Aerosol Penetration Research Articles

Protection Against Dust by Respirators.

This article is a brief review of the mechanism of action of fibrous filters and of the performance of respirators; it neglects many of the complications discussed in longer and more detailed articles. An expression is given for the pressure drop across a filter in terms of fibre diameter and filtration velocity. The particle capture mechanisms of interception and diffusional deposition are introduced and the way in which filtration efficiency varies with particle size is discussed. Filters with fibres of small diameter are shown to be the most efficient, but their use can cause problems. Electrically charged materials are widely used in respirators because of their high efficiency and low pressure drop. Types of material, their means of charging, and their method of action are described. An account is given of respirator leakage, the protection factor, and of the way that these may vary in a period of use. The leakage of air and particles through face seal leaks and leaky valves is discussed. The frequent discrepancy in the protection given by respirators in the workplace, on the one hand, and that suggested by laboratory measurements, on the other, is reviewed, and the article ends with an account of the combined effect of aerosol penetration through a filter and through a leak.

Fit test for filtering facepieces: search for a low-cost, quantitative method.

Conventional fit-testing methods use HEPA filter cartridges to distinguish face-seal leakage from filter penetration and thereby test a respirator's ability to face-seal. These methods cannot be applied to low-efficiency filtering facepieces that also protect the wearer through aerosol particle retention by the filter material. Therefore, the ability of a filtering facepiece to face-seal is of interest to the developer for improving the design and to the user for finding the conditions for optimal face-seal. A unique difference has been found between the combined aerosol penetration through filter medium and leak site at low versus high flow rate. This feature has been used to differentiate face-seal leakage from filter penetration. A "fit index" has been introduced as the most sensitive indicator of fit. When normalized by reference to the aerosol penetration through the filter material, this index displays a unified behavior irrespective of the filter material used. The fit index is determined by relating the measured total aerosol concentration at a high flow rate to that at a low flow rate. Tests during normal breathing of a human subject compare well with the data obtained during breath-holding experiments. Available instruments may be used for this test, but need to be modified for tests on humans.

Fit Test for Filtering Facepieces: Search for a Low-Cost, Quantitative Method

Conventional fit-testing methods use HEPA filter cartridges to distinguish face-seal leakage from filter penetration and thereby test a respirator's ability to face-seal. These methods cannot be applied to low-efficiency filtering facepieces that also protect the wearer through aerosol particle retention by the filter material. Therefore, the ability of a filtering facepiece to face-seal is of interest to the developer for improving the design and to the user for finding the conditions for optimal face-seal. A unique difference has been found between the combined aerosol penetration through filter medium and leak site at low versus high flow rate. This feature has been used to differentiate face-seal leakage from filter penetration. A “fit index” has been introduced as the most sensitive indicator of fit. When normalized by reference to the aerosol penetration through the filter material, this index displays a unified behavior irrespective of the filter material used. The fit index is determined by relating the measured total aerosol concentration at a high flow rate to that at a low flow rate. Tests during normal breathing of a human subject compare well with the data obtained during breath-holding experiments. Available instruments may be used for this test, but need to be modified for tests on humans.

Aerosol Penetration and Leakage Characteristics of Masks Used in the Health Care Industry

Aerosol Penetration and Leakage Characteristics of Masks Used in the Health Care Industry

Aerosol Penetration and Leakage Characteristics of Masks Used in the Health Care Industry

Aerosol Penetration and Leakage Characteristics of Masks Used in the Health Care Industry

31.O.04 Aerosol dispersion in human airways during one breathing cycle: The dependence of the aerosol penetration

31.O.04 Aerosol dispersion in human airways during one breathing cycle: The dependence of the aerosol penetration

33.O.01 Physical and biological aerosol penetration and face-seal leak characteristics of industrial and health-care respirators

33.O.01 Physical and biological aerosol penetration and face-seal leak characteristics of industrial and health-care respirators

A personal sampler for inhalable mixed-phase aerosols: modification to an existing sampler and validation test with three pesticides

A modified personal air sampler with an inhalable entry efficiency for collecting pesticide aerosols and vapours simultaneously was studied. An XAD 2 cartridge was constructed to fit into the sampler housing and the vapour trapping efficiency of the cartridge was determined for three pesticides using a dynamic U-tube test system. Tests were performed with different amounts of pesticides (1.7 up to 1450 μg) and duration of sampling (30 - 120 min) under various environmental conditions. Trapping efficiency varied from 87% up to 100% for dichlorvos and methomyl, but was slightly lower for chlorothalonil (72% up to 79%). No break-through was observed. The efficiency was not affected by humidity, temperature, pesticide loading and sampling duration. Penetration of solid aerosols through the cartridge at normal sampling flow rate (21.min −1) was below 5%. It is concluded that the present sampler enables adequate simultaneous sampling of pesticide aerosols and vapours.

