The toxic threat from any chemical-whether it is released as a gas or evaporates from a puddle-will depend on how the chemical disperses as it travels downwind. (To use ALOHA, you need to specify more information about the potential release than you do in the Green Book procedures.) This page in the series discusses several reasons why ALOHA's calculations differ from the Green Book recommendations.
The primary reason for this is because the ALOHA model uses more complex equations to give you better estimates of the area affected by a chemical release.
You can download the Green Book from the Environmental Protection Agency site.įor a given release scenario, if you compare the Green Book estimate for vulnerable zone distance and the ALOHA estimate for threat zone length, you will find that they are often quite different. Note: Published in 1987, the Green Book is more properly known as Technical Guidance for Hazards Analysis: Emergency Planning for Extremely Hazardous Substances. (The CAMEO Data Manager Screening & Scenarios tool implements the Green Book procedures.) Once the worst hazards are identified, planners may analyze those locations more thoroughly using a hazard model like ALOHA. The Green Book method uses simple calculations to provide an initial assessment of the hazards based on just a few pieces of information about the stored chemicals. The "Green Book" provides a method that planners can use to quickly determine the relative hazards of chemicals stored in a community, as required by the Emergency Planning and Community Right-to-Know Act (EPCRA).
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