Scope

The following are within the scope of this Data Exchange Specification (DEX):

• Identification of the PSE to which the safety case relates.
• Reference to all proposed PSE modes of operation to which the safety case applies.
• Reference to context of the usages of PSE (that conform to the design) including the environment and/or theatre in which the safety case applies.
• Definition of hazards in respect of the PSE in consideration, in specified modes of use and environment/theatre of operation.
• Definition of risks that may derive from the hazards identified.
• Identification of the preventive and mitigating actions planned to reduce the incidence and/or the impact of risk to an acceptable level.
• One or more assertions on the assessed safety of the aspect of the PSE under consideration, each assertion being regarded as a ‘Safety Claim.
• Definition of each Safety Claim made for the PSE. Each claim will relate to a different aspect of the PSE and may include for example:
  • reliability and availability
  • security (from external attack)
  • functional correctness
  • time response.
  • maintainability
  • usability (by the operator)
  • fail-safety
  • accuracy
  • robustness to overload
  • modifiability
• Definition of the type of argument that supports the safety claim. This may be:
  • Deterministic - application of predetermined rules to derive a true/false claim (given some initial assumptions), e.g. formal proof of compliance to a specification, or demonstration of a safety requirement (such as execution time analysis or exhaustive test of the logic)
  • Probabilistic - quantitative statistical reasoning, to establish a numerical level (e.g. MTTF, MTTR, reliability testing).
  • Qualitative - compliance with rules that have an indirect link to the desired attributes (e.g. compliance with QMS standards, staff skills and experience).
• Reference to the evidence that supports the safety argument. This may be drawn from:
  • the product design itself
  • the product design development processes
  • simulated experience (via reliability testing)
  • prior field experience of similar products
  • field experience of actual product
  • compliance with existing standards
• Recording of “release to service” approval of the PSE for which the safety case is defined.

The following are outside the scope of this Data Exchange Specification (DEX):

• The record of predicted failures to the PSE and their associated criticality and predicted frequency identified through performance of FMECA or other related reliability analyses, or feedback on the occurrence or prevention of such predicted failures. This data is defined in other DEXs and will be reused or referenced by this DEX.

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