" We chose the quality because the luck had become too expensive. " (Jean Abraham) " In the running in the quality, there is no finishing line. " (David Kearns) " The quality is never an accident; it is always the result of an intelligent effort. " (John Ruskin)

It is now a question of quantifying the risks. For that, method FMECA defines criteria of quantification to which a note will be allotted. Are used in general:
•   The frequency of appearance (F) or "occurrence" (O): it is the probability F so that the cause of the failure occurs and that it involves the mode of failure concerned.
 F=P1 x P2
Or        Pl  = probability that the cause of failure occurs.
P2 = probability that the failure occurs when the cause is present.

•    Gravity (G) or severity (S): it is gravity effects of the failure on the people and/or the installation.
•    The risk of non-detection (ND), called often paradoxically detection (D): it is the probability which the cause and the mode having appeared, the failure reaches the user. With regard to the notation, plus the risk is large not to detect the failure, plus the note will be strong. It is the same for the frequency and gravity.

In practice, one proceeds by a semi-quantitative evaluation: each one of these criteria will be estimated using grids. There are several examples and most current are on 10 levels. However, a system with 4 or 6 levels often proves to be sufficient.

All these criteria will now be used to define criticality.