C. Keil, Bowling Green State University, Bowling Green, OH.
Capture efficiency quantifies the effectiveness of local exhaust ventilation (LEV) hoods at preventing the release of chemicals into the workplace. Capture efficiency information is important when planning engineering controls and when modeling workplace exposures. Design guidelines such as the ACGIH Ventilation Manual provide recommendations for hood design and flow rates (Qrec). These guidelines do not, however, indicate what capture efficiency can be expected. Capture efficiency measurements are often done using tracer gas methods.
A unique method for measuring capture efficiency using water vapor as a tracer gas has been developed. A known mass of water is placed in front of the hood to be evaluated. It is heated to complete evaporation. Absolute humidity is measured in the air entering the room and in the air exhausted through the hood. The water vapor mass flow through the hood in excess of the amount expected based on the incoming room air conditions is water vapor mass from the evaporating source. The total excess water vapor mass captured during the evaporation process divided by the total mass of water evaporated is a measure of the capture efficiency of the hood.
Plain opening and slot hoods have been evaluated using this method. A positive trend was observed for increased capture efficiency as Q approached and reached ACGIH Qrec. Capture efficiencies of over 90% were seen for systems near or meeting Qrec. Plain opening hoods operating at 30% of Qrec had efficiencies measured between 20 and 60%. Slot hoods operating below 50% Qrec had capture efficiencies less that 50%.This method provides a tool for the broad evaluation of hood capture efficiencies. This broad evaluation will provide information for estimating hood efficiencies based on LEV system’s percentage of Qrec.
C. Simmons, F. Boelter, G. Crawford, Boelter & Yates Inc., Park Ridge, IL.
Situation: A method to measure the air change rate in single zone boiler rooms and isolation test chamber was needed.
Problem: Existing methods allow for the use of a variety of tracer gases to be used. Each gas has advantages and disadvantages associated with its use and measurement. The method selected needed to be highly portable, easily measured, non-toxic or with a very low toxicity, and inexpensive to use. In addition, some of the measurements would be collected in occupied schools; therefore, the methods and tracer gas would need to be acceptable to school district personnel.
Resolution: Carbon dioxide was selected as the tracer gas to use for the project. The concentration decay test method was selected to determine the air change rate. Carbon dioxide is inexpensive, easy to obtain and measure, and has a high permissible exposure limit. In addition, school administrators were familiar with carbon dioxide, easily understood how it would be used and measured, and accepted the use of carbon dioxide gas in the schools. The air change rates were easily measured under various conditions in the boiler rooms and isolation chamber.
Benefit to Others: Using carbon dioxide as a tracer gas to measure the air changes per hour in a single zone provides an inexpensive, reliable, accurate, and easy procedure for industrial hygienists to determine ventilation rates. The equipment needed to conduct the measurements is used in routine indoor environmental and industrial hygiene evaluations and is often already part of the equipment inventory. The method provides an additional opportunity for industrial hygienists to better characterize workplace conditions during the initial stages of an exposure assessment. Additionally, ventilation information is critical to the ability to perform and validate mathematical modeling for exposure estimation.
S. Waisanen, T. Johnson, 3M Company, St, Paul, MN.
Occupational Exposure Limits (OELs) contribute valuable information to the exposure assessment process for managing respirator programs, PPE programs, hazard communication, and ventilation programs. Where OELs do not exist, and where there is limited toxicological data, a procedure is used to develop internal working OELs. Working OELs do not replace more formal exposure guidelines, but they are valuable tools in the face of limited toxicological information. The use of working OELs can facilitate more complete exposure assessment, and improved employee protection. Working OELs were introduced in a large manufacturing organization 2 years ago. The exposure assessment system assigns pending priorities to all chemical materials without OELs. These priorities can be used to initiate the working OEL process, or a facility may initiate the process for business reasons. This presentation provides an overview of the working OEL process, and describes some of the implementation challenges of the first 2 years. Specifically:
R. Goldman, 3M Company, St. Paul, MN.
Well-designed medical surveillance for employees exposed to chemicals will assure that the right programs are implemented and that the right employees are included in the programs. Efforts to improve this assurance and to increase the cost-effectiveness of medical surveillance programs at a large manufacturing company with numerous plant sites and diverse operations led to the development and use of several tools related to exposure assessment.
