More Models: A Software Program from EPA Can Help You Evaluate the Health and Safety Impact of Different Process Activities during Initial Planning. (Computers)

Article excerpt

Last month, we looked at how computers can model real-world environments to help improve safety and health analysis and design decisions. We saw how the National Institute of Standards and Technology's (NIST) indoor air quality and ventilation analysis program CONTAMW (www.bfrl.nist.gov/IAQanalysis/CONTAMWdesc.htm), can create detailed models of complex building environments to predict air flows, contamination concentrations and building occupant exposure to airborne contaminants.

Creating accurate models in CONTAMW requires careful attention to details. Information on building design, materials and construction, occupancy loading, the ventilation system and contaminant generation rates must be collected and included in the model.

In many cases, safety and health professionals don't have time to gather the information needed for such a detailed analysis. Or the required design information simply isn't available. Take the U.S. Environmental Protection Agency (EPA), for good example.

Under the Toxic Substances Control Act (TSCA), EPA's Office of Pollution Prevention and Toxics (OPPT) screens about 2,000 new and existing chemicals annually to identify those that may be hazardous to the environment or human health. Based upon their analysis, EPA can require testing and reporting of hazardous chemicals, and ban the manufacture and import of chemicals that pose an unreasonable risk.

To help in this effort, EPA developed ChemSTEER (Chemical Screening Tool for Exposures and Environmental Releases). According to Senior Chemical Engineer Scott Prothero: "The EPA uses ChemSTEER methods and models to generate screening-level workplace release and exposure assessments of chemicals, primarily in the New Chemicals Program. These screening-level workplace assessments use generally conservative models when monitoring data are not available. The workplace release estimates are used in E-FAST, which complements ChemSTEER by generating screening level exposure assessments for consumer, general population and environmental exposures. The two assessments from these two tools form a complete life cycle exposure assessment of each chemical."

While designed to help the EPA meet its obligations under TSCA, Prothero believes ChemSTEER can help safety, health and environmental professionals screen chemical and process alternatives. "Safety and health professionals can use ChemSTEER to identify potential workplace releases and exposures of concern for any part of a chemical's life cycle. ChemSTEER can fill data gaps for the professional's workplace or may be used as part of a product stewardship effort for examining downstream workplaces."

Imagine you're the safety manager at a small chemical company that produces surface cleaning products. The company is planning a new product with 10 percent methylene chloride. Methylene chloride is a carcinogen, heavily regulated by OSHA. You need to evaluate the safety and health implications of the proposed new product line and turn to ChemSTEER.

ChemSTEER models are based on manufacturing processes, so the first step is to describe the process. Your company plans to produce one 550-gallon batch of the new product per day for 100 days each year. Methylene chloride will be transferred from a 55-gallon drum into a closed mixing vessel. After mixing, the product will be packaged in 5-gallon containers for sale.

Modeling this operation in ChemSTEER is a seven-step process, each step guided by a separate tab in ChemSTEER's main window (Figure 1). The first and last tabs contain general information that appears in printed reports. The real modeling work is done in the middle five tabs.

Basic chemical properties -- molecular weight, vapor pressure, density and water solubility -- are entered in the "Chemical" tab, along with annual chemical use in kilograms per year.

Next, a description of the manufacturing process is created. …