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Synergetic Dissimilarity: Design Validation/Verification and Process Validation

A Simple Analogy

Verification and validation are intertwined engineering tools with very important differences. To illustrate the concepts, consider a building (e.g. an office building) design analogy. In a typical scenario, the senior architect establishes the design input requirements and sketches the general appearance and construction of the building, but associates or contractors typically elaborate the details of the various mechanical systems. Verification is the process of checking at each stage whether the output conforms to requirements for that stage. For example: does the air conditioning system deliver the specified cooling capacity to each room? Is the roof rated to withstand so many newtons per square meter of wind loading? Is a fire alarm located within 50 meters of each location in the building?

At the same time, the architect has to keep in mind the broader question of whether the results are consistent with the ultimate user requirements. That’s why architects and engineers sometimes don’t see eye to eye. Does the air conditioning system keep the occupants comfortable throughout the building? Will the roof withstand weather extremes expected at the building site? Can the fire alarm be heard throughout the building? Those broader concerns are the essence of validation.

In the initial stages of design, verification is a key quality assurance technique. As the design effort progresses, verification activities can become progressively more comprehensive and detailed. For example, heat or cooling delivery can be calculated and verified by the air conditioning designer, but the resultant air temperature can only be estimated. Occupant comfort is a function not only of delivered air temperature, but also humidity, heat radiation to or from nearby thermal masses, heat gain or loss through adjacent windows, etc. During the latter design phases, the interaction of these complex factors may be considered during verification of the design.

Validation follows successful verification, and ensures that each requirement for a particular use is fulfilled. Validation of user needs is possible only after the building is built. The air conditioning and fire alarm performance may be validated by testing and inspection, while the strength of the roof will probably be validated by some sort of analysis linked to building codes, which are accepted as meeting the needs of the user-subject to possible confirmation during a subsequent severe storm.

The Manufacturing Factors

Some manufacturers equate production testing with verification. That is not accurate. Whereas verification testing establishes conformance of design output with design input, the goal of production testing is to determine whether the unit being tested has been correctly manufactured. In other words, production testing is designed to efficiently screen out manufacturing process errors and perhaps also to detect early process failures. Typically, a small subset of functional and performance tests accomplish this objective with a high degree of accuracy. Therefore, production testing is rarely comprehensive enough to verify the design. For example, a leakage test may be used during production to ensure that a hermetically-sealed enclosure was properly assembled. However, the leakage test may not be sensitive enough to detect long-term diffusion of gas through the packaging material, e.g. as early as with ethylene oxide sterilization. Permeability of the packaging material is an intrinsic property of the material rather than an assembly issue, and would likely be verified using a more specialized test than is used during production.

Whereas verification is a detailed examination of aspects of a design at various stages in the development, design validation is a cumulative summation of all efforts to assure that the design will conform to user needs and intended use(s), given expected variations in components, materials, manufacturing processes and the use environment.

Definition: Equipment Qualification (as part of Process Validation)

  • The Installation Qualification (IQ) is the documented proof that facilities and equipment have been delivered and installed in accordance with the requirements and statutory safety regulations stipulated in the design qualification
  • The Operational Qualification (OQ) is a demonstration that the process will produce acceptable results and establishment of the limits (worst case) of the process parameters
  • The Performance Qualification (PQ) is the establishment of long-term process stability

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