Ernest S. Moyer

Electrostatic Respirator Filter Media: Filter Efficiency and Most Penetrating Particle Size Effects

New electrostatic filter media has been developed for use in 42 CFR 84 negative pressure particulate respirator filters. This respirator filter media was not available for evaluation prior to the change from 30 CFR 11 to 42 CFR 84. Thus, characterization of this filter media is warranted. In this study, the new 42 CFR 84 electrostatic respirator filters were investigated with respect to filter penetration and most penetrating particle size. Three different models of N95 filters, along with one model each of the N99, R95, and P100 class filters were used in this study. First, three of each filter were loaded with a sodium chloride (NaCl) aerosol, and three of each filter were loaded with a dioctyl phthalate (DOP) aerosol to obtain normal background penetration results for each filter. Then, two new filters of each type were dipped in isopropanol for 15 seconds and allowed to dry. This isopropanol dip should reduce or eliminate any electrostatic charge on the fibers of each filter, as reported in the technical literature. These dipped filters, along with controls of each filter type, were tested on a TSI 8160 filter tester to determine the most penetrating particle size. These same filters were then tested against a NaCl aerosol to get final penetration values. Electret filters rely heavily on their electrostatic charge to provide adequate filter efficiencies, and correlations between penetration and a filters electrostatic characteristics are found in the technical literature. In all six of the filter models tested, filter penetration values increased considerably and the most penetrating particle size noticeably shifted toward larger particles. These results are important in better understanding how these new filter materials perform under various conditions, and they indicate the need for additional research to define environmental conditions that may affect electrostatic filter efficiency.

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.

A review and comparison of adsorption isotherm equations used to correlate and predict organic vapor cartridge capacities

Four adsorption isotherm equations for describing measured capacities of organic vapor air-purifying cartridges were compared. Experimental breakthrough curves were measured for five organic vapors: ethanol, carbon tetrachloride, acetone, chloroform, and hexane. Plots of service life at 1% breakthrough versus bed weight (stacked cartridges) yielded capacities over concentration ranges for three brands of cartridges. The Freundlich, Langmuir, Dubinin/Radushkevich, and Hacskaylol/LeVan isotherm equations fit the capacity versus vapor concentration data equally well, except in the case of ethanol. The ethanol fit was worse for the Freundlich equation. Other characteristics of these equations were related to their usefulness for correlating service life.

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, contaminants 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 ...

Reducing Enclosed Cab Drill Operator's Respirable Dust Exposure with Effective Filtration and Pressurization Techniques

Many different types of surface mining equipment use enclosed cabs to protect equipment operators from health and safety hazards. The overburden removal and mining process can be extremely dusty and can cause excessive dust exposure. To study this issue, a cooperative research effort was established between the National Institute for Occupational Safety and Health, U.S. Silica Co., Clean Air Filter Co., and Red Dot Corp. in an effort to lower respirable dust levels in an enclosed cab on an older surface drill at a silica sand operation. Throughout this research effort, a number of modifications were incorporated into the drills filtration and pressurization system, as well as in other areas, to improve its design and performance. An average cab efficiency of 93.4% was determined with the gravimetric sampling instruments when comparing the outside with the inside cab dust levels on the final design. Although this study considered just one operation, the goal was to identify cost-effective improvements that could be implemented on all types of enclosed cabs to lower respirable dust concentrations. Two critical components for an effective enclosed cab system are having a properly designed, installed, and maintained filtration and pressurization system, along with a method for maintaining structural cab integrity, which allows the cab to be positively pressurized. Another important component is maintaining cab cleanliness. Although this research was originally directed toward the mining industry, it is also applicable to agricultural or construction equipment.

