Eight-hour Time-weighted Average Research Articles

Evaluation of personal exposure of workers to indium concentrations in total dust and its respirable fraction at three Japanese indium plants.

This study aimed to evaluate personal exposures of 27 workers to indium compounds as “total” dust and its “respirable” fraction in their breathing zones at 3 Japanese indium plants. Eight-hour time-weighted average (TWA) indium concentrations of personal exposure to dust collected in sampling periods of 6 h or longer were determined by ICP-MS. The arithmetic means of exposure concentrations were 0.095 mg indium (In)/m3, when sampled as total dust, and 0.059 mg In/m3, as respirable fraction. ACGIH’s TLV-TWA of 0.1 mg In/m3 for total particulate matter and Acceptable Exposure Concentration Limit (AECL) of 3×10−4 mg In/m3 for the respirable fraction notified by the Japanese Ministry of Health, Labour and Welfare were used to evaluate the exposure concentrations. Twenty-five out of 27 workers were exposed to indium concentrations lower than TLV-TWA, while all of the workers were exposed to the indium concentrations higher than AECL. We noted that there was a large discrepancy between the two occupational exposure limits referred to in this report, and these differences were attributed to the sampling strategies and health effects used as the prevention targets. Carcinogenicity of the respirable fraction of indium-containing particulates was considered in setting AECL, whereas it was not in ACGIH’s TLV.

Innovative IAQ Organic Sensor

An innovative organic sensor for the monitoring of indoor air quality is described. For office buildings and schools the main requirements are: temperature, RH %, O2 and CO2 concentrations. Moreover low O2 and high CO2 concentrations can be hazardous. There are a lot of sensors based on different principal transducers that are able to detect very low concentrations of CO2, O2, and RH%.The system is based on a resistive interdigital sensor based on an organic sensing material, anthocyanin. Anthocyanins are natural pigments widely distributed in nature: they are produced by plants as secondary metabolites responsible for the pigmentation of many flowers, fruits and vegetables. In this work authors show the possibility to use this innovative organic sensor to monitor indoor air quality by measuring O2 concentration shifts with respect to a standard of 20% (20.000ppm) and the critical CO2 concentration value of about 5% (5000ppm) which is comparable with OSHA (Occupational Safety & Health Administration) standard in an eight-hour time-weighted average (TWA).

Using Caution Around Ethylene Oxide

I would like to comment on Becky Crossley's “Troubleshoot It” column (November/December 2011 issue of BI&T) concerning ethylene oxide (ETO). The article raised a number of excellent points, but there were some that I felt needed amplification, since ETO is and will be a part of our sterile processing world for years to come, and, if it is not managed properly, can be a real hazard. Note that my company, H&W Technology, LLC, formerly manufactured FDA-cleared ETO control systems, and still do for industry. We sit on the relevant AAMI standards committees for this type of sterilization, so I am speaking from an informed position.There are good reasons to be cautious when working around ethylene oxide, and engineering controls must be maintained for its safe use. The one, overriding regulation is promulgated by the Occupational Safety and Health Administration (OSHA) in 29 CFR 1910.1047. It says that the action level for ethylene oxide is a time-weighted average of 0.5 PPM, that no employee shall be exposed to more than 1 PPM in an eight-hour time-weighted average, and that the maximum 15-minute exposure is 5 PPM average. That's the law. If your facility is not measuring to make certain that these limits are observed, it should be.Safety features built into all ETO sterilizers built in the past 20–25 years make them quite safe in normal usage and if maintained properly. These features include door locks/interlocks, which Ms. Crossley mentions, integrated ventilation systems, and controllers that will not allow an uncontrolled release of ETO into the environment if the sterilizer is working at all. Most ETO sterilizers these days operate under a vacuum at all times, so opening the door becomes impossible. Even on rather old machines (those from the 1980s), the door switch will lock out the valve that delivers the ETO to the sterilizer chamber, making it nearly impossible for ETO to be released when the door is open. (Anything can, and will happen, but this is good safety engineering at work.)AAMI ST41 and AAMI ST79 are quite explicit on the needs for room ventilation (number of air changes per hour and negative pressure relative to the surrounding area) to remove ETO from the work areas, and are, as U.S. National Standards, a requirement for healthcare facilities. Also, scrubbers and thermal burners destroy the ethylene oxide, which is the only toxin in the exhaust stream from these sterilizers. These devices convert the ETO into carbon dioxide and water. The scrubbers/thermal burners should be the only path for the exhaust of the sterilizer to release to the environment if the system is properly designed and maintained.In the current state of the art, and with proper equipment maintenance, ETO may be used safely. If anything goes wrong in a cycle, only persons with specific training on the machines and ETO safety should be allowed to deal with the problem and remove the goods, which must be aerated or reprocessed.I think that the article raised excellent points and hope that my contribution to it will add to the demystification of this process. Remember, all sterilization processes are hazardous. If they weren't, they wouldn't sterilize. The point is to know enough about the process to keep it where it needs to be—inside the sterilizer chamber—and away from the staff and patients.

