What is System Safety?

System safety uses systems theory and systems engineering approaches to prevent foreseeable accidents and to minimize the result of unforeseen ones.Losses in general, not just human death or injury, are considered.Suc h losses may include destruction of property, loss of mission, and environmental harm.
The primary concern of system safety is the management of hazards: their identification, evaluation, elimination, and control through analysis, design and management procedures.Mueller, in 1968, described the then new discipline of system safety engineering as “organized common sense”
It is a planned, disciplined, and systematic approach to identifying, analyzing, and controlling hazards throughout the life cycle of a system in order to prevent or reduce accidents. System safety activities start in the earliest concept development stages of a project and continue through design, production, testing, operational use, and disposal.One aspect that distinguishes system safety from other approaches to safety is its primary emphasis on the early identification and classification of hazards so that corrective action can be taken to eliminate or minimize those
hazards before final design decisions are made. Although system safety is a relatively new discipline and still evolving, some general principles
are constant throughout its various manifestations and distinguish it from other approaches to safety and risk management.

• System safety emphasizes building in safety, not adding it on to a completed design: Safety
considerations must be part of the initial stage of concept development and requirements definition: From 70 to 90 percent of the design decisions that affect safety will be made in these early project phases. The degree to which it is economically feasible to eliminate a hazard rather than to control it depends upon the stage in system development at which the hazard is identified and considered.Early integration of safety considerations into the system
development process allows maximum safety with minimal negative impact.The alternative is to design the plant, identify the hazards, and then add on protective equipment to control the hazards when they occur—which is usually more expensive and less effective.

• System safety deals with systems as a whole rather than with subsystems or components:
Safety is an emergent property of systems, not a component property.One of the principle responsibilities of system safety is to evaluate the interfaces between the system components and determine the effects of component interaction, where the set of components includes humans, machines, and the environment.

• System safety takes a larger view of hazards than just failures:
Hazards are not always caused by failures, and all failures do not cause hazards.Serious accidents have occurred while system components were all functioning exactly as specified—that is, without failure.If failures only are considered in a safety analysis, many potential accidents will be missed.In addition, the engineering approaches to preventing failures (increasing reliability) and reventing hazards(increasing safety) are different and sometimes conflict.

• System safety emphasizes analysis rather than past experience and standards: Standards and codes of practice incorporate experience and knowledge about how to reduce hazards, usually accumulated over long periods of time and resulting from previous mistakes.While such standards and learning from experience are essential in all aspects of engineering, including safety, the pace of change today does not always allow for such experience to accumulate and for proven designs to be used.System safety analysis attempts to anticipate and prevent accidents and near-accidents before they occur.

• System safety emphasizes qualitative rather than quantitative approaches: System safety places major emphasis on identifying hazards as early as possible in the design stage and then designing to eliminate or control those hazards.A t these early stages, quantitative information usually does not exist.Although such quantitative information would be useful in prioritizing hazards, subjective judgments about the likelihood of a hazard are usually adequate and all that is possible at the time that design decisions must be made.

• Recognition of tradeoffs and conflicts:
Nothing is absolutely safe, and safety is not the only,and is rarely the primary, goal in building systems.Most of the time, safety acts as a constraint on the possible system designs and may conflict with other design goals such as operational effectiveness, performance, ease of use, time, and cost.System safety techniques
and approaches focus on providing information for decision making about risk management tradeoffs.

• System safety is more than just system engineering:
System safety engineering is an important part of system safety, but the concerns of system safety extend beyond the traditional boundaries of engineering.In 1968, Jerome Lederer, then the director of the NASA Manned Flight Safety Program for Apollo wrote:
System safety covers the total spectrum of risk management.It goes beyond the
hardware and associated procedures of system safety engineering.It involves: attitude
and motivation of designers and production people, employee/management rapport, the relation of industrial associations among themselves and with government,human factors in supervision and quality control, documentation on the interfaces of industrial and public safety with design and operations, the interest and attitudes of top management, the effects of the legal system on accident investigations
and exchange of information, the certification of critical workers, political
considerations, resources, public sentiment and many other non-technical but vital
influences on the attainment of an acceptable level of risk control.These ontechnical
aspects of system safety cannot be ignored.
Using these general principles, system safety attempts to manage hazards through analysis,design, and management procedures.Key activities include top-down system hazard analyses(starting in the early concept design stage to eliminate or control hazards and continuing during the life of the system to evaluate changes in the system or the environment), documenting and tracking hazards and their resolution (establishing audit trails); designing to eliminate or control hazards and minimize damage, maintaining safety information systems and documentation; and establishing reporting and information channels.