Engineering Controls Database
Evaluation of the Ability of Commercially Available Portable Air Cleaners to Remove Bioaerosols.
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Indoor air contains suspended biological particulate matter (bioaerosols) that can pose a threat to public health through infectious diseases. The possibility for disease transfer associated with bioaerosols has prompted an effort to design appropriate systems and methods to remove causative agents. Transmission of tuberculosis is a good example of an airborne contagion. Although the number of cases of tuberculosis in the United States has declined in the last several years, there is still a continuing need to protect healthcare workers from risk of infection. Currently, the primary risk to healthcare workers is believed to be exposure to individuals with unsuspected or undiagnosed infectious tuberculosis. Exposures of this type may occur in healthcare facilities such as hospitals, correctional institutions, nursing homes, or clinics. While mechanical ventilation systems can provide protection to workers in these situations, there are limitations such as engineering constraints, comfort considerations, and cost. One method of supplementing mechanical ventilation systems and other engineering controls is the use of portable air cleaners (PACs) to remove or inactivate infectious microorganisms such as those that cause tuberculosis. |
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Airborne transmission of infectious agents resulting in disease has been well documented. In addition to tuberculosis, other common airborne diseases include meningitis, chicken pox, and influenza. Airborne transmission occurs when bacteria or viruses travel on dust particles or on small respiratory droplets that may become aerosolized when people sneeze, cough, or exhale. They can travel on air currents over considerable distances. Because the biological particles are small, they may remain airborne for long periods, which increase their potential for being inhaled. Infection can occur when a person inhales the biological particle(s) that may be deposited deep in the lungs in the alveoli. Some of the environmental factors affecting the potential for disease transmission are the concentration of infectious particles in the air and the exposure duration. |
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A study by EPHB examined the ability of four commercially available PACs to remove or inactivate bioaerosols of Micrococcus luteus and Escherichia coli. The evaluated PACs utilized different types of air cleaning mechanisms including a high-efficiency particulate air (HEPA) filter, electrostatic precipitator, enhanced filter, and an ozone/ion generator. A bench-scale bioaerosol chamber was used to study their ability to remove or inactivate bacteria. • Ozone/Ion Generator [Alpine Air Model XL-15: Living Air - Blaine, MN]. This unit has an adjustable fan and ozone plate configurations that allow the amount of ozone produced to be varied based on the room size. The PAC also contains an ion generator. The ozone plates, in addition to generating ozone, ionize particles in the air as they pass by the plates. The ionized particles are released into the air and, according to the manufacturer, attract oppositely charged particles. The particles then, due to their increased mass, fall from the air where they may be removed by general cleaning methods. According to the manufacturer, the ozone output of this unit is 33 to 320 milligrams (mg) per hour and approximately 4,000 negative ion and 3,000 positive ion per cubic centimeter (cm3). • Electrostatic Precipitator [UAS Electronic Air Cleaner Model GC: United Air Specialist, Inc. - Cincinnati, OH]. A power pack supplies 6,000 and 12,000 DC volts to the ionizer and collecting cell respectfully and a Atube axial fan@ that controls the air volume that passes through the unit. Contaminated air passes through the ionizing section where a charge is applied and the particle is collected downstream on the collection plates. • Enhanced Filter [Electromedia Portable Air Cleaner Model 35F: It’s All About Clean Air, Inc. - Glasgow, KY]. This PAC contains an electrically charged filter, pre-filter, ionizer (grid wires) and carbon filter. As contaminated air passes through the unit, particles are charged by the ionizer and are collected on the oppositely charged filter. • HEPA Filter [Enviracaire Model 13500 Series: Honeywell Environmental Air Control, Inc. - Hagerstown, MD]. HEPA filters provide a minimum removal efficiency of 99.97% of particles 0.3 micrometers (µm) in diameter. This unit contains a HEPA filter with an optional charcoal pre-filter and has an adjustable fan control. The charcoal pre-filter was not used during the experiments.      |
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| 222-03; 222-05-A; 222-05-B; | |
| 622;6221;62211 | |
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clinics health care facilities health care workers hospital indoor air nurse portable air cleaners |
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The results indicate that there is a substantial difference in the effectiveness of the PACs. Also, the measured airflow of each unit varied considerably and was generally much less than the nominal rate provided by the manufacturer. The unit using an electronic precipitator as the capture/inactivation mechanism was the most effective while the least effective was the ozone/ion generator. However, it should be noted that the effectiveness of the HEPA filter unit was undoubtedly affected by the use of the wrong size filter. This indicates the importance of ensuring that the units are properly constructed, maintained, and are functioning properly before use. The engineering control information provided in this write-up was taken primarily from the following EPHB report: Rumble AM, Jensen PA, Green CF, Mickelsen RL, Whalen JJ [2003]. Evaluation of the ability of commercially available portable air cleaners to remove bioaerosols. Cincinnati, OH: U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, DHHS (NIOSH), EPHB 222-056, DART 03-149. |