Benzene Inhalation by Parts Washers: New Estimates Based on Measures of Occupational Exposure to Solvent Coaromatics

Questions persist regarding assessment of workers' exposures to products containing low levels of benzene, such as mineral spirit solvent (MSS). This study summarizes previously unpublished data for parts-washing activities, and evaluates potential daily and lifetime cumulative benzene exposures incurred by workers who used historical and current formulations of a recycled mineral spirits solvent in manual parts washers. Measured benzene concentrations in historical samples from parts-washing operations were frequently below analytical detection limits. To better assess benzene exposure among these workers, air-to-solvent concentration ratios measured for toluene, ethylbenzene, and xylenes (TEX) were used to predict those for benzene based on a statistical model, conditional on physical-chemical theory supported by new thermodynamic calculations of TEX and benzene activity coefficients in a modeled MSS-type solvent. Using probabilistic methods, the distributions of benzene concentrations were then combined with distributions of other exposure parameters to estimate eight-hour time-weighted average (TWA) exposure concentration distributions and corresponding daily respiratory dose distributions for workers using these solvents in parts washers. The estimated 50th (95th) percentile of the daily respiratory dose and corresponding eight-hour TWA air concentration for workers performing parts washing are 0.079 (0.77) mg and 0.0030 (0.028) parts per million by volume (ppm) for historical solvent, and 0.020 (0.20) mg and 0.00078 (0.0075) ppm for current solvent, respectively. Both 95th percentile eight-hour TWA respiratory exposure estimates for solvent formulations are less than 10% of the current Occupational Safety and Health Administration permissible exposure limit of 1.0 ppm for benzene.

Assessing Noise Exposures in Farm Youths

Objective: This exploratory study evaluated the feasibility of field exposureassessment methods to characterize the noise sources and levels that farm youthsexperience during a typical workday. Methods: Detailed exposure assessments were performed with a sample of 10 farm youths working on Vermont dairy farms to characterize potential noise hazards typical in the farm setting. Personal and area noise measurements were taken using noise dosimeters. Information concerning work- and non-work-related noise exposure histories was collected via questionnaire. Results: The average age was 15.5 years (SD 2.5, range 10-18). Youths started working at an average age of 8.4 years (SD 2.3, range 6-12) and during the summer months worked an average of 41.3 hours per week (SD 32.3, range 2-68). Two youths exceeded the OSHA action level, having eight-hour time-weighted averages of 95 dBA and 92 dBA, or alternatively, doses of 206% and 127%. (The OSHA action level for the hearing conservation amendment is an eight-hour time-weighted average of 85 dBA or a dose of 50%.) Participants exceeding the action level reported working with tractors, skid steers (Bobcats), and all-terrain vehicles and doing general barn work. Additional sources of noise exposure included a mechanical silo elevator, chain saw, and wood splitter. Conclusion: Two of the monitored subjects were overexposed to noise in their farm work. Youths may be exposed to noise levels that exceed adult OSHA hearing conservation amendment action level as part of their daily farm activities.

