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PubMed1984

Application of gas adsorption kinetics--II. A theoretical model for respirator cartridge service life and its practical applications.

A previously introduced theoretical model addressing respirator cartridge contaminant breakthrough was further developed in this study. This development involved the introduction of a new theoretical parameter, a, to complement the parameters k' and tau employed in the initial theoretical approach. The extension of the theory permits the theoretical investigation of the following: (1) the effect of contaminant concentration on breakthrough time; (2) the effect of flow rate on breakthrough time; (3) the influence of contaminant concentration on percentage of breakthrough; and (4) the effect of contaminant concentration on the weight of adsorbed contaminant at a given time. We also compared new theoretical expressions with previously published empirical equations. Utilizing the parameter a, we derived a set of equations of significant practical value. These equations relate the ratio of two contaminant concentrations (one experimental reference concentration and any other concentration of interest) to either the ratio of the corresponding breakthrough times or the corresponding weights of adsorbed contaminant. Three practical examples are provided demonstrating that the new theoretical model reduces experimental work required to predict respirator cartridge service life.

Adsorption↗
PubMed1984

Respirator evaluation for carbon setters with beards.

Studies of several types of disposable respirators were carried out in a prebake aluminum reduction plant to determine the protection factors associated with airborne particulates in the potroom environment. Seventy-five (75) individual tests of respirator performance were carried out on 60 different carbon setters during the actual carbon setting task. Acceptable performance was achieved with all types of respirators tested. There was no significant difference in respirator performance for employees with or without beards.

Aluminum↗
PubMed1984

Workplace protection factor measurements on powered air-purifying respirators at a secondary lead smelter: results and discussion.

A study was conducted at a secondary lead smelter to evaluate the workplace performance of the 3M W-344 and Racal AH3 powered air-purifying respirators equipped with helmets and high efficiency filters. The research protocol developed for the study has been described in a companion paper. The results of the study indicate that the mean lead concentrations, measured inside the facepiece of both PAPRs, were significantly less than the OSHA lead exposure limit of 50 micrograms/m3. The means of the workplace protection factor measurements on both PAPRs were significantly less than the PAPR selection guide protection factor classification of 1000. Correlation analysis of preshift quantitative fit factors and corresponding workplace protection factors indicated no linear association between these two measures of performance. This finding suggests that for PAPRs equipped with helmets and high efficiency filters quantitative fit factors as presently determined are not indicative of the workplace protection which the respirators provide. Since the PAPR protection factor classification of 1000 was originally based on quantitative fit factors, the lack of a demonstrated association between quantitative fit factors and workplace protection as found in this study may explain why their performance was significantly less than expected.

Air Pollutants, Occupational↗
PubMed1985

Effects of air temperatures and humidities on efficiencies and lifetimes of air-purifying chemical respirator cartridges tested against methyl iodide.

Methyl iodide penetration curves through three types of respirator cartridges and canisters were determined at several temperatures to identify the significance of temperatures of testing and use. Three charcoal types showed similar results: triethylenediamine (5% TEDA-impregnated, (2% TEDA + 5% KI3)-impregnated, and unimpregnated. Penetration curves were shifted at higher temperatures in the range 25-38 degrees C, keeping relative humidity constant in the range 50-70%, but allowing absolute humidities to increase correspondingly. These shifts were such that penetrations were increased and service lives were decreased significantly (4-15% per degrees C). At constant water vapor concentration, service life of the (2% TEDA + 5% KI3)-impregnated charcoal increased with temperature, illustrating the complexity of temperature effects. For one case (5% TEDA) using cartridges at humidity equilibrium, temperature and humidity effects were sorted out. Until these effects are better understood, air-purifying respirator cartridge and canister testing should be done at conditions more representative of possible use and at more closely controlled temperatures.

Humidity↗
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↗
PubMed1985

Residence time model for respirator sorbent beds.

An experimental bed residence time model has been developed to characterize the performance of sorbent beds in removing gaseous contaminants. This model is applicable to both adsorption and chemisorption processes. The fundamental characteristics produced can be used to predict the performance of respirator cartridges and canisters over a wide range of operating conditions. A family of performance curves can be constructed for a specific product type for application in determining minimum service life and renewal frequency. This model is described in terms of a dynamic sorption concept, and is demonstrated using ASC I carbon and sulfur dioxide in air at concentrations of 500 ppm, 1000 ppm and 5000 ppm. Adsorption data is also provided for carbon tetrachloride. The effects of bed depth and superficial velocity reduce to a unique relationship between breakthrough time and bed residence time. The influences of moisture, concentration and heat transfer at the walls of the sorbent containment have all been investigated in this study. The dynamic sulfur dioxide capacity of ASC I carbon was found to increase significantly at increasing levels of adsorbed moisture for decreasing sulfur dioxide concentrations. The interrelation of moisture and concentration of sulfur dioxide produces a secondary removal mechanism for which the chemistry is briefly described.

