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Showing posts with the label Safety Requirements

How do you derive SSRs from TSR?

We recently conducted a training on Functional Safety Software. We started to discuss Software Safety requirements (SSRs), stating something like “SSRs are derived from the Technical Safety requirements (TSRs). Start by looking into those requirements in TSR that are assigned to SW”. Immediately, one of the trainees asked “oh, all we need to do is to filter out the TSRs for SW, and put them into a new document, name this document as SSR and that’s it we are done?” No marks for guessing that we shouted a loud and clear “NOOOO!!!” This is the subject of this blog. Once you have the TSR, how should you derive the SSR? We will tell you the actionable steps that you can take and also give you an example of how we have derived SSRs from TSRs. Firstly, let’s look at the actionable steps in the process of deriving the SSR: Read and understand the TSRs assigned to SW. What is the Software supposed to do? Is this clearly specified? The first step before starting the SSR is to ensure that SW Requ

8 Topics for Technical Safety Requirements

In this blog, we present a simple yet comprehensive approach of how to write a high-quality Technical Safety Requirement (TSR) document, which considers all the Safety relevant aspects of the System and sets the right direction for the Software and Hardware teams. To begin with, it is important to understand what is the difference between an FSR and TSR. FSR (Functional Safety Requirements) describe the WHAT , i.e., WHAT must be done to achieve Safety Goals. TSR describes the HOW . i.e., How the Safety requirements should be achieved. It describes the technical realization of the Functional Safety Requirements of the project. TSR is the starting point for SW and HW Safety. For a specific item, there are 8 topics that TSR should cover. The topics are: 1. Intended Functionality 2. Fault Handling 3. Graceful degradation and Safe State 4. Freedom from Interference and Independence 5. HW Metrics 6. Special cases 7. Production and Service 8. Fault Injection Testing 1. Intended Functionalit