Airborne asbestos concentration from brake changing does not exceed permissible exposure limit

The use in the past, and to a lesser extent today, of chrysotile asbestos in automobile brake systems causes health concerns among professional mechanics. Therefore, we conducted four separate tests in order to evaluate an auto mechanic’s exposure to airborne asbestos fibers while performing routine brake maintenance. Four nearly identical automobiles from 1960s having four wheel drum brakes were used. Each automobile was fitted with new replacement asbestos-containing brake shoes and then driven over a predetermined public road course for about 2253 km. Then, each car was separately brought into a repair facility; the brakes removed and replaced with new asbestos-containing shoes. The test conditions, methods, and tools were as commonly used during the 1960s. The mechanic was experienced in brake maintenance, having worked in the automobile repair profession beginning in the 1960s. Effects of three independent variables, e.g., filing, sanding, and arc grinding of the replacement brake shoe elements, were tested. Personal and area air samples were collected and analyzed for the presence of fibers, asbestos fibers, total dust, and respirable dust. The results indicated a presence in the air of only chrysotile asbestos and an absence of other types of asbestos. Airborne chrysotile fiber exposures for each test remained below currently applicable limit of 0.1 fiber/ml (eight-hour time-weighted average).

Respirable Concrete Dust--Silicosis Hazard in the Construction Industry

Concrete is an extremely important part of the infrastructure of modern life and must be replaced as it ages. Many of the methods of removing, repairing, or altering existing concrete structures have the potential for producing vast quantities of respirable dust. Since crystalline silica in the form of quartz is a major component of concrete, airborne respirable quartz dust may be produced during construction work involving the disturbance of concrete, thereby producing a silicosis hazard for exposed workers. Silicosis is a debilitating and sometimes fatal lung disease resulting from breathing microscopic particles of crystalline silica. Between 1992 and 1998, the National Institute for Occupational Safety and Health (NIOSH) made visits to construction projects where concrete was being mechanically disturbed in order to obtain data concerning respirable crystalline silica dust exposures. The construction activities studied included: abrasive blasting, concrete pavement sawing and drilling, and asphalt/concrete milling. Air samples of respirable dust were obtained using 10-mm nylon cyclone pre-separators, 37-mm polyvinyl chloride (PVC) filters, and constant-flow pumps calibrated at 1.7 L/min. In addition, high-volume respirable dust samples were obtained on 37-mm PVC filters using 1/2" metal cyclones (Sensidyne model 18) and constant-flow pumps calibrated at 9.0 L/min. Air sample analysis included total weight gain by gravimetric analysis according to NIOSH Analytical Method 600 and respirable crystalline silica (quartz and cristobalite) using x-ray diffraction, as per NIOSH Analytical Method 7500. For abrasive blasting of concrete structures, the respirable crystalline silica (quartz) concentration ranged up to 14.0 mg/m3 for a 96-minute sample resulting in an eight-hour time-weighted average (TWA) of 2.8 mg/m3. For drilling concrete highway pavement the respirable quartz concentrations ranged up to 4.4 mg/m3 for a 358-minute sample, resulting in an eight-hour TWA of 3.3 mg/m3. For concrete wall grinding during new building construction the respirable quartz measurements ranged up to 0.66 mg/m3 for a 191-minute sample, resulting in an eight-hour TWA of 0.26 mg/m3. The air sampling results for concrete sawing ranged up to 14.0 mg/m3 for a 350-minute sample resulting in an eight-hour TWA of 10.0 mg/m3. During the milling of asphalt from concrete highway pavement, the sampling indicated a respirable quartz concentration ranging up to 0.34 mg/m3 for a 504-minute sample, resulting in an eight-hour TWA of 0.36 mg/m3. The results of this work indicate the potential for respirable quartz concentrations involving disturbance of concrete to range up to 280 times the NIOSH Recommended Exposure Limit (REL) of 0.05 mg/m3 assuming exposure for an eight- to ten-hour workday. Considering the aging of the concrete infrastructure in the United States, these results pose a challenge to all who have an interest in preventing silica exposures and the associated disease silicosis.

