The Office of Environmental Health Hazard Assessment (OEHHA) adopted the revised Air Toxics Hot Spots Program Guidance Manual for Preparation of Health Risk Assessments (Revised OEHHA Guidance Manual). The final version of this Revised OEHHA Guidance Manual, which can be found here, was developed by OEHHA, in conjunction with the California Air Resources Board (ARB) for use in implementing the Air Toxics Hot Spots Program. This manual updates health effects values, exposure pathway variates (e.g., breathing rates), and continues to use a tiered approach for performing HRAs based on current science and policy assessment.

In comparison to the OEHHA 2003 document, the exposure pathways remain the same while revisions were made to the exposure and risk algorithms to accept new data or variables that are used in the tiered risk assessment approach.

The Revised OEHHA Guidance Manual incorporates the new scientific information about age sensitivity to early life exposures of air toxics and its impacts on lifetime risk of developing cancer and other adverse health effects. The Revised OEHHA Guidance Manual accounts for age sensitivity factors which can result in an increase of cancer risk estimates to residential and sensitive receptors by approximately three times, and more than three times in some cases where toxic air contaminant has multiple pathways of exposure.

ARB has released an updated version of the Hot Spots Analysis and Reporting Program (HARP 2). This version replaces the prior version and incorporates the information presented in the 2015 Revised OEHHA Guidance Manual. HARP 2 is now available for use in developing facility emission inventories and conducting health risk assessments. HARP 2 can calculate Tier 1 and Tier 2 risk assessments. The ability to conduct Tier 3 and Tier 4 risk assessments should be completed by summer 2015. The HARP software is available for download here.

The intent of the Revised OEHHA Guidance Manual and the HARP software is to incorporate children’s health concerns, update risk assessment practices, and to provide consistent risk assessment procedures. Various California air districts are either currently working or planning on extensive outreach efforts and conducting workshops to discuss the implementation of Revised OEHHA Guidance Manual into risk assessment procedures for various risk-based programs such as permitting, CEQA, and AB2588.