Respirator Cartridges Research Articles

Performance of Respirator Cartridges and Dust Filters for Protecting Passive Smoking

Performance of Respirator Cartridges and Dust Filters for Protecting Passive Smoking

Adsorption Characteristics of Activated Carbon Fibers in Respirator Cartridges for Toluene.

Respirator use has been shown to be associated with overall discomfort. Activated carbon fiber (ACF) has potential as an alternative adsorbent for developing thinner, lightweight, and efficient respirators due to its larger surface area, microporosity, and fabric form. The purpose of this pilot study was to determine the adsorption characteristics of commercially available ACF in respirator cartridges with varying ACF composition for toluene protection. Seven ACF types (one cloth, six felt) with varying properties were tested. Seven ACF cartridge configurations with varying ACF composition were challenged with five toluene concentrations (20–500 ppm) at constant air temperature (23 °C), relative humidity (50%), and air flow (32 LPM). Breakthrough curves were obtained using photoionization detectors. Breakthrough times (10%, 50%, and 5 ppm) and adsorption capacities were compared among ACF cartridge configurations to determine their suitable application in respiratory protection. Results showed that ACF cartridges containing the densest ACF felt types had the longest average breakthrough times (e.g., ~250–270 min to reach 5 ppm breakthrough time) and those containing ACF felt types with the highest specific surface areas had the highest average adsorption capacity (~450–470 mg/g). The ACF cartridges demonstrated breakthrough times of <1 h for 500 ppm toluene and 8–16 h for 20 ppm toluene. The ACF cartridges are more reliable for use at low ambient toluene concentrations but still have potential for use at higher concentrations for short-term protection. ACF felt forms with appropriate properties (density of ~0.07 g/cm3; specific surface area of ~2000 m2/g) have shown promising potential for the development of lighter and thinner respirators for protection against toluene.

The Uncertainty of a Residual Life Indicator Measurement by the Thermal Method for a Respirator Cartridge

The Uncertainty of a Residual Life Indicator Measurement by the Thermal Method for a Respirator Cartridge

The uncertainty of residual life indicator measurement by thermal method for respirator cartridge

Filtering and absorbing products in the form of a plate and working under conditions of convective blowing with cleared air residual life indicator uncertainties of measurement analysis is carried out. It is shown that for 0.8 mm thick KO2-based sorbent plates at a relative humidity of 60…90 % and a CO2 concentration of 1…4 %, the main factor of the uncertainty of indirect measurement of the residual life indicator is the Biot parameter characterizing the conditions of heat transfer from the plate surface. It has been experimentally proven that for Biot parameter in the range of 0–0.08, this factor contributes up to 30 % in the total uncertainty.

Preparation of a sepiolite/Cu-BDC nanocomposite and its application as an adsorbent in respirator cartridges for H2S removal

A newly developed Cu-BDC MOF nanocomposite based on natural sepiolite (Sep) was prepared and characterized using XRD, SEM, EDS, BET, and FTIR techniques for removal of hydrogen sulfide from the air.

Predicting the lifetime of organic vapor cartridges exposed to volatile organic compound mixtures using a partial differential equations model

ABSTRACTIn this study, equilibria, breakthrough curves, and breakthrough times were predicted for three binary mixtures of four volatile organic compounds (VOCs) using a model based on partial differential equations of dynamic adsorption coupling a mass balance, a simple Linear Driving Force (LDF) hypothesis to describe the kinetics, and the well-known Extended-Langmuir (EL) equilibrium model. The model aims to predict with a limited complexity, the BTCs of respirator cartridges exposed to binary vapor mixtures from equilibria and kinetics data obtained from single component. In the model, multicomponent mass transfer was simplified to use only single dynamic adsorption data. The EL expression used in this study predicted equilibria with relatively good accuracy for acetone/ethanol and ethanol/cyclohexane mixtures, but the prediction of cyclohexane uptake when mixed with heptane is less satisfactory. The BTCs given by the model were compared to experimental BTCs to determine the accuracy of the model and the impact of the approximation on mass transfer coefficients. From BTCs, breakthrough times at 10% of the exposure concentration t10% were determined. All t10% were predicted within 20% of the experimental values, and 63% of the breakthrough times were predicted within a 10% error. This study demonstrated that a simple mass balance combined with kinetic approximations is sufficient to predict lifetime for respirator cartridges exposed to VOC mixtures. It also showed that a commonly adopted approach to describe multicomponent adsorption based on volatility of VOC rather than adsorption equilibrium greatly overestimated the breakthrough times.

