Assessment of Occupational Health Risks for Maintenance Work in Fabrication Facilities: Brief Review and Recommendations.

Background: This study focuses on assessing occupational risk for the health hazards encountered during maintenance works (MW) in semiconductor fabrication (FAB) facilities. Objectives: The objectives of this study include: 1) identifying the primary health hazards during MW in semiconductor FAB facilities; 2) reviewing the methods used in evaluating the likelihood and severity of health hazards through occupational health risk assessment (OHRA); and 3) suggesting variables for the categorization of likelihood of exposures to health hazards and the severity of health effects associated with MW in FAB facilities. Methods: A literature review was undertaken on OHRA methodology and health hazards resulting from MW in FAB facilities. Based on this review, approaches for categorizing the exposure to health hazards and the severity of health effects related to MW were recommended. Results: Maintenance workers in FAB facilities face exposure to hazards such as debris, machinery entanglement, and airborne particles laden with various chemical components. The level of engineering and administrative control measures is suggested to assess the likelihood of simultaneous chemical and dust exposure. Qualitative key factors for mixed exposure estimation during MW include the presence of safe operational protocols, the use of air-jet machines, the presence and effectiveness of local exhaust ventilation system, chamber post-purge and cooling, and proper respirator use. Using the risk (R) and hazard (H) codes of the Globally Harmonized System alongside carcinogenic, mutagenic, or reprotoxic classifications aid in categorizing health effect severity for OHRA. Conclusion: Further research is needed to apply our proposed variables in OHRA for MW in FAB facilities and subsequently validate the findings.

Recommendation for the establishment of a poison control center at the Korea Disease Control and Prevention Agency.

There is currently no governmental body in South Korea resembling the type of poison center (PC) recommended by the World Health Organization (WHO). All Organization for Economic Cooperation and Development (OECD) member countries except for South Korea maintain such a PC tasked with both preventing poisoning accidents and supporting the prompt treatment of poisoned patients. Such a PC could very possibly have allowed the country to more promptly recognize the widespread wave of humidifier disinfectant (HD) associated health effects, including fatal lung injury and death, that lasted started roughly in 2000 and continued through 2011. Despite this chemical poisoning tragedy, South Korea still lacks a surveillance system to monitor health effects caused by the use and consumption of materials that include products containing chemicals, foodborne pathogens, drugs, pesticides, etc. There have been no legal procedures for examining the potential risk of products or materials manufactured by industry. The reporting of national poisoning data or causes of poisoning, which is near ubiquitous in advanced countries with a PC, has not taken place We recommend that a PC should be established within the Korea Disease Control and Prevention Agency (KDCA). In addition, in order to perform surveillance of poisoning cases across the country, a certain number of regional PCs, including at large hospitals, will also be necessary.

Chemical use in the semiconductor manufacturing industry.

BACKGROUND: The semiconductor industry is known to use a number of chemicals, but little is known about the exact chemicals used due to the ingredients being kept as a trade secret. OBJECTIVES: The objective of this study was to analyze chemical use using a safety data sheet (SDS) and chemical inventory provided by a major semiconductor company, which operated two factories (A and B). METHODS: Descriptive statistics were obtained on the number of chemical products and ingredients, photoresists, and carcinogens, classified by the International Agency for Research on Cancer (IARC), as well as trade secret ingredients. The total chemical use per year was estimated from chemical inventories mass (kg). RESULTS: A total of 428 and 432 chemical products were used in factories A and B, respectively. The number of pure chemical ingredients, after removing both trade secret ingredients and multiple counting, was 189 and 157 in factories A and B, respectively. The number of products containing carcinogens, such as sulfuric acid, catechol, and naphthalene was 47/428 (A) and 28/432 (B). Chemicals used in photolithography were 21% (A) and 26% (B) of all chemical products, and more than 97% among them were chemicals containing trade secret ingredients. CONCLUSIONS: Each year, 4.3 and 8.3 tons of chemicals were used per person in factories A and B, respectively. Because of the high level of commercial secrecy and the use of many unregulated chemicals, more sustainable policies and methods should be implemented to address health and safety issues in the semiconductor industry.

Comprehensive Evaluation of Hazardous Chemical Exposure Control System at a Semiconductor Manufacturing Company in South Korea.

