WorkCare

Case Presentation

A 49 year-old lead electrician, who had been employed for six years on an petroleum drilling site, received an unsatisfactory performance evaluation due to lateness. During a counseling session this employee claimed that medical problems were the reason for his lateness.

Clinical Evaluation

In a clinical evaluation on January 7, 1999 the following information was gathered. This employee has been late 6 times in the last year, 4 times in the last 3 months. All latenesses were over 2 hours. Employee was also noted to fall asleep during meetings.

Past medical history was positive for a history of low blood sugar in 1981, and a history of allergies and asthma

Employee denies current drug use. Does drink 2-3 beers/night. Medications include: over-the-counter cold tables, vitamins, antihistamines and asthma inhalers.

The physical exam was unremarkable.

Assessment at medical evaluation

Tardiness to work, drowsiness at work, the etiology is unclear.

Plan

Fasting chemistries

CBC -to rule out medical causes

Thyroid panel

Urine drug screen

Employee was put off work pending results of the above tests.

Results

All blood work was within normal limits.

Drug screen was Positive

Amphetamine: 5474

Methamphetamine: 23577

Confirmed by GC/MS

MRO

Medicine review is significant for Vicks inhaler use. Employee denies drug use. The medical department referred employee to the Employee Assistance Program (EAP) for evaluation and treatment of possible over-the-counter medication abuse.

Follow-up

A return to work drug screen performed by medical on January 21 was negative. Employee returned to work on January 24. The supervisor called for a follow-up medical evaluation on February 6, when the employee was again very sleepy. A repeat drug screen and evaluation were performed.

The physical exam was negative. A repeat drug screen was done on February 6 with the employee off work pending results.

The results of the drug screen registered positive for Methamphetamine: 1734 and Dextroamphetamine: 571. Results could be consistent with inhaler abuse, so a special test for drug isomers was requested. In illegally manufactured amphetamines and methamphetamines the L (levo) forms of the drug are present.

The Isomer results received February 22 were L-methamphetamine – Negative, D-methamphetamine – 1813. The D-isomer is the illegal form

Current Status

Management was notified of the positive drug screen. Employee continued to deny drug use and refused further counseling. He was terminated on March 7.

Importance of medical evaluations

Medical evaluations of performance problems are invaluable because they can help sort out the root cause of employee performance problems. These evaluations can rapidly determine if there is a medical emergency present, and if employees are a danger to themselves or others. Employees can then be quickly routed to appropriate medical intervention. Sometimes, substance abuse is involved. Medical evaluation can make that determination. The medical department can then make appropriate referrals and follow-up for return to work and random drug testing.

The bottom line is: medical evaluations are an integral part of KEEPING THE WORKPLACE SAFE.

Environmental Health Decisions

Environmental Health Decisions has prepared a number of Material Safety Data Sheets for clients in United States and Canada. These MSDSs are in full compliance with WHMIS regulations. Since requirements for preparation of MSDSs in Canada are specific to each province, it was necessary for this consultant to become familiar with a variety of regulations. MSDSs prepared to be compliant with WHMIS regulations provide companies in the United States with the ability to sell their product in Canada. This consultant has extensive experience in the preparation of MSDSs for solvents, pesticides, fertilizers, metals, and petroleum hydrocarbon products.

McDaniel Lambert, Inc

International Environmental Strategy and Media Program

Major Energy Resources Company

Thailand

Occupational medical physician and toxicologist developed a communication strategy and media program to answer questions raised in the press about the safety of fish around oil platforms in the Gulf of Thailand. Consultants trained and advised upper management and frontline personnel in working with the press and public. The media strategy included an editorial board presentation to The Bangkok Post as well as press tours of the platforms. They also designed and oversaw health and ecological risk assessments designed to determine the potential for human health effects from mercury in the Gulf and assisted with the scientific presentation of the study results. The program resulted in improved relationships with Thai oversight agencies and provided positive media coverage for the company.

