When properly used, the class column (aka Residual Risk column) of the
PFMEA is used to identify lines of the PFMEA whose failure cause will expose the customer to an objectionable level of risk. Risk has two components, the severity of harm and probability of exposure to the harm. If you place a CC (aka Critical Characteristic) in the class column of the PFMEA, you are stating that the type of Harm the customer will be exposed to due to the process failure cause at an unacceptable probability is safety related or government regulation violation related. If you place an SC (aka Significant Characteristic) in the class column, you are stating the type of Harm the customer will be exposed to due to the process failure cause at an unacceptable probability is not safety related or a violation of a government regulation but is a returnable issue that will cost the company money. One can remove a CC or SC from a PFMEA by improving the Prevention Control to reduce the probability of the failure cause which is the source or risk exposure. CC and SC are Ford Symbols. Other companies have different symbols to indicate similar information. Due to the auto companies investment in training in their own symbols, they have never agreed harmonize the class symbols.
The Ford symbol for safety related objectionable residual risk in a
DFMEA is YC (aka Potentially Critical). The symbol for non-safety objectionable residual risk in a DFMEA is SC (aka Potentially Significant). When properly used in the Design
FMEA, the symbols identify product hardware specifications that are improperly specified and consequently leading to unacceptable risk exposure.
The removal of the class column (residual risk) column from the AIAG VDA DFMEA is just one of the reasons why the AIAG VDA DFMEA methodology leads to DFMEAs that are ineffective for managing risk.