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PubMed1983

Personal sampling impactor with respirable aerosol penetration characteristics.

Single stage impactors with penetration characteristics approximating those of the BMRC, AEC and ACGIH respirable criteria have been developed for use as personal samplers. Three impactors were built for flow rates of 2 L/min. Experimental calibration data of these impactors are compared to the respective respirable criteria for which they were designed. Oil soaked impaction plates were used in these impactors so particles impacting on the plates would always strike an oiled surface and not bounce from the plate. Experiments with coal dust using these plates showed little particle bounce. Finally, a procedure is introduced by which samplers can be designed with penetration characteristics that differentiate between the AEC and ACGIH respirable criteria.

Aerosols↗
PubMed1984

Evaluation of saccharin qualitative fitting test for respirators.

The results of a qualitative fitting test for half-mask respirators utilizing a sodium saccharin aerosol were compared to the results of a quantitative fitting test utilizing an oil mist aerosol. For a respirator-wearer combination having a fit factor less than 10, as determined by the quantitative test, the point estimate of the probability of that combination not being rejected by the saccharin qualitative test was found to be 0.00 with 95% confidence that this statistic is not expected to exceed 0.05. For a respirator-wearer combination having a fit factor less than 100, the point estimate of the probability of that combination not being rejected by the qualitative test was found to be 0.03 with 95% confidence that this statistic is not expected to exceed 0.08. The effects of temperature and relative humidity on the size distribution of the saccharin aerosol were also investigated and found to be slight.

Aerosols↗
PubMed1984

Effects of exercise using industrial respirators.

Respirators (respiratory personal protective devices), used for protection against occupational toxic exposures, may impose flow resistance and dead space respiratory loading. Effects of exercise level, a 300 mL deadspace and single respirator cartridge inspiratory load were determined in ten healthy volunteers. Subjects tended to limit peak work rate (pressure generated and pressure X flow) and to prolong the inspiratory portion of the respiratory cycle due to respirator use. O2 consumption and heart rate were not significantly affected. The qualitative response was not affected by exercise level. During submaximal exercise, normal subjects did not reach their compensation limits for the variables studied.

Heart Rate↗
PubMed1985

Efficacy of the helmet respirator in occupational asthma due to laboratory animal allergy (LAA).

The efficacy of the Racal Airstream helmet respirator in preventing symptoms due to Laboratory Animal Allergy (LAA) was assessed in ten patients. Eight of these were established cases of asthma and two had severe rhinitis. Peak expiratory flow rate (PEFR) readings, recorded every two hours, were kept for seven weeks (six in exposure), together with a diary of subjective symptoms. Objective evidence of good protection was obtained in six out of the eight asthmatic patients; overt asthma was seen in the other two. The helmet respirator would appear to be a valuable adjunct in the management of occupational asthma in those who opt to remain in exposure. Those asthmatics who use a helmet respirator need to be monitored carefully and regularly to ensure that their respiratory function has not deteriorated. Persons with severe local symptoms of rhinitis and conjunctivitis also benefit subjectively from the use of the helmet although symptoms are not completely suppressed nor may progression towards asthma be prevented. The findings may well be applicable to the management of other types of occupational asthma but any inferences should be drawn with caution.

Animals↗
PubMed1987

Occupational exposure to airborne dust, respirable quartz and metals arising from refuse handling, burning and landfilling.

Industrial hygiene investigations were conducted in 1983 at a refuse derived fuel (RDF) burning plant, a refuse transfer station and three municipal landfill sites. The field surveys were conducted during the warmer and drier seasons of the year. The investigations included air sampling for total dust, respirable quartz and airborne metals. Bulk samples of soil cover, precipitator/boiler ash and transfer station baghouse fines were analyzed for quartz, elements, asbestos and polychlorinated biphenyls (PCBs) content. Asbestos and PCBs were not detected in any of the bulk samples taken. Quartz content of the bulk samples varied from 8% to 31%. Except for the boiler grate inspector and the precipitator cleaner at the RDF burning plant, exposure to airborne metals was not excessive at the sites tested. One personal sample (at landfill site A) for total dust exceeded 10 mg/m3 out of a total of eighteen personal and area samples. Significant exposure to respirable quartz was found at all the sites (up to 0.20 mg/m3). Respirable quartz exposures in excess of the NIOSH criteria concentration of 0.05 mg/m3 were found in three out of seven personal samples at the RDF burning plant, two out of three personal samples at the refuse transfer station and six out of nine personal samples taken at the three landfill sites.

Air Pollutants, Occupational↗
PubMed1987

Penetration of methyl isocyanate through organic vapor and acid gas respirator cartridges.

