Exposure Estimation and Interpretation of Occupational Risk: Enhanced Information for the Occupational Risk Manager

Micro-environmental factors impact breathing zone exposures: A simulated petrochemical manufacturing facility task

This study investigates the impact of micro-environmental factors on worker breathing zone exposure levels in petrochemical facilities. A laboratory simulation study evaluated near-field exposure to methane for a typical maintenance task. Individual and combinations of micro-environmental factors significantly affected methane exposure. Airflow direction and speed were significant determinants of exposure concentration reduction. A side airflow direction at medium to high speed produced the lowest gas concentration in the breathing zone. Worker body orientation relative to the methane emission point was also a critical factor affecting gas concentration in the worker's breathing zone. The study provides insights into how variations in airflow and small changes in position impact near-field exposures for petrochemical tasks, guiding industrial hygiene professionals' training on qualitative exposure estimation and providing input for near-field exposure modeling to guide quantitative exposure and risk assessment.

Visualizing the NIOSH Pocket Guide: Open-source web application for accessing and exploring the NIOSH Pocket Guide to Chemical Hazards

The NIOSH Pocket Guide to Chemical Hazards is a trusted resource that displays key information for a collection of chemicals commonly encountered in the workplace. Entries contain chemical structures-occupational exposure limit information ranging from limits based on full-shift time-weighted averages to acute limits such as short-term exposure limits and immediately dangerous to life or health values, as well as a variety of other data such as chemical-physical properties and symptoms of exposure. The NIOSH Pocket Guide (NPG) is available as a printed, hardcopy book, a PDF version, an electronic database, and a downloadable application for mobile phones. All formats of the NIOSH Pocket Guide allow users to access the data for each chemical separately, however, the guide does not support data analytics or visualization across chemicals. This project reformatted existing data in the NPG to make it searchable and compatible with exploration and analysis using a web application. The resulting application allows users to investigate the relationships between occupational exposure limits, the range and distribution of occupational exposure limits, and the specialized sorting of chemicals by health endpoint or to summarize information of particular interest. These tasks would have previously required manual extraction of the data and analysis. The usability of this application was evaluated among industrial hygienists and researchers and while the existing application seems most relevant to researchers, the open-source code and data are amenable to modification by users to increase customization.

Integrating Exposure Assessment and Process Hazard Analysis: The Nano-Enabled 3D Printing Filament Extrusion Case

Nanoparticles are being used in novel applications of the thermoplastics industry, including automotive parts, the sports industry and leisure and consumer goods, which can be produced nowadays through additive manufacturing. However, there is limited information on the health and safety aspects during the production of these new materials, mainly from recycled sources. This study covers the exposure assessment to nano- and micro-size particles emitted from the nanocomposites during the production of filaments for 3D printing through a compounding and extrusion pilot line using recycled (post-industrial) thermoplastic polyurethane (TPU) and recycled polyamide 12 (PA12), which have been also upcycled through reinforcement with iron oxide nanoparticles (Fe₃O₄ NPs), introducing matrix healing properties triggered by induction heating. The assessment protocol included near- and far-field measurements, considering the extruder as the primary emission source, and portable measuring devices for evaluating particulate emissions reaching the inhalable zone of the lab workers. A Failure Modes and Effects Analysis (FMEA) study for the extrusion process line was defined along with a Failure Tree Analysis (FTA) process in which the process deviations, their sources and the relations between them were documented. FTA allowed the identification of events that should take place in parallel (simultaneously) or in series for the failure modes to take place and the respective corrective actions to be proposed (additional to the existing control measures).

Comparison of ConsExpo estimated exposure levels to glycol ethers during professional cleaning work to existing regulatory occupational exposure limit values

Objectives. Researchers have shown that cleaning workers have an increased risk of asthma and rhinitis, mainly due to exposure to chemical substances present in the cleaning products they use. Among the important substances are glycol ethers, increasingly used as components in cleaning products. This study aimed to assess exposure levels of glycol ether in professional cleaning products and compare them to existing regulatory exposure limit values. Methods. Information from safety data sheets of the products is used to identify the glycol ethers present in the cleaning products and their respective concentrations. Other sources were used to obtain the relevant data required for use in the tool to generate exposure assessments. Exposure levels for various cleaning work exposure scenarios were estimated using the ConsExpo Web tool. Results. The estimated exposure values are significantly lower than the existing regulatory occupational exposure limit (OEL) values for the different glycol ethers. Conclusions. The study showed that the risk of exposure to glycol ethers by inhalation from professional cleaning products is minimal as exposure estimates were much below the regulatory OEL values.

