Microsoft Excel and Visual Basic for Applications were used to model process time variability in a cell culture facility. A deterministic simulation had already established that the plant had sufficient buffer, media, water and CIP (clean-in-place) capacity. The Excel model was built to answer the question, "How many batches per year can be expected, as a minimum, knowing that random failures occur and that processing time variability results in a failed batch if a queue exceeds a set value?" Aspects to be presented: a) simplifying assumptions that drilled into the question of interest, b) use of VBA to create the multi-batch per year simulation, c) drawing timelines on the screen that speak to the customer without requiring simulation jargon, d) design of modeling experiments that simulated 250 years of operation with a variety of assumptions, and e) use of statistical functions to obtain confidence intervals and probability data.
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