Toxic emissions continuous releases

As mentioned earlier, toxic releases may consist of continuous releases or instantaneous emissions. Continuous releases usually involve low levels of to.xic emissions, wiiich are regularly monitored and/or controlled. Such releases include conlinuous slack emissions and open or aerated chemical processes in wliich certain volatile compounds are allowed to be stripped off into the atmosphere tliroiigh aeration or agitation. Mathematical models for these releases to tlie enviroiuncnt are covered in detail in Part III. 

There are three types of TAP emissions continuous, intermittent, and accidental. Both routine emissions associated with a batch process or a continuous process that is operated only occasionally can be intermittent sources. A dramatic example of an accidental emission was the release of methyl isocyanate [624-83-9] in Bhopal, India. As a result of this accident, the U.S. Congress created Tide III, a free-standing statute included in the Superfund Amendments and Reauthorization Act (SARA) of 1986. Title III provides a mechanism by which the pubHc can be informed of the existence, quantities, and releases of toxic substances, and requires the states to develop plans to respond to accidental releases of these substances. Eurther, it requires anyone releasing specific toxic chemicals above a certain threshold amount to aimuaHy submit a toxic chemical release form to EPA. At present, there are 308 specific chemicals subject to Title III regulation (37). 

The next two sections discuss accidents tiiat result in the release of a toxic emission or a liazardous spill. In general, a to.xic emission can be considered to be either continuous or instantaneous. In tliis section only tlie atmospheric effects of toxic emissions are considered. Hower cr, hazardous spills (ne 1 section) usutilly denote a liquid contamination of either soil or water systems in addition a liazardous chemical spill may lead to tlie release of toxic emissions. 

Improvements in the monitoring and operation of incinerators could minimize the accidental release of hazardons efflnents. In particular, fast-acting, continuous, on-line monitors are needed to detect excursions in operating conditions that could lead to toxic emissions. 

SIPs are intended to prevent air pollution emergency episodes. The phms are directed toward preventing excessive buildup of air pollutants tliat me known to be harmful to the population and the enviroiunent when concentrations exceed certain limits. The compounds affected under the implementation plans are sulfur dioxide, particulate matter, ctirbon monoxide, nitrogen dioxide, and ozone. A contingency plan, which will outline the steps to be taken in tlie event tliat a particular pollutant concentration reaches tlie level at wliich it can be considered to be hannful, must be included in each implementation plan. The implementation plans are solely based on tlie continuous emission of tlie previously stated air pollutants. They do not mandate any actions to be taken in tlie event of an accidental toxic release. 

For toxic gas clouds, concentration-time information is estimated using dispersion models (Section 2.3). Probit models are used to develop exposure estimates for situations involving continuous emissions (approximately constant concentration over time at a fixed downwind location) or puff emissions (concentration varying with time at a downwind location). It is much more difficult to apply other criteria that are based on a standard exposure duration (e.g., 30 or 60 min) particularly for puff releases that involve short exposure times and varying concentrations over those exposure times. The object of the toxic effects model is to determine whether an adverse health outcome can be expected following a release and, if data permit, to estimate the extent of injury or fatalities that are likely to result. 

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