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Updates to the CMM Data Set

The CMM Revision 27 utilizes chemical concentration limit data from PAC Revision 27.  CMM Revision 27 includes the most recent set of updated HCNs and PACs for all of the 3,300+ chemicals in the Revision 27 data set. 

In PAC Revision 27, the PAC development team incorporated a number of significant changes in the PAC derivation methodology.  These changes were based on a series of technical recommendations proposed by an external peer review panel.  In some cases, PAC values for individual chemicals have changed by several orders of magnitude (either upward or downward); though for many chemicals the PAC values are unchanged or the changes are relatively small.  In addition, TEEL-0 values are no longer provided in the PAC data set; instead the data set offers only PAC-1, PAC-2, and PAC-3 values for each chemical.  TEEL-0 values were dropped because of their lack of relevance in emergency planning and for the tendency by some to misinterpret this "no health impact" concentration limit. 

As a result of changes to the PAC derivation methodology, CMM Revision 27 estimates may significantly differ from those computed using CMM Revision 26.    

General Update Information

A new revision of the CMM data set is generally released every year and incorporates the addition of new chemicals, updates to HCN values, and major revisions to the PAC data set.  Minor revisions to the CMM Workbook (as indicated by the addition of a letter after the revision number) may be released on occasion to correct a limited number of errors or incorporate minor revisions to the PAC data set.  CMM updates will generally be synchronized with revisions to the PAC data set. 

Users of the CMM may wish to periodically review past CMM analyses for their key facilities.  In many cases, updated information will reduce over-conservatism in previous analyses.  However, in some cases updated information may warrant more stringent emergency preparedness actions.