Principles of System Safety

Definition of System Safety

System safety is a specialty within system engineering that supports program risk management. It is the application of engineering and management principles, criteria and techniques to optimize safety. The goal of System Safety is to optimize safety by the identification of safety related risks, eliminating or controlling them by design and/or procedures, based on acceptable system safety precedence. System Safety Management as a critical functional discipline to be applied during all phases of the life cycle of an acquisition. SSM contains a five step approach:

1. Planning
2. Hazard Identification
3. Analysis
4. Assessment
5. Decision.

The system safety principles involved in each of these steps are discussed in the following paragraphs.

Planning

System safety must be planned. It is an integrated and comprehensive engineering effort that requires a trained staff experienced in the application of safety engineering principles. The effort is interrelated, sequential and continuing throughout all program phases. The plan must influence facilities, equipment, procedures and personnel. Planning should include transportation, logistics support, storage, packing, and handling, and should address Commercial Off-the-Shelf (COTS) and Non-developmental Items (NDI). A System Safety Management Plan is needed in the Preinvestment Decision phases to address the management objectives, responsibilities, program requirements, and schedule (who?, what?, when?, where?, and why?). After the Investment Decision is made and a program is approved for implementation, a System Safety Program Plan is needed.

Managing Authority (MA) Role

Throughout this document, the term Managing Authority (MA) is used to identify the responsible entity for managing the system safety effort. In all cases, the MA has responsibility for the program, project or activity. Managerial and technical procedures to be used must be approved by the MA. The MA resolves conflicts between safety requirements and other design requirements, and resolves conflicts between associate contractors when applicable.

Defining System Safety Requirements

System safety requirements must be consistent with other program requirements. A balanced program attempts to optimize safety, performance and cost. System safety program balance is the product of the interplay between system safety and the other three familiar program elements of cost, schedule, and performance as shown in the figure below.

Programs cannot afford accidents that will prevent the achievement of the primary mission goals. However, neither can we afford systems that cannot perform due to unreasonable and unnecessary safety requirements. Safety must be placed in its proper perspective. A correct safety balance cannot be achieved unless acceptable and unacceptable conditions are established early enough in the program to allow for the selection of the optimum design solution and/or operational alternatives. Defining acceptable and unacceptable risk is as important for cost-effective accident prevention as is defining cost and performance parameters.

Source: FAA Office of System Safety

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