Definition
A common cause failure is a single underlying event or condition (a shared power supply, a software defect, an environmental factor) that triggers multiple failures across otherwise independent components or redundant paths simultaneously. It is significant because it can defeat the protection redundancy is designed to provide.
Key facts
- Triggers multiple failures across supposedly independent items, undermining the assumption of independence redundancy relies on.
- Common sources include shared power, shared software or firmware, environmental conditions, or a shared maintenance error.
- Directly threatens redundancy: if redundant paths share a common vulnerability, the redundancy does not provide the expected protection.
- A key consideration in reliability analysis for safety-critical or highly redundant systems.
What does Common cause failure reveal about failures?
A common cause failure means multiple components or systems, believed to fail independently, actually fail together because they share an underlying vulnerability (the same power feed, the same firmware bug, the same environmental exposure) so an event affecting one affects all simultaneously.
How do teams use Common cause failure in failure analysis?
Redundancy assumes that backup paths fail independently of the primary path; a common cause failure breaks that assumption by affecting multiple paths at once. In effect, an unrecognized common cause can turn a system that appears to have no single point of failure into one that effectively does, because the shared vulnerability behaves like a hidden single point of failure.
FAQ
Frequently asked questions
How can multiple failures trace back to the same cause?
Through a common cause failure: a single underlying event or condition (such as shared power or software) that triggers multiple, otherwise independent failures at the same time, which can defeat the protection redundancy is meant to provide.
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