Systematic evaluation of the adsorption of organic vapors onto a miniaturized cartridge device using breakthrough tests in parallel experiment with a full size respirator cartridge

Breakthrough experiments are essential for the characterization of the adsorption capacity and micropore volume of activated carbon respiratory cartridges and for the validation and determination of cartridge service life models. In an effort to gain better control over environmental conditions in breakthrough tests and to obtain reliable data, a novel experimental approach using a miniaturized (Mini) cartridge was designed to replicate a small section of a respiratory cartridge. The Mini device and the organic vapor respiratory cartridge were tested in single and parallel experiments where in the former, one filter was tested one at a time and in the latter both devices were exposed simultaneously to the same conditions. The Mini device gave comparable results to the 10% breakthrough times and adsorption capacities of the organic vapor cartridges. The reproducibility of the packed carbon bed of the Mini provided strong support for using the Mini in breakthrough experiments for the characterization of the activated carbon adsorption capacity and estimation of cartridge service life.

Development of a hydrogen sulfide end-of-service-life indicator for respirator cartridges using cobinamide

An inexpensive paper-based sensor was developed for detecting low ppm concentrations of hydrogen sulfide gas. A piece of filter paper containing aquohydroxocobinamide [OH(H2O)Cbi] was placed on the end of a bifurcated optical fiber, and the reflectance spectrum of the OH(H2O)Cbi was monitored during exposure to 10.0ppm hydrogen sulfide gas (NIOSH recommended exposure limit). Reaction of sulfide (HS-) yielded an increase in reflectance from 400–450nm, and decrease from 470–550nm. Spectral changes were monitored as a function of time at 25, 50, and 85% relative humidity. Spectral shifts at high-er humidity suggested reduction of the Cbi(III) compound. The sensor was used to detect hydrogen sulfide breakthrough from respirator carbon beds and results correlated well with a standard electrochemical detector. The simple paper-based sensor could provide a real-time end-of-service-life alert for hydrogen sulfide gas.

Evaluation of a passive optical based end of service life indicator (ESLI) for organic vapor respirator cartridges

ABSTRACTA passive visual end of service life indicator (ESLI) for certain organic vapors has been attached to the inside wall of an organic vapor respirator cartridge. The opposite side of the ESLI touches activated carbon inside the cartridge. During use, organic vapors moving through the cartridge adsorb into both the carbon and the ESLI. The cartridge body is clear so that when vapor concentrations meet a certain threshold, the user may observe the progressive development of an indicator bar down the side of the ESLI. The cartridge is deemed ready to change when any part of the indicator bar touches a marked end line. The performance of the ESLI was observed when the cartridge was tested against a variety of organic vapors, exposure concentrations above the minimum indication level, humidities, temperatures, flow rates, and mixtures. In all cases, the ESLI indicated end of service life with more than 10% cartridge service life remaining (which is a NIOSH test criteria). The results were also compared to mathematical predictions of cartridge service life.