The goal of this study was to evaluate the hazardous chemical exposure control system in a semiconductor manufacturing company and recommend an appropriate exposure surveillance system for hazardous agents. We reviewed compliance-based chemical exposure data compiled between 2012 and 2014 by the study company. The chemical management system, characteristics of chemical use and hazardous gas monitoring system were also investigated. We evaluated the airborne isopropyl alcohol (IPA) and acetone generally used as cleaning solvents, volatile organic compounds and metals levels using internationally recommended sampling and analytical methods. Based on the results of past working environment measurement data and of our investigation, the overall current exposure to chemicals by semiconductor workers during routine production work appears to be controlled below occupational exposure limits. About 40% of chemical products used were found to contain at least one unidentifiable trade-secret substance. There are several situations and maintenance tasks that need special attention to reduce exposure to carcinogens as much as possible. In addition, a job-exposure matrix as a tool of surveillance system that can examine the exposure and health status of semiconductor workers according to type of operation and type of job or task is recommended.

Extremely Low Frequency-Magnetic Field (ELF-MF) Exposure Characteristics among Semiconductor Workers.

We assessed the exposure of semiconductor workers to extremely low frequency-magnetic fields (ELF-MF) and identified job characteristics affecting ELF-MF exposure. These were demonstrated by assessing the exposure of 117 workers involved in wafer fabrication (fab) and chip packaging wearing personal dosimeters for a full shift. A portable device was used to monitor ELF-MF in high temporal resolution. All measurements were categorized by operation, job and working activity during working time. ELF-MF exposure of workers were classified based on the quartiles of ELF-MF distribution. The average levels of ELF-MF exposure were 0.56 µT for fab workers, 0.59 µT for chip packaging workers and 0.89 µT for electrical engineers, respectively. Exposure to ELF-MF differed among types of factory, operation, job and activity. Workers engaged in the diffusion and chip testing activities showed the highest ELF-MF exposure. The ELF-MF exposures of process operators were found to be higher than those of maintenance engineers, although peak exposure and/or patterns varied. The groups with the highest quartile ELF-MF exposure level are operators in diffusion, ion implantation, module and testing operations, and maintenance engineers in diffusion, module and testing operations. In conclusion, ELF-MF exposure among workers can be substantially affected by the type of operation and job, and the activity or location.

Estimates of the Number of Workers Exposed to Diesel Engine Exhaust in South Korea from 1993 to 2013.

BACKGROUND: The aim of this study was to estimate the number of workers exposed to diesel engine exhaust (DEE) by industry and year in the Republic of Korea. METHOD: The estimates of workers potentially exposed to DEE in the Republic of Korea were calculated by industry on the basis of the carcinogen exposure (CAREX) surveillance system. The data on the labor force employed in DEE exposure industries were obtained from the Census on Establishments conducted by the Korea National Statistical Office from 1993 to 2013. The mean values of prevalence rates adopted by EU15 countries were used as the primary exposure prevalence rates. We also investigated the exposure prevalence rates and exposure characteristics of DEE in 359 workplaces representing 11 industries. RESULTS: The total number of workers exposed to DEE were estimated as 270,014 in 1993 and 417,034 in 2013 (2.2% of the total labor force). As of 2013, the industry categorized as "Land transport" showed the highest number of workers exposed to DEE with 174,359, followed by "Personal and household services" with 70,298, "Construction" with 45,555, "Wholesale and retail trade and restaurants and hotels" with 44,005, and "Sanitation and similar services" with 12,584. These five industries, with more than 10,000 workers exposed to DEE, accounted for 83% of the total DEE-exposed workers. Comparing primary prevalence rates used for preliminary estimation among 49 industries, "Metal ore mining" had the highest rate at 52.6%, followed by "Other mining" with 50.0%, and "Land transport" with 23.6%. CONCLUSION: The DEE prevalence rates we surveyed (1.3-19.8%) were higher than the primary prevalence rates. The most common emission sources of DEE were diesel engine vehicles such as forklifts, trucks, and vans. Our estimated numbers of workers exposed to DEE can be used to identify industries with workers requiring protection from potential exposure to DEE in the Republic of Korea.

Impact of Partial and Comprehensive Smoke-Free Regulations on Indoor Air Quality in Bars.