Strategies for refinement of occupational inhalation exposure evaluation in the EPA TSCA risk evaluation process

The focus on occupational exposures in the first published risk evaluations of existing chemicals by the Environmental Protection Agency (EPA) under the amended Toxic Substances Control Act (TSCA) puts a welcome spotlight on protecting the health of workers in the United States. Because new, fit-for-purpose occupational exposure assessment methodologies were developed by EPA, the objective of this analysis was to evaluate these methodologies in light of other existing occupational risk assessment frameworks. We focused our analysis on three chlorinated chemicals (methylene chloride, carbon tetrachloride, perchloroethylene). The EPA's methods were evaluated relative to peer-reviewed and professional organizations' guidelines for conducting site- and facility-based exposure assessment. Analyses of several key phases in the EPA approach were conducted to evaluate the effect of alternative approaches on exposure estimates. The revised exposure estimates using these alternative approaches yielded substantially different exposure estimates from those in the TSCA risk evaluations for these chemicals. The results also demonstrated the importance of utilizing a tiered approach to exposure estimation that includes collecting qualitative data, defining similar exposure groups, and integrating well-parameterized models with empirical data. These approaches aid in preventing mischaracterization of exposures and generating exposure estimates representative of current industrial practices. Collaboration among industry, EPA, and other government agencies to develop a harmonized approach to exposure assessment would improve the methodological rigor of, and increase stakeholder confidence in, the results of TSCA risk evaluations.

Review and Improvement of Chemical Hazard Risk Management of Korean Occupational Safety and Health Agency

In 2012, the Korean Occupational Safety and Health Agency developed Chemical Hazard Risk Management (CHARM) as a risk assessment tool. This study aims to reorganize the CHARM technique by complementing its logical loopholes, while evaluating the risk to enterprises and verifying this technique by applying it to some enterprises in Korea. The optimized technique changed the method of quantitative assessment and evaluation criteria, matched the risk level with the required control level, and specified the use of control practice. For the target enterprises, for several assessment methods, risk levels, hazard bands, exposure bands, and the risk assessment results were derived, and the same types of options were compared. Fewer informational methods resulted in more conservative results of risk levels and hazard bands. Since the control status of the enterprises could not be confirmed and the substances handled at the target enterprises were limited in this study, a follow-up study should be performed with more target materials and additional information on the current control status of the enterprises.

Review of Workplace Based Aerosol Sampler Comparison Studies, 2004-2020

We provide a narrative review on published peer-reviewed scientific literature reporting comparisons of personal samplers in workplace settings published between 2004 and 2020. Search terms were developed for Web of Science and PubMed bibliographic databases. The retrieved studies were then screened for relevance, with those studies meeting the inclusion criteria being taken forward to data extraction (22 studies). The inhalable fraction was the most common fraction assessed with the IOM sampler being the most studied sampler. The most common workplace environment where samplers had been compared was that where metals/metalloids were present. The requirements of EN13205 standard (Workplace exposure. Assessment of sampler performance for measurement of airborne particle concentrations) have also been considered, with these requirements not currently being met, or at least referred to, in the included published literature. A number of conclusions have been drawn from this narrative review. For studies that reported correction factors, no discernible trends could be identified. Correction factors also varied between samplers and settings, with correction factors varying from 0.67 for Button/IOM in agriculture settings to a correction factor of 4.2 for the closed face cassette/IOM samplers in aluminium smelters. The need for more detailed and informative data sharing from authors is highlighted, providing more context to both the sampling strategy and methodology, as well as the data analysis. It is recommended that the requirements of EN13205 are taken into account when designing sampler comparison studies at the workplace and that these are also reported. It is also considered that there is a need for a clear standardized workplace sampler comparison protocol to be developed, which can be used by the research and occupational hygiene community to allow more robust and transparent assessment of aerosol samplers and better-quality evidence for use by industrial hygienists, epidemiologists, and occupational safety specialists alike.

