User requirement specification

The prospective owner of the system creates a user requirement specification (URS). From a practical perspective, and to obtain good traceability, it is important that requirements are clear, well-structured, numbered and testable. A requirement such as 'heat exchangers must be of a high quality' becomes difficult to handle in validation because it is not a tangible statement. The requirements must also be at the right level regarding acceptance criteria (e.g., what temperature or hardness has to be reached or what materials are required?). It is also essential to avoid setting requirements unnecessarily high during start-up, testing or operation that, on closer inspection, do not need to be met. In fast-track projects where time is an important factor, changes and updates take time and it is preferable to assess the installation carefully at the start in the requirements specification. A risk analysis regarding the end product (e.g., water quality) should be performed before compiling the URS. The requirements relating to the safety of plant operators must be part of the risk analysis that occurs for CE marking of the installation, according to the machinery directive.

It is an advantage to divide the requirement specification into 'C' and 'Q' requirements with the help of the risk analysis performed. This is described in the ISPE Baseline Guide Volume 5, Commissioning & Qualification.¹² C stands for commissioning and the requirement will then be tested under a factory acceptance test (FAT) or a site acceptance test (SAT). Q stands for qualification and the requirement is tested under an installation qualification (IQ) or an operation qualification (OQ). To find and select the typical Q requirements for the system, the ISPE's Baseline Guide Volume 4, Water & Steam Systems¹³ and FDA's Guide to Inspection of High-Purity Water Systems¹⁴ can provide assistance.

The easiest way to create traceability in the project is to write the requirement specification in table format, with the requirements divided into C and Q requirements, which can then be given to the supplier as a Word document for further processing and completion of the references to design documents and tests. The supplier can then create a traceability matrix from the file, or copy the requirements to an Excel table. This avoids having to write the requirements in the matrix again, thus eliminating a possible source of errors and saving time.