Answer - Anyone who needs or wants an independent assessment of safety.

Reasons include:

• To comply with a Standard that requires an ISA
• To be sure that a contractor's product is safe
• To assure your customer that what you are producing is safe
• To assure yourself that your product is safe
• To demonstrate to a regulator that your system is safe

Because the safety assessment provided by the ISA is independent of existing safety analysis and assessment, it provides confidence that safety claims are justified and any weaknesses are identified and dealt with.

In some situations an ISA is mandatory. For instance, when carrying out work in accordance with Defence Standard 00-56 or for safety critical systems for the UK railway industry.

In some other cases, use of an ISA is good practice. For instance, the generic functional safety Standard IEC 61508 represents best practice for safety-related electrical/electronic/programmable electronic systems (E/E/PES). It requires the use of independent safety assessment (called functional safety assessment in the Standard) where the degree of independence depends on the Safety Integrity Level of the system.

Independent safety assessment is retained in the industry-specific instantiations of the generic Standard. Within the motor industry, the MISRA (Motor Industry Software Reliability Association) Development Guidelines for Vehicle Based Software recommend the use of an independent assessor and/or auditor in order to act as an advocate for the level of confidence in the safety delivered to the end customer.

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. However, in addition, an ISA is often able to offer generic guidance that does not compromise independence, particularly in the early stages of a project.