Adsorption↗
PubMed1985

The quality of respirator programs: an analysis from OSHA compliance data.

The quality of respirator programs in typical workplaces was investigated by analyzing the history of compliance with OSHA Standard 29 CFR 1910.134 (respiratory protection). Analysis was focused on the approximately 47 000 health inspections conducted in the manufacturing industries [Standard Industrial Classification (SIC) Codes 2000-3999] in the period of October 1, 1976 to September 30, 1982. During this period, approximately 27% of inspections in which respirator programs were reviewed resulted in a citation for a specific program deficiency. Of inspected worksites in which respirators were in use to provide protection from concentrations of air contaminants in excess of OSHA Permissible Exposure Limits, 56% had deficiencies in at least one program area. Since the violations were of the type that have been shown to lower the level of protection provided by respirators, many workers may have been exposed to inhalation hazards as the result of ineffective respirator programs.

Air Pollutants, Occupational↗
PubMed1986

Determination of organic vapor respirator cartridge variability in terms of degree of activation of the carbon and cartridge packing density.

The protection provided by carbon-containing organic vapor respirator cartridges depends in part on the packing density of the carbon in the cartridges and its degree of activation. Large variations in these parameters could have significant effects on the service-life of respirator cartridges. Variability among commercially available organic vapor respirator cartridges was examined with regard to the following characteristics: the particle size distribution, amount of carbon and packing density of the carbon in the cartridges and the degree of activation of the carbon. The degree of activation was determined by measuring the maximum adsorption space and the structural constant of the carbon. These two parameters--Wo (cm3/g) and k (cal/M)-2--are constants in the Dubinin/Radushkevich (D/R) model from which physical absorption onto microporous adsorbents, such as activated carbon, are described. Respirator cartridges from three different suppliers were examined. Significant variability (11-40%) in the amount and the degree of activation of the carbon occurred between cartridges of different manufacturers, as well as among cartridges of an individual manufacturer.

Carbon↗
PubMed1987

Chemical cartridge respirator performance: 1,3-butadiene.

The chemical 1,3-Butadiene recently has been classified as a potential occupational carcinogen; subsequently, a reduction in the 8 hr TWA from 1000 ppm to 10 ppm has been proposed. Substantial quantities of 1,3-Butadiene are produced annually for use in the manufacture of a variety of rubber compounds, foams, resins and chemicals. Existing process environments may present a potential health hazard under the proposed standards, and the need for proper respiratory protection is evident. As a result, the performance of Scott organic vapor (642-OV), organic vapor/acid gas (642-OA) and acid gas (642-AG) twin cartridges has been determined for 1,3 butadiene. A cartridge test system was developed to generate challenge concentrations of 100 ppm and 1000 ppm; an infrared analyzer was used to measure breakthrough at 10 ppm. The residence time modeling concept developed previously was used to produce the performance characteristics for three types of activated carbon for residence times of 0.1 less than or equal to tau less than or equal to 1.0 sec. Kinetic adsorption capacities and adsorption rate constants were computed from this data, and cartridge performance also was predicted. The twin cartridges tested demonstrated reasonable adsorption capacity for 1,3 butadiene. Cartridge service life was found to be inversely proportional to airflow rate; it was reduced at elevated temperature and humidity conditions. Breakthrough times were approximately three times longer at 100 ppm than at 1000 ppm. When clean air was drawn through cartridges saturated with 1000 ppm 1,3 butadiene, desorption occurred readily. The rate of desorption and the peak concentration were found to be dependent upon the temperature, humidity and degree of saturation.

Adsorption↗
PubMed1987

The effect of temperature and humidity levels in a protective mask on user acceptability during exercise.

