Software Safety Case Composition

Independent Safety Assessment


System Work Package

Software Safety Case Composition

MSL offer a range of Software Safety Case related services to provide assistance in compiling the body of evidence to achieve compliancy against any of the standards (e.g MISRA, EN 50128, IEC 61508, DO 178B/C).


This is where MSL provides effort to write the software section of the Safety Case.


When in-house staff write the software section of the Safety Case, MSL provides support in the form of advice.


We provide support when MBSE Tools are used.


We provide a service to define the processes required to construct the software safety case.

Independent Safety Assessment

The ISA Working Group (BCS/IET/IMechE) definition of an ISA:

“Independent safety assessment is the formation of a judgement, separate and independent from
any system design, development or operational personnel, that the safety requirements for the
system are appropriate and adequate for the planned application and that the system satisfies those
safety requirements.”.

This statement encapsulates the service that we provide at MSL Ltd to verify software compliance
with the specified standard associated with the software development of a client’s product.

An ISA requires that essential tasks are performed:

  • Acquiring an appreciation of the scope and context of the assessment
  • Selecting and planning a cost-effective assessment strategy
  • Constructing a body of relevant evidence
  • Forming a judgement
  • Managing any outcomes

Gathering the evidence is a combination of auditing for conformance to planned arrangements, reviewing project documentation and performing additional analyses.
An ISA may be required for many reasons for example:

  • To comply with a standard that requires an ISA
  • To be assured that a contractor’s product is safe
  • To assure yourself or the customer that what your product is safe
  • To demonstrate to a regulator that your product is safe

MSL Ltd provides the ISA is independent of existing safety analysis and assessment, it can provide
confidence that safety claims are justified and that any weaknesses that are identified have been
dealt with appropriately.

In some situations, an ISA is mandatory in other cases, use of an ISA is good practice. As well as
providing assurance of safety, using an ISA can help to focus safety planning and analyses. This can
come about naturally by answering questions and providing safety information for the ISA.

MSL Techniques

To construct the body of evidence we use the following techniques to assist us:

Software Hazzard Analysis at Requirements and Code levels
Interface Analysis
Testing Analysis
Fault Tree Analysis
Software Prelim Hazard Analysis
Traceability Analysis
Failure Modes & Effects Analysis
Requirements Modelling/Analysis
Source Code Analysis
Test Coverage Analysis
Cross Reference Tools
Model Based Systems Engineering (MBSE)

System Work Package

A work package is a group of related tasks within a project. Tasks are typically grouped into work packages based on the System Architecture or the time needed to implement them. The work package originates from the Work Breakdown Structure WBS and is a hierarchical reflection of all the work in the project in terms of deliverables. In order to produce these deliverables the work packages need to be implemented, A work package may contain any deliverable element of the system. MSL Ltd has the capability to take on work packages and complete them in a way which is compliant with project objectives.

MSL has the capability to use the following industry standard MBSE Tools:

Matlab Simulink