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Ideally, safety-engineers take an early design of a system, analyze it to find what faults can occur, and then propose safety requirements in design specifications up
front and changes to existing systems to make the system safer. In an early design stage, often a fail-safe system can be made acceptably safe with a few sensors and
some software to read them. Probabilistic fault-tolerant systems can often be made by using more, but smaller and less-expensive pieces of equipment.
Far too often, rather than actually influencing the design, safety engineers are assigned to prove that an existing, completed design is safe. If a safety engineer
then discovers significant safety problems late in the design process, correcting them can be very expensive. This type of error has the potential to waste large sums of money.
The exception to this conventional approach is the way some large government agencies approach safety engineering from a more proactive and proven process perspective, known as
"system safety". The system safety philosophy is to be applied to complex and critical systems, such as commercial airliners, complex weapon systems, spacecraft, rail and transportation
systems, air traffic control system and other complex and safety-critical industrial systems..... Read more
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