Determination of pressure drop across activated carbon fiber respirator cartridges

ABSTRACTActivated carbon fiber (ACF) is considered as an alternative adsorbent to granular activated carbon (GAC) for the development of thinner, lighter, and efficient respirators because of their larger surface area and adsorption capacities, thinner critical bed depth, lighter weight, and fabric form. This study aims to measure the pressure drop across different types of commercially available ACFs in respirator cartridges to determine the ACF composition and density that will result in acceptably breathable respirators. Seven ACF types in cloth (ACFC) and felt (ACFF) forms were tested. ACFs in cartridges were challenged with pre-conditioned constant air flow (43 LPM, 23°C, 50% RH) at different compositions (single- or combination-ACF type) in a test chamber. Pressure drop across ACF cartridges were obtained using a micromanometer, and compared among different cartridge configurations, to those of the GAC cartridge, and to the NIOSH breathing resistance requirements for respirator cartridges. Single-ACF type cartridges filled with any ACFF had pressure drop measurements (23.71–39.93 mmH2O) within the NIOSH inhalation resistance requirement of 40 mmH2O, while those of the ACFC cartridges (85.47±3.67 mmH2O) exceeded twice the limit due possibly to the denser weaving of ACFC fibers. All single ACFF-type cartridges had higher pressure drop compared to the GAC cartridge (23.13±1.14 mmH2O). Certain ACF combinations (2 ACFF or ACFC/ACFF types) resulted to pressure drop (26.39–32.81 mmH2O) below the NIOSH limit. All single-ACFF type and all combination-ACF type cartridges with acceptable pressure drop had much lower adsorbent weights than GAC (≤15.2% of GAC weight), showing potential for light-weight respirator cartridges. 100% ACFC in cartridges may result to respirators with high breathing resistance and, thus, is not recommended. The more dense ACFF and ACFC types may still be possibly used in respirators by combining them with less dense ACFF materials and/or by reducing cartridge bed depth to reduce pressure drop to acceptable levels. ACFF by itself may be more appropriate as adsorbent materials in ACF respirator cartridges in terms of acceptable breathing resistance.

Micropore characterization of activated carbons of respirator cartridges with argon, carbon dioxide, and organic vapors of different vapor pressures

Activated carbon is the preferred adsorbent to remove organic vapor (OV) because of its micropore structure. For ten activated carbons of commercially available respirator cartridges, the microstructure were characterized using argon at 87.3K, carbon dioxide at 273K, and five organic vapors having different vapor pressures (dichloromethane, n-hexane, methyl isobutyl ketone (MIBK), m-xylene, and toluene) at 500ppm, 294K, and 40% relative humidity. The corresponding OV adsorption isotherm at relative vapor pressures ranging from 9×10−4 to 0.1 exhibited the characteristic Type I isotherm as verified by the Langmuir model. The Dubinin Radushkevish (DR) equation was applied to the argon and OV data to extrapolate the micropore volumes and the specific relative structural constants, B. The micropore volumes obtained with the OV experimental data were within 0–19% from the values of the argon data. Comparison between the DR predicted and experimental adsorption capacities showed that the OV approach could successfully predict the adsorption capacity for the tested OV. The complementary characterization with carbon dioxide showed that narrow micropores might play an important role in the adsorption.

Air monitoring of aromatic hydrocarbons during automobile spray painting for developing change schedule of respirator cartridges

In the absence of End of Service Life Indicator (ESLI), a cartridge change schedule should be established for ensuring that cartridges are changed before their end of service life. Factors effecting service life of cartridges were evaluated, including the amount of atmospheric contamination with aromatic hydrocarbon vapors in the workplace, temperature, and relative humidity of the air. A new change schedule was established based on comparing the results of air monitoring and workplace conditions, laboratory experiment, and the NIOSH MultiVapor software. Spray painters were being exposed to aromatic hydrocarbons in a range exceeding occupational exposure limits. The cartridge change schedule was not effective and could no longer provide adequate protection against organic contaminants for sprayers. Change schedules for respirator cartridges should be reduced from 16–24 hours to 4 hours. NIOSH’s service life software program could be applied to developing cartridge change schedules.

