Library Contents

What is System Safety?

The system safety discipline involves the application of special technical and managerial skills to the systematic, forward-looking identification and control of hazards throughout the life cycle of a project, program, or activity. The primary objective of system safety is accident prevention. Proactively identifying, assessing, and eliminating or controlling safety-related hazards, to acceptable levels, can achieve accident prevention.

Key Definitions

• A hazard is a present condition, event, or circumstance that could lead to or contribute to an unplanned or undesired event.
• The term risk is an expression of the future impact of an undesired event in terms of event severity and event likelihood.

Throughout the system safety process, the task is to identify hazards and then to analyze, assess, and prioritize risk, with results documented for decision-making. The continuous loop process provides for validation of decisions and evaluation for desired results and/or the need for further action.

A systematic approach to process improvement requires proactively searching for opportunities to improve the process at every step, not simply identifying deficiencies after an undesired event. The steps in the system safety process are depicted graphically in the graphic below. It is a formal, but flexible, process that generally follows the steps in the FAA Safety Risk Management Order (8040.4).

1. Define Objectives

The first step in the system safety process is to define the objectives of the system under review. These objectives are typically documented in business plans and operating specifications

2. System Description

A description of the interactions among people, procedures, tools, materials, equipment, facilities, software, and the environment. This also includes descriptions of data available

3. Hazard Identification: Identify Hazards and Consequences

Potential hazards may be identified from a number of internal and external sources. Generally, hazards are initially listed on a Preliminary Hazard List (PHL), then grouped by functional equivalence for analysis. Prior to risk analysis you must also include the consequence (undesired event) resulting from the hazard scenarios. Hazard scenarios may address the following: who, what where, when, why and how. This provides an intermediate product that expresses the condition and the consequences that will be used during risk analysis.

4. Risk Analysis: Analyze Hazards and Identify Risks

Risk analysis is the process whereby hazards are characterized for their likelihood and severity. Risk analysis looks at hazards to determine what can happen when. This can be either a qualitative or quantitative analysis. The inability to quantify and/or the lack of historical data on a particular hazard does not exclude the hazard from the need for analysis. Some type of a risk assessment matrix is normally used to determine the level of risk.

5. Risk Assessment: Consolidate and Prioritize Risks

Risk assessment is generally defined as the process of combining the impacts of risk elements discovered in risk analysis and comparing them against some acceptability criteria. Risk assessment can include the consolidation of risks into risk sets that can be jointly mitigated, combined, and then used in decision making.

Risk management is defined as the process by which risk assessment results are integrated with political, social, economic, and engineering considerations for decisions about need/methods for risk reduction.

6. Decision Making: Develop Action Plans

This step begins with the receipt of a prioritized risk list. Review the list to determine how to address each risk, beginning with the highest prioritized risk. There are four basic options for dealing with risk: transfer, eliminate, accept, or mitigate (TEAM). Generally, design engineering follows the "safety order of precedence:"

• 1) Design for minimum risk,
• 2) Incorporate safety devices,
• 3) Provide warning devices, or
• 4) Develop procedures and training, which may result in alternative action plans.

7. Validation and Control: Evaluate Results of Action Plan for Further Action

Validation and control begins with:

• (1) Evaluating the results of scheduled analyses on the effectiveness of actions taken (to include identification of data to be collected and identification of triggering events if possible; then developing a plan to review the data collected) and
• (2) Determining the status of each prioritized risk. If the residual risk is acceptable, then documentation is required to reflect the modification to the system, and the rationale for accepting the residual risk. If it is unacceptable, an alternate action plan may be needed, or a modification to the system/process may be necessary.

8. Modify System/Process As Needed

If the status of a risk should change, or if the mitigating action does not produce the intended effect, a determination must be made as to why. It may be that the wrong hazard was being addressed, or the system/process needs to be modified. In either case, the next step is to re-enter the system safety process at the hazard identification step.