What is Safety?

Safety Definition
There are different definitions of safety. Safety can be defined as “freedom from those conditions that can cause death, injury, occupational illness, or damage to or loss of equipment or property, or damage to the environment” (MIL-Std-882C, 1993).

According to APR 4761A, safety can be defined as the condition in which the risk of harm to persons or damage to property is reduced to, and maintained at or below, an acceptable level through a continuing process of hazard identification and risk management.
This definition highlights the importance of identifying hazards and assessing risks in order to mitigate them and maintain an acceptable level of safety. It emphasizes the need for a continuous process of risk management to ensure that safety is maintained over time, as new hazards and risks may arise. Additionally, it recognizes that safety is ultimately about reducing the risk of harm to people and property.

IEEE Std-1228 (1994) defines software safety as "freedom from software hazard," where software hazard is defined as "a software condition that is a prerequisite to an accident," and an accident is defined as "an unplanned event or series of events that results in death, injury, illness, environmental damage, or damage to or loss of equipment or property". Here we assume that the term "property" also includes intellectual property.
The EN IEC 60601-1 identifies basic safety as freedom for unacceptable risks directly caused by physical hazards when equipment is used under normal conditions and single fault conditions.
In another words, Safety is "the degree to which accidental harm is prevented, detected, and reacted to". It is important to emphasize when we are speaking about Safety when the damages are unintentional.
The earlier in the design process an organization/program/project defines and verifies its Safety Requirements, the shorter will be Time-to-market of its product.
ALD Software, Safety Commander, is built to be a nucleus of Safety Assessment and Management of an OEM.

Safety vs. Reliability
In many cases safety and reliability are in full accord. This happens when proper straightforward failure-free functioning of a system is enough for both reliable and safe operation. For example, an elevator's mechanical system: the more reliable the mechanical elements, the more reliable and safer the elevator.
Engineers routinely assume that the more reliable a system is, the safer it is, and vice versa. This assumption is sometimes somewhat erroneous, while sometimes very erroneous and leads to a lot of confusion in systems failure analysis.

Indeed, it is often true that the safer the system, the less reliable it is. Consider an elevator: The maximum level of safety is provided by an inoperative elevator—its doors won't shut on you or your dog; pressing buttons won't cause anything unsafe to happen. Enter the inoperative elevator, stay inside as long as you wish, exit it—you are 100% safe.

What about reliability? As the inoperative elevator is functionally ineffective, it's absolutely unreliable and unavailable for moving you up and down to different floors of the building— its reliability is zero.

To improve the safety of a reliable (moving) elevator, designers add elements and controls that limit and even decrease the probability of its adequate operation. For example, a sensor that indicates proper door closure may be added. If the sensor is out of order, the elevator won't move: reliability decreases while safety improves.
This trivial example demonstrates that in some cases there is an apparent contradiction between safety and reliability.


System Safety
System Safety is the application of engineering and management principles, criteria and techniques to achieve acceptable hazard risk within the constraints of operational effectiveness and reliability, time and cost throughout all phases of the system life cycle.

System Safety is a rational pursuit of acceptable hazard risk in which the system is treated as an integral part of a System-of-Systems , taking into account the interactions among system's constituent parts. System Safety is an integral part of the interdisciplinary approach of systems engineering and its pursuit of systems that meet stakeholder expectations.


The methods of System Safety are diverse and are driven by many factors, including:

System Safety Assessment relies on analytical results, in part due to the high cost of testing limiting the ability to rely on test-fail-fix strategies for designing a safe and reliable system.


Increasing system complexity, which makes it necessary to leverage both traditional and modern hazard evaluation mechanisms in order to identify and analyze comprehensively the full set of credible mishap scenarios that have the potential to lead to adverse consequences, considering all hazard causes and propagation pathways through the system.


The development of systems that operate at the edge of engineering capability, requiring a high degree of discipline in system realization and system operation management and oversight.

The use of unproven technology, requiring engineering conservatism to protect against unknown mishap risks while at the same time requiring allowances for novel solutions.





See also:
Safety Assessment 
Safety Management 
ALD Safety Services for Certification
SAE 4754A