McDaniel Lambert, Inc

Overseas Community Outreach Program

Major Energy Resources Company

The Philippines

Occupational medical physician and toxicologist developed a risk communication and outreach strategy to assist a geothermal operation in The Philippines located in a region where people were living in geothermal fields and regularly blockading roads leading to geothermal wells to express their displeasure with the operation. The consultants initiated proactive communications with the local community and the national utility, which buys the energy produced at the geothermal wells to sell to the public. The team conducted sensitivity training for frontline employees and participated in several meetings with local residents and community leaders. The effort led to the establishment of a community notification system to facilitate the exchange of information between the facility and local residents.

McDaniel Lambert, Inc

Crisis Planning and Response

Agricultural Chemicals Company, Alaska

Occupational medical physician and toxicologist provided risk communication training and assisted with crisis response planning for large agricultural chemicals company. The plan and other preparatory work allowed the facility to quickly resolve issues following the capsizing of a barge carrying 12,500 tons of urea granules. The consultant team worked with the Coast Guard to develop safe urea exposure levels following the spill and assisted with communications for both internal and external audiences, including emergency responders. The effort effectively managed the crisis and mitigated its impacts on the organization. The effort was so successful that local residents took out a newspaper advertisement thanking the company for its prompt and thorough response.

McDaniel Lambert, Inc

Risk Communication Training Program

Industrial facilities, Agency Representatives and others

Worldwide

Occupational physician and toxicologist developed a risk communication training program which they have conducted for industrial facilities and agency representatives worldwide. The training includes discussion of such topics as risk perception, the importance of trust and credibility, public meeting preparation, and media training. The course provides ample opportunity for hands-on practice and videotaping of participants. The consultants have conducted more than 100 training sessions at locations including Southeast Asia, Western Europe, and throughout the United States. The success of the training program led one major energy resources company to establish a Risk Communication Policy which requires facilities worldwide to engage in two-way communication concerning health, environment, and safety issues. The consultants had an active role in the creation of this policy.

The consultant has performed comprehensive industrial hygiene sampling during normal processing, routine maintenance, and special investigation activities at numerous semiconductor manufacturing and assembly facilities. A typical project includes development of a detailed sample collection plan based on process information, predictive by-product chemistry, and potential exposures. Company then assembles a matrix of operations, equipment, and materials to prioritize monitoring activities. Hazard analyses are used to determine “worst case” scenarios to sample for each compound of concern. Sample collection and analyses are performed in accordance with the most appropriate National Institute of Occupational Safety and Health (NIOSH), Occupational Safety and Health Administration (OSHA), or other applicable methods. Surface wipe samples are collected in accordance with OSHA guidance, where applicable, and are analyzed using the most appropriate NIOSH or OSHA method. Exposure assessments also include Best Industry Practices review of process tools and procedural exposure controls. Results and prioritized recommendations are provided to the client in a manner that facilitates communication to employees.

EORM

Semiconductor Industrial Hygiene Monitoring: New Challenges and a Few Old Favorites in the World of Hazard Identification and Exposure Evaluation

Abstract

What are the industrial hygiene concerns in a basic semiconductor fabrication facility? This paper highlights key industrial hygiene monitoring strategies for selected normal production operations and maintenance tasks. Monitoring for airborne and surface chemicals, ionizing radiation, radiofrequency and microwave radiation, ultraviolet and infrared light, static magnetic fields, and ventilation effectiveness is discussed. Areas of traditional industrial hygiene focus, such as photolithography, are addressed, with an emphasis on best available assessment approaches. Maintenance tasks, such as wet etch/deposition tool chamber cleans and ion implanter parts cleaning, often present the greatest potential for employee exposure to health hazards. Specific exposure issues are presented, such as cyanide compounds in metal etch chamber residues and arsenic surface contamination from ion implanter parts, with a discussion of commonly reported monitoring results.

Introduction

The art and science of industrial hygiene involves the recognition, evaluation, and control of workplace hazards. At first glance, the typical semiconductor fabrication facility (fab) appears to be a pristine, clean environment. Great care is taken to ensure ambient air purity, with newer processing tools isolated in mini-environments to minimize potential product contamination. Fab employees appear well protected in uniformly white head-to-toe garments. The fab itself is quiet relative to a typical heavy manufacturing environment, and production employees are rarely exposed to extreme safety conditions.

