Air-purifying Respirator Cartridges Research Articles

Estimating Reusability of Organic Air-Purifying Respirator Cartridges

Reuse of organic vapor air-purifying respirator cartridges after a job or shift can provide economy and energy savings. However, standards and manufacturers' guidance discourage reuse, presumably due to a lack of quantitative objective exposure and use information. Storage and simulated reuse laboratory studies and modeling have been done to provide such information. Two important parameters of breakthrough curves, midpoint time (related to adsorption capacity) and midpoint slope (related to adsorption rate), have been shown to be unchanged during storage for reuse. Extrapolations to smaller breakthrough concentrations and times can be made from this reference breakthrough and time. Significant step increases in breakthrough concentration upon cartridge reuse have been observed in some cases. Values of immediate breakthrough concentrations upon reuse (IBURs) have been measured and correlated. The Dubinin/Radushkevich adsorption isotherm equation has been used to estimate maximum IBURs, which depend on many factors, including conditions and duration of first use. An empirical equation describing rate of approach to maximum IBUR as a function of storage time has been developed to provide intermediate IBUR estimates, which are also very dependent on the vapor identity and extent of first-use loading. Using these equations, IBUR estimates with appropriate safety factors can be compared with the allowable breakthrough concentration to help the Industrial Hygienist make reusability decisions.

Estimating Service Lives of Organic Vapor Cartridges III: Multiple Vapors at All Humidities

A published model for estimating service lives of organic vapor (OV) air-purifying respirator cartridges has been extended to include multiple organic vapors at all humidities. Equilibria among the OVs are calculated using Ideal Adsorbed Solution Theory, whereas the effects of adsorbed water are considered as due to micropore volume exclusion. Solubilities of OVs in water must also be taken into account. Adsorption kinetics of components of mixtures are based on published correlations of the effects of covapors and water vapor. The dynamics of adsorption and competition are incorporated using expanding zones within the carbon bed, taking into account vapor and water displacements. Measurements of breakthrough curves for two ternary OV mixtures at high humidities have been done for a single cartridge type. The service life estimation model, implemented as a spreadsheet and a computer program, has been tested against these data as well as data for OV mixtures from literature sources. Good agreements were obtained between model predictions and experimental breakthrough times at dry conditions and humid conditions.

Estimating Service Lives of Air-Purifying Respirator Cartridges for Reactive Gas Removal

A mathematical model has been developed to estimate service lives of air-purifying respirator cartridges that remove gases reactively from flowing air. Most gases, because of their high volatility and low polarizability, are not effectively removed by physical adsorption on activated carbon. Models previously developed for toxic organic vapors cannot estimate service lives of cartridges for toxic gases. Often, an activated carbon is impregnated with a chemical to enhance gas removal by chemical reaction(s). The kinds of reactions, types and amounts of impregnants, and effects of the presence of water vary; therefore, the model requires user inputs of gas capacity and water effect parameters. Ideally, these should be available from manufacturers of the cartridges. If they are not, they can be extracted from measured breakthrough times using this model. The key to this model is the observation that adsorption rates of gases can be adequately quantified by the same correlations that have been reported for organic vapors. The resulting model has been used to correlate and predict breakthrough times for several common toxic gases.

Estimating Service Lives of Organic Vapor Cartridges II: A Single Vapor at All Humidities

A widely used equation model for estimating service lives of organic vapor air-purifying respirator cartridges has been updated with more recent research results. It has been expanded to account for effects of high relative humidities. Adsorption capacity competition between water vapor and organic vapor is largely explained by mutual exclusion of adsorption volume of the activated carbon. The Dubinin/Radushkevich equation is used to describe the adsorption isotherms of both water and organic vapors. Effects of relative humidity and adsorbed water on adsorption rates are described by an empirical correlation with breakthrough times. The dynamic natures of adsorption and competition are incorporated using an expanding zone model with displaced water rollup. The complete model has been tested and verified with published and unpublished data from many sources.

An Extended Equation for Rate Coefficients for Adsorption of Organic Vapors and Gases on Activated Carbons in Air-Purifying Respirator Cartridges

Organic vapor adsorption rates in air-purifying respirator cartridges (and other packed beds of activated carbon granules) need to be known for estimating service lives. The correlation of Lodewyckx and Vansant [AIHAJ 61:501–505 (2000)] for mass transfer coefficients for organic vapor adsorption onto activated carbon was tested with additional data from three sources. It was then extended to better describe all the data, including that for gases. The additional parameter that accomplished this was the square root of molar equilibrium capacity of the vapor or gas on the carbon. This change, along with skew corrections when appropriate, resulted in better correlations with all experimental rate coefficients.

An extended equation for rate coefficients for adsorption of organic vapors and gases on activated carbons in air-purifying respirator cartridges.

Organic vapor adsorption rates in air-purifying respirator cartridges (and other packed beds of activated carbon granules) need to be known for estimating service lives. The correlation of Lodewyckx and Vansant [AIHAJ 61:501-505 (2000)] for mass transfer coefficients for organic vapor adsorption onto activated carbon was tested with additional data from three sources. It was then extended to better describe all the data, including that for gases. The additional parameter that accomplished this was the square root of molar equilibrium capacity of the vapor or gas on the carbon. This change, along with skew corrections when appropriate, resulted in better correlations with all experimental rate coefficients.

Health effects of tank cleaners.

