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At least 19 recordsLinked to original sources
PubMed1997

[Fungi and bacteria on air filters from heating, ventilation and air-conditioning systems: a method for determination of fungi and bacteria on air filters].

A method was developed for the determination of microorganism concentrations on air filters of HVAC systems, and the influence of different test parameters on the microbiological results was examined by considering various used air filters from several such systems. Microorganisms are detected by shaking air filter samples in fluid, where their concentration is then determined as surface cultures. Since varying the shaking time (30, 60, 90 min) had no influence on the quantitative microorganism determination, a shaking time of 60 minutes was chosen for detection of bacteria, yeasts and moulds. Incubation of blood agar plates either for 4 days at 20 degrees C +/- 2 degrees C or for 2 days at 36 degrees C +/- 1 degree C yielded identical concentrations of bacteria and yeasts. Since results obtained with malt extract agar and Czapek-Dox agar are comparable, one of the two culture media is sufficient for the quantitative determination of moulds on air filters. For statistical evaluation, the inoculation of three parallel agar plates per growth medium was found to be adequate, and the arithmetic mean and the median proved to be equivalent. Investigation on the detection rate showed that, on the average, the method developed demonstrated 80% of the microorganisms detectable on an air filter sample. Thus a simple method is available for quantitative determination of microorganisms on air filters.

Agar↗
PubMed1998

Identification of Pneumocystis carinii f. sp. hominis gene sequences in filtered air in hospital environments.

To evaluate the risk of a nosocomial spread of Pneumocystis carinii f. sp. hominis (P. carinii hominis), air filter samples from rooms of P. carinii pneumonia (PCP) patients, adjacent corridors, and other hospital environments have been investigated for the presence of P. carinii hominis. Amplified DNA from air filters and sputum or bronchoalveolar lavage samples from the PCP patients have been genotyped with the P. carinii hominis genes of the mitochondrial large-subunit (mtLSU) rRNA and the internal transcribed spacers (ITS1 and ITS2) of the rRNA. Genotypes of the two loci were identified by direct sequencing, and for site 85 of the mtLSU locus, three allele-specific PCR assays were used. P. carinii hominis DNA was identified in the air of five of seven PCP patient rooms and in the air of two of four air filtrations from the ward corridors. The P. carinii hominis genotypes were the same in four of the five room air samples as those in the corresponding patients, suggesting a risk of person-to-person transmission of P. carinii hominis from PCP patients. Three of 16 air samples collected in infectious disease wards without the presence of PCP patients and one sample from a cardiology unit in a separate hospital building were also positive, which further strengthens the possibility of acquisition of P. carinii hominis from the environment.

Air Microbiology↗
PubMed1978

Efficiency of bacterial filtration in various commercial air filters for hospital air conditioning.

Filtration efficiency of high-efficiency particulate air (HEPA) filters is said to be over 99.97% of removal rate against the mist of thermogenerating-type of dioctyl phthalate with average particles diameter of 0.3 micrometer, as tested by the U.S. Military Standard 282 (1956). Filtration of bacterial aerosols through commercial air filters was tested to examine the efficiency of bacterial filtration with eight kinds of air filters. Percentage of bacterial filtration efficiency (% BFE) of three kinds of HEPA filters showed 100% BFE, while NBS-95 and NBS-85 showed over 99% BFE. BFE of NBS-75 air filter was 91.75%.

Aerosols↗
PubMed1963

TESTING AIR-FILTERING SYSTEMS. I. PROCEDURE FOR TESTING HIGH-EFFICIENCY AIR FILTERS ON EXHAUST SYSTEMS.

A procedure was developed for evaluating high-efficiency filters mounted in exhaust ducts at the National Animal Disease Laboratory. An aerosol of the test organism, Escherichia coli B T(3) bacteriophage, was generated in a chamber attached to a ceiling exhaust register in concentrations of at least 1000 viable organisms per ft(3) of air. Samples were collected from both the pre- and postfilter areas, and the number of organisms per ft(3) of air was determined. The efficiency of the filter was calculated from these figures. A total of 269 high-efficiency filters were tested. Of these, 249 had efficiencies of 98% or greater. The remaining 20, with efficiencies of less than 98%, were repaired and retested. No filter was accepted with an efficiency of less than 98%.

Aerosols↗
PubMed1997

Fungal colonization of air filters from hospitals.

Air filters of various types, selected on the basis of discoloration, were collected from the primary and secondary filter banks of the heating, ventilating, and air-conditioning systems in seven hospitals in the eastern United States and examined with direct microscopy for fungal colonization. Microscopic observations and culture results showed that filters from five of the hospitals were colonized with fungi including species of Acremonium, Alternaria, Aspergillus, Cladosporium, Epicoccum, Penicillium, and Rhinocladiella, and a Beauveria-like fungus. Several of these commonly airborne species, e.g., Epicoccum purpurescens (syn. E. nigrum) and Rhinocladiella sp., had not been previously reported to colonize (with conidiogenesis) air filters.