Subjective and physiological responses were obtained from six subjects wearing a ventilated face mask while exercising (3.8 met) for 15 min on a bicycle ergometer. Different combinations of ambient air temperatures (7 degrees, 16 degrees, 25 degrees C) and mask air temperatures (22 degrees, 27 degrees, 33 degrees C) were studied together with two different air humidities inside the mask (61% and 86% RH). Control experiments were performed without the mask at the same ambient temperatures. Skin temperatures, heart rates and skin wettedness were monitored during exercise. The subject's acceptance of the mask and thermal environment, thermal sensation, sensations of discomfort, sweating and skin wettedness, and their judgment of the work of breathing were assessed at the end of the 15 min exercise period. The acceptance of both the ambient thermal environment and of the thermal microclimate in the mask primarily was determined by the ambient air temperature, but it was influenced by the air temperature and humidity inside the mask. At ambient temperatures of 7 degrees C and 25 degrees C, the acceptance of the thermal work conditions decreased. In the warm environment a mask air temperature less than or equal to 27 degrees C was 100% acceptable and increased the acceptance of thermal environment. In the cool environment, a mask air temperature greater than or equal to 27 degrees C was 100% acceptable. The humidity content of the mask air was only important when the mask air was warm. Warm humid air significantly decreased acceptance of the mask conditions.

Adult↗
PubMed1987

Organic vapor (OV) respiratory cartridge testing--potential Jonas model applicability.

More efficient methods of characterizing organic vapor (OV) respirator performance against the wide range of compounds and environmental conditions found in industrial settings are needed to improve respiratory protection in the workplace. One method, based on Jonas' kinetic model, has potential application for evaluating OV cartridges and more efficiently utilizing available research, testing and certification resources. Jonas has shown that the kinetic adsorption capacity and gas adsorption rate of a small packed charcoal sorbent bed is described by the linear relationship between gas breakthrough time and sorbent weight as predicted by the modified Wheeler equation. This research is based on the hypothesis that characterizing sorbent performance against a reference compound will allow prediction of breakthrough times, and therefore prediction of cartridge life, for other compounds under similar conditions. Baseline data on dried cartridges at dry conditions are presented that demonstrate that the linear relationship between breakthrough time and and sorbent weight that Jonas showed for small sorbent columns also holds when commercially manufactured respiratory cartridges are stacked in series to resemble a packed column of varying bed length and sorbent weight. This suggests the potential applicability of the Jonas model for characterizing and evaluating commercially available OV respirator cartridges.

Acetone↗
PubMed1987

Performance of dust respirators with facial seal leaks: I. Experimental.

The ability of representative half-mask and single-use respirators with facial seal leaks to provide protection against aerosols was evaluated by experimental measurement. Respirators were mounted on a manikin in a test chamber and operated at seven steady flow rates over the range of 2 to 150 L/min. Samples of polydisperse and monodisperse aerosols were taken from inside and outside the respirator and analyzed by a calibrated optical particle counter over the particle-size range 0.1 to 11.3 microns. Measurements were made separately for filter performance as a function of particle size and flow rate, and simulated leak performance (penetration) as a function of particle size, pressure drop, and leak size. Flow rate vs. pressure drop measurements were made for all filters and leaks tested. For a given leak condition the percentage of the total flow traversing the leak varied several fold over the usual range of airflow rates through a respirator. Aerosol penetration was found to depend strongly on particle size and flow rate for filters, and to depend strongly on particle size and less strongly on pressure drop for leaks. One can conclude from these measurements that the aerosol-size distribution inside a respirator will nearly always be significantly different from that outside the respirator.

Aerosols↗
PubMed1987

Performance of dust respirators with facial seal leaks: II. Predictive model.

A performance model for half-mask and single-use respirators is presented. It represents a possible alternative to field measurements of respirator performance. Experimental data on filter and leak performance given in Part I were used to develop a model that allows one to predict 1) the overall respirator penetration as a function of particle size for any work rate and 2) overall total mass penetration for any work rate and exposure aerosol-size distribution for a known respirator filter and facial seal leak condition. A simplified method based on general regression equations is presented that allows one to estimate these quantities based on QNFT (quantitative fit testing) measurements and a knowledge of the exposure aerosol-size distribution. Example calculations are given for a situation in which QNFT gives a fit factor of 50 for a half-mask with dust, fume and mist filter cartridges, but predicted protection factors for various use conditions range from 20 to 81 depending on exposure particle-size distribution and work rate of the wearer.

Aerosols↗
PubMed1987

Particle size-dependent leakage and losses of aerosols in respirators.

Measuring particle size-dependent leakage into and losses inside a respirator reveals the deposition mechanisms occurring at the leak site and the flow dynamics inside the respirator. This study investigated particle size-dependent leakage and deposition within the mask by examining the leakage into the mask for different hole locations, probe locations, hole shapes, hole lengths and hole sizes. The shape of the leak has an effect on particle size-dependent leakage. Probe and leak location tests indicated that not only does the total measured leakage change but also the size-dependence of the leakage changes depending on the leak and probe locations. When the leak site is in the chin area, the clean air entering through the filters at the chin helps to carry the inward leakage into the breathing zone. Particle size-dependent leakage does occur and is due to both inertial entry losses at the leak site and within the mask, and diffusional losses within the mask and leak site. Particle size-dependent curves change shape as the hole size changes with relatively more larger particles entering through the small hole size.