So the new industrial hygienist gowns up once, wanders around, becomes entranced by the coaters for a while, and leaves thinking all is well and she better get back to that flickering computer monitor problem near the electrical panel…

Scratching the surface a bit, a more complex world unfolds. The typical fab presents a variety of chemical and radiation hazards, many of which are unique to the semiconductor industry. In many cases, these hazards are well recognized before the equipment is installed. The processing tools use an array of toxic gases, solvents, and metals during normal production. Maintenance activities may introduce additional chemicals, and often create opportunities for employee exposure that do not exist during normal production. Radiation sources include ionizing radiation generated from high voltage/current processes, radiofrequency (Rf) and microwave (MW) radiation from plasma operations, ultraviolet (UV) and infrared (IR) radiation often as secondary hazards from plasma and other processes, and static magnetic fields from tools with large magnets.

This paper reviews hazard evaluation techniques for the semiconductor facility, then presents examples of some specific exposure situations.

Industrial Hygiene Evaluation

Before conducting any field monitoring, the industrial hygienist must create an evaluation strategy. Instead of classifying employees into similar exposure groups only by job classification, it is especially important in the fab environment to assess exposures by task. Such a strategy should include information on the tasks conducted, tools and equipment used, associated hazards, and controls in place. Each item on the strategy should be prioritized, and the monitoring plan designed to capture the high priority tasks first. In reality, industrial hygiene monitoring is often strongly focused on employee concerns and odor complaints, in addition to the prioritized tasks.

Industrial hygiene monitoring in the fab typically includes some or all of the following equipment:

Chemicals:

- Air sampling pumps and media or passive dosimeters for integrated personal and area samples

- Direct-reading equipment such as the MDA TLD-1 or colorimetric indicator tubes

- Filter media for collecting surface wipe samples

Radiation:

- Geiger-Mueller meter and ion chamber for ionizing radiation

- Rf/MW meter

- UV/IR radiometer

- Static magnetic field meter

At the same time that chemical and radiation hazards are evaluated, ventilation controls are typically evaluated, too. This will almost always include evaluation of wet bench face velocity, which is quite different from laboratory fume hood face velocity evaluation. The tools required include a thermal anemometer or velometer, a tape measure, and a vapor visualization device.

Normal Production Monitoring

The “normal production” environment refers to the (sometimes rare) state of production tools processing wafers under standard operating conditions. In this environment, the tool enclosures minimize chemical and radiation exposures to the fab operators. Some direct chemical exposures may still exist, as when using open chemical baths or performing routine cleaning steps, but these exposures are usually of short duration. Radiation exposures would typically only result during normal production from tool leakage due to inadequate tool maintenance.

Photolithography

One frequent area of odor generation, and resulting employee concern, is photolithography. Newer photolithography equipment is designed to keep contaminants out of the process, which conveniently keeps odors in. Many facilities, though, are still plagued by recurring nuisance solvent odors. Because of the toxic nature of photoresist solvents previously used in the industry, media attention, and the relative lack of odors in other areas of the fab, among other factors, this area frequently induces employee concerns and, therefore, ends up near the top of the industrial hygiene priorities list.

Photolithography solvents can be monitored in a variety of ways, from traditional air sampling pumps and media to portable gas chromatography units (ref. Gunderson, Fall 1998 SSA Journal). Gas chromatography has low enough detection limits to record background solvent concentrations in the ppb range. These detection limits are required to detect and track concentrations of chemicals with low odor thresholds, such as those present in photolithography areas.

Wet Chemistry

Wet benches containing either solvent or acid chemistry are prevalent throughout most facilities, presenting some of the most common direct chemical exposures to fab operators. The primary exposure controls are covers on the chemical baths themselves and ventilation. In order to assess airborne exposure, air sampling pumps can be used to collect both personal and area samples.