Compliance Testing and Homogenous Exposure Group Assessment in the South African Coal Mining Industry

OBJECTIVES

Globally, several strategies for compliance testing and within-group exposure variability have been suggested. This study aimed to evaluate the performance of the South African Mining Industry Code of Practice (SAMI CoP) approach for grouping and compliance testing against international standards.

METHODS

A total of 28 homogenous exposure groups (HEGs) with 728 underground coal mine workers' eight-hour time-weighted average coal dust concentration data were obtained. Compliance testing was assessed using 10% exceedance above occupational exposure limit (OEL) for SAMI CoP, and the 95th percentile of the lognormal distribution was computed for the European Standardization Committee (CEN) and American Industrial Hygiene Association (AIHA). Comparison of the homogeneity of the HEGs was done between SAMI CoP which mandates that both the arithmetic mean (AM) and 90th percentile must fall in the same exposure band to certify homogeneity and the global geometric standard deviation (GSD) and Rappaport ratio (R-ratio) with specific acceptability criteria. To test the homogeneity of exposure within job titles, eight non-homogenous HEGs that have two or more job titles with three measurements were investigated using GSD and the SAMI CoP criteria.

RESULTS

A total of 21 HEGs out of 28 were non-compliant to the OEL across SAMI CoP, CEN, and AIHA criteria. Compliance to the OEL was observed for seven HEGs according to the SAMI CoP approach, whereas only one HEG was compliant according to both the SAMI CoP and CEN approaches. The GSD criterion and SAMI CoP revealed that 11 and 6 HEGs were homogenous, respectively, and only on 4 occasions, the 2 approaches agreed. The job titles of the majority of non-homogenous HEGs in both SAMI CoP and GSD were actually homogenous. Five out of 10 sub-groups have their AM above that of HEG B. Other HEGs had at least one of their AM and 90th percentile values above that of their respective parent HEGs.

CONCLUSIONS

All three approaches mainly confirmed non-compliance of HEGs. SAMI CoP tended to show compliance of HEGs more than CEN. Non-homogenous HEGs had many job titles that were homogenous according to both SAMI CoP and GSD criteria. There was no perfect agreement of homogeneity by all the indicators. For both future constitutions of HEGs as well as a retrospective assessment of high exposure groups, homogeneity can be improved by using job titles.

Occupational Health Hazards: Employer, Employee, and Labour Union Concerns

This review paper examines the extent of employer, worker, and labour union concerns to occupational health hazard exposure, as a function of previously reported and investigated complaints. Consequently, an online literature search was conducted, encompassing publicly available reports resulting from investigations, regulatory inspection, and enforcement activities conducted by relevant government structures from South Africa, the United Kingdom, and the United States. Of the three countries’ government structures, the United States’ exposure investigative activities conducted by the National Institute for Occupational Safety and Health returned literature search results aligned to the study design, in the form of health hazard evaluation reports reposited on its online database. The main initiators of investigated exposure cases were employers, workers, and unions at 86% of the analysed health hazard evaluation reports conducted between 2000 and 2020. In the synthesised literature, concerns to exposure from chemical and physical hazards were substantiated by occupational hygiene measurement outcomes confirming excessive exposures above regulated health and safety standards in general. Recommendations to abate the confirmed excessive exposures were made in all cases, highlighting the scientific value of occupational hygiene measurements as a basis for exposure control, informing risk and hazard perception. Conclusively, all stakeholders at the workplace should have adequate risk perception to trigger abatement measures.

