What caution is advised when using the vector approach to security levels?

ISA/IEC 62443 allows Security Levels to be expressed as vectors across the seven Foundational Requirements, providing granular control. However, the standard cautions against using vectors in isolation.

Step 1: Purpose of the vector approach

The vector represents Target Security Levels (SL-T) for each foundational requirement within a zone, derived from risk assessment.

Step 2: Risk alignment requirement

ISA/IEC 62443-3-2 requires that SL determination be grounded in the asset owner’s risk assessment methodology, including defined risk tolerance and acceptance criteria.

Step 3: Avoiding misuse

Using vectors without alignment to the organization’s risk matrix can lead to inconsistent or unjustified security requirements.

Therefore, vector values must align with the asset owner’s risk matrix and risk appetite.