Reason distinguished between active failures—the unsafe acts of front‑line operators—and latent conditions, the hidden pathogens introduced by designers, managers, and regulators long before the accident. In his 1997 treatise Managing the Risks of Organizational Accidents, he refined the model into four tiers: organizational influences, unsafe supervision, preconditions for unsafe acts, and the unsafe acts themselves. The ICAO Human Factors and Flight Safety Working Group adopted the framework in the early 1990s; the U.S. Navy and FAA later sponsored Shappell and Wiegmann’s Human Factors Analysis and Classification System (HFACS), derived directly from Reason’s architecture. The Swiss Cheese Model ended the era of blaming the last person who touched the controls and ushered in the era of system‑wide safety management.