TITLE:
Risk Assessment Methodology to Support Shutdown Plant Decision
AUTHORS:
Eduardo Calixto, Carlos Daniel Cunha de Moraes, Cid Atusi Outi, Wilson Alves dos Santos
KEYWORDS:
Preliminary Risk Analysis; Fault Tree Analysis; Layer of Protection Analysis; Tolerable Risk
JOURNAL NAME:
Open Journal of Safety Science and Technology,
Vol.3 No.4,
December
27,
2013
ABSTRACT:
Nowadays one of the most important decisions in safety issues in
Brazilian Oil and Gas industry is that it’s necessary to shut down
plant because one specific failure or required maintenance in protection system makes influence on risk level. Most of time, experienced operators make decisions based on their background despite carrying out a risk analysis to support
their decision. Therefore in so many cases, refinery plants work on
catastrophic risk level due to subjective decisions. In order to
improve the operator decision, a specific methodology was established to apply
risk assessment using PRA (Preliminary Risk Analysis), LOPA (Layer of
Protection Analysis) and FTA (Fault Tree Analysis) in order to check risk level
or layer of protection availability. By this way, as the first step, the
Preliminary Risk Analysis will be carried out in order to qualify risk and
mainly define consequences severity. The second step will carry out the LOPA in
order to find out the failure probability of all layers of protection and
without one of those layers of protection which requires maintenance or
even failure. In addition, when is necessary to check that contingency
systems availability FTA will be carried out? In the first
case, it is possible to substitute the layer of protection for another in order to keep risk on acceptable level. In the second case, it is necessary to
check if contingency system is available and assess if consequence gets worse
or keeps on the same level. In both cases, the final risk will be assessed
and compared with the previous one defined on PRA. In case of risk, it is
unacceptable that the final decision will shut down plant. The
refinery study case will be shown as an instance of such methodology.