Fiber release during the removal of asbestos-containing gaskets: a work practice simulation.

Work practice studies were conducted involving the removal of asbestos-containing sheet gaskets from steam flanges. These studies were performed to determine potential exposure levels to individuals who have worked with these types of materials in the past and may still work with these products today. The work practices were conducted inside an exposure characterization laboratory (ECL) and were performed by scraping and wire brushing, chrysotile-containing (65% to 85%) sheet gaskets from a number of used steam flanges. Airborne asbestos levels were measured by phase contrast microscopy (PCM) and transmission electron microscopy (TEM) for the personnel and area air samples collected during the study. These workplace simulations showed substantial asbestos fiber release using scraping, hand wire brushing, and power wire brushing techniques during the gasket removal process. The range of concentration was 2.1 to 31.0 fibers/cc greater than 5 micrometers when measured by PCM. These results contrasted with the few reported results in the published literature where lower airborne asbestos levels were reported. In these studies the airborne asbestos fiber levels measured in many of the samples exceeded all current and historical Occupational Safety and Health Administration (OSHA) excursion limits (15-30 minutes) and some previous permissible exposure limits (PEL) based on eight-hour time-weighted average (TWA) standards. Also, individuals who performed this type of work in the past may have had exposures higher than previously suspected. The results demonstrated that employees who remove dry asbestos-containing gaskets with no localized ventilation should wear a full face supplied air respirator with a HEPA escape canister and the work area should be designated a regulated area.

Evaluation of organic-vapor respirator cartridge efficiency for hexamethylene diisocyanate vapor in the presence of organic solvents.

Hexamethylene diisocyanate (HDI)-based polyisocyanates are widely used in formulating polyurethane coatings. These polyisocyanates contain a small amount of HDI monomer and the American Conference of Governmental Industrial Hygienists (ACGIH) recommends an eight-hour time-weighted average (TWA) threshold limit value (TLV) of 5 ppb for HDI. Some polyurethane (PU) paint applicators have used air-purifying paint spray respirators with organic vapor cartridges and particulate pre-filters. In this study, the effect of typical paint solvents on the efficiency of organic vapor cartridges (OVC) for HDI vapor was tested. A Teflon-coated polycarbonate exposure chamber was constructed. Three OVCs were simultaneously tested in an atmosphere containing HDI vapor and solvents. The test atmosphere was generated by evaporating a mixture of paint solvents containing n-butyl acetate, propylene glycol mono methyl ether acetate, toluene and methyl ethyl ketone, and neat HDI. The target challenge concentrations were 20 times the TLV for HDI and 10 times the combined TLV for the solvent mixture. The test atmosphere, with 20 or 80 percent relative humidity and at room temperature, was drawn through each cartridge at 32 L/min for 40 hours. However, in the last 8 hours of the test, the atmosphere had only HDI vapor. The pre- and the post-cartridge atmospheres were periodically sampled for HDI and the solvents. The study concluded that under the test conditions there was no detectable breakthrough of HDI from the OVCs. The average calculated efficiency of the OVCs, based on the HDI analytical limit of quantitation, was >99.4 percent for the 40 hours tested. The overall average challenge concentration of HDI was 105 ppb and the average combined solvent concentration was 3,176 mg/m3. The cartridges were saturated with solvents within the first 10 hours of testing; nevertheless, continued challenging with HDI vapor and solvents did not show any HDI breakthrough. Solvent breakthrough and breathing resistance, rather than HDI breakthrough, would be the key parameters in life expectancy calculations for cartridge change out schedules.