Aerosols↗
PubMed1987

The effect of aerosol size distribution and measurement method on respirator fit.

The particle size-dependent leakage into a respirator was examined by measuring the leakage of particle sizes between 0.07 to 4.4 microns through three hole sizes in a negative-pressure half-mask respirator worn by a human subject. This investigation showed that the size distribution of an aerosol test agent and the measurement method have an effect on the leakage measured in a quantitative fit test. For instance, the ratio of percent leakage measured by light scattering between test aerosols with count median diameters of 2.2 and 0.28 microns can be as large at 5:1. Likewise, the ratio of the percent leakage measured by a particle count method vs. a mass method of detection of the same polydisperse aerosol with a count median diameter equal to 2.2 microns can be as high as 4:1. The mass leakage into a mask with a leak is also greater for an exposure aerosol with a count median diameter between 0.15 to 0.30 micron compared to exposure aerosols with larger count median diameters for aerosols with the same mass concentration.

Aerosols↗
PubMed1988

Facial hair and respirator fit: a review of the literature.

The effect of facial hair on the quality of fit obtained while wearing a tight-fitting respirator has been and continues to be a controversial subject. Many people hold strong opinions on both sides of the issue, but it is not opinion that is needed. Rather what is needed is quantitative study of the situation to determine precisely what effect facial hair has on respirator fit. The results of fourteen studies of the facial hair leakage question have been summarized. All but two of the fourteen studies found that in the presence of facial hair, face seal leakage increases from 20 times to 1000 times. In addition both intersubject and interrespirator face seal leakage variability increased when facial hair was present. In the other two studies, one completed with positive pressure SCBAs and the other completed in the workplace, no statistically significant leakage differences were found.

Equipment Failure↗
PubMed1988

Penetration of respirator filters by an asbestos aerosol.

Five models of respirator filters were challenged with a chrysotile aerosol, and the asbestos fiber penetration of the media was measured in five experimental series simulating different environmental conditions. Penetration of the facial seal was not evaluated. The penetration of each filter was determined from the ratio of the downstream to upstream concentrations of airborne asbestos fibers as measured by the standard National Institute for Occupational Safety and Health (NIOSH) asbestos fiber counting method P&CAM 239. Penetrations measured in this project and presented are indicative of penetrations of filters used a) fresh from the package, b) after exposure to an organic oil mist, c) after storage at high humidity at room and elevated temperatures, and d) after preexposure to water mist. Penetrations varied between less than 0.1% and 2.7% for filters tested fresh from the package and up to 18% after exposure to simulated field/environmental conditions. The data indicate that each of the filter models tested, except for the high efficiency filter, was affected adversely to some degree by one or more of the simulated field/environmental conditions.

Aerosols↗
PubMed1988

Effects of adsorbed water vapor on the adsorption rate constant and the kinetic adsorption capacity of the Wheeler kinetic model.

A recent trend in occupational safety and health has focused on the use of respiratory protective equipment to supplant engineering controls as the primary means of protecting workers from toxic substances. Respirator adsorbent cartridges have been demonstrated to have a finite capacity to adsorb toxic vapors. The knowledge of when this limit is approached or has been exceeded is crucial to the user. The Wheeler kinetic breakthrough model has been shown to describe accurately organic vapor penetration through beds of activated carbon. The model, however, does not account for competitive adsorption of water vapor or other organic vapors. The investigations reported here demonstrate the effect of adsorbed water vapor on the kinetic adsorption parameters (kinetic rate constant and kinetic saturation capacity) of the Wheeler equation. Adsorbent beds were equilibrated at varying concentrations of water vapor and then challenged with carbon tetrachloride vapor-laden air. Dry carbon had an initial rate constant of 62.5 s-1 and a kinetic adsorption capacity of 0.36 g of adsorbed CCl4/gram (g/g) of adsorbent. These parameters decreased in proportion to the amount of water vapor adsorbed, with the minimum predicted values occurring at 100% relative humidity. The minimum experimental value for the kinetic rate constant was 17.6 s-1, a decrease of 73% from the dry carbon values. The minimum predicted value for the kinetic adsorption capacity was 0.16 g/g, a decrease of 45%.

Adsorption↗