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At least 1,225 records · Page 68Linked to original sources
PubMed1988

Experiments supporting the use of ambient aerosols for quantitative respirator fit testing.

Most methods for testing facial seal leakage on subjects undergoing respirator fit tests involve comparing the generated aerosol particulate concentration inside the subject's respirator to the concentration in a test chamber. These aerosols are produced by fogging substances such as corn oil, dioctyl sebacate, or dioctyl phthalate (DOP) into the test chamber. The health effects of these substances and of their aerosols on respiratory systems are uncertain. The proposed alternate method uses as a test medium ambient particles which exist in most room atmospheres. The proposed method eliminates the need for a test chamber and for an intentionally produced aerosol. The subject is tested for respirator inleakage by comparing the particulate count concentration inside the subject's respirator to that of the room atmosphere outside the respirator. This method is less expensive and simpler to administer than the use of oil or other deliberately produced aerosols because it uses an existing ambient test medium. Statistical analysis of the test data indicates favorable comparison with the conventional chamber-aerosol method.

Aerosols↗
PubMed1989

Physical performance during combinations of hypercapnic, resistive, and hot air breathing.

Performance time for a 3.2-km (2-mi) run at maximal voluntary speed was determined for 12 subjects under seven experimental conditions: resistance breathing (R), hypercapnia (C), hot air breathing (H), and combinations R + C, R + H, H + C, and R + H + C. The tests were performed on a treadmill at 5% grade. Performance time was increased significantly when the subjects were exposed to resistance breathing alone (9%) or to any combination condition containing resistance (16%-31%). The effect of breathing resistance was not specific to the presence or absence of C, H, or their combination. Nevertheless, the physiological effects were not additive and could not be predicted by knowing the effects of the individual stresses. Performance time also was increased in Condition H + C (9%). Pulmonary ventilation was the most affected physiological variable, significantly reduced in Conditions R, H, C + R, H + R, and H + C + R. In conclusion, a multistress approach should be used when determining physiological responses or performance limitations brought about by real or simulated industrial respirator-wear conditions.

Adult↗
PubMed1989

"Worst case" aerosol testing parameters: I. Sodium chloride and dioctyl phthalate aerosol filter efficiency as a function of particle size and flow rate.

The efficiency of filter media is dependent on the characteristics of the challenge aerosol and the filter's construction. Challenge aerosol parameters, such as particle size, density, shape, electrical charge, and flow rate, are influential in determining the filter's efficiency. In this regard, a so-called "worst case" set of conditions has been proposed for testing respirator filter efficiency in order to ensure wearer protection. Data collected on various types of filters (dust and mist; dust, fume, and mist; paint, lacquer, and enamel mist; and high efficiency) challenged with a worst case-type sodium chloride (NaCl) and dioctyl phthalate (DOP) aerosol are presented. The particle size of maximum penetration varies as a function of filter type and was less than 0.25-micron count mean diameter (CMD) in all cases. The count efficiency for high efficiency filters was greater than 99.97% at worst case testing conditions, but the worst case count efficiencies for dust and mist; dust, fume and mist; and paint, lacquer and enamel mist filters were not nearly as efficient as existing test methods indicate. Also, as the test flow rate is increased, the count efficiency decreases. Thus, respirator filters were found to conform to the prediction of single-fiber filtration theory.

Aerosols↗
PubMed1989

"Worst case" aerosol testing parameters: II. Efficiency dependence of commercial respirator filters on humidity pretreatment.

Previous studies have shown that relative humidity has a degrading effect on the performance of commercially available particulate air-purifying respirator filters. That degradation results from a reduction of charge within the filter. This study was done to evaluate the time-dependent effects of relative humidity pretreatment and the reduction of charge on filter penetration against a most penetrating, "worst case" aerosol challenge. Filters of the dust and mist; dust, fume, and mist; paint, lacquer, and enamel mist; and high efficiency types were tested after being pretreated in an environment of 38 degrees C and 85% relative humidity for periods up to 42 days. After various intervals of pretreatment (1, 7, 14, 28, and 42 days), the filters were tested against neutralized worst-case sodium chloride (NaCl) and dioctyl phthalate (DOP) aerosols for percent penetration. The results showed a drop in filter efficiency of approximately 2%-6% depending on preconditioning time, except for the high efficiency filters tested which showed no detectable change.

Aerosols↗
PubMed1989

"Worst-case" aerosol testing parameters: III. Initial penetration of charged and neutralized lead fume and silica dust aerosols through clean, unloaded respirator filters.

The National Institute for Occupational Safety and Health (NIOSH) tests and certifies respirator filter media according to Title 30, Code of Federal Regulations, Part 11 (30 CFR 11). Subpart K of those regulations specifies that a silica dust test, silica mist test, and/or lead fume test will be used to test and certify dust and mist; and dust, fume, and mist particulate air-purifying respirator filter media. NIOSH studies have shown that an aerosol particle of a certain size can be identified as the most penetrating particle ("worst case") size. Commercial filter media of various types have been studied and the filter's performance against a worst-case sodium chloride (NaCl) and dioctyl phthalate (DOP) aerosol evaluated. This investigation was done to complement those previous studies by determining how one manufacturer's particulate filters performed against the existing certification aerosol challenges as compared with the worst-case size DOP and NaCl aerosols. Only initial penetration values were determined, and no loading effects were considered. Both neutralized (Boltzman charge distribution) and unneutralized aerosols were used in order to assess the contribution of charging. The results show the dramatic effect of particle size on filter efficiency, and they show that the present methods are not as sensitive as the worst-case aerosol method.