Incorporating Exposure Measurement Data from Similar Exposure Scenarios to Inform Exposure Modeling Estimates: A Demonstration Using Cluster Analysis and Bayesian Modeling

Addressing occupational health and safety concerns early in the design stage anticipates hazards and enables health professionals to recommend control measures that can best protect workers' health. This method is a well-established tool in public health. Importantly, its success depends on a comprehensive exposure assessment that incorporates previous exposure data and outcomes. Traditional methods for characterizing similar occupational exposure scenarios rely on expert judgment or qualitative descriptions of relevant exposure data, which often include undisclosed underlying assumptions about specific exposure conditions. Thus, improved methods for predicting exposure modeling estimates based on available data are needed. This study proposes that cluster analysis can be used to quantify the relevance of existing exposure scenarios that are similar to a new scenario. We demonstrate how this method improves exposure predictions. Exposure data and contextual information of the scenarios were collected from past exposure assessment reports. Prior distributions for the exposure distribution parameters were specified using Stoffenmanager® 8 predictions. Gower distance and k-Medoids clustering algorithm analyses grouped existing scenarios into clusters based on similarity. The information was used in a Bayesian model to specify the degree of correlation between similar scenarios and the scenarios to be assessed. Using the distance metric to characterize the degree of similarity, the performance of the Bayesian model was improved in terms of the average bias of model estimates and measured data, reducing from 0.77 (SD: 2.0) to 0.49 (SD: 1.8). Nevertheless, underestimation of exposures still occurred for some rare scenarios, which tended to be those with highly variable exposure data. In conclusion, the cluster analysis approach may enable transparent selection of similar exposure scenarios for factoring into design-phase assessments and thereby improve exposure modeling estimates.

Fate and contaminant transport model-driven probabilistic human health risk assessment of DNAPL-contaminated site

In this study, fate and contaminant transport model-driven human health risk indexes were calculated due to the presence of dense non-aqueous phase liquids (DNAPLs) in the subsurface environment of air force base area in Florida, USA. Source concentration data of DNAPLs was used for the calculation of transport model-driven health risk indexes for the children and adult sub-population via direct oral ingestion and skin dermal contact exposure scenario using 10,000 Monte Carlo type simulations. The highest variation in the probability distribution of transformed DNAPL compound (cis-dichloroethene (cis-DCE) > vinyl chloride (VC)) was observed as compared to parent DNAPL (tetrachloroethene (PCE)) based on the 50-year simulation timespan. Transformed DNAPL compounds (VC, cis-DCE) posed the highest risk to human health for a longer duration (up to 15 years) in comparison to parent DNAPL (PCE), as non-carcinogenic hazard quotient varied from 400 to 1100. Carcinogenic health risks were observed as 3-order of magnitude higher than safe limit (HQ_Safe < 10^-6) from 2nd to 5th year timespan and fall in the high-risk zone, indicating the need for a remediation plan for a contaminated site. Variance attribution analysis revealed that concentration, body weight, and exposure duration (contribution percentage - 70 to 95%) were the most important parameters, highlighting the impact of dispersivity and exposure model in the estimation of risk indexes. This approach can help decision-makers when a contaminated site with partial data on hydrogeological properties and with higher uncertainty in model parameters is to be assessed for the formulation of remediation measures.

Modeling occupational exposure to solvent vapors using the Two-Zone (near-field/far-field) model: a literature review

The Two-Zone model is used in occupational hygiene to predict both near-field and far-field airborne contaminant concentrations. A literature review was carried out on 21 scientific publications in which the Two-Zone model was used to assess occupational exposure to solvent vapors. Data on exposure scenarios, solvents, generation/emission rates, near- and far-field parameters, and model performance were collected and analyzed. Over the 24 exposure scenarios identified, 18 were evaluated under controlled conditions, 5 under normal workplace activities, and 1 was reported based on literature data. The scenarios involved a variety of tasks which consisted, mostly, of cleaning metal parts, spraying solvents onto surfaces, spilling liquids, and filling containers with volatile substances. Twenty-eight different solvents were modeled and the most commonly tested were benzene, toluene, and acetone. Emission rates were considered constant in 16 scenarios, exponentially decreasing in 6 scenarios, and intermittent in 2 scenarios. Four-hundred-and-forty-six (446) predicted-to-measured concentration ratios were calculated across the 21 studies; 441 were obtained in controlled conditions, 4 under normal workplace activities, and 1 was calculated based on the literature data. For controlled studies, the Two-Zone model predictive performance was within a factor of 0.3-3.7 times the measured concentrations with 93% of the values between 0.5 and 2. The model overestimated the measured concentrations in 63% of the evaluations. The median predicted concentration for the near-field was 1.38 vs. 1.02 for the far-field. Results suggest that the model might be a useful tool for predicting occupational exposure to vapors of solvents by providing a conservative approach. Harmonization in model testing strategies and data presentation is needed in future studies to improve the assessment of the predictability of the Two-Zone model. Moreover, this review has provided a database of exposure scenarios, input parameter values, and model predictive performances which can be useful to occupational hygienists in their future modeling activities.

