In Chemical business residuals have a defined meaning, and - under defined conditions - are statistically "normal". But - since chemistry has to do with natural processes and their outputs  - unpredictability, and therefore statistical anomalies, is all that can be predicted of these processes. Chemical residuals cannot - must not! - be treated in statistical terms only: they are not off-specs pieces of metal, they can be very hazardous substances. and, in such a case, no statistical analysis would help to minimize or prevent the risk.