Aerosols↗
PubMed1989

A review of the wheeler equation and comparison of its applications to organic vapor respirator cartridge breakthrough data.

This project was undertaken to study the effect of dry airflow rate and bed weight on organic vapor respirator cartridge breakthrough curves for a single vapor (acetone) and challenge concentration (1060 ppm average). Dried cartridges from a single manufactured lot were used. The data were analyzed using three applications of the Wheeler equation, including (1) varying bed weight, (2) varying residence time, and (3) fitting the breakthrough curve. These approaches are discussed and equations given. Values for the adsorption capacity (We) and the rate coefficient (kv) are presented and compared. Based on these comparisons, limitations of the Wheeler equation are discussed and guidelines given concerning its use.

Acetone↗
PubMed1989

Ozone removal capability of a welding fume respirator containing activated charcoal.

Development of air purifying respirators for protection against ozone has been slowed by concerns about oxidation of charcoal and other available sorbents. The suitability of a charcoal sorbent for low concentrations of ozone was evaluated as a part of the development of a half-mask air purifying respirator designed for welding fumes and ozone. Testing of the respirator confirmed that charcoal can be a suitable sorbent for low levels of ozone. Where the respirator is properly selected, fit tested, and worn, respirator use against welding fumes and ozone at concentrations not exceeding 10 times the permissible exposure limit had been recommended.

Charcoal↗
PubMed1989

Development of a field method for evaluating the service life of organic vapor cartridges: results of laboratory testing using carbon tetrachloride.

A new method for determining the service life of respirator cartridges has been developed and tested in a laboratory setting. The method involves using small respirator carbon tubes (RCTs) packed with sorbent obtained from a respirator cartridge of interest. The tubes may be taken into an industrial setting and used to evaluate the work environment. A sample tube is placed directly behind the RCT and periodically replaced. This tube acts as a backup section to the RCT. The sample tube can be brought back to a laboratory and analyzed for the contaminant of interest using validated sampling methods specific for the contaminant. Alternatively, a direct-reading instrument can be placed at the exit end of the RCT to obtain "real-time" breakthrough information. The results, when combined with existing sorbent theories, can be used to predict the service life of a respirator cartridge. The advantage of using RCTs is that, unlike respirator cartridges, they can be taken into the field and used with traditional high-flow air sampling pumps. This method is designed to be able to determine the service life of respirator cartridges even when multiple contaminants are present in the workplace. Results of initial laboratory studies, using carbon tetrachloride as a challenge agent, indicated that RCTs were capable of predicting cartridge service life within an accuracy of +/- 15%.

Carbon Tetrachloride↗
PubMed1989

Collection efficiency of respirator filters challenged with monodisperse latex aerosols.

Collection efficiency was evaluated for 10 respirator manufacturers' electrostatically-charged dust/mist filters challenged with eight sizes of latex spheres in a range representative of the silica aerosol used in National Institute for Occupational Safety and Health (NIOSH) certification tests. Minimum efficiency occurred at or below the smallest size of 0.102 microns. Appreciable differences were found in the performances of filters distributed by the 10 manufacturers. Filters produced by 1 manufacturer exhibited significantly lower collection efficiency than other filters tested; those produced by 2 manufacturers performed somewhat better than the others tested. Statistical evaluation of Weibull-transformed data using analyses of covariance and Tukey's significant difference test allowed classification of the 10 manufacturers into three performance categories.

Aerosols↗
PubMed1990

Effects of humidity and contaminant concentration on respirator cartridge breakthrough.

A model described previously was developed further to examine the effect of both test humidity and contaminant assault concentration on respirator cartridge service life. The model emphasized the characterization of cartridge performance in the range of 0% to 50% breakthrough. This study specifically addressed a contaminant concentration range of 250-2000 ppm and test humidities ranging from 0% to 80%. The preconditioning humidity was fixed at 50%. The compounds studied were benzene and methyl chloroform. Two parameters, k' and tau, were described and values of these parameters were determined for each of several different sets of experimental conditions. The determined values of k' and tau were applied using derived expressions to generate each of several complete breakthrough curves for benzene and for methyl chloroform at specified contaminant assault concentrations and test humidities. The effect of humidity on the value of an additional theoretical parameter, a, was investigated. Values of this parameter and the parameters, k and K", were determined for specific test conditions. These values were substituted into pertinent expressions to produce a complete set of breakthrough curves (each curve corresponding to a particular contaminant assault concentration) for a given compound at a fixed test humidity. Several examples of breakthrough curves were generated for methyl chloroform. The results derived from the study agreed with corresponding experimental data.

Equipment Failure↗
PubMed1990

Identification of faceseal leak sites on a half-mask respirator.

A method has been developed to identify the location and shape of respirator faceseal leak sites by the deposition of a fluorescent tracer. An aerosol generation, conditioning, and exposure system to provide a test environment with stable aerosol concentration and size distribution of 4-methyl-7-diethylaminocoumarin was designed and tested. Faceseal leak sites on a respirator mounted on a mannequin and worn by human subjects were identified by deposition of the tracer aerosol and subsequent observation under long-wave ultraviolet lighting. Test parameters were identified for the optimal definition of leaks. Photographic techniques were developed to document the identified leak sites.

Adult↗
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↗