In addition to chemical monitoring, the effectiveness of the ventilation system should be periodically checked. Wet bench local exhaust ventilation functions differently from a traditional laboratory-type fume hood. The typical wet bench design uses the room laminar flow to increase capture efficiency at the chemical baths. This design moves the capture plane from the lab-type hood “face” to the chemical bath surface (see Figures).

Although a wet bench is not the same as a lab hood, many facilities in California, as well as facilities located in other states, use the 100 fpm face velocity requirement from the California regulation “Ventilation Requirements for Laboratory-Type Hood Operations” (8 CCR 5154.1) as an internal wet bench ventilation standard. This standard can be used as a guideline, but should be supplemented with qualitative capture efficiency data such as that obtained with a vapor visualization device.

Radiation Monitoring

If equipment is well maintained, it is unusual for fab operators to be exposed to any type of radiation during normal production. Ion implanters are periodically surveyed, by running the survey meters along all surfaces of the tool, to ensure that no ionizing radiation leakage is present. Plasma tools are periodically surveyed for Rf or MW radiation to ensure that no leakage is present at the back of the tool (many instances of Rf leakage result from missing screws in the matching network or other parts of the tool directly exposed to Rf). Viewports of plasma tools are surveyed for UV and/or IR exposure. As long as the viewports have UV shielding, exposures are unlikely. IR radiation may also be present at horizontal diffusion furnaces. That warm, orange “glow” actually presents a significant source of IR exposure. Finally, any tool with a static magnet should be surveyed to determine the extent of the magnetic field, so that hazard alerts can be posted for pacemaker wearers.

Maintenance Tasks

Maintenance tasks, particularly those that require opening enclosures or tools, can lead to employee exposures not present during normal operation. The loss of ventilation and the influx of room air create chemical exposures for maintenance personnel (ref. Frist, Spring 1996 SSA Journal). Maintenance exposures may arise during routine preventative maintenance and during trouble shooting.

Chamber Cleans

Etch and deposition chamber tools are at the forefront of maintenance exposures. The chemicals used in these tools often leave highly corrosive residues of fluoride or chloride compounds. Because of the nature of plasma processing, the residues left in these chambers are of unknown chemical composition, so the industrial hygienist needs to do some predictive chemistry, look at previous monitoring reports, and use professional judgement in the hazard recognition stage of sampling strategy development.

For example, over the past year or so, several reports of cyanide and cyanogen compound presence in the air during manual metal etch wet chamber cleans have been reported (ref. Pais, 1998 SSA proceedings). The typical metal etch process gases include some combination of chlorinated compounds (Cl2, BCl3), halogenated organics (CF4, CHF3), fluorinated compounds (SF6, NF3), and inerts (N2, Ar). While integrated personal air samples are almost always non-detectable for most potential process by-products, area samples located in a worst-case position and direct-reading measurements have shown halogen (HF, HCl) and cyanide compound (HCN, CNCl) concentrations above the American Conference of Governmental Industrial Hygienists (ACGIH) exposure limits. This is significant in that the exposure limits for these four compounds are all Ceiling values, which should not be exceeded during any part of the work day.

Ion Implanter Tasks

Ion implanters use materials such as arsenic, arsine gas, boron, boron trifluoride, and antimony in semiconductor wafer processing. Exposure to arsenic, a carcinogen, is a particular concern during maintenance activities. Some activities, such as source chamber cleaning, present significant arsenic exposure to maintenance technicians. Other activities, such as source removal or parts cleaning, may present lesser exposures. In most cases, arsenic surface contamination is a concern (ref: Roberge, 1998 SSA proceedings).

Conclusion

Industrial hygiene monitoring provides a means to evaluate potential hazards to human health in the semiconductor manufacturing environment. The monitoring techniques available continue to evolve, as with portable gas chromatography, and decreasing chemical detection limits. Even with state-of-the-art monitoring equipment, the industrial hygienist must use professional judgment in evaluating results and making recommendations, particularly when multiple monitoring techniques are used. As new semiconductor processes are introduced, industrial hygiene techniques can be used to help identify potential hazards before introduction of the process to the manufacturing environment, in addition to monitoring in the production fab.