A total of 29 tank cleaners and 31 referent controls participated in the study. In most cases, the tank cleaners were employed in small companies, usually specialized subcontractors such as firms only working in refineries cleaning oil tanks and handling oil spills. The air concentrations of hydrocarbons (HCs) in tanks containing residuals from heavy fuel oil were generally low, unless the oil was still warm. Addition of light fuel oil to facilitate the cleaning of tanks containing viscous, heavy fuel oils resulted in total airborne HC levels of 1000-1500 mg/m3. High levels of HC were measured in tanks with low-boiling petroleum fractions (naphtha and light fuel oils) of 1000-2600 mg/m3 (maximum). Today, most cleaners use air-supplied respirators or air-purifying respirator cartridges inside tanks with petroleum products or other chemicals. The exception is small firms handling fuel oils for heating purposes where only 50% of the workers use protective equipment regularly; the other workers only occasionally use protective equipment even if the air concentrations of HC are high. Protective equipment is rarely used in small, domestic tanks. Measurements of heart rate showed that tank cleaning is, at times, a highly strenuous job. No differences between tank cleaners and controls were found with respect to spirometry, liver enzymes, or frequency of micronuclei. Acute intoxications were not frequently reported in this group. However, this investigation may underestimate the true risk, as it is a cross-sectional study that found that exposures were highly variable, both quantitatively and qualitatively. In many cases, the tank cleaners knew very little about the potential hazards or the proper use of protective equipment.(ABSTRACT TRUNCATED AT 250 WORDS)

Health Effects of Tank Cleaners

A total of 29 tank cleaners and 31 referent controls participated in the study. In most cases, the tank cleaners were employed in small companies, usually specialized subcontractors such as firms only working in refineries cleaning oil tanks and handling oil spills. The air concentrations of hydrocarbons (HCs) in tanks containing residuals from heavy fuel oil were generally low, unless the oil was still warm. Addition of light fuel oil to facilitate the cleaning of tanks containing viscous, heavy fuel oils resulted in total airborne HC levels of 1000–1500 mg/m3 High levels of HC were measured in tanks with low-boiling petroleum fractions (naphtha and light fuel oils) of 1000–2600 mg/m3 (maximum). Today, most cleaners use air-supplied respirators or air-purifying respirator cartridges inside tanks with petroleum products or other chemicals. The exception is small firms handling fuel oils for heating purposes where only 50% of the workers use protective equipment regularly; the other workers only occasionally use protective equipment even if the air concentrations of HC are high. Protective equipment is rarely used in small, domestic tanks. Measurements of heart rate showed that tank cleaning is, at times, a highly strenuous job. No differences between tank cleaners and controls were found with respect to spirometry, liver enzymes, or frequency of micronuclei. Acute intoxications were not frequently reported in this group. However, this investigation may underestimate the true risk, as it is a cross-sectional study that found that exposures were highly variable, both quantitively and qualitatively. In many cases, the tank cleaners knew very little about the potential hazards or the proper use of protective equipment. Implementation of training programs, protective equipment, better ventilation, and more automated cleaning techniques are needed. Medical attention and industrial hygiene surveillance of these workers is also recommended.

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.

Review of Influential Factors Affecting the Performance of Organic Vapor Air-Purifying Respirator Cartridges

Industrial hygienists must consider numerous diverse factors prior to selecting a respirator. An accurate evaluation of environmental conditions as well as work functions is essential if an organic vapor air purifying device is to be properly chosen. Environmental factors which need careful consideration are oxygen level, contaminant composition, contaminant concentration, contaminant's warning properties, temperature, and relative humidity. In addition, work rate and numerous other work-related factors must be carefully evaluated to assure worker safety. In fact, safety precautions are built into the regulations themselves (30 CFR Part 11) by imposing environmental and use limitations for organic vapor respirator cartridges. These include: 1. not for atmospheres which are immediately dangerous to life and health (IDLH), 2. not for use against gases or vapors with poor warning properties (unless permitted by MSHA/OSHA), and 3. not for use against gases or vapors which generate high heats of reaction with the sorbent. Further, there are concentration limitations for use of an organic vapor chemical cartridge respirator: the IDLH concentration of the specific organic vapors, a maximum use concentration (MUC) of 1000 PPM for organic vapors, and the allowable faceseal and exhalation valve leakages. Chemical cartridge respirators are not approved for use at concentrations above the lower of these three values. Thus, extreme care must be exercised when selecting organic vapor cartridges due to these constraints. It is therefore essential that one be knowledgeable concerning the influential factors affecting cartridge performance. This paper reviews and discusses some critical cartridge performance factors (environmental and other) which must be considered prior to the appropriate selection of an organic vapor air purifying cartridge respirator.

Review of Influential Factors Affecting the Performance of Organic Vapor Air-Purifying Respirator Cartridges

Industrial hygienists must consider numerous diverse factors prior to selecting a respirator. An accurate evaluation of environmental conditions as well as work functions is essential if an organic vapor air purifying device is to be properly chosen. Environmental factors which need careful consideration are oxygen level, contaminant composition, contaminant concentration, contaminant's warning properties, temperature, and relative humidity. In addition, work rate and numerous other work-related factors must be carefully evaluated to assure worker safety. In fact, safety precautions are built into the regulations themselves (30 CFR Part 11) by imposing environmental and use limitations for organic vapor respirator cartridges. These include: 1. not for atmospheres which are immediately dangerous to life and health (IDLH), 2. not for use against gases or vapors with poor warning properties (unless permitted by MSHA/OSHA), and 3. not for use against gases or vapors which generate high heats of reaction with ...