Environmental Agricultural Tractor Cab Filter Efficiency and Field Evaluation

To evaluate filter efficiency and performance of environmental enclosures for tractors, 3- to 4-year-old tractor enclosure combinations (cabs retrofitted to tractors after manufacturing) were studied at a custom pesticide applicators facility. Optical particle counters were used to measure the aerosol number concentration inside and outside the cab. The ratio of these concentrations multiplied by 100 is termed percentage penetration, the amount of the aerosol that penetrates into the enclosure. For particles in the 0.3 to 0.4 microm range, penetration into the cab was reduced from 11 to 0.4% in the following sequential steps. First, manufacturing mistakes were corrected by fixing a bowed flange and inappropriate sealing of the sheet metal used to separate incoming air from air that had passed through the filter. This reduced aerosol penetration from 11 to 4.8%. Replacing gasket material on the used filter reduced penetration from 4.8 to 0.65%. This suggests that the filter gaskets are deforming and allowing leakage. Also, the filter media were evaluated for aerosol penetration as a function of particle size and were tested per the criteria stipulated in 42 CFR 84 for negative pressure air-purifying particulate respirators. These results showed penetration through the filter media of less than 0.03%, indicating that filter media were not a major source of aerosol leakage into the cab. The results suggest that the manufacturer should implement a quality control program to ensure that minimal aerosol penetration criteria into the cabs are met and an acceptable maintenance program exists to ensure compliance. Furthermore, the degradation of filter gasket material over time needs to be minimized to ensure that the environmental cabs continue to provide acceptable performance.

Organic Vapor (OV) Respirator Cartridge and Canister Testing Against Methylene Chloride

Abstract The Occupational Safety and Health Administration (OSHA) has proposed amending its existing exposure regulations for methylene chloride. The National Institute for Occupational Safety and Health (NIOSH) tested organic vapor cartridges and canisters for their breakthrough characteristics against methylene chloride. These tests were conducted to determine breakthrough times for methylene chloride with commercially available, negative-pressure organic vapor cartridge and canister respirators. Various methylene chloride challenge concentrations, from a low of 50 ppm to a high of 1000 ppm, were employed. Cartridges and canisters were tested “as received” from the manufacturer at a flow rate of 64 L/min through the respirator; 50 percent and 80 percent relative humidities were used. Breakthrough times (tb) were determined for individual cartridges and canisters, as well as for stacked cartridges. The results indicate that cartridge breakthrough times (tb) were extremely short when tested at 80 percent ...

Chemical Protective Clothing Breakthrough Time: Comparison of Several Test Systems

This study compared chemical permeation data obtained with a photo-ionization detector in both open- and closed-loop test systems. Also, chemical permeation data obtained at two flow rates with an infrared detector in a closed-loop test system were compared. Breakthrough times for acetone-neoprene were obtained using all systems. Results were evaluated and determined to be system dependent.

Frailty models of manufacturing effects.

The median service lifetime of respirator safety devices produced by different manufacturers is determined using frailty models to account for unobserved differences in manufacturing processes and raw materials. The gamma and positive stable frailty distributions are used to obtain survival distribution estimates when the baseline hazard is assumed to be Weibull. Frailty distributions are compared using laboratory test data of the failure times for 104 respirator cartridges produced by 10 different manufacturers tested with three different challenge agents. Likelihood ratio tests indicate that both frailty models provide a significant improvement over a Weibull model assuming independence. Results are compared to fixed effects approaches for analysis of this data.

Evaluation of Carbon Tetrachloride Replacement Agents for Use in Testing Nonpowered Organic Vapor Cartridges

Abstract Carbon tetrachloride has been used for years as a standard material for evaluating charcoals ability to adsorb organic materials. It has also been the standard organic compound for testing organic vapor breakthrough characteristics of respirator cartridges and canisters. However, due to the potential carcinogenic characteristic of carbon tetrachloride and the lack of commercial availability, a suitable substitute organic vapor cartridge test agent is needed. Four potential replacement agents were tested (ethyl acetate, pentane, n-hexane, and heptane). Initially, testing was performed using the stacked-cartridge test system. This screening method identified replacement agent challenge concentrations which gave breakthrough characteristics equivalent to 1000 parts per million (ppm) carbon tetrachloride. Breakthrough time was the critical criterion. Two test conditions (550 ppm pentane and 1000 ppm n-hexane) were selected for side-by-side testing with 1000 ppm carbon tetrachloride. The results show...