"The flying public needs to be armed with the facts and informed about the risks of cabin air transmission of viruses, bacteria and fungi that can cause illness," says Joe Lundquist, an airplane air filtration technology expert at Pall Corporation (NYSE: PLL). A new study published in Lancet concluded that the risk of transmission of infectious diseases in airplanes is not as great as people perceive it to be. The risk is low, even in aircraft that recirculate air, provided that the airplane is equipped with HEPA (High Efficiency Particulate Air) filters.
However, Lundquist points out that not all filters used by aircraft, even some designated HEPA, provide the highest level of microbial removal efficiency available today. In order to prevent the dissemination of infectious diseases, the filters must be able to stop microbes of all shapes and sizes on the first pass before they can be dispersed throughout the cabin.
HEPA is Not Enough
The efficiency standards for filters to be classified as HEPA can vary considerably. These standards, however, are based on chemical challenge tests, which do not simulate the removal of microorganisms and do not reflect a filter's true microbial removal efficiency. The most accurate way to determine whether a filter can remove microorganisms efficiently is with bacteria and viral challenge tests.
The reason is because of aerosol physics. Capturing a microscopic particle within a filter depends upon many interrelated factors, including particle size, shape, surface-to-mass ratio, electrical surface charges, surface tension and compressibility. For example, when a small particle comes into contact with the filter, whether or not the particle sticks to the surface and is captured by the filter depends, in part, on the surface chemistry and the particle overall net charge.
The results can differ significantly from the liquid chemical challenges used in testing most air filters. The surface chemistry and shape of bacteria, fungi and viruses (which all have very complex organic shells) act differently. To ensure accurate measurement of microbial capture efficiency, cabin air filters must be tested with a microbial challenge.
Bacterial and viral challenges have shown that Pall cabin air filters have greater than 99.999% efficiency in bacterial removal efficiency and greater than 99.9995% in virus removal efficiency. They can effectively remove bacteria, viruses and fungi from recirculated air on the first pass, providing airplane recirculation systems with the microbial equivalent of outside or fresh air. Tests have shown that the air downstream of Pall cabin air filters is cleaner than outside air, both on the ground and during flights.
The corona virus that causes SARS and the avian flu virus are in similar size ranges and parameters to the microbes used to test the Pall filters, which would imply comparable efficiencies for their removal from cabin air. In fact, Pall cabin filters have shown even greater efficiency for even smaller virus particles.
"Fortunately for the flying public, most of the world's leading airlines use Pall filters," says Lundquist. "Our decades of experience providing filtration products for the pharmaceutical and health care industries enabled us to develop the technology for both designing and testing filters for effective protection against microbes in the air."
The latest state-of-the-art aircraft including the Airbus 380, which will go into service soon, and the Boeing Dreamliner, currently in development, are all being equipped with Pall cabin air filters. Pall is the world's leading designer and manufacturer of advanced fluid clarification products for the commercial aviation industry as well as for military aircraft, marine and mobile equipment. In addition to aircraft cabin air filters, Pall manufactures a wide range of filters that are used in a variety of environments to prevent exposure to microorganisms. The Company's breathing filter is designated by health authorities in many countries around the globe as the recommended filter to use with respiratory and ventilation equipment to protect patients and health care workers in hospitals from SARS.
Advice to the Flying Public
Although helpful, Lundquist explains that even state-of-the-art cabin air filters cannot prevent the possibility of direct person-to-person transmission within the aircraft cabin. Direct contact, such as touching common surfaces, sneezing, coughing and talking with an infected individual on an airplane, can transmit infections. Proximity to an infected individual increases risk more than the duration of a flight.
Infectious disease specialists recommend that air travelers should wash their hands frequently. Lundquist also recommends that opening the overhead gasper nozzles available on most airplanes to provide a steady flow of filtered air can help reduce the direct transmission of microbes from neighboring passengers.