Engineering UiO-66-NH2 for Toxic Gas Removal

The metal–organic framework UiO-66-NH2 was synthesized in a scaled batch of approximately 100 g. The material was then pressed into small pellets at pressures ranging from 5000 to 100000 psi to determine the effects on porosity and crystal structure. Nitrogen isotherm data and powder X-ray diffraction data indicate that the structure remains intact up to 25000 psi, with only a slight decrease in surface area. The structure exhibits significant degradation at pressures above 25000 psi. Subsequently, the powder was pressed at 5000 psi and then crushed and sieved into 20 × 40 mesh granules for evaluation against ammonia and cyanogen chloride in a breakthrough system simulating individual protection filters and respirator cartridges. The MOF showed capacity similar to that of a broad-spectrum carbon for both ammonia and cyanogen chloride; however, the breakthrough times, especially for cyanogen chloride, were dramatically reduced, likely as a result of mass-transfer limitations from the completely microporous...

Revising Organic Vapour Respirator Cartridge Change Schedule: a Case Study of a Paint Plant in Iran

After having revised the change schedule for organic vapour respirator cartridges in a paint plant in Iran, we established that it did not provide adequate protection against organic vapours at some workplaces and needed shortening from (48 to 72) h to 4 h. The revision also showed that relying on odour thresholds as the primary means to determine the time to change a chemical cartridge was not effective and that the National Institute for Occupational Safety and Health (NIOSH) MultiVapor service life software program could be applied to develop cartridge change schedules adjusted to specific workplaces.

Preparation of a new adsorbent from activated carbon and carbon nanofiber (AC/CNF) for manufacturing organic-vacbpour respirator cartridge

In this study a composite of activated carbon and carbon nanofiber (AC/CNF) was prepared to improve the performance of activated carbon (AC) for adsorption of volatile organic compounds (VOCs) and its utilization for respirator cartridges. Activated carbon was impregnated with a nickel nitrate catalyst precursor and carbon nanofibers (CNF) were deposited directly on the AC surface using catalytic chemical vapor deposition. Deposited CNFs on catalyst particles in AC micropores, were activated by CO2 to recover the surface area and micropores. Surface and textural characterizations of the prepared composites were investigated using Brunauer, Emmett and Teller’s (BET) technique and electron microscopy respectively. Prepared composite adsorbent was tested for benzene, toluene and xylene (BTX) adsorption and then employed in an organic respirator cartridge in granular form. Adsorption studies were conducted by passing air samples through the adsorbents in a glass column at an adjustable flow rate. Finally, any adsorbed species not retained by the adsorbents in the column were trapped in a charcoal sorbent tube and analyzed by gas chromatography. CNFs with a very thin diameter of about 10-20 nm were formed uniformly on the AC/CNF. The breakthrough time for cartridges prepared with CO2 activated AC/CNF was 117 minutes which are significantly longer than for those cartridges prepared with walnut shell- based activated carbon with the same weight of adsorbents. This study showed that a granular form CO2 activated AC/CNF composite could be a very effective alternate adsorbent for respirator cartridges due to its larger adsorption capacities and lower weight.

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.

Porous Silicon‐Based Optical Microsensors for Volatile Organic Analytes: Effect of Surface Chemistry on Stability and Specificity

AbstractSensing of the volatile organic compounds (VOCs) isopropyl alcohol (IPA) and heptane in air using sub‐millimeter porous silicon‐based sensor elements is demonstrated in the concentration range 50–800 ppm. The sensor elements are prepared as one‐dimensional photonic crystals (rugate filters) by programmed electrochemical etch of p++ silicon, and analyte sensing is achieved by measurement of the wavelength shift of the photonic resonance. The sensors are studied as a function of surface chemistry: ozone oxidation, thermal oxidation, hydrosilylation (1‐dodecene), electrochemical methylation, reaction with dicholorodimethylsilane and thermal carbonization with acetylene. The thermally oxidized and the dichlorodimethylsilane‐modified materials show the greatest stability under atmospheric conditions. Optical microsensors are prepared by attachment of the porous Si layer to the distal end of optical fibers. The acetylated porous Si microsensor displays a greater response to heptane than to IPA, whereas the other chemical modifications display a greater response to IPA than to heptane. The thermal oxide sensor displays a strong response to water vapor, while the acetylated material shows a relatively weak response. The results suggest that a combination of optical fiber sensors with different surface chemistries can be used to classify VOC analytes. Application of the miniature sensors to the detection of VOC breakthrough in a full‐scale activated carbon respirator cartridge simulator is demonstrated.