Using benchmark dose modeling for the quantitative risk assessment: Carbon nanotubes, asbestos, glyphosate

Benchmark dose method is one of the most famous quantitative approaches available for toxicological risks prediction. However, it is not fully clear how occupational health professionals can use it for specific workplace scenarios requiring carcinogen risk assessment. The paper explores the hypothesis that benchmark dose method allows to effectively approximate dose-response data on carcinogenic response, providing reasonable estimations of risks in the situations when a choice between more complex models is not warranted for practical purposes. Three case studies were analyzed for the agents with different levels of scientific confidence in human carcinogenicity: carbon nanotubes, amosite asbestos, and glyphosate. For each agent, a critical study was determined, and a dose-response slope factor was quantified, based on the weighted average lower bound benchmark dose. The linear slope factors of 0.111 lifetime excess cases of lung carcinoma per mg/m³ of MWCNT-7 (in rats exposure equivalent), 0.009 cases of mesothelioma per f/cc-years of cumulative exposure to amosite asbestos, and 0.000094 cases of malignant lymphoma per mg/kg/day of glyphosate (in mice equivalent) were determined. The correlations between the proposed linear predictive models and observed data points were R = 0.96 (R² = 0.92) for carbon nanotubes, R = 0.97 (R² = 0.95) for amosite asbestos, and R = 0.89 (R² = 0.79) for glyphosate. In all three cases, the linear extrapolation yielded comparable level of risk estimations with the "best fit" nonlinear model; for nanoparticles and amosite asbestos, linear estimations were more conservative. By performing a simulation study, it was demonstrated that a weighted average benchmark dose expressed the highest correlation with multistage and quantal-linear models.

Exposures and Emissions in Coffee Roasting Facilities and Cafés: Diacetyl, 2,3-Pentanedione, and Other Volatile Organic Compounds

Roasted coffee and many coffee flavorings emit volatile organic compounds (VOCs) including diacetyl and 2,3-pentanedione. Exposures to VOCs during roasting, packaging, grinding, and flavoring coffee can negatively impact the respiratory health of workers. Inhalational exposures to diacetyl and 2,3-pentanedione can cause obliterative bronchiolitis. This study summarizes exposures to and emissions of VOCs in 17 coffee roasting and packaging facilities that included 10 cafés. We collected 415 personal and 760 area full-shift, and 606 personal task-based air samples for diacetyl, 2,3-pentanedione, 2,3-hexanedione, and acetoin using silica gel tubes. We also collected 296 instantaneous activity and 312 instantaneous source air measurements for 18 VOCs using evacuated canisters. The highest personal full-shift exposure in part per billion (ppb) to diacetyl [geometric mean (GM) 21 ppb; 95th percentile (P95) 79 ppb] and 2,3-pentanedione (GM 15 ppb; P95 52 ppb) were measured for production workers in flavored coffee production areas. These workers also had the highest percentage of measurements above the NIOSH Recommended Exposure Limit (REL) for diacetyl (95%) and 2,3-pentanedione (77%). Personal exposures to diacetyl (GM 0.9 ppb; P95 6.0 ppb) and 2,3-pentanedione (GM 0.7 ppb; P95 4.4 ppb) were the lowest for non-production workers of facilities that did not flavor coffee. Job groups with the highest personal full-shift exposures to diacetyl and 2,3-pentanedione were flavoring workers (GM 34 and 38 ppb), packaging workers (GM 27 and 19 ppb) and grinder operator (GM 26 and 22 ppb), respectively, in flavored coffee facilities, and packaging workers (GM 8.0 and 4.4 ppb) and production workers (GM 6.3 and 4.6 ppb) in non-flavored coffee facilities. Baristas in cafés had mean full-shift exposures below the RELs (GM 4.1 ppb diacetyl; GM 4.6 ppb 2,3-pentanedione). The tasks, activities, and sources associated with flavoring in flavored coffee facilities and grinding in non-flavored coffee facilities, had some of the highest GM and P95 estimates for both diacetyl and 2,3-pentanedione. Controlling emissions at grinding machines and flavoring areas and isolating higher exposure areas (e.g., flavoring, grinding, and packaging areas) from the main production space and from administrative or non-production spaces is essential for maintaining exposure control.

