This paper elaborates three novel contributions in the
field of
chemical process safety. The first contribution is the identification
and classification of chemical system variabilities into seven broad
categories, namely, media, equipment, component, operator, procedural,
management, and external (MECOPME). The identified variabilities lead
to epistemic and aleatory types of uncertainties in the probabilistic
safety analysis. To deal with the uncertainties caused due to the
variabilities, a concept of the flexible node is proposed, which demands
a failure probability in the flexible range of a lower level to a
higher level instead of a fixed static probability. Since the existing
techniques are not robust enough to handle the probability range,
the classical fault tree is mapped into a statistically more reliable
approach of the response surface method (RSM). The unique idea of
using RSM in the failure analysis is demonstrated over the fault tree
of an overtemperature scenario in a semipilot scale setup for the
hydrogenation process and successfully evaluated over an industrial
accident of the release prevention barrier scenario. The contour and
surface plots of RSM reveal more information than the traditional
approach of minimal cut sets. The statistical markers of RSM are a
better substitute for the improvement index for sensitivity analysis.
The proposed approach deals with chemical system variabilities and
the lack of knowledge of exact occurrence probabilities more effectively.