In Korea, smoke-free regulations have been gradually implemented in bars based on venue size. Smoking bans were implemented in 2013 for bars ≥150 m², in 2014 for bars ≥100 m², and in 2015 for bars of all sizes. The purpose of this study was to determine indoor fine particle (PM2.5) concentrations in bars before and after implementation of the smoke-free policies based on venue size. Indoor PM2.5 concentrations were measured with real-time aerosol monitors at four time points: (1) pre-regulation (n = 75); (2) after implementing the ban in bars ≥150 m² (n = 75); (3) after implementing the ban in bars ≥100 m² (n = 107); and (4) when all bars were smoke-free (n = 79). Our results showed that the geometric mean of the indoor PM2.5 concentrations of all bars decreased from 98.4 µg/m³ pre-regulation to 79.5, 42.9, and 26.6 µg/m³ after the ban on smoking in bars ≥150 m², ≥100 m², and all bars, respectively. Indoor PM2.5 concentrations in bars of each size decreased only after the corresponding regulations were implemented. Although smoking was not observed in Seoul bars after smoking was banned in all bars, smoking was observed in 4 of 21 bars in Changwon. Our study concludes that the greatest decrease in PM2.5 concentrations in bars was observed after the regulation covering all bars was implemented. However, despite the comprehensive ban, smoking was observed in bars in Changwon. Strict compliance with the regulations is needed to improve indoor air quality further.

Short-Term Impact of a Comprehensive Smoke-Free Law Following a Partial Smoke-Free Law on PM2.5 Concentration Levels at Hospitality Venues on the Peripheries of College Campuses.

Tobacco-free policies on college campuses are spreading in Korea. However, the impact of the smoking ban legislation at venues on the boundary of a college campus is still limited. This study aimed to assess short-term changes in PM2.5 concentrations before and after the enactment of the smoking ban legislation to evaluate the impact. In this cross-sectional study, PM2.5 measurements (pre-ban: n = 99, post-ban: n = 64) were conducted in randomly selected billiards, pubs, and computer game rooms on the peripheries of college campuses in October 2013, prior to implementation of the smoking ban, and in May 2014, after the ban. The median (interquartile range, IQR) of the PM2.5 concentration for all venues was 31 µg/m³ (0-80 µg/m³) in the pre-ban period and 11 µg/m³ (0-36 µg/m³) in the post-ban period implying indoor PM2.5 concentration levels of the peripheries of college campuses likely decreased one year after implementation of the ban. However, the differences were not significant yet. The results support the introduction of more rigorous monitoring of SHS exposure levels toward the ultimate goal of encouraging a complete smoking ban in hospitality venues, including billiards, pubs, and computer game rooms located on the peripheries of college campuses.

Occupational Exposure to Diesel Particulate Matter in Municipal Household Waste Workers.

OBJECTIVE: The purposes of this study were to determine the following: 1) the exposure levels of municipal household waste (MHW) workers to diesel particulate matter (DPM) using elemental carbon (EC), organic carbon (OC), total carbon (TC), black carbon (BC), and fine particulate matter (PM 2.5) as indicators; 2) the correlations among the indicators; 3) the optimal indicator for DPM; and 4) factors that influence personal exposure to DPM. METHODS: A total of 72 workers in five MHW collection companies were assessed over a period of 7 days from June to September 2014. Respirable EC/OC samples were quantified using the thermal optical transmittance method. BC and PM 2.5 were measured using real-time monitors, an aethalometer and a laser photometer. All results were statistically analyzed for occupational and environmental variables to identify the exposure determinants of DPM. RESULTS: The geometric mean of EC, OC, TC, BC and PM 2.5 concentrations were 4.8, 39.6, 44.8, 9.1 and 62.0 µg/m3, respectively. EC concentrations were significantly correlated with the concentrations of OC, TC and BC, but not with those of PM 2.5. The exposures of the MHW collectors to EC, OC, and TC were higher than those of the drivers (p<0.05). Workers of trucks meeting Euro 3 emission standard had higher exposures to EC, OC, TC and PM 2.5 than those working on Euro 4 trucks (p<0.05). Multiple regression analysis revealed that the job task, European engine emission standard, and average driving speed were the most influential factors in determining worker exposure. CONCLUSIONS: We assessed MHW workers' exposure to DPM using parallel sampling of five possible indicators. Of these five indicators, EC was shown to be the most useful indicator of DPM exposure for MHW workers, and the job task, European emission standard, and average driving speed were the main determinants of EC exposure.

Estimating Benzene Exposure Level over Time and by Industry Type through a Review of Literature on Korea.