ABSTRACT

This study describes a comparison of worker exposure to total and inhalable dust, inorganic arsenic, and borates using two types of particulate sampling assemblies as part of a comprehensive industrial hygiene evaluation in a borate mining and processing facility. Employees were segmented into similar exposure groups (SEG) based on work location within the facility, job classification, and type of chemical agent. Approximately 10% of the employees from each SEG wore two personal sampling devices simultaneously for the purpose of collecting total and inhalable particulate fractions using a closed face, 37mm mixed cellulose ester matched-weight filters (MMW) and Institute of Occupational Medicine (IOM) sampling assembly, respectively. Sample results indicated that the IOM concentrations were consistently higher than the corresponding MMW concentrations for all three agents. An analysis was performed to investigate a relationship between MMW and IOM. The data revealed correlation coefficient values of 0.72, 0.82 and 0.84 for total dust (n=197), inorganic arsenic (n=137), and borates (n=194), respectively. These positive correlation coefficients indicate that the IOM and MMW measurements are consistent with each other, and can be used for predicting exposure levels. The total dust and borate large mean ratios should be considered in developing inhalable fraction-based regulatory standards.

INTRODUCTION

With the introduction of the Institute of Occupational Medicine (IOM) sampling assembly for inhalable dusts, questions have been raised as to whether the 37mm cassette assembly or the IOM sampling assembly is better at approximating the amount of particles that enter the respiratory tract, and whether exposures can be estimated when comparing the results between the sampling assemblies.

Currently, most Occupational Safety and Health Administration (OSHA) and National Institute of Occupational Health (NIOSH) sampling methods for particulates rely on the use of a 37mm filter cassette assembly. In particular, arsenic and borate sampling requires the use of a 37mm 0.8 micron mixed cellulose ester (MCE) filter in-line with personal sampling pump, whereas total dust sampling requires a 37mm 5.0 micron polyvinyl chloride (PVC) filter in-line. However, when sampling arsenic, borate, and total dust simultaneously, it is recommended that a 37mm MCE matched weight sampling (MMW) assembly is used. The MMW allows for the gravimetric analysis of total dust, as well as the speciation of arsenic via atomic absorption spectrophotometry, and boron via inductively coupled plasma.

Inhalable particles form the fraction of particulates with diameters of 100 microns or less, which can be inhaled through the upper respiratory system. This range of particulates can actually be deposited anywhere in the respiratory tract. The IOM sampling assembly was designed to simulate particle collection behavior that occurs during breathing.

The IOM sampler is a personal sampling device that has a cylindrical body 37mm in diameter and 27mm long. The sampler has a 15mm circular orifice with a thin lip protruding outward, minimizing sample variations due to loss of particulates from the outer surfaces of the sampler. The orifice and lip are an integral part of the filter cassette assembly. When analyzing a total dust sample, the filter and cassette are weighed together before and after sample collection. All of the particles that are deposited on the filter and filter cassette are analyzed by the laboratory. The MMW sampling assembly is a 37mm plastic cassette containing two MCE filters supported on a cellulose pad (see Figure 1). During gravimetric analysis, the weight of the unexposed second filter is tared from the filter that is exposed to the environment, thereby minimizing the effect of the hygroscopic nature of MCE filters. At 5mm, the orifice of the MMW is substantially smaller than that of the IOM. When collecting a total dust sample with a MMW cassette, only the filter is weighed before and after collection. Therefore, any particulate that has been deposited on the surface of the cassette wall will not be analyzed, resulting in an underestimation of exposure.

METHOD

Sample Collection

Samples were colleted at U.S. Boron facility, a major boron mining, processing, and distribution center. Employees in the Boron, California facility were grouped in accordance to similar exposure groups (SEGs). A SEG is a group of employees with similar exposure to an environmental agent. Owing to the exposure similarity within each group, a subgroup of randomly selected individuals, representative of the exposure distribution, were used to evaluate trends within each SEG.

SEG characterization was based on three parameters: 1) work location (department) within the facility, 2) job classification, and 3) chemical agent monitored. All monitored employees within a given SEG were selected randomly by U.S. Borax personnel.

