Safety engineers base this assessment on two poles: demonstrate, that the software is written by an engineering process which is suited to reduce human errors. In other words, the sources of systematic errors should be reduced. The other pole is the demonstration that the system is correct, by make evident the correct implementation of requirements, the appropriateness of tests and the handle of possible and foreseeable faults and failures. Roughly said, this pole is about to demonstrate that the real concrete system in our hands is observable safe.
As you might guess, this task is much more easy when the software engineering is well developed and if it is possible in principle to know about all functional construction and to control it. In fact, safety is about control. Now it may be clear, why I'm interested in software engineering and the question of control. If the Onion Model of Control is right, we Safety Engineers and system users have no problem at all.
But - what if the Calculating Universe Model is true ? Look at the system biology, the construction of biologic artificial life, the construction of DNA - Cell machines emerging a non calculable behavior. What if the Grown Universe Hypothesis is true ?
Well, I am convinced that the way we work with functional and product safety today is not feasible for the technical or technobiological systems in front of us. I argue that we have to drop the idea of everywhere and every time control. A system can not only be safe because we know every branch of its behavior and therefore know that nothing danger can occur. Powerful and future proof safety is when a system can be full of failures and faults, but the system handles them for itself. See the correction and fault tolerance mechanisms in biology: cells, bodies, populations ! But this needs new insights in a different class of construction principles, which is not available for human kind yet.
Without having a solution in back, my opinion is that we need another approach to engineering, to build systems doing what we need to solve problems. Computer science, understand as science of information, may take us one step further and let us build safe complex computer systems as well as designed life forms.