The major purpose of this study is to construct a retrospective exposure assessment for benzene through a review of literature on Korea. Airborne benzene measurements reported in 34 articles were reviewed. A total of 15,729 individual measurements were compiled. Weighted arithmetic means [AM(w)] and their variance calculated across studies were summarized according to 5-year period intervals (prior to the 1970s through the 2010s) and industry type. Industries were classified according to Korea Standard Industrial Classification (KSIC) using information provided in the literature. We estimated quantitative retrospective exposure to benzene for each cell in the matrix through a combination of time and KSIC. Analysis of the AM(w) indicated reductions in exposure levels over time, regardless of industry, with mean levels prior to the 1980-1984 period of 50.4 ppm (n = 2,289), which dropped to 2.8 ppm (n = 305) in the 1990-1994 period, and to 0.1 ppm (n = 294) in the 1995-1999 period. There has been no improvement since the 2000s, when the AM(w) of 4.3 ppm (n = 6,211) for the 2005-2009 period and 4.5 ppm (n = 3,358) for the 2010-2013 period were estimated. A comparison by industry found no consistent patterns in the measurement results. Our estimated benzene measurements can be used to determine not only the possibility of retrospective exposure to benzene, but also to estimate the level of quantitative or semiquantitative retrospective exposure to benzene.

Characteristics of particulate matter generated while handling municipal household waste.

OBJECTIVES: This study was conducted to assess the size characteristics of particulate matter (PM) generated during waste collection and sorting, and to assess the effect of the type of waste-handling activity on levels of coarse and fine PM. METHODS: A portable aerosol spectrometer calibrated to 1.2 //min was used to monitor PM generated during four types of waste-handling activities. The types of PM measured included inhalable particulate matter (IPM), PM10, respirable particulate matter (RPM), PM2.5 and PM1. Twenty-eight data sets with 3,071 subsets recorded every 6 sec were categorized according to occupational and environmen¬tal classifications, including type of waste-handling activity. An ANOVA was used to compare PM levels characterized by size. Significant variables with p-values <0.25 were included in a multiple regression model for predicting levels of each PM. RESULTS: The average levels of PM10 and PM2.5 greatly exceeded the air-quality levels enforced by the Korean Ministry of the Environment. The highest PM2.5 fine-particle levels monitored were during waste-transfer work, while the highest IPM and PM10 coarse-particle levels monitored were during waste-sorting work. The type of waste-collection activity was the only factor that significantly affected both PM25 and IPM, accounting for 36% (p=0.0034) and 40% (p=0.0049), respectively, of the observed variations. None of the factors affected PM10 or RPM levels. CONCLUSIONS: Waste-collection and Waste-transfer work may be associated with the generation of high levels of fine PM, which can be influenced by environ Workmental conditions such as traffic levels and the type of waste transport vehicle.

Penetration of fiber versus spherical particles through filter media and faceseal leakage of N95 filtering facepiece respirators with cyclic flow.

This study investigated differences in penetration between fibers and spherical particles through faceseal leakage of an N95 filtering facepiece respirator. Three cyclic breathing flows were generated corresponding to mean inspiratory flow rates (MIF) of 15, 30, and 85 L/min. Fibers had a mean diameter of 1 µm and a median length of 4.9 µm (calculated aerodynamic diameter, d(ae) = 1.73 µm). Monodisperse polystyrene spheres with a mean physical diameter of 1.01 µm (PSI) and 1.54 µm (PSII) were used for comparison (calculated d(ae) = 1.05 and 1.58 µm, respectively). Two optical particle counters simultaneously determined concentrations inside and outside the respirator. Geometric means (GMs) for filter penetration of the fibers were 0.06, 0.09, and 0.08% at MIF of 15, 30, and 85 L/min, respectively. Corresponding values for PSI were 0.07, 0.12, and 0.12%. GMs for faceseal penetration of fibers were 0.40, 0.14, and 0.09% at MIF of 15, 30, and 85 L/min, respectively. Corresponding values for PSI were 0.96, 0.41, and 0.17%. Faceseal penetration decreased with increased breathing rate for both types of particles (p ≤ 0.001). GMs of filter and faceseal penetration of PSII at an MIF of 30 L/min were 0.14% and 0.36%, respectively. Filter penetration and faceseal penetration of fibers were significantly lower than those of PSI (p < 0.001) and PSII (p < 0.003). This confirmed that higher penetration of PSI was not due to slightly smaller aerodynamic diameter, indicating that the shape of fibers rather than their calculated mean aerodynamic diameter is a prevailing factor on deposition mechanisms through the tested respirator. In conclusion, faceseal penetration of fibers and spherical particles decreased with increasing breathing rate, which can be explained by increased capture by impaction. Spherical particles had 2.0-2.8 times higher penetration through faceseal leaks and 1.1-1.5 higher penetration through filter media than fibers, which can be attributed to differences in interception losses.

