Defenses in Depth
The Defenses in Depth (DID) (Swiss-cheese model) model is centered around seven standard defense layers.
- Understanding of Hazard
- Guidance on Avoiding Hazard
- Alarms and Warnings
- Restore System to Safe State
- Interpose Safety Barrier
- Contain and Eliminate Hazards
- Escape and Rescue
This concept is based on the layers of defenses just prior to the accident representing defenses that should mitigate the results of the unsafe condition. The boxes (slices of cheese) represent other layers of unsafe conditions and preconditions, such as fatigue, stress, operating practices, training, maintenance, or decision-making, etc.
If the system's defenses function as intended, the hazard is controlled and an accident is prevented. Safety deficiencies are represented as holes in the defenses to show the importance of reducing or eliminating safety deficiencies.
Click on the graphic to see an animation of this model.
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