Thermal Reconditioning Characteristics of a Respirator Cartridge for Organic Vapors Using Humid Air as the Desorption Gas

Thermal reconditioning characteristics of organic vapors from a respirator cartridge were studied by introducing humid air into a cartridge that had adsorbed organic vapors in order to develop a thermal reconditioning method. Five different organic vapors (methanol, 2-propanol, acetone, dichloromethane and methyl acetate), most of which have relatively weak adsorption affinity to charcoal, were used in this study. Adsorption was carried out at a temperature of 25 degrees C. The relative humidity of the adsorption air with organic vapor was 50%. When the vapor concentration in the downstream of the respirator exceeded the breakthrough concentration, that is, the occupational exposure limits in Japan, the vapor supply was stopped. Then, desorption was started by introducing clean humid air from opposite side of the cartridge under a heated condition. When the desorbed vapor concentration fell below the limit of quantification, desorption process was ended and the next adsorption cycle was started after the temperature had returned to room temperature. This adsorption - desorption cycle was repeated more than three times. The desorption temperature was 65 degrees C and the relative humidity of desorption air was 20%, 50% or 70% at 25 degrees C. When the relative humidity was 20%, the breakthrough times of regenerated cartridges were shorter than that of a new one, but no difference was observed in the breakthrough curves when the relative humidity was greater than 50%. The results suggest that the thermal reconditioning of respirator cartridges using humid air is possible for these vapors.

CMOS-MEMS Capacitive Humidity Sensor

A high-sensitivity capacitive humidity sensor intended for use as part of a respirator end-of-service-life indicator system is presented. This paper reports a method for improving the sensitivity of integrated capacitive chemical sensors by removing the underlying substrate. The sensor is integrated with CMOS testing electronics using maskless postprocessing followed by ink-jet deposition of a sensitive polymer. Two different methods of depositing polymer, namely, capillary wicking and coating the top surface directly, were investigated. The sensors had measured sensitivities of 0.16% to 0.18% change in capacitance per percent relative humidity, which is the highest demonstrated for an integrated capacitive humidity sensor. Temperature sensitivity of the sensor, which is an important criterion for a sensor intended for a variety of different ambient conditions, was measured to be 0.07%/°C. The cross sensitivities to toluene and acetone, which are two common industrial solvents that are filtered by respirator cartridges, were measured to be 2.4 × 10-4 and 9.0 × 10-5%/ppm, respectively.

Adsorption of elemental mercury vapor by impregnated activated carbon from a commercial respirator cartridge

In order to protect workers from the harmful effects of mercury vapor, adsorption technology using impregnated activated carbon is currently in use in respirator cartridges to capture mercury vapor in breathing air. Adsorption onto the activated carbon can be improved through the modification of the carbon surface by impregnation with certain reagents that enhance the bonding of mercury either physically or chemically. The first objective of this study was to characterize the chemisorption behavior of a commercial adsorbent (3M-6009) by measuring the mercury breakthrough using a bench-top apparatus. The second objective was to develop a kinetic model describing the breakthrough behavior. Dynamic breakthrough concentrations were measured using a fixed bed to study the effects of the following adsorption parameters at room temperature: air flow-rate, adsorbent amount, inlet mercury concentration, and bed diameter. A model was developed in which, the rate of irreversible chemisorption was proportional to the concentration of mercury in the airflow, and the concentration of active sites of the surface of the carbon. A model incorporating two different types of the active sites was applied in an effort to differentiate the high initial adsorption rate mediated by readily accessible open sites from the lower adsorption rate mediated by the availability of hindered sites within micro-pores. The model developed herein was superior to a traditional isotherm model for describing the chemisorption behavior of impregnated activated carbon.