Estimating Factors to Convert Chinese ‘Total Dust’ Measurements to ACGIH Respirable Concentrations in Metal Mines and Pottery Industries

Historical data on the dust exposures of Chinese workers in metal mines (iron/copper, tin, tungsten) and pottery industries are being used in an ongoing joint Chinese/United States epidemiological study to investigate the exposure–response relationship for the development of silicosis, lung cancer, and other diseases. The historical data include ‘total dust’ concentrations determined by a Chinese method. Information about particle size distribution and the chemical and mineralogical content of airborne particles is generally not available. In addition, the historical Chinese sampling strategy is different from a typical American eight-hour time-weighted average (TWA) sampling strategy, because the Chinese samples were collected for approximately 15 minutes during production so the sample could be compared to their maximum allowable concentration (MAC) standard. Therefore, in order to assess American respirable dust exposure standards in light of the Chinese experience, factors are needed to convert historical Chinese total dust concentrations to respirable dust concentrations. As a part of the joint study to estimate the conversion factors, airborne dust samples were collected in 20 metal mines and 9 pottery factories in China during 1988 and 1989 using three different samplers: 10mm nylon cyclones, multi-stage ‘cassette’ impactors, and the traditional Chinese total dust samplers. More than 100 samples were collected and analysed for each of the three samplers. The study yielded two different estimates of the conversion factor from the Chinese total dust concentrations (measured during production processes) to respirable dust concentrations. The multivariate analysis of variance (MANOVA) reveals that, with a fixed sampling/analysis method, conversion factors were not statistically different among the different job titles within each industry. It also indicates that conversion factors among the industries were not statistically different. However, the two estimates consistently showed that conversion factors were the lowest in the pottery industry. Average conversion factors were then calculated for each of the estimates across the industries studied. A pooled mean conversion factor, 0.25±0.04, was then derived for all the job titles and industries. Respirable dust levels were estimated from the historical ‘total dust’ concentrations collected between 1952 and 1992 by adopting the American standard.

Estimating Factors to Convert Chinese ‘Total Dust’ Measurements to ACGIH Respirable Concentrations in Metal Mines and Pottery Industries

Historical data on the dust exposures of Chinese workers in metal mines (iron/copper, tin, tungsten) and pottery industries are being used in an ongoing joint Chinese/United States epidemiological study to investigate the exposure–response relationship for the development of silicosis, lung cancer, and other diseases. The historical data include ‘total dust’ concentrations determined by a Chinese method. Information about particle size distribution and the chemical and mineralogical content of airborne particles is generally not available. In addition, the historical Chinese sampling strategy is different from a typical American eight-hour time-weighted average (TWA) sampling strategy, because the Chinese samples were collected for approximately 15 minutes during production so the sample could be compared to their maximum allowable concentration (MAC) standard. Therefore, in order to assess American respirable dust exposure standards in light of the Chinese experience, factors are needed to convert historical Chinese total dust concentrations to respirable dust concentrations. As a part of the joint study to estimate the conversion factors, airborne dust samples were collected in 20 metal mines and 9 pottery factories in China during 1988 and 1989 using three different samplers: 10mm nylon cyclones, multi-stage ‘cassette’ impactors, and the traditional Chinese total dust samplers. More than 100 samples were collected and analysed for each of the three samplers. The study yielded two different estimates of the conversion factor from the Chinese total dust concentrations (measured during production processes) to respirable dust concentrations. The multivariate analysis of variance (MANOVA) reveals that, with a fixed sampling/analysis method, conversion factors were not statistically different among the different job titles within each industry. It also indicates that conversion factors among the industries were not statistically different. However, the two estimates consistently showed that conversion factors were the lowest in the pottery industry. Average conversion factors were then calculated for each of the estimates across the industries studied. A pooled mean conversion factor, 0.25±0.04, was then derived for all the job titles and industries. Respirable dust levels were estimated from the historical ‘total dust’ concentrations collected between 1952 and 1992 by adopting the American standard.