Methyl isocyanate (MIC) is a volatile, toxic chemical [Threshold Limit Value (TLV) = 0.02 ppm] used to manufacture carbamate pesticides. The principal manufacturer of MIC is Union Carbide, and the site of production is Institute, West Virginia. In light of the December 1984 Bhopal, India disaster and possible safety problems at the Institute facility, NIOSH conducted this research as a basis upon which to recommend protective equipment that might be used in an emergency situation where extremely high MIC concentrations might be encountered. Both protective clothing and respirators were evaluated. In particular, NIOSH studied air-purifying respirators in order to assess their effectiveness against MIC vapor penetration. NIOSH does not recommend any air purifying respirator for MIC because of its high toxicity and lack of warning properties and because no effective end of service life indicator currently is available for MIC. This report addresses only MIC penetration through air-purifying cartridges at challenge concentrations designed to simulate emergency escape conditions. Another report addresses the protective clothing issue. The results presented are for two different manufacturers' organic vapor (OV) and acid gas cartridges. Penetration tests were conducted at three or four MIC challenge concentrations and at three different humidity conditions. In general, breakthrough times (1% of challenge concentration) were very short (less than 20 min). Also, high relative humidity was found to decrease the breakthrough time of MIC.

Cyanates↗
PubMed1990

Collection of silica and asbestos aerosols by respirators at steady and cyclic flow.

Air purifying dust/mist respirators are presently tested using a silica aerosol under conditions of steady flow. In experiments, the predictive validity of such tests was evaluated by testing respirators using silica and asbestos aerosols under conditions of both steady and cyclic flow. Silica penetration at steady flow was reasonably predictive of silica penetration under cyclic flow. However, asbestos penetration under cyclic flow was not predicted well by penetration of either silica or asbestos at steady flow. Furthermore, the potential for exhalation valve failure under cyclic flow was identified. Current NIOSH protocols for evaluating respirator performance should be reconsidered in light of these findings.

Aerosols↗
PubMed1990

Aerosol penetration through respirator exhalation valves.

Exhalation valves are a critical component of industrial respirators. They are designed to permit minimal inward leakage of air contaminants during inhalation and provide low resistance during exhalation. Under normal conditions, penetration of aerosol through exhalation valves is minimal. The exhalation valve is, however, a vulnerable component of a respirator and under actual working conditions may become dirty or damaged to the point of causing significant leakage. Aerosol penetration was measured for normal exhalation valves and valves compromised by paint or fine copper wires on the valve seat. Penetration increased with increasing wire diameter. A wire 250 microns in diameter allowed greater than 1% penetration into the mask cavity. Dirt or paint accumulated on the exhalation valve allowed a similar level of penetration. Work rate had little effect on observed penetration. Penetration decreased significantly with increasing aerosol particle size. The amount of material on the valve or valve seat necessary for significant (greater than 0.5%) inward leakage in a half-mask respirator could be readily observed by careful inspection of the exhalation valve and its seat in good lighting conditions.

Aerosols↗
PubMed1990

Variability in protection afforded by half-mask respirators against styrene exposure in the field.

Concentrations of styrene were measured in the breathing zone and inside the facepiece of air-purifying half-mask respirators of 13 workers for three to six 1-hr periods while they were engaged in the production of fiberglass-reinforced products. These data were used to estimate the protection afforded by the respirators. In arriving at these estimates, it was necessary to correct the concentration measured inside the mask for pulmonary retention of styrene by the workers. Workers were classified as sprayers or as other production line workers not directly carrying out spraying operations. An analysis of variance showed no evidence of differences in the level of protection afforded by the respirators between the two job classes. A second analysis of variance showed that protection varied between workers as well as for a single worker during different wearing periods. The geometric standard deviation (GSD) between workers was 1.92, the common within-worker GSD was 2.93, and the total GSD was 3.51. One-half of a population of wearers with similar protection would be expected to experience long-term average workplace protection factors in excess of 44 and one-half below that value. The observation of between-worker and within-worker variability in protection indicates that both sources of variability have to be taken into account in the specification of maximum use concentrations.

Air Pollutants, Occupational↗
PubMed1992

Measurement of 3-D facial contours for the design of half-face respirators.

A portable anthropometric test rig capable of obtaining three-dimensional face shape data was developed and used to obtain information relating to facial shape, stiffness, and variance for a selected subgroup of respirator users in the Australian work force. A respirator seal shape most suited to the sample population was obtained by studying the central portion of the face of all the subjects. The optimum seal shape was established by following the path of minimum variance among all the faces; the method provided information on the shape, dimensions, and stiffness of the optimum seal for a respirator suited to the sample population. The seal surface flexibility required for a comfortable fit was determined by measuring the deflection of the skin caused by an applied pressure and using this information along with face shape variance data. Results indicated that the required flexibility in the seal surface increased toward the lower portion of the face.