Setting occupational exposure limits for antimicrobial agents: A case study based on a quaternary ammonium compound-based disinfectant

Antimicrobial agents have become an essential tool in controlling the transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), and guidelines on their use have been issued by various public health agencies. Through its Emerging Viral Pathogen Guidance for Antimicrobial Pesticides, the US Environmental Protection Agency has approved numerous surface disinfectant products for use against SARS-CoV-2. Despite their widespread use and range of associated health hazards, the majority of active ingredients in antimicrobial products, such as surface disinfectants, lack established occupational exposure limits (OELs) to assist occupational health professionals in characterizing risks from exposures to these chemicals. Based on established approaches from various organizations, a framework for deriving OELs specific to antimicrobial agents was developed that relies on a weight-of-evidence evaluation of the available data. This framework involves (1) a screening-level toxicological assessment based on a review of the existing literature and recommendations, (2) identification of the critical adverse effect(s) and dose-response relationship(s), (3) identification of alternative health-based exposure limits (HBELs), (4) derivation of potential OELs based on identified points of departure and uncertainty factors and/or modification of existing alternative HBELs, and (5) selection of an appropriate OEL. To demonstrate the use of this framework, a case study is described for selection of an OEL for a disinfectant product containing quaternary ammonium compounds (quats). Three potential OELs were derived for this product based on irritation toxicity data, developmental and reproductive toxicity (DART) data, and modification of an existing HBEL. The final selected OEL for the quats-containing product was 0.1 mg/m3, derived from modification of an existing HBEL. This value represented the lowest resulting value of the three approaches, and thus, was considered protective of irritation and potential DART.

A suitable biomarker of effect, club cell protein 16, from crystalline silica exposure among Thai stone-carving workers

Exposure to respirable crystalline silica (RCS) reportedly induces chronic lung injury. We investigated the association between RCS exposure and two biomarkers of the effect, plasma club cell protein 16 (CC16) and heme oxygenase-1 (HO-1) levels, in stone-carving workers. Fifty-seven exposed workers (EWs) and 20 unexposed workers (UWs) were enrolled onto the study. Cumulative exposure to RCS was individually estimated using a filter-based gravimetric method. The plasma CC16 and HO-1 levels were determined using commercial kits. The 8-h time-weighted average for RCS concentration in the EW was significantly greater than this concentration in the UW ( p < 0.001). The health risk characterization for RCS exposure expressed as a hazard quotient (HQ) indicated that crystalline silica might be a risk factor where there is chronic exposure (HQ = 4.48). The EW group presented a significant decrease in CC16 and an increase in HO-1 levels in comparison to the UW group ( p < 0.001). In addition, we found a significant association between RCS concentration and plasma CC16 only. Therefore, our findings representing a significant decrease in CC16 in the plasma of stone-carving workers and this biological marker were significantly associated with RCS concentration. Our data indicated that CC16 might be a suitable biomarker to use to predict the health risk to stone-carving workers of exposure to RCS.

Assessment of Occupational Exposure to Organic Flame Retardants: A Systematic Review

BACKGROUND

Flame retardants (FRs) are widespread in common goods, and workers in some industries can be exposed to high concentrations. Numerous studies describe occupational exposure to FRs, but the diversity of methods and of reported results renders their interpretation difficult for researchers, occupational hygienists, and decision makers.

