Safety vs Security Tradeoffs
Safety protects people from the system; security protects the system from people. Their measures sometimes pull in opposite directions.
Two Disciplines, Different Aims
Safety engineering keeps a system from harming people and the environment, guarding against accidents, failures, and hazards. Security engineering keeps people from harming the system, guarding against deliberate attack. They share techniques and often reinforce each other, but their goals differ, and in places their measures conflict. Recognizing where is essential in safety-critical plants.
Classic Tensions
- A locked door improves security but can trap people in an emergency
- Encryption protects data but can slow a time-critical control response
- Access restrictions block attackers but may delay an operator acting in a crisis
- Fail-secure locks resist intrusion; fail-safe locks release for evacuation
Resolving the Conflict
The resolution is not to pick one discipline over the other but to design so that safety functions remain available regardless of security state, while security controls surround them without gating them. A safety system should not depend on a cyber component that could be disabled by attack, and a security measure should never be able to prevent a safety action from occurring.
Independence as the Key
The cleanest designs make the safety function independent of the security perimeter: it acts on physical conditions through dedicated instrumentation that no network can reach or override. Security then protects everything around it without ever standing between a hazard and its mitigation.
Fusion Context
In the Hyperion breeder and burner designs, the machine-protection and safety instrumented systems act on physics limits through independent channels, so that no cyber compromise can defeat a safety action and no safety action waits on a security check. This is a deliberate design stance, worked out now during simulation, where the boundary between the two disciplines can still be drawn cleanly.