June 13, 2024 / Dylan Staack

Overcoming the Challenges of HEPA Filtration in Commercial Buildings: Enhancing CNC Respirator Fit Testing

Sponsored by OHD.

High-efficiency particulate air (HEPA) filtration systems in commercial buildings can make condensation nuclei counting (CNC) fit testing using ambient aerosols difficult. HEPA filters are designed to remove 99.97 percent of particles in the air that are 0.3 microns or greater. These particles include dust, pollen, mold, bacteria, and viruses. HEPA filters are a cost-effective option for increasing or maintaining air quality and helping to keep environments clean enough for specific practices. Unfortunately, CNC fit testing is not one of those practices.

CNC fit testing is the practice of counting particle concentrations inside and outside a respirator to determine if the respirator seals on a fit-test subject. According to the theory of CNC fit testing, if both the concentration of particles in the air and the efficiency of the respirator filter material are known, then a comparison of the particle concentration inside and outside the respirator can be executed to determine if the respirator fits the test subject in a protective manner. If a respirator is protective, it will seal to the user's face, filter particles, and reduce particle concentrations in the respirator to at least 100 times lower than ambient concentrations. If the respirator were to leak, the particle concentration in the respirator would increase, and the comparison ratio of concentrations (and, therefore, the fit factor) would be less than 100.

For CNC fit testing, the test agent is aerosolized particles. To ensure a valid test, it is imperative for the particle concentration in the test environment to be high enough to complete an accurate comparative analysis. In fact, a minimum of four comparative analyses need to be completed to accurately execute a fit test. When tests are conducted in buildings with HEPA filtration, achieving the necessary particle concentration in the test environment can be challenging.

To ensure the test environment is filled with particles, CNC fit-test machine manufacturers have recommended the use of particle generators. This practice requires the user to assess the particle concentration in the room using the machine. Next, the test administrator decides whether more particles are needed and how many to generate, continually checks the particle concentration in the room, and manages the concentration by adjusting the particle generator. Administrators have felt that this is a cumbersome process. Often, particle generators are turned on to the highest setting and never adjusted. The result is an environment flooded with particles. Concentrations in these environments often exceed manufacturer recommendations and can cause clogging of the instrument.

The AeroFit by OHD is the newest CNC fit-test machine on the market. The AeroFit is designed to enhance and simplify the user experience. It includes features that help make it the most efficient and easiest-to-use CNC fit-test machine on the market. These features will reduce long training sessions on particle generation and management, as well as improve instrument setup, operation, and testing. Setup and daily verification are also greatly improved through the user interface and specific guidance on machine setup for each day of testing. The AeroFit simplifies the process of CNC fit testing and ensures that the process is fast, accurate, and easy to execute.

More information on the AeroFit is available from the OHD website.

Dylan Staack

Dylan Staack is an industrial hygienist and the technical applications and development manager at OHD.


There are no submissions.

Add a Comment