The approach requires development of OELs where none exist and program inclusion “triggers” for employees exposed to chemicals covered by medical surveillance programs. The inclusion triggers were adopted from regulatory action levels when possible, but non-regulated chemicals required a different approach. Some triggers were based on specific chemical health effect knowledge and previous corporate experience with the chemical. For others a model similar to regulatory action levels (i.e., half of the OEL) was applied.
Several focused reports drawn from the exposure assessment database were developed to indicate locations (including site, department, process, and task) where medical surveillance chemicals are handled and to display exposure assessment information (both qualitative and quantitative) for those chemicals. Guidance for interpretation of exposure data was written to promote consistency in judgments regarding the need for programs and for employee inclusion in medical surveillance programs from site to site.
R. Newton, Liberty Mutual, Marietta, GA.
This Qualitative Exposure Assessment (QEA) Model is a risk assessment process used to qualify hazards and demonstrate risk reduction from interventions.
Following established Job Safety Analysis (JSA) methods, activities, or processes which are completed by employees or work groups are identified and listed on a task assessment sheet. Priority can be set for the activities or processes to be examined based on the perception of risk for a given activity or all activities can be examined during this QEA process.
For each hazard that exists during completion of a task or process, current or established control measures are listed. Three characteristics of the current risk presented by each hazard are rated on a scale of 1 to 5. The QEA process considers the frequency of the work activity which includes exposure to the hazard, the likelihood of injurious contact with the hazard, and the severity of injury or illness that may result from exposure to this hazard. After the five point scale is used to rate each of these three characteristics, an overall risk rating is calculated that ranges from 1 to 125.
Defined parameters for each step on the five point scale are used to help the user rate the frequency, likelihood, and severity components of the QEA analysis. These defined parameters are situation-dependent and may be modified to fit the corporate culture or the needs of an organization. However, the defined parameters must be uniformly applied throughout the organization.
In those situations where risk is identified at a level that is unacceptable to the organization, interventions (engineering controls, process controls, chemical substitutions, etc.) are implemented and level of reduction in the calculated risk rating is measured to identify a reduction in risk for a given hazard.
L. Leger, DuPont Canada, Mississauga, ON, Canada.
Microbial mapping is a unique process used to identify and show the impact of the microbes in a particular environment, whether it be a food-processing plant or an entire value chain. It helps to locate the source of the problem and traces the movement of pathogens or spoilage organisms. Using state-of-the-art technology we genetically identify and fingerprint microorganisms, such as Listeria, Salmonella, and Escherichia coli O157:H7, to create the microbial maps.
To develop meaningful microbial maps, you must thoroughly evaluate data from multiple sources including in-house microbial test results, customer/consumer and employee feedback, as well as operational procedures. A rigorous sampling plan is then created to address, determine, and understand a plant’s specific microbial ecological issues. For example, a customized sampling plan may focus on gaining insight into the distribution and movement of pathogens found in a facility. The genetic fingerprints obtained from the sampling plan are mapped onto a plant (or value chain) schematic. An analysis of matching fingerprints from different locations is completed to identify microbial pathways, evaluate the root cause of a problem, and make recommendations to eliminate the contaminants. This information can then be used by food safety and operations managers to take appropriate action to extend product shelf life, reduce the likelihood of a product recall, and/or enhance food safety, resulting in increased customer satisfaction. Microbial maps provide a way to look at the impact of changes in a facility and become a tool for quality improvement. This has been successfully used in meat and dairy plants in North America to gain a better understanding of the nature and distribution of microorganisms within a particular environment or product, to address specific microbial contamination problems associated with product quality (for instance spoilage and shelf life), and to address specific microbial contamination problems associated with food safety.