The Transport of Aerosols through Ultrafine Leak Paths

Abstract The aim of the programme has been to provide generic information to enable a valid assessment to be made of the potential leakage of airborne particles through the seals of containers used to transport nuclear materials in which material in powdered form may be present. A series of experiments has been undertaken using model leak paths based on ultrafine capillaries to quantify the penetration behaviour of a variety of aerosols, varying from spherical calibration standards to irregularly shaped particles more typical of those likely to be encountered under transport conditions. These experiments have been supported by the development of a model that explains the findings and enables aerosol penetration behaviour to be predicted over a much wider range of conditions. These studies lend support to the argument that the current IAEA recommended air leakage rate limit of 10–6 Pa·m3·s−1 is sufficient to prevent the migration of significant particulate-borne radioactivity from a single leak path, altho...

A new method of quantification of the pulmonary regional distribution of aerosols using combined CT and SPECT and its application to nedocromil sodium administered by metered dose inhaler.

Aerosols of nedocromil sodium labelled with 99Tcm were delivered on 20 separate occasions to healthy male volunteers. Planar and single photon emission computerized tomography (SPECT) gamma scintigraphy were immediately performed to assess the pulmonary regional distribution of delivered aerosol. On a separate occasion volunteers were imaged using X-ray computed tomography (CT). Alignment of SPECT and CT images was performed using marked anatomical features and the anterior and lateral skin outlines. CT images provided data for attenuation correction and were used to define the anatomical lung volume. Central to peripheral (CP) ratios of deposited activity were calculated from volumes of interest in coronal and transverse sections of the right lung. These were compared with CP ratios obtained from planar images obtained immediately following aerosol inhalation. Volumetric CP ratio correlated significantly with immediate planar CP ratio (p < 0.001). Analysis of deposition in the whole right lung was performed by separating the SPECT lung data into a series of thin concentric shells centred on the entry of the right main bronchus. Measures were defined for describing the variation of deposition density and cumulative total deposition with distance from the lung centre. These showed significant correlation with planar CP ratio (p < 0.001). SPECT analysis using CT is consistent with planar measures of aerosol deposition but offers a more complete quantification of aerosol penetration and absolute deposited activity within the whole lung. It is a valuable new tool for aerosol analysis.

Arctic aerosols in Greenland

Elemental composition of Arctic aerosols is being studied on the Greenland Icecap and in northeast Greenland to determine the level, composition, seasonal variation and origin of the aerosols, of which little is known in the remote and elevated central region. In particular, the degree of penetration of arctic haze aerosols is of interest since this may cause perturbations of climatic parameters. Arctic haze aerosols have previously been found at four coastal sites notably in north Greenland. Receptor modelling of the aerosol by factor analysis revealed three to fivecomponents of remote origin from both natural and anthropogenic sources. In north Greenland the anthropogenic components exhibited large annual cycles with pronounced maxima in winter caused by long-range atmospheric transport from midlatitude areas. These measurements have been resumed as a reference to the Icecap Experiment. On the Icecap, aerosol samples are being collected in two size ranges on a continuous basis concurrent with the Greenland Icecore Programme 1989–1993 at Summit, 3200 m a.s.l. The sampling equipment is designed for collection of weekly samples especially suited for PIXE analysis, retrieval once a year, automatic operation under extremely cold conditions and very low energy consumption. Preliminary results from samples covering for the first time also the winter season on the central Icecap are discussed in relation to arctic haze occurrences at sea level.

Exposure to ozone alters regional function and particle dosimetry in the human lung

Effects of experimental exposure to O3 (0.33 ppm) or filtered air on regional lung function were assessed in nine healthy male subjects. Immediately after 2-h chamber exposures, regional ventilation and particle dosimetry were measured by gamma camera imaging. The vertical distributions of a radiolabeled gas (133Xe) and aerosol (3.5-microns-diam insoluble 99mTc-tagged Fe2O3 particles) were quantitated for upper, middle, and lower lung regions; distribution data were corrected for regional differences in lung volume and tissue attenuation. Indexes of mechanical function, inspiratory capacity, and mid-maximal expiratory flow rates were significantly reduced after O3, but functional residual capacity remained unchanged. Exposure to O3 significantly enhanced the fraction of respired aerosol retained by the lung and altered the distribution pattern of deposited aerosol by increasing particle deposition to the middle lung region (P < 0.05). Aerosol penetration indexes, i.e., ratio of particle deposition in central lung regions to that in peripheral lung regions, and particle retention 24 h postinhalation (an index of aerosol deposition within alveoli and slowly clearing bronchioles) indicated that particle filtration efficiency had increased for tracheobronchial and parenchymal lung regions. For seven of the nine subjects, regional ventilation after O3 was reduced by 14% to the lung base and enhanced by 8 and 6% to the upper and middle lung regions, respectively; these changes were significant (P < 0.02) compared with ventilation after filtered air.(ABSTRACT TRUNCATED AT 250 WORDS)

