Stepwise implementation

Although a new system or a change to an existing system can be implemented completely in one step, it is common for implementation to be in several steps. The Safety Case Report format needs to show how the Safety Case Report can present the safety argument for each step (including the end state) addressed by the safety case. It facilitates this by defining a report section, section 4, that is instantiated once for each step (referred to as a transitional stage).

Each instantiation of section 4 is defined to present the safety argument for the relevant transitional stage in a stand-alone manner. This has multiple benefits:

• it ensures that each instantiation of section 4 specifically presents the arguments and evidence items that are relevant to the individual transitional stage, and prevents the potential confusion that could occur if multiple transitional stages were addressed collectively

• it prevents the false assumption that something applies to more than one transitional stage

• it enables the parallel creation of instantiations of section 4 in the Safety Case Report

• it enables parallel reviews to be performed by multiple reviewers

Additionally, each transitional stage may bring with it various activities associated with preparing for subsequent transitional stages, or clearing up. Examples are installation and removal of equipment, and commissioning tests. The format has to allow for where a safety case has addressed the potential impact of these transitional activities on the safety of the services, to allow for the Safety Case Report to represent these arguments.