E. Lee, C. Feigley, K. Lakshman, J. Khan, M. Ahmed, S. Tamanna, University of South Carolina, Columbia, SC.
The contaminant dispersion patterns in an enclosed space predominantly depend on airflow rate, emission rate, room configuration, and temperature differences. However, most mathematical methods for estimating room concentration only consider the airflow rate and emission rate. Here the impact of temperature difference between a wall and room air was studied in an experimental room (2.86 m(L) x 2.35 m(H) x 2.86 m(W)). Tracer gas (99.5% propylene) concentrations were monitored automatically at 144 sampling points with a photoionization detector. The north wall was chosen to represent a building’s external wall and could be heated or cooled. The desired temperature was obtained by circulating heated or chilled water through the copper tubes attached to the north wall. To promote uniform wall temperature, the inside of the wall was covered by 1/16”-thick aluminum sheets. A total of 12 factorial combinations were investigated: two flow rates (5.5 and 3.3 m3/min) and six thermal conditions (one isothermal condition, three summer conditions, and two winter conditions).
For the lower flow rate, winter conditions produced greater variability of concentration with location in the room (coefficient of variation (CV) = 0.99 and 1.35) than isothermal or summer conditions (CV = 0.29 to 0.35). For the higher flow rate, the CVs (CV = 0.36 to 0.43) and the room average concentrations (36.8 to 42.8 ppm) were similar for all thermal conditions. However, the dispersion patterns for isothermal and non-isothermal conditions were substantially different.
This study indicates that contaminant dispersion patterns depend upon both flowrate and temperature difference. The effect of temperature difference, especially for simulated winter conditions, was much more pronounced at the lower flow rate, causing more spatial variability of concentration within the room. Thus, mathematical methods for estimating room concentrations are expected to be less precise at lower flow rates.
J. Sherrill, T. Ford, BWXT Y-12, LLC, Oak Ridge, TN.
Medical surveillance programs often perform hundreds or even thousands of evaluations on workers with little reason, creating long-term legal problems as well as immediately costing productive time and money. The Department of Energy Oak Ridge BWXT Y-12 Site has taken this problem head-on to help reduce the number of low- to no-risk workers on medical surveillance programs by automating an industrial hygiene worker risk review process utilizing quantitative and qualitative workplace risk data that supports a concur or no-concur decision from industrial hygiene that an employee meets the exposure criteria for a medical surveillance program. The process implemented at Y-12 also significantly enhances our ability to identify and establish routine monitoring programs for those workers who perform tasks that actually have a more significant potential workplace exposure.
H. Harapan, 3M Company, St. Paul, MN.
Exposure assessment is a multidisciplinary program central to deciding whether and how to use knowledge and resources for reducing workplace exposures, and to defining exposure response relationships. Rapid measurement tools and improved data analysis methods are needed for the collection of adequate exposure data and for effective intervention. These advancements would lead to better identification of at-risk workers, better identification of the most cost-effective control and intervention strategies, better understanding of exposure-response relationships, and improved baseline data for standard setting and risk assessment. In a Fortune 500 company, these advancements will require a successful exposure assessment program that must be “sold” to management. Management must understand the assurance that prioritization is necessary, tiered and continuous improvements are required, and that there are gaps in the existing program that a comprehensive exposure assessment can effectively address. But exposure assessment is often a tough sell. The hygienist must deliver a layman’s version of exposure assessment that makes sense to business people. In this presentation, I will discuss how a model program may be packaged and sold into a business unit. The application of the program would require support from top and middle level management as well as facility industrial hygienists to buy into the application. Program improvement and efficiency should be identified as well as the benefits in completing an exposure assessment program. The discussion will look into challenges on how to obtain management buy in, to acquire additional resources, and finally to maintain a successful level of performance.
Posted May 30, 2004