Evaluation of workers exposed to ethylene glycol monomethyl ether and ethylene glycol monomethyl ether acetate.

OBJECTIVES: Ethylene glycol monomethyl ether (EGME) and ethylene glycol monomethyl ether acetate (EGMEA) are widely used in industries as solvents for coatings, paint and ink, but exposure data are limited because they are minor components out of mixed solvents, as well as because of inconsistency in desorption solvent use. The objective of this study was to investigate the worker exposure profile of EGME and EGMEA. METHODS: Our study investigated 27 workplaces from June to September 2008 and detected EGME and EGMEA in 20 and 13, respectively. Both personal and area sampling were conducted using a charcoal tube to collect EGME and EGMEA. Gas chromatography with a flame ionization detector was used to analyze these compounds after desorption using a mixture of methylene chloride and methanol. RESULTS: The arithmetic mean concentrations of EGME and EGMEA during periods of full work shifts were 2.59 ppm and 0.33 ppm, respectively. The exposure levels were lower than the Korean Ministry of Labor (MOL) OEL (5 ppm) but higher than the ACGIH TLV (0.1 ppm). CONCLUSIONS: In general, the working environments were poor and required much improvement, including the use of personal protective equipment. Only 50% of the workplaces had local exhaust ventilation systems in operation. The average capture velocity of the operating local exhaust ventilation systems was 0.27 m/s, which did not meet the legal requirement of 0.5 m/s. Educating workers to clearly understand the handling and use of hazardous chemicals and improving working conditions are strongly suggested.

A comprehensive review of arsenic levels in the semiconductor manufacturing industry.

This paper presents a summary of arsenic level statistics from air and wipe samples taken from studies conducted in fabrication operations. The main objectives of this study were not only to describe arsenic measurement data but also, through a literature review, to categorize fabrication workers in accordance with observed arsenic levels. All airborne arsenic measurements reported were included in the summary statistics for analysis of the measurement data. The arithmetic mean was estimated assuming a lognormal distribution from the geometric mean and the geometric standard deviation or the range. In addition, weighted arithmetic means (WAMs) were calculated based on the number of measurements reported for each mean. Analysis of variance (ANOVA) was employed to compare arsenic levels classified according to several categories such as the year, sampling type, location sampled, operation type, and cleaning technique. Nine papers were found reporting airborne arsenic measurement data from maintenance workers or maintenance areas in semiconductor chip-making plants. A total of 40 statistical summaries from seven articles were identified that represented a total of 423 airborne arsenic measurements. Arsenic exposure levels taken during normal operating activities in implantation operations (WAM = 1.6 µg m⁻³, no. of samples = 77, no. of statistical summaries = 2) were found to be lower than exposure levels of engineers who were involved in maintenance works (7.7 µg m⁻³, no. of samples = 181, no. of statistical summaries = 19). The highest level (WAM = 218.6 µg m⁻³) was associated with various maintenance works performed inside an ion implantation chamber. ANOVA revealed no significant differences in the WAM arsenic levels among the categorizations based on operation and sampling characteristics. Arsenic levels (56.4 µg m⁻³) recorded during maintenance works performed in dry conditions were found to be much higher than those from maintenance works in wet conditions (0.6 µg m⁻³). Arsenic levels from wipe samples in process areas after maintenance activities ranged from non-detectable to 146 µg cm⁻², indicating the potential for dispersion into the air and hence inhalation. We conclude that workers who are regularly or occasionally involved in maintenance work have higher potential for occupational exposure than other employees who are in charge of routine production work. In addition, fabrication workers can be classified into two groups based on the reviewed arsenic exposure levels: operators with potential for low levels of exposure and maintenance engineers with high levels of exposure. These classifications could be used as a basis for a qualitative ordinal ranking of exposure in an epidemiological study.

Characteristics of PM10, PM2.5, CO2 and CO monitored in interiors and platforms of subway train in Seoul, Korea.

