Early approaches in engineering safety were based on deterministic concepts,
according to which, safety was assured by making conservative assumptions in the
design of industrial systems, as well as through the use of safety factors, based on
engineering judgement.
Recent safety approaches are based on probabilistic concepts, in reliability techniques
and accident consequence modelling, according to which safety is defined in terms of
probabilities or frequency of failures and severity of consequences. These two items
compose the basis for the evaluation of industrial risks.
Risk assessment techniques are particularly relevant for those working offshore, who
are exposed full-time to several different hazards from process equipment, risers or
blow-outs, ship collisions, helicopter accidents, extreme weather, etc.
At present, there are several sophisticated techniques, models and software already
developed, that can be used in probabilistic risk analysis. However, general criteria for
the acceptability of estimated risks have not been suitably developed, although several
attempts have been made, and the question: "How safe is safe enough?" still remains
without an appropriate answer.
Within this context, this Thesis presents a brief description of techniques and models
presently used for risk evaluation, as well as legislation concerning risk tolerability
criteria and other proposed safety targets. Regarding the establishment of global
safety criteria for offshore oil units, the focus of this work will be the development of
a risk and reliability allocation methodology to achieve them.
From data collected from more than thirty Brazilian offshore oil units, some of them
operating for more then ten years, individual risk values for offshore employees are
going to be calculated.
Based on these values, obtained for the individual risk, and on a quantitative risk
assessment performed for a Brazilian Floating Production Storage Offloading vessel, a
risk and re1iability allocation methodology will be proposed. This methodology
provides a feasible" model to allocate reliability and risk criteria for the main safety
functions of an offshore unit in a self-consistent manner. It provides a method for
design engineers to establish minimum reliability levels for the safety systems of an
industrial facility, in order to achieve safety targets previously defined for it.
The application of a risk and reliability allocation model to the problem of setting
criteria for a range of hazardous scenarios presented in the operation of an offshore
oil production unit is a novel approach.
It is hope that the proposed methodology can contribute to a wider discussion about
the establishment of a global measure for the evaluation of safety performance of
offshore oil units.