Exposures to 1,6-hexamethylene diisocyanate during polyurethane spray painting in the U.S. Air Force.

1,6-Hexamethylene diisocyanate (HDI) exposures were measured during polyurethane enamel spray painting at four Air Force bases. Breathing zone samples were collected for HDI monomer and polyisocyanates (oligomers) using three sampling methods: NIOSH Method 5521, the Iso-Chek sampler, and the total aerosol mass method (TAMM). Exposures to HDI monomer are low when compared to current occupational exposure limits; the highest 8-hr time-weighted average (TWA) exposure found was 3.5 micrograms/m3, below the American Conference of Governmental Industrial Hygienists (ACGIH) threshold limit value (TLV) of 34 micrograms/m3. HDI oligomer levels were higher; mean task exposures indicated by either the Iso-Chek sampler or TAMM are above the Oregon ceiling limit of 1 mg/m3. Eight-hour TWA exposures, however, were much lower, with only one exceeding the Oregon standard of 0.5 mg/m3. Poor worker practices commonly observed during this study included: standing in downwind positions so paint overspray passed through breathing zones; spraying toward other painters; and using excessive paint spray gun air cap pressures. Workers should stand in upwind orientation relative to the aircraft being painted, causing overspray to move away from the painter's breathing zone; adjust their position to prevent spraying other painters or limit paint application to one worker at a time; and use air cap pressure gauges prior to spraying to limit spray gun air cap pressures and reduce paint overspray generation rates. These improved techniques will result in reduced worker exposures to isocyanates.

Validation of Parachlorobenzotrifluoride, Benzotrifluoride, and Monochlorotoluene on Diffusive Samplers

Three solvents (OXSOL 10, monochlorotoluene or mixed isomers of 1- chloro-2-methyl benzene and 1-chloro-4-methyl benzene; OXSOL 100, parachlorobenzotrifluoride or 1-chloro-4-(trifluoromethyl) benzene; and OXSOL 2000, benzotrifluoride or trifluoromethyl benzene) produced by Occidental Chemical Corporation (Niagara Falls, NY) were considered as candidates for SKC, Inc.'s on-going diffusive sampler validation program. The 575-series diffusive sampler contains coconut-shell charcoal (575-001) or Anasorb 747 (575-002). Both samplers were used in this study. Desorption efficiency was tested at loadings equivalent to eight-hour time-weighted average (TWA) exposures to 0.01-2 times the Occidental Chemical Corporation in-house limit values (respectively: 50 ppm, 25 ppm, and 100 ppm,. All results met the National Institute for Occupational Safety and Health (NIOSH) criteria of > 75 percent, and, except for the lower loadings of parachlorobenzotrifluoride, the results were in the range of 90-110 percent. The calculated uptake rates were verified for different periods of exposure, up to eight hours, and found to be within 5 percent of the calculated for all three compounds on both samplers. A detailed comparison of the results from different time periods indicated no significant reverse diffusion effects for any combination of sampler and analyte. Samplers exposed to standard atmospheres of each compound were stored for three weeks at ambient temperatures and reanalyzed with results between 94 and 107 percent of expected. Based on full validation of samplers for the lower homologue (benzene), the bi-level theory of sample validation as endorsed by international validation protocols establishes this as a complete validation of the featured samplers for sampling vapors of these chemicals in air.

Formaldehyde exposure, acute pulmonary response, and exposure control options in a gross anatomy laboratory.