Aerosol penetration and leakae characteristics of masks used in the health care industry

Background: Historically, surgical masks have been worn to protect patients from being infected by large, pathogen-containing aerosol droplets emitted by health care personnel. Today, emphasis has shifted from solely protecting the patient to protecting the health care worker as well. As a result of new procedures used in operating rooms and clinical areas, aerosolized hazardous agents in the submicrometer size range are being produced, posing a potential threat to health care workers. Methods: Eight surgical masks were tested for aerosol particle penetration through their filter media and through induced face-seal leaks. Results: The percentage of filter penetration ranged from 20% to nearly 100% for submicrometer-sized particles. In comparison, a dust-mist-fume respirator used in industrial settings had significantly less penetration through its filter medium. When the surgical masks had artificially induced face-seal leaks, the concentration of submicrometer-sized particles inside the mask increased slightly; in contrast, the more protective dust-mist-fume respirator showed a fourfold increase in aerosol penetration into the mask with an artificial leak 4 mm in diameter. Conclusion: We conclude that the protection provided by surgical masks may be insufficient in environments containing potentially hazardous submicrometer-sized aerosols.

Loading and Filtration Characteristics of Filtering Facepieces

Most filtering facepieces used today are made of electret material (material with significant electrical charges on the filter fibers). Because of the addition of this electrical removal force, the filtration efficiency can be significantly increased without increasing the air pressure drop inside the respirator; pressure drop is closely related to physiological load. However, the removal by electrical forces is reduced in time, as aerosols deposit on the filter fibers. We have studied the contribution of this electrical removal and its change in time as a function of aerosol loading. To prove the change in aerosol penetration is due to the reduction of electrical force, the electrical charges were removed from new facepieces by the application of appropriate chemicals.The dust-mist filtering facepieces tested have similar fiber diameters and packing densities, as determined by scanning electron microscopy and pressure drop data. At a face velocity of 10 cm/s (corresponding to 100 L/min through a complete filtering facepiece) and an aerosol size of 0.16 μm, electrical force removal accounts for 69% of the total filtration for the respirator found to have the best filter quality but only 25% for the respirator (from a different manufacturer) found to have the worst filter quality. Our experimental data show that the removal efficiency of these facepieces is reduced in time by as much as this amount. However, under normal wear conditions, the total aerosol particle load is not as high as shown and the filtering facepieces are likely to be discarded before the fiber charges (i.e., the electrostatic attractions) are significantly diminished.

LOADING AND FILTRATION CHARACTERISTICS OF FILTERING FACEPIECES

Most filtering facepieces used today are made of electret material (material with significant electrical charges on the filter fibers). Because of the addition of this electrical removal force, the filtration efficiency can be significantly increased without increasing the air pressure drop inside the respirator; pressure drop is closely related to physiological load. However, the removal by electrical forces is reduced in time, as aerosols deposit on the filter fibers. We have studied the contribution of this electrical removal and its change in time as a function of aerosol loading. To prove the change in aerosol penetration is due to the reduction of electrical force, the electrical charges were removed from new facepieces by the application of appropriate chemicals. The dust-mist filtering facepieces tested have similar fiber diameters and packing densities, as determined by scanning electron microscopy and pressure drop data. At a face velocity of 10 cm/s (corresponding to 100 L/min through a complete filtering facepiece) and an aerosol size of 0.16 microns, electrical force removal accounts for 69% of the total filtration for the respirator found to have the best filter quality but only 25% for the respirator (from a different manufacturer) found to have the worst filter quality. Our experimental data show that the removal efficiency of these facepieces is reduced in time by as much as this amount. However, under normal wear conditions, the total aerosol particle load is not as high as shown and the filtering facepieces are likely to be discarded before the fiber charges (i.e., the electrostatic attractions) are significantly diminished.

