given values of V, d1, and d2:

                                    f1 = (W/V – d2)/(d1 – d2).

For example, if the liquids are ethanol alcohol (d1 = 0.79 g/cc) and water (d2 = 1.00 g/cc), and V = 25 cc, then the fraction of alcohol in the mixture is given by

                                     f1 = (1.00g/cc - W/25cc)/(0.21g/cc).

If the measured weight W is 20.00g, then f1 = 0.95, and if W = 22.00g, then f1 = 0.57.

If a third substance (density d3 and fraction f3) is in the mixture, then the liquid 1 fraction is

                                   f1’ = (W/V – d2)/(d1 – d2) – (d3 – d2)f3/(d1 – d2).

 The correction is small if d3 – d2 and f3 are small.  The fraction ratio

                          f1’/f1 = 1 - (d3 – d2)f3/(W/V – d2).

 W can be measured using a scale accurate to 0.001 g. V can be set using a test tube with the volume V indicated by a horizontal line, or, more accurately, using a tube with a screw- on cap with a small vertical exit spout.  These are illustrated in Figure 1.   

A prototype of this concentration measurement invention has been designed and fabricated by LexDesigns.  It includes a vessel for receiving a pre-determined volume of the mixture of two substances of known densities, and a measuring scale for determining a weight of the known volume of the mixture.  It also includes a display system for displaying an indication of the concentration of at least one of the first and second substances, wherein the display system is configured to display a binary indication of the concentration of at least one of the first and second substances.