OBJECTIVES

The objectives of this paper are to compile and summarize the scientific knowledge on occupational exposure to FRs as well as to identify research gaps and to formulate recommendations.

METHODS

Five databases were consulted for this systematic literature review (Embase, Medline [Pubmed], Global health, Web of Science, and Google Scholar), with terms related to occupational exposure and to FRs. Selected studies report quantitative measurements of exposure to organic FRs in a workplace, either in air, dust, or in workers' biological fluids. The Preferred Reporting Items for Systematic reviews and Meta-Analyses statement guidelines were followed.

RESULTS

The search yielded 1540 published articles, of which 58 were retained. The most frequently sampled FRs were polybrominated diphenyl ethers and novel brominated FRs. Offices and electronic waste recycling facilities were the most studied occupational settings, and the highest reported exposures were found in the latter, as well as in manufacturing of printed circuit boards, in aircrafts, and in firefighters. There were recurrent methodological issues, such as unstandardized and ill-described air and dust sampling, as well as deficient statistical analyses.

CONCLUSIONS

This review offers several recommendations. Workplaces such as electronic waste recycling or manufacturing of electronics as well as firefighters and aircraft personnel should be granted more attention from researchers and industrial hygienists. Methodical and standardized occupational exposure assessment approaches should be employed, and data analysis and reporting should be more systematic. Finally, more research is needed on newer chemical classes of FRs, on occupational exposure pathways, and on airborne FR particle distribution.

Expostats: A Bayesian Toolkit to Aid the Interpretation of Occupational Exposure Measurements

INTRODUCTION

Interpretation of exposure measurements has evolved into a framework based on the lognormal distribution. Most available practical tools are based on traditional frequentist statistical procedures that do not satisfactorily account for censored data and are not amenable to simple probabilistic risk statements. Bayesian methods offer promising solutions to these challenges. Such methods have been proposed in the literature but are not widely and freely available to practitioners.

METHODS

A set of computer applications were developed aimed at answering typical inferential questions that are important to occupational health practitioners: Is a group of workers compliant with an occupational exposure limit? Are some individuals within this group likely to experience substantially higher exposure than its average member? How does an intervention influence the distribution of exposures? These questions were addressed using Bayesian models, simultaneously accounting for left, right, and interval-censored data with multiple censoring points. The models are estimated using the JAGS Gibbs sampler called through the R statistical package.

RESULTS

The Expostats toolkit is freely available from www.expostats.ca as four tools accessible through a Web application, an offline standalone application or algorithms. The tools include a variety of calculations and graphical outputs useful according to current practices in analysis and interpretation of exposure measurements collected by occupational hygienists. Tool1 and its simplified version Tool1 Express focus on inferences from data from a similarly exposed group. Tool2 evaluates within- and between-worker components of variability, as well as the probability that an individual worker might be overexposed. Tool3 compares exposure data across groups, e.g. evaluates the effect of an intervention. Uncertainty management includes the calculation of credible intervals and produces probabilistic statements about the exposure metrics (e.g. probability that over 5% of exposures are above a limit).

DISCUSSION

Expostats is the first freely available toolkit that leverages the flexibility of Bayesian analysis to perform an extensive list of calculations recommended in several international guidelines on the practice of occupational hygiene.

Interzonal airflow rates for use in near-field far-field workplace concentration modeling

Interzonal air flow rates (β) for a workspace above a table were measured in 12 indoor air spaces using an experimental apparatus simulating a vapor release into an occupied near zone. The near field was modeled as a 0.32 m³ rectangular cube volume 0.60 m high above the 0.60 m × 0.90 m table. A total of 74 experimental measurements of β were made. The apparatus consisted of photoionization detectors measuring concentrations of acetone around an evaporating liquid surface with a robot arm simulating worker motion in the near field. The vapor release rate and the resulting concentrations were used in a near-field far-field (NF-FF) model to calculate β. Measures of mixing within the near-field supported the assumption of the NF-FF model that the near field is well-mixed. Measured values of β ranged from 0.4-19 m³/min with an average of 4.8 m³/min. This corresponds to 1.2-59 air changes per minute in the near field and an average of 15 air changes per minute. The values of β were log normally distributed with a geometric mean of 3.4 m³/min and a geometric standard deviation of 2.3. The 95% confidence interval on the geometric mean of β was 2.8-4.2 m³/min. The product of the random air speed in the room and one half of the near-field free surface area was shown to be a good method of determining β. There was a slight correlation seen between room volume and β, but the effect size was small. Room air change rate was not found to be correlated with β. The observed distribution of β will be helpful in selecting values for interzonal airflow rate in NF-FF modeling of worker exposures.