43 O 03 The influence of pressure on the penetration of aerosols through fine capillaries

43 O 03 The influence of pressure on the penetration of aerosols through fine capillaries

Respirator Leak Detection by Ultrafine Aerosols: A Predictive Model and Experimental Study

The leak performance of half-mask, maintenance-free respirators was studied theoretically and experimentally. A predictive model for the theoretical protection factor and leakage flow has been developed that uses the equation of particle conservation inside and outside the respirator. An experimental study was conducted using NaCl particles of 10 nm in diameter and a condensation nucleus counter as the particle detector. A respirator fitted with controlled leak holes of 20–3000 μm in diameter was tested at steady flow rates of 10, 32, and 100 L/min. Results showed that the aerosol penetration into a respirator was strongly influenced by the filter efficiency, leak hole size, and flow rate through the respirator. The results are in good agreement with theory, but some discrepancy has been noted at lower flow rates and smaller leak hole sizes. For the dust/mist respirators, the experimental protection factor for ultrafine 0.01-μm NaCl particles ranged from 3145 to as low as 3. For the high efficiency dust/m...

Aerosol penetration through filtering facepieces and respirator cartridges.

Air-purifying respirators must be certified following the National Institute for Occupational Safety and Health (NIOSH) filter test criteria (30 CFR 11). The criteria specify a range for the mean particle size and the measure of spread permissible for the test aerosol. The authors' experiments have shown that aerosol penetration as a function of particle size differs considerably among certified respirators of the same type. Filtering facepieces (disposable respirators) and cartridges of the dust-mist, dust-mist-fume, and high-efficiency particulate air type were tested. The respirators were sealed to mannequins in a test chamber. The aerosol concentrations inside and outside the respirator were measured by an aerodynamic particle sizer and a laser aerosol spectrometer over a particle size range of 0.1 to 15 microns. Five flow rates ranging from 5 to 100 L/min were used to study flow dependency. The aerosol penetration through the filters is presented as a function of particle size. Aerosol penetration and pressure drop are combined to express the performance of each filter in terms of "quality factor." Under the same test conditions, the quality factor of one respirator may be as much as 6.6 times more than that of another respirator of the same type. The filter quality factor has a greater aerosol size dependency as airflow and aerosol size increase. In general, cartridges have a larger surface area than filtering facepieces but not necessarily lower filter penetration or higher filter quality.(ABSTRACT TRUNCATED AT 250 WORDS)

Aerosol Penetration through Filtering Facepieces and Respirator Cartridges

Air-purifying respirators must be certified following the National Institute for Occupational Safety and Health (NIOSH) filter test criteria (30 CFR 11). The criteria specify a range for the mean particle size and the measure of spread permissible for the test aerosol. The authors' experiments have shown that aerosol penetration as a function of particle size differs considerably among certified respirators of the same type. Filtering facepieces (disposable respirators) and cartridges of the dust-mist, dust-mist-fume, and high-efficiency particulate air type were tested. The respirators were sealed to mannequins in a test chamber. The aerosol concentrations inside and outside the respirator were measured by an aerodynamic particle sizer and a laser aerosol spectrometer over a particle size range of 0.1 to 15 µm. Five flow rates ranging from 5 to 100 L/min were used to study flow dependency. The aerosol penetration through the filters is presented as a function of particle size. Aerosol penetration and pressure drop are combined to express the performance of each filter in terms of “ quality factor.” Under the same test conditions, the quality factor of one respirator may be as much as 6.6 times more than that of another respirator of the same type. The filter quality factor has a greater aerosol size dependency as airflow and aerosol size increase. In general, cartridges have a larger surface area than filtering facepieces but not necessarily lower filter penetration or higher filter quality. An analysis of the data shows that the best dust-mist respirator tested may provide five times more protection than the worst dust-mist respirator tested when exposed to the aerosol size distribution specified by the NIOSH filter test criteria.

Characteristics of face seal leakage in filtering facepieces.

Several studies have found that aerosol size, testing method, leak size, leak position, sampling probe location, and the mixing condition inside the respirator affect the results of fit factor measurements. This study focuses on the effect of leak shape and filter resistance because leaks have been reported to vary in shape from circular to slit-like. Four leaks of different shape but the same cross-sectional area were used to study their effect on aerosol penetration. Dust-mist and high-efficiency particulate air filtering facepieces provided different filter resistances. An aerodynamic particle sizer and a laser aerosol spectrometer were used to measure the particle size-dependent aerosol concentrations inside and outside the respirators. The filtering facepieces were sealed to a mannequin and artificial leaks were inserted near the right cheek. Aerosol penetration was measured for five flow rates ranging from 5 to 100 L/min. The pressure drop across the mask was monitored with an inclined manometer. At a given pressure differential, a slit-like leak and multiple circular leaks have been found to pass less aerosols than a single circular leak of equal cross-sectional area because the leak flow decreases with an increase in leak shape complexity. If there is substantial lack of face seal fit and the breathing rate is low, a HEPA respirator may provide less protection than a dust-mist respirator because the pressure drop is considerably higher for a HEPA respirator, resulting in more aerosol flow through the leak.