Which statement about barrier performance across sequences of events is true?

• A. Barriers should be the same in all scenarios.
• B. Barriers should be redundant but not independent.
• C. Barriers should be independent and diverse to reduce common-mode failures.
• D. Barriers are optional.

Answer: (C)

In protecting against an incident, barriers must be independent and diverse across the sequence of events. Independence means each barrier operates with its own separate mechanism, data sources, and control system so a single fault or shared data error can’t disable multiple barriers at once. Diversity means using different technologies or approaches to cover different failure modes, so a single problem doesn’t defeat all barriers. This combination reduces the risk of common-mode failures as the situation evolves, ensuring that if one barrier misses an opportunity or is compromised, others can still perform.

Choosing barriers that are the same in every scenario creates a single point of failure if that barrier encounters a condition it can’t handle. Relying on redundancy without independence can still be undermined by a common cause affecting all redundant barriers. And barriers being optional contradicts the purpose of barrier management, which is to prevent or mitigate hazards.