Air Conditioning↗
PubMed1994

The response of spruce shoot aphid Cinara pilicornis hartig to ambient and filtered air at two elevations and pollution climates.

The effects of ambient air compared to filtered air on the reproduction of females and mean relative growth rate (MRGR) of nymphs of C. pilicornis on Norway spruce was determined in open-top chambers at Wengernalp in the Swiss Alps (1900 m a.s.l.) and at Schönenbuch near the city of Basle (400 m a.s.l.). The ambient concentration of O(3), the main pollutant at both sites, varied between 45 and 120 microg m(-3) (24-h mean) at both sites. A 5-8 day exposure of spruce saplings to ambient compared to filtered air enhanced the MRGR of nymphs of C. pilicornis of local and northern origins at Schönenbuch. The cumulative numbers of offspring of C. pilicornis were higher in ambient air chambers than in filtered air chambers at Schönenbuch, but not at Wengernalp. Filtration of ambient air did not affect significantly the levels of total free amino acids or reducing sugars in phloem sap or concentration of total phenolics in needles at the end of the growing season. The results suggest that ambient air with elevated O(3) and with high daily fluctuations, as it can be observed in Schönenbuch, affects aphid performance on conifers more than ambient air with also elevated, but rather constant levels of O(3), as it can be observed in mountain forest areas.

Journal Article↗
PubMed2001

Preparation and characterization of a set of IAEA reference air filters for quality control in air-pollution studies.

Several sets of reference air filters were prepared as part of an IAEA evaluation of the performance of laboratories involved in air-pollution studies. Each set comprised three polycarbonate membrane filters, two of which were loaded with urban air particulate matter (APM) obtained in Vienna or Prague, and one unloaded filter. The filters were loaded by filtration of a suspension of the APM materials in water. The homogeneity both of bulk APM materials and of the loaded filters was evaluated and found suitable by determining several elements by instrumental neutron-activation analysis (INAA), proton-induced X-ray emission (PIXE), and micro-X-ray energy-dispersive fluorescence analysis (micro-EDXRF). After evaluation of the homogeneity, INAA, PIXE, EDXRF, atomic absorption spectrometry (AAS), inductively coupled plasma optical emission spectrometry (ICP-OES), and ICP mass spectrometry (ICP-MS) were used to characterize the filter materials and establish "target values" and their associated standard deviations for 15 elements. Problems encountered during the preparation of these unique, simulated air filters and the criteria for setting both the target values and standard deviations are presented.

Air Pollutants↗
PubMed1998

Investigations on the survival time of outdoor microorganisms on air filters.

Outdoor microorganism survival on air filters was examined in 16-day field investigations. Using a mobile filter testing device, samples of fiberglass pocket filters (filter class F7) were ventilated with outdoor air, and their microorganism contents were determined at 1, 2, 4, 8 and 16-day intervals. The results showed a mean survival time of microorganisms deposited on the air filters of 1 to 3 days.

Air Microbiology↗
PubMed2001

Capability of air filters to retain airborne bacteria and molds in heating, ventilating and air-conditioning (HVAC) systems.

The capability of air filters (filterclass: F6, F7) to retain airborne outdoor microorganisms was examined in field experiments in two heating, ventilating and air conditioning (HVAC) systems. At the beginning of the 15-month investigation period, the first filter stages of both HVAC systems were equipped with new unused air filters. The number of airborne bacteria and molds before and behind the filters were determined simultaneously in 14 days-intervals using 6-stage Andersen cascade impactors. Under relatively dry (< 80% R. H.) and warm (> 12 degrees C) outdoor air conditions air filters led to a marked reduction of airborne microorganism concentrations (bacteria by approximately 70% and molds by > 80%). However, during long periods of high relative humidity (> 80% R. H.) a proliferation of bacteria on air filters with subsequent release into the filtered air occurred. These microorganisms were mainly smaller than 1.1 microns therefore being part of the respirable fraction. The results showed furthermore that one possibility to avoid microbial proliferation is to limit the relative humidity in the area of the air filters to 80% R. H. (mean of 3 days), e.g. by using preheaters in front of air filters in HVAC-systems.

Air Conditioning↗
PubMed1996

A constant flow filter air sampler for workplace environments.