Anthropometry↗
PubMed1992

Breakthrough time and adsorption capacity of respirator cartridges.

A model developed in previous studies was applied to investigate the respirator cartridge contaminant breakthrough of 121 different chemical compounds. Included in this set of 121 contaminants are representative examples of various types of organic compounds, (e.g., acetates, ketones, aromatics, alcohols, amines, alkanes, chlorinated hydrocarbons). Intrinsic to the model are two important parameters, k' (a rate constant) and tau (50% breakthrough time). Values of the two parameters pertinent to an assault concentration of 1000 ppm were determined for each of the 121 organic compounds. These values were used to calculate the breakthrough time at specified fractional breakthrough as well as the respirator cartridge loading capacity under various conditions. An approach was presented that permits the determination of contaminant loading capacity (on carbon) as a function of breakthrough time at a specified assault concentration. The effect of contaminant assault concentration on the saturation capacity was investigated for various combinations of nine different compounds and three different types of respirator cartridges. Calculated saturation capacity data derived from application of the model compare favorably (+/- 5%) with corresponding experimental data. Saturation capacities calculated by using the model addressed in this study were compared with corresponding results previously calculated by others using the Dubinin adsorption isotherm.

Acetates↗
PubMed1992

Determination of program protection factors for half-mask respirators used at a mineral sands separation plant.

A study was conducted at a mineral sands separation plant to evaluate the workplace performance of half-mask filter cartridge respirators. Inhalation exposure was estimated by measuring the dust and radioactivity concentration inside the respirator while it was worn or hanging around the worker's neck. The program protection factor was determined by simultaneously measuring inside-mask and ambient (outside-mask) concentrations. A total of 27 tests were conducted, covering three brands of half-mask respirators; facial hair on test subjects ranged from clean-shaven to bearded. Program protection factors varied from 1.8 to 13 for dust exposure and 2.5 to 21 for radioactivity exposure. The geometric mean program protection factor over all tests was 5.1 (geometric standard deviation [GSD] = 1.7) for dust exposure and 7.5 (GSD = 1.7) for radioactivity exposure. A minimum program protection factor of 3.5 could be applied to ambient airborne concentration data to obtain a conservative, but more realistic, estimate of inhalation exposure on a worker category basis.

Air Pollutants, Radioactive↗
PubMedDate not supplied

Specific toxicity and crystallinity of alpha-quartz in respirable dust samples.

alpha-Quartz dust of respirable size--on inhalation--deposits in the lung, where it may remain for long duration and be a risk factor in the development of silicosis and (with increasing weight of evidence) lung cancer in humans. The risk assessment for these end points is fundamentally based on those properties of alpha-quartz that allow it to persist over time in the lung. For individual samples of respirable alpha-quartz it is likely that the specific toxicity of the alpha-quartz in the sample is related to this residence time, which, in turn, will be a function of its crystallinity because of the latter's potential influence on alpha-quartz's cytotoxicity and solubility. Current X-ray powder diffraction technology allows for the routine assessment of diffraction line broadening by measuring the full-width-at-half-maximum (FWHM) of a diffraction line. The FWHM for any accessible alpha-quartz diffraction line in a sample can then be used to directly assess Murata and Norman's Crystallinity Index for the alpha-quartz. This method greatly enhances the practicability of determining alpha-quartz crystallinity on individual respirable dust microsamples collected by personal sampling. It is likely that the Crystallinity Index will prove to be a useful measure of the specific toxicity of alpha-quartz and, hence, find incorporation into the risk assessment for alpha-quartz exposure.

Crystallization↗
PubMed1994

Modeling respirator penetration values with the beta distribution: an application to occupational tuberculosis transmission.

The lognormal distribution typically is used to model variability in respiratory penetration values. The lognormal model is a good descriptor where the average penetration value is low, but may be a poor descriptor where the average penetration value is high because a significant fraction of penetration values could be predicted to exceed unity. In this regard, the beta distribution offers greater flexibility than the lognormal in modeling penetration values over the physically plausible interval [0,1]. The beta distribution also is shown to be mathematically convenient for describing the risk of airborne transmission of tuberculosis among a respirator-wearing population. Infection can occur following inhalation of respirable particles, termed droplet nuclei, carrying viable Mycobacterium tuberculosis bacilli. Based on the expected number of infectious doses inhaled, the Poisson probability model traditionally is used to predict an individual's risk of infection. This article synthesizes the beta distribution, as applied to average penetration values among a respirator-wearing population, and the Poisson distribution, as applied to an individual's infection risk, to describe the population risk of M. tuberculosis infection.

