This document is intended to provide simple methods and reference tables for determining distances to toxic and flammable endpoints for worst-case and alternative release scenarios. The generic approach is based on parameters required by the rule and on conservative assumptions about other conditions and may not reflect site-specific conditions. Use of the guidance is not required; facilities may conduct their own air dispersion modeling, provided that they use the parameters specified in the rule and a model appropriate for the substance. EPA also developed industry-specific guidance for ammonia refrigeration (AR) and wastewater treatment plants (WWTPs). In developing these documents, EPA conducted chemical-specific modeling for anhydrous ammonia, aqueous ammonia, chlorine, and sulfur dioxide, including consideration of liquid droplet formation (except in the case of aqueous ammonia). This chemical-specific modeling was incorporated into the RMP Offsite Consequence Analysis Guidance (OCAG). The modeling for these four toxic substances is different from, and less conservative than, the generic modeling that applies to other regulated substances covered in the OCAG. The purpose of this document is to provide the technical background of the methodology and assumptions used to develop the chemical-specific tables.