Formaldehyde exposure, acute pulmonary response, and exposure control options were evaluated in a group of 34 workers in a gross anatomy laboratory. Time-weighted average (TWA) exposure to formaldehyde ranged from 0.07-2.94 parts per million (ppm) during dissecting operations. More than 94% were exposed to formaldehyde in excess of the ceiling value of 0.3 ppm recommended by the American Conference of Governmental Industrial Hygienists (ACGIH). The eight-hour TWA exposure of 31.7% of the subjects exceeded the action level of 0.5 ppm set by the Occupational Safety and Health Administration (OSHA). Reported symptoms included irritation of eye (88%), nose (74%), throat (29%), and airways (21%). Forced vital capacity (FVC) and forced expiratory volume in 3 seconds (FEV3) decreased, and FEV1/FVC increased during the exposure. The changes of FEV3 were statistically different from those of the controls. The results strongly support the necessity for designing and testing special local exhaust-ventilated worktables with necessary flexibility for dissecting operations.

Characterization of Worker Exposures to Methylene Chloride Resulting from Application of Aerosol Glue in the Asbestos Abatement Industry

Abstract Adhesives containing large percentages of methylene chloride are commonly utilized in the asbestos abatement industry. The adhesive is used to seal polyethylene sheeting to the underlying surfaces, which in turn is used to contain the work area. When completely contained, the work area is essentially a confined space. During subsequent asbestos removal procedures, High Efficiency Particulate Air filter (HEPA)-equipped exhaust systems provide dilution ventilation to the work area, exhausting 1000 to 2000 cubic feet of air per minute per machine. This study characterizes worker exposure levels to methylene chloride when applying these adhesives during the construction of asbestos abatement containments. Personal samples were collected with both 3M organic vapor monitors and standard SKC charcoal tubes. Analysis of the sampling media was conducted by gas chromatography according to NIOSH Method 1005. Exposure periods, ranging from four to six hours, corresponded to a personal time-weighted average (TWA) of 0.09 to 270 ppm. This corresponded to an eight-hour TWA range from 0.06 to 140 ppm, respectively. Short-term exposure limits (STEL), 15 minutes in duration, ranged in concentration from non-detectable to 1294 ppm. Exposure concentrations greatly varied depending upon dilution ventilation, exposure period, adhesive quantity, and room volume. Sample results revealed that use of large quantities of adhesive in a confined area can result in high concentrations of methylene chloride. It is recommended that the HEPA-equipped exhaust systems, primarily designed to control airborne asbestos fiber levels during subsequent removal procedures, be utilized to provide dilution ventilation to the work area when applying these adhesives. It is a current Environmental Protection Agency and Occupational Safety and Health Administration recommendation to start the HEPA-equipped exhaust systems after the work area is completely sealed off and the decontamination unit has been constructed. If these systems are activated at the beginning of the preparation phase, they will create dilution ventilation that can decrease methylene chloride concentrations by a minimum of fourfold. In addition, air purifying respirators equipped with organic vapor cartridges or supplied air respirators should be worn by the workers to reduce their exposure levels even more. Finally, the aerosol manufacturers should substitute the methylene chloride in these products with a suitable, less toxic replacement.

Benzene and leukemia. A review of the literature and a risk assessment.

Benzene is widely recognized as a leukemogen, and the Occupational Safety and Health Administration is currently attempting to limit exposure to it more strictly. The proposed new regulation is a limit of an eight-hour time-weighted average of 1 ppm in place of the current limit of 10 ppm. The fundamental rationale for the change is a perception that the current standard is associated with an inordinate excess of leukemia. The epidemiologic literature on benzene and leukemia supports the inference that benzene causes acute myelocytic leukemia. However, the available data are too sparse, or suffer other limitations, to substantiate the idea that this causal association applies at low levels (i.e., 1-10 ppm) of benzene. Nonetheless, under the assumption that causation does apply at such low levels, a number of authors, including ourselves, have performed risk assessments using similar data but different methodologies. The assessments that we consider acceptable suggest that, among 1,000 men exposed to benzene at 10 ppm for a working lifetime of 30 years, there would occur about 50 excess deaths due to leukemia in addition to the baseline expectation of seven deaths. However, this estimate is speculative and whether or not enough confidence can be placed in it to justify a lower occupational benzene standard remains a decision for policy makers.