Humans↗
PubMed1994

The effects of respirator use on workers' productivity in a mentally stressing task.

This article quantitatively determines the effect of wearing half-facepiece respirators, the most widely used type in industry, on worker productivity and efficiency in a mentally stressing task. An experiment investigated the performance of 10 subjects in a task simulating inspection of printed circuit boards. Accuracy and mean reaction time were tested automatically. Paced and unpaced task simulations were used to evaluate the effect of wearing the respirator on response times and the accuracy of subjects' responses for different product complexities and quality levels. The results indicated that wearing the respirator, in general, did not affect the speed or accuracy of subjects performing simulated inspection tasks. Pacing the task resulted in longer response times but did not affect accuracy. More complex products resulted in longer response times but also did not affect accuracy. High product quality resulted in longer response times and a higher miss rate. In terms of accuracy and reaction times a statistically significant difference was found in the performance of subjects.

Adult↗
PubMed1995

Development of a new qualitative test for fit testing respirators.

A new qualitative fit test was developed using Bitrex (Macfarland Smith Limited) as the test agent. It was validated by running a series of paired qualitative and quantitative fit tests. Quantitative tests were conducted with a small corn oil aerosol, using a condensation nucleus counter as a detector. Qualitative fit tests were run with Bitrex and saccharin, following the established protocol for the saccharin fit test. Four models of National Institute for Occupational Safety and Health--approved replaceable filter respirators were used in the study. All were half mask models equipped with high efficiency filters. In some cases, respirators expected to be the correct size for test subjects were tested. In other cases, respirators expected to be too small or too large for the subjects were tested. Test results were analyzed using fit test method validation criteria recommended in the American National Standards Institute draft standard on fit testing (ANSIZ88.10). The Bitrex and saccharin tests were found to have virtually identical performance. Both met proposed American National Standards Institute requirements for a valid qualitative fit test.

Female↗
PubMed1997

Effect of leak location on measured respirator fit.

A significant difference in leak detection as a function of leak location was observed during a study assessing how well current models of quantitative fit-test systems detect leakage. Known sources of leakage (matched hypodermic needles) were introduced at three fixed locations into factory-probed half-mask and full-face respirators mounted on a headform-breathing machine system. The leak locations were the bridge of the nose, the cheek, and the chin. Baseline leakage into each respirator was determined by conducting a fit-test with all fixed leak sources capped. Fit tests were repeated with each individual source uncapped. Study objectives included determining (1) how well each system measured the leakage, and (2) whether leak location had any effect on leak measurement. An ambient aerosol fit-test system (Portacount Plus) and a controlled negative pressure (CNP) fit-test system (FitTester 3000) were used. The ambient aerosol system detected an overall average of 37.2% of the known leakage, with a coefficient of variation of 44.7%. An analysis of variance showed significant differences in aerosol system measurements of leakage as a function of leak location and mask type (p < 0.001). A different pattern of aerosol leak detection as a function of leak location was observed between half-mask and full-face respirators, which appears to be related to differences in in-mask airflow dynamics. The CNP system detected an overall average of 97.9% of the known leakage through the same hypodermic needles, with a coefficient of variation of 4.3%. CNP system results were not affected by leak location (p > 0.43) or mask type (p > 0.32).

Aerosols↗
PubMed1998

Development of respirable aerosol samplers using porous foams.

Workplace aerosols must be sampled to assess the degree of health hazard caused by the particulate matter. By adjusting the sampling flow rate, most of the samplers can match the 50% cutoff size, but not the slope of the respirable convention defined by the American Conference of Governmental Industrial Hygienists, the International Organization for Standardization, and the European Committee for Standardization (CEN). Combinations of foams (or other porous material) of different nominal sizes (10-100 ppi) and thicknesses (5-35 mm) were employed to overcome this bias. A foam disk 25 mm in diameter was placed in an asbestos sampling cowl. Dioctylphthalate was the liquid test agent. An aerodynamic particle sizer and an Aerosizer were calibrated against a settling chamber and were employed to measure the aerosol number concentrations and size distributions upstream and downstream of the foams. The sampling efficiency data showed that the 50% cutoff size could be met for foams in series, but that the slope remained sharper than the new definition. Foams in parallel showed great flexibility and many of the parallel combinations flattened the slope, closer to that of the new international respirable convention. For instance, when the total flow rate is set at 10.1 L/min the aerosol penetration through foams in parallel (100 ppi, 20 mm thick, diameter 25 mm + 10 ppi, 20 mm thick, diameter 13 mm) nearly matched the new international standard for respirable fraction. This sampler can be further miniaturized for smaller sampling flow rates to fit the capacity of personal sampling pumps.

Aerosols↗