Historical Context and Recent Advances in Exposure-Response Estimation for Deriving Occupational Exposure Limits

Virtually no occupational exposure standards specify the level of risk for the prescribed exposure, and most occupational exposure limits are not based on quantitative risk assessment (QRA) at all. Wider use of QRA could improve understanding of occupational risks while increasing focus on identifying exposure concentrations conferring acceptably low levels of risk to workers. Exposure-response modeling between a defined hazard and the biological response of interest is necessary to provide a quantitative foundation for risk-based occupational exposure limits; and there has been considerable work devoted to establishing reliable methods quantifying the exposure-response relationship including methods of extrapolation below the observed responses. We review several exposure-response modeling methods available for QRA, and demonstrate their utility with simulated data sets.

The Scientific Basis of Uncertainty Factors Used in Setting Occupational Exposure Limits

The uncertainty factor concept is integrated into health risk assessments for all aspects of public health practice, including by most organizations that derive occupational exposure limits. The use of uncertainty factors is predicated on the assumption that a sufficient reduction in exposure from those at the boundary for the onset of adverse effects will yield a safe exposure level for at least the great majority of the exposed population, including vulnerable subgroups. There are differences in the application of the uncertainty factor approach among groups that conduct occupational assessments; however, there are common areas of uncertainty which are considered by all or nearly all occupational exposure limit-setting organizations. Five key uncertainties that are often examined include interspecies variability in response when extrapolating from animal studies to humans, response variability in humans, uncertainty in estimating a no-effect level from a dose where effects were observed, extrapolation from shorter duration studies to a full life-time exposure, and other insufficiencies in the overall health effects database indicating that the most sensitive adverse effect may not have been evaluated. In addition, a modifying factor is used by some organizations to account for other remaining uncertainties-typically related to exposure scenarios or accounting for the interplay among the five areas noted above. Consideration of uncertainties in occupational exposure limit derivation is a systematic process whereby the factors applied are not arbitrary, although they are mathematically imprecise. As the scientific basis for uncertainty factor application has improved, default uncertainty factors are now used only in the absence of chemical-specific data, and the trend is to replace them with chemical-specific adjustment factors whenever possible. The increased application of scientific data in the development of uncertainty factors for individual chemicals also has the benefit of increasing the transparency of occupational exposure limit derivation. Improved characterization of the scientific basis for uncertainty factors has led to increasing rigor and transparency in their application as part of the overall occupational exposure limit derivation process.

The Global Landscape of Occupational Exposure Limits--Implementation of Harmonization Principles to Guide Limit Selection

Occupational exposure limits (OELs) serve as health-based benchmarks against which measured or estimated workplace exposures can be compared. In the years since the introduction of OELs to public health practice, both developed and developing countries have established processes for deriving, setting, and using OELs to protect workers exposed to hazardous chemicals. These processes vary widely, however, and have thus resulted in a confusing international landscape for identifying and applying such limits in workplaces. The occupational hygienist will encounter significant overlap in coverage among organizations for many chemicals, while other important chemicals have OELs developed by few, if any, organizations. Where multiple organizations have published an OEL, the derived value often varies considerably-reflecting differences in both risk policy and risk assessment methodology as well as access to available pertinent data. This article explores the underlying reasons for variability in OELs, and recommends the harmonization of risk-based methods used by OEL-deriving organizations. A framework is also proposed for the identification and systematic evaluation of OEL resources, which occupational hygienists can use to support risk characterization and risk management decisions in situations where multiple potentially relevant OELs exist.