Research Program Area: Emissions Monitoring & Control
In October 1991, the California Air Resources Board (ARB) identified PERC as a toxic air contaminant and discovered that PERC is a human carcinogen. Exposure to PERC also causes acute and chronic health effects such as irritation of the respiratory tract, skin and eyes, dizziness, diminished cognitive abilities and kidney and liver damage. The dry cleaning industry is the largest user of PERC solvent in California and it is used by a majority of dry cleaners. In October 1993, the ARB adopted an airborne toxics control measure to reduce PERC emissions from dry cleaning operations based on their assessment of the dry cleaning industry.
Dry cleaners usually have either natural or general ventilation systems installed at their facilities. A natural ventilation sytem consists of open doors, windows, and vents in a dry cleaning facility in conjuction with the wind and convective forces including temperature and PERC concentration profiles. Many facilities also have general ventilation such as air conditioning units or large fans on top of their building. Emissions from these systems are released at ground level or on rooftops. The public, particularly those living downwind, can be exposed to relatively high levels of PERC from these facilities.
No data existed on the effectiveness of room enclosures with ventilation systems in reducing risk to the public at dry cleaning facilities that perchloroethylene. The first objective of this project was to obtain emission data for estimating perchloroethylene capture efficiencies for the types of room enclosures currently in use. Then the source testing data is used as an input parameter to the industry wide risk assessment model, which is employed to estimate the health risk posed by these facilities.
The second objective was to develop guidelines for dry cleaning industry in terms of specifications, methods of installation, kids of control systems, cost of operation, estimates of the capture efficiencies of these systems and their risk reduction potential. The control measures on the nine facilities varied from full vapor barrier room enclosures (three facilities), partial vapor barrier room enclosure (three facilities), to local ventilation system (three facilities).
Risk created by a dry cleaner is dependent on the amount of emissions, the proximitiy to receptors, and how the emissions are released and dispersed. Various ventilation system's perchloroethylene emission rates were measured and were entered into the ISCST3 model to calculate the dispersion of the system, and determine the risk using dispersion and risk assessment parameters. It is very difficult to evaluate the Cancer Risk related to different types of vapor collection systems associated with the cleaning equipment inside the building. There are many variables not related to the vapor collection system that directly affect the dispersion model results. The modeling results suggested that height of the stack, exit velocity of the stack, and location of the stack on the building roof (downwash) are the most critical parameters in risk reduction.
After analysis of the data, it was concluded that cancer risks were found to be generally highest for facilities equipped with natural ventilation and lowest for facilities with full vapor barrier rooms.
For questions regarding this research project, including available data and progress status, contact: Research Division staff at (916) 445-0753
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