This study was performed to investigate the concentration of PM(10) and PM(2.5) inside trains and platforms on subway lines 1, 2, 4 and 5 in Seoul, KOREA. PM(10), PM(2.5), carbon dioxide (CO(2)) and carbon monoxide (CO) were monitored using real-time monitoring instruments in the afternoons (between 13:00 and 16:00). The concentrations of PM(10) and PM(2.5) inside trains were significantly higher than those measured on platforms and in ambient air reported by the Korea Ministry of Environment (Korea MOE). This study found that PM(10) levels inside subway lines 1, 2 and 4 exceeded the Korea indoor air quality (Korea IAQ) standard of 150 microg/m(3). The average percentage that exceeded the PM(10) standard was 83.3% on line 1, 37.9% on line 2 and 63.1% on line 4, respectively. PM(2.5) concentration ranged from 77.7 microg/m(3) to 158.2 microg/m(3), which were found to be much higher than the ambient air PM(2.5) standard promulgated by United States Environmental Protection Agency (US-EPA) (24 h arithmetic mean: 65 microg/m(3)). The reason for interior PM(10) and PM(2.5) being higher than those on platforms is due to subway trains in Korea not having mechanical ventilation systems to supply fresh air inside the train. This assumption was supported by the CO(2) concentration results monitored in tube of subway that ranged from 1153 ppm to 3377 ppm. The percentage of PM(2.5) in PM(10) was 86.2% on platforms, 81.7% inside trains, 80.2% underground and 90.2% at ground track. These results indicated that fine particles (PM(2.5)) accounted for most of PM(10) and polluted subway air. GLM statistical analysis indicated that two factors related to monitoring locations (underground and ground or inside trains and on platforms) significantly influence PM(10) (p<0.001, R(2)=0.230) and PM(2.5) concentrations (p<0.001, R(2)=0.172). Correlation analysis indicated that PM(10), PM(2.5), CO(2) and CO were significantly correlated at p<0.01 although correlation coefficients were different. The highest coefficient was 0.884 for the relationship between PM(10) and PM(2.5).

Effect of metalworking fluid mist exposure on cross-shift decrement in peak expiratory flow.

Exposure to metalworking fluids (MWF) mist and cross-shift decrements in peak expiratory flow (PEF) were evaluated and their relationship was analyzed using several statistical methods. The objective of this study was to assess workers, exposure to MWF mineral mist and to find the MWF mist level for predicting cross-shift decrements in PEF. A total of 158 workers handling water-soluble MWF had MWF mist exposures with an arithmetic mean (AM) of 0.4 mg/m(3) (range: LOD-13.5 mg/m(3)), and 9.2% of workers (219) showed a cross-shift decline greater than 10% in PEF. MWF mist exposure and cross-shift decrements in PEF that were matched (n=113) were linearly significantly associated (R(2)=0.036, p=0.045) although the correlation was quite weak (r=0.189). We found a slight increase in cross-shift decrements in PEF with increased exposure to MWF aerosol mass concentration. The MWF mist exposure level was categorized into two or three groups by the cutoffs of either the National Institute for Occupational Safety and Health's Recommended Exposure Level (NIOSH REL: 0.5 mg/m(3)) or the American Conference of Governmental Industrial Hygienists Notice of Intended Change (ACGIH NIC: 0.2 mg/m(3)). The cross-shift decrement in PEF observed from workers exposed to > or =0.2 mg/m(3) was slightly higher than that of the exposure level of < or =0.2 mg/m(3) at p=0.207 while significant differences among categorized exposure groups (2 categories, <0.5 and > or =0.5 mg/m(3), or 3 categories, <0.2, 0.2-0.5 and > or =0.5 mg/m(3)) were not detected. In order to find out whether there is a specific level that allows us to predict cross-shift decrements in PEF, several statistical models were constructed. Logistic regression showed that the MWF concentration, whether treated as a continuous variable or a categorical variable, was not significantly associated with cross-shift decrements dichotomized by a cutoff of either 10% or 15% in PEF. We couldn't find evidence of a significant PEF decrement increase with increasing exposure category. Thus, we concluded that PEF decrements measured in workers exposed to MWF mist concentrations greater than either 0.2 mg/m(3) or 0.5 mg/m(3) was not significantly different from those found in workers exposed to lower MWF mist concentrations. Further study is needed to establish the level of MWF mineral mist predicting non-malignant respiratory health effects.