Chemical Mixture Methodology

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 The Chemical Mixture Methodology (CMM) provides recommended default emergency exposure guidelines for mixtures of chemicals. The CMM makes extensive use of Health Code Numbers (HCNs) to examine the additive impact that each chemical component in a chemical mixture may have on specific target organs. The CMM is a more realistic predictor of potential human health impacts than can be obtained using the (1) non-conservative method of separately analyzing the consequences of each chemical component or the (2) overly-conservative method of adding the exposures from each chemical together regardless of the human organ targeted by the chemical. The CMM is recommended by SCAPA for potential use in emergency planning hazards assessments (EPHAs), safety analyses, and in emergency response situations. To use the CMM, download the CMM workbook and carefully review the CMM user’s guide.
 
The latest version of the Chemical Mixture Methodology Workbook*(“CMM Revision 29”, September 2016)​ is available for use.  This workbook can process up to 15 chemicals in a given mixture.  *Note: To use this workbook, its embedded macros must be enabled. After opening the workbook, you may notice a security warning that states “macros” or “content” have been disabled. If you see this, please select the option to enable this content. 
 
A User's Guide for the Chemical Mixture Methodology (“CMM Revision 29", finalized in September 2016) provides step-by-step instructions on how to use the CMM workbook.  It also includes an explanation of how the CMM uses chemical concentration information, PAC data, and HCN values to compute hazard indices to support emergency preparedness decision making.  
A summary technical description of the CMM and HCNs are provided in the CMM and HCN background information webpage.​