A Safety Layer is an independent protective system of the specific hazards that has its own level of risk reduction. Each Safety Layer must be protected and not affected from a failure of any other protective layers.
Reference Definition by Aiche.org: Safety Layer is a system or subsystem that is considered adequate to protect against a specific hazard. The safety layer; cannot be compromised by the failure of another safety layer, is totally independent of any other protective layers, may be a non-control alternative (e.g., chemical, mechanical), may be an administrative procedure, may require diverse hardware and software packages, must be approved according to company policy and procedures, must have acceptable reliability, and must meet proper equipment classification.
Related Definitions in the Project: The Process Safety Engineering; HSE Management