A filter air sampler has been developed for sampling radionuclide aerosol particles from the workplace environment. It provides easy filter changing, constant flow sampling, and a visual display to indicate proper operation. An experimental study was conducted to characterize the collection efficiency of the sampler as affected by variations in room air velocity, particle size, sampling flow rate, inlet geometry, and inlet orientation to the free stream. Tests were carried out in a wind tunnel at velocities between 0.3 m s(-1) and 2.0 m s(-1), which is a range that covers anticipated velocities in the typical highly ventilated workplace environment of a nuclear facility. Nearly monodisperse aerosols with sizes between 5 and 20 microm aerodynamic diameter were sampled at flow rates between 28.3 and 84.9 L min(-1). Inlet orientations of 0 degrees, 90 degrees, and 180 degrees from the horizontal were selected for evaluation. When the sampler was oriented at 0 degrees over various ranges of free stream velocities, sampling flow rates and particle sizes, the transmission efficiency of aerosol was typically greater than 95%. The transmission efficiencies varied from 80% to 106% for 10-microm aerodynamic diameter particles over the previously noted range of free stream velocities and inlet orientations. Uniformity of deposits of 10 microm aerodynamic diameter particles on collection filters was examined for a sampling rate of 57 L min(-1), a sampler orientation of 90 degrees into the wind and wind speeds of 0.3-2 m s(-1). The coefficients of variation for the areal density of the deposits ranged from 6.1% to 37.2%. A miniature critical flow venturi with a constant sampling flow rate of 57 L min(-1) was developed for application to the new filter air sampler. It was demonstrated that the performance of the new filter air sampler is quite acceptable over a wide range of conditions. Overall the new filter air sampler design has been shown to provide enhanced performance with regard to sample handling, constant calibrated volumetric sample flow rate, and relatively unbiased sample aspiration performance compared with a traditional filter air sampler design.

Aerosols↗
PubMed1999

Efficiency of automotive cabin air filters to reduce acute health effects of diesel exhaust in human subjects.

OBJECTIVES: To evaluate the efficiency of different automotive cabin air filters to prevent penetration of components of diesel exhaust and thereby reduce biomedical effects in human subjects. Filtered air and unfiltered diluted diesel exhaust (DDE) were used as negative and positive controls, respectively, and were compared with exposure to DDE filtered with four different filter systems. METHODS: 32 Healthy non-smoking subjects (age 21-53) participated in the study. Each subject was exposed six times for 1 hour in a specially designed exposure chamber: once to air, once to unfiltered DDE, and once to DDE filtered with the four different cabin air filters. Particle concentrations during exposure to unfiltered DDE were kept at 300 micrograms/m3. Two of the filters were particle filters. The other two were particle filters combined with active charcoal filters that might reduce certain gaseous components. Subjective symptoms were recorded and nasal airway lavage (NAL), acoustic rhinometry, and lung function measurements were performed. RESULTS: The two particle filters decreased the concentrations of diesel exhaust particles by about half, but did not reduce the intensity of symptoms induced by exhaust. The combination of active charcoal filters and a particle filter significantly reduced the symptoms and discomfort caused by the diesel exhaust. The most noticable differences in efficacy between the filters were found in the reduction of detection of an unpleasant smell from the diesel exhaust. In this respect even the two charcoal filter combinations differed significantly. The efficacy to reduce symptoms may depend on the abilities of the filters investigated to reduce certain hydrocarbons. No acute effects on NAL, rhinometry, and lung function variables were found. CONCLUSIONS: This study has shown that the use of active charcoal filters, and a particle filter, clearly reduced the intensity of symptoms induced by diesel exhaust. Complementary studies on vehicle cabin air filters may result in further diminishing the biomedical effects of diesel exhaust in subjects exposed in traffic and workplaces.

Acute Disease↗
PubMed1968

Evaluation of a commercial air filter for removal of viruses from the air.

The effectiveness of a commercial absolute air filter for removal of viruses from air was tested with an actinophage, under the usual conditions of a laminar airflow clean room. A new method of dry phage dispersion is described. The filter showed an average reduction of 99.996% of airborne actinophage.

Aerosols↗
PubMed1994

Efficiency of air filter sets for the prevention of airborne infections in laboratory animal houses.

Air filter sets (classes EU6 and EU9, or EU6 and S) were tested for their efficiency in protecting laboratory animals against potential airborne infections. Flexible-film isolators were used as a smaller scale model. In the first experiment, lasting 7 months, it was tested whether minute virus of mice (MVM) was able to penetrate the air filters between one isolator containing experimentally infected mice and another with MVM negative mice. In the second experiment we tested whether microorganisms in the incoming air were able to penetrate air filter sets. To assess this gnotobiotic mice in an isolator were monitored for 9 months for changes of their microbial flora. In both experiments a combination of EU6 and EU9 air filters proved to be sufficient to maintain the microbiological status of the animals. The same combination of medium efficiency filters (EU6 and EU9) is used on the air supply to 4 SPF-barrier units in which infections with MVM occurred repeatedly soon after the initial stocking. After a thorough disinfection no reinfection has been detected to date. This demonstrates that the relatively low efficiency of the air filters was not the cause of the repeated infection. The procedure for disinfection is described.

Air Conditioning↗
PubMed1995

Fungal colonization of air filters for use in heating, ventilating, and air conditioning (HVAC) systems.

New and used cellulosic air filters for HVAC systems including those treated with antimicrobials were suspended in vessels with a range of relative humidities (55-99%) and containing non-sterile potting soil which stimulates fungal growth. Most filters yielded fungi prior to suspension in the chambers but only two of 14 nontreated filters demonstrated fungal colonization following use in HVAC systems. Filters treated with antimicrobials, particularly a phosphated amine complex, demonstrated markedly less fungal colonization than nontreated filters. In comparison with nontreated cellulosic filters, fungal colonization of antimicrobial-treated cellulosic filters was selective and delayed.

Air Conditioning↗