Each selected employee was monitored for personal airborne exposures to total dust and borate. In addition, if an employee had a potential exposure to arsenic, then he/she was monitored for inorganic arsenic along with total dust and borate. Personal air samples were collected by attaching a MSA Escort personal sampling pump to each monitored employee’s belt. The sampling pump was calibrated with an in-line 37mm closed-face 0.8-micron MMW sampling cassette assembly to a flow rate of 2 liters per minute (lpm) using a Gilibrator, a primary calibration standard. Borates, total dust, and arsenic were collected simultaneously on a MMW sampling cassette. During sample collection, the MMW was positioned in the breathing zone of the employee.

Approximately 10% of the employees in each SEG were required to wear the MMW and IOM filter assemblies simultaneously in order to compare the variation in sampling methods. The personal IOM air samples were collected by attaching a MSA Escort personal sampling pump to each monitored employee’s belt. The sampling pump was calibrated with an in-line 25mm 0.8 micron IOM sampling assembly to a flow rate of 2 lpm with a Gilibrator. Borates, total dust, and arsenic were collected simultaneously on the IOM that was placed in the breathing zone of the employee.

Employees were monitored for at least 7 hours of an 8-hour workshift. Whenever a workshift exceeded 8 hours, monitoring time was extended so that a sample representative of 88% of the work shift was collected. The employees had "zero" or negligible exposure during non-sampled time.

U.S. Borax employees performed routine duties and tasks that were assigned at the plant. The monitored employees were observed throughout the sampling period in order to collect detailed information regarding exposure conditions, such as daily tasks conducted, production/equipment run, production equipment used, any visible elevated dust conditions, personal protective equipment worn, engineering controls in place, and the predominant species of borate dust to which the worker was exposed. These data were collected to document and characterize the sampling conditions for each sample.

Sample Analysis

All of the MMW and IOM samples were sent to NATLSCO, a laboratory accredited by the American Industrial Hygiene Association. Arsenic, boron, and total dust were analyzed in accordance with NIOSH method 7900 (atomic absorption with arsine flame generation), OSHA 125G (inductively coupled plasma), and modified NIOSH method 0500 (gravimetric analysis), respectively. NIOSH method 0500 was modified for total dust sampling in order to allow for the collection of arsenic, boron and total particulates on the same filter. Unlike a PVC filter that is specified in NIOSH 0500, a MMW filter can easily be digested for additional agent speciation of a total particulate sample.

RESULTS AND DISCUSSION

Laboratory results for arsenic, boron, and total dust were provided in micrograms (mg) of agent detected on the filter. A borate correction factor was applied to the boron analytical results in order to take into account the hydration state of the borate species monitored. This information was used to calculate an 8-hour time-weighted average (TWA) for each employee. All results presented in this section are based on 8-hour TWA values.

Pairs of MMW and IOM measurements collected in each similar exposure group (SEG) were compared to investigate a relationship between MMW and IOM so that observed MMW values could be converted to equivalent IOM values. Total dust and borate personal exposure data were collected for 197 U.S. Borax employees. Of these employees, 137 were also monitored for inorganic arsenic.

The ratio of IOM/MMW, or the slope (S), has been used to measure the relationship between IOM and MMW, assuming that individual exposure measurements are random and normally distributed. The personal exposure results from industrial hygiene sampling methods using MMW and IOM are always positive. Particulate deposition results often follow a lognormal distribution. Therefore, prior to using the S measurement, MMW and IOM data for the total dust, inorganic arsenic, and borate were examined in order to assess whether a normal or lognormal distribution should be applied to the data sets. It was found that the statistical distributions for MMW and IOM for the three agents were closer to a lognormal than to a normal distribution. Thus, for the analyses it was assumed that MMW and IOM are lognormally distributed. Under this assumption, natural logarithms of the measurements MMW and IOM can be assumed to follow normal distributions. In this study ln(MMW) and ln(IOM) are represented by MMW_L and IOM_L, respectively.