Benzene Exposure in the Petroleum Refining Industry

Abstract Benzene exposure data, submitted by nine petroleum refining companies, were studied with the general objective of characterizing the distribution of exposures within work operations and job categories. The data were collected by company hygienists over the period of years between 1978 and 1984. All measurements were of personal exposures determined using charcoal tubes or organic vapor monitors. Of the 123 location and unit specific job groups studied, most eight-hour time-weighted average (TWA) exposures were below 1.0 ppm. For some groups, however, the variability in exposure was such that ten percent or more of exposures exceeded 1.0 ppm. For nineteen of the most highly exposed groups, sufficient data were available to study the variability in exposure associated with individual workers versus the common work environment. Results indicate that there were some cases in which variability in exposure was mostly associated with the environment and others in which it was mostly associated with diff...

An analysis of exposure to styrene in the reinforced plastic boat-making industry.

To evaluate patterns of occupational exposure to styrene monomer in the boat-building industry, we conducted industrial hygiene surveys in seven fiberglass-reinforced plastic boat-fabrication plants. A total of 397 personal breathing zone air samples were collected on workers in four key job categories: gel coating and hull, deck, and small-parts lamination. We found that exposure to styrene in 234 (59%) of the personal samples exceeded the NIOSH-recommended time-weighted average (TWA) standard of 50 parts per million (ppm), and 96 (24%) of these samples exceeded the OSHA eight-hour TWA permissible exposure limit of 100 ppm. From highest to lowest average exposure potential, the job categories ranked in the following order: hull lamination (range 2-183 ppm, mean 78 ppm), deck lamination (range 12-160 ppm, mean 73 ppm), gel coating (range 5-94 ppm, mean 48 ppm), and small-parts lamination (range 9-130 ppm, mean 45 ppm). The former two categories composed a higher-exposure group, and the latter two tended to form a lower-exposure group. Exposures in these jobs appear to be proportional to resin consumption. Statistical analyses indicated that the parameter that most affects exposure potential is job category. Within a job category, part size, configuration, and surface area are important determinants of exposure. The principal reason for high exposures was the absence of control technologies and, in particular, the absence of adequate ventilation.

Effectiveness of a New Tissue Processor in Meeting OSHA Limits for Certain Tissue Processing Reagents

During the operation of a Tissue-Tek III ® Vacuum Infiltration Processor in a small unventilated room, the concentration of three reagent vapors—formalin, xylenes and isopropyl alcohol—was measured by continuous air sampling. The experimental data indicate that an employee's exposure to these vapors while operating this particular tissueprocessing unit during an eight-hour shift would be less than OSHA's eighthour time-weighted average (TWA) limits by one to two orders of magnitude. Furthermore, calculations reveal that these OSHA limits would not be exceeded even if the employee were positioned directly in front of the tissueprocessing unit during its entire 13-hour cycle. Even when the activated-carbon filter was removed from the air venting system, the vapor levels remained below OSHA limits. This study indicates that a substantial margin of safety regarding inhalation exposure to these toxic substances has been engineered into the unit's design, which incorporates a closed retort and controlled air system.

Benzene exposures during gasoline loading at bulk marketing terminals.

A study was conducted at 20 gasoline bulk marketing terminals to determine benzene exposure levels to both Gulf and outside carrier personnel operating at these facilities. Emphasis was placed on breathing zone samples of short duration during loading of trucks at the rack. Racks utilizing various methods of product transfer were surveyed. From the results of the study, it can be seen that the largest employee exposure to benzene occurs at facilities utilizing top loading without vapor recovery. Exposures during loading can exceed 0.5 ppm for an eight-hour time-weighted average.