The “Swiss-Cheese” Model, developed by Professor James Reason, illustrates that accidents involve successive breaches of multiple system defenses. These breaches can be triggered by a number of enabling factors such as equipment failures or operational errors. Since the Swiss-Cheese Model contends that complex systems are extremely well defended by layers of defenses, single-point failures are rarely consequential in such systems. Breaches in safety defenses can be a delayed consequence of decisions made at the highest levels of the system, which may remain dormant until their effects or damaging potential are activated by specific operational circumstances. Under such specific circumstances, human failures or active failures at the operational level act to breach the system’s inherent safety defenses.
The Reason Model proposes that ALL accidents include a combination of both active and latent conditions.