To investigate a predictive relationship between MMW and IOM, linear regression analyses were considered on the pairs (MMW_L, IOM_L). However prior to performing the regression analyses, pairs (MMW_L, IOM_L) were evaluated statistically for identification of outliers. Outlier pairs were identified by using the characteristic of a standard normal distribution (Z, with mean = 0, standard deviation =1) where more than 99% probability accounts for Z values within this interval (-3,3) around the means. To apply this characteristic, MMW_L and IOM_L were standardized so that they are comparable to a standard normal distribution. These standardized values were labeled as MMW_z and IOM_z. Then the pair (MMW_L, IOM_L) was identified as an outlier at a 99% level of confidence. Identified outliers from the data of the three agents were excluded from the regression analysis. The results are shown in Table 1.

The least square method was used to predict average IOM_L given a MMW_L value representative of a SEG. The predicted value IOM_p is derived from the linear regression equation IOM_p = a + b MMW_L, where ‘a’ is the regression intercept and ‘b’ is the regression coefficient representing the slope of the regression line. Multiple correlation coefficients (R) between zero and one from these analyses were used to assess the strength of the linear regression relationship between IOM_L and MMW_L. A value of R closer to one indicates that prediction of IOM_L given MMW_L can be made with a high degree of confidence. Number of employees, the intercepts, regression coefficients, and multiple correlations are shown in Table 2. These regression equations and plots are shown in Figures 1 through 3.

A reverse transformation of the regression equation to the original scale of data shows that the given MMW value of the SEG and the average predicted IOM for the SEG can be expressed by exp [a+b ln (MMW)]. These equations are shown in Table 2.

Table 1: Identification of Outliers

Agent	Total Dust	Arsenic	Borate
Number of Employees in SEG	197	143	197
Number of Outliers Identified	5	3	3

Table 2: Regression Analysis and Prediction Equation

Prediction Equation: IOM_p = a MMW^b where IOM_p = Predicted IOM given MMW = X

CONCLUSIONS

This article reprinted from Biological Trace Element Research, Vol. 66, 1998, with permission from Humana Press, Inc.

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A Comparison of Worker Exposure to Inhalable and Total Dust, Inorganic Arsenic, and Borates Using Two Types of Particulate Sampling Assemblies in a Borate Mining and Processing Facility The Phylmar Group, Inc. ABSTRACT This study describes a comparison...

Comprehensive Semiconductor Processing Facility Industrial Hygiene Surveys The consultant has performed comprehensive industrial hygiene sampling during normal...

Design and Implementation of a Strategic Employee Exposure Assessment and Tracking (SEEAPT®) System The Phylmar Group, Inc. designed a computer-based industrial hygiene strategic...

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The Phylmar Group, Inc.

This study describes a comparison of worker exposure to total and inhalable dust, inorganic arsenic, and borates as part of a comprehensive industrial hygiene evaluation in a borate mining and processing facility. Employees were segmented into similar exposure groups (SEG) based on work location within the facility, job category and agent. At least 10 percent of the employees in each SEG for total dust (n=197), inorganic arsenic (n=140), and borates (n=194) wore two personal dust samplers simultaneously to collect total (closed face, 37-mm mixed cellulose matched-weight filters (MMW)) and inhalable (Institute of Occupational Medicine type (IOM)) particulates. IOM concentrations were consistently higher than the corresponding MMW concentrations for all three agents. Analysis of the log transformed data revealed correlation coefficient values of 0.72, 0.82 and 0.84 for total dust, inorganic arsenic, and borates, respectively. These high correlation coefficients indicate that the IOM and MMW measurements are consistent with each other, and can be used for predicting exposure levels. Further, the spread of IOM/MMW ratios can be expressed for total dust, inorganic arsenic, and borates as 5.28±8.19, 1.27±0.91, and 3.36±2.50, respectively. The relatively low spread of the inorganic arsenic results, in comparison with total dust and borates, may be because approximately 78 percent of the IOM-MMW paired samples were below the detection limit. The total dust and borate large mean ratios should be considered in developing inhalable fraction-based regulatory standards.

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