401
1 INTRODUCTION
An offshore platform is a large structure (floating or
fixed) which is used to house workers and machinery
needed to drill wells in the ocean bed, extract oil
and/or natural gas, process the produced fluids, and
ship or pipe them to shore. Based on the geographic
location a platform cab is fixed to the ocean floor, can
consist of an artificial island, or can be a floating
structure. The offshore platforms can be classified
based on operating water depths, and the two
classifications are shallow water offshore platforms
and deep-water offshore platforms. Also, the offshore
platforms can be classified based on their objective,
and the two classifications are drilling offshore
platforms, offshore storage platforms and
drilling/storage/offloading platforms. The shallow
water offshore platforms can be of two types: fixed
offshore platforms and floating offshore platforms.
The classification of the offshore platforms is listed in
Table 1.1. Until recently, the production economics
ensured that most of the offshore platforms were
located on the continental shelf at shallow water
depths. However, because of drying resources at the
shallow water depths and with advances technology
and increasing crude oil prices, drilling and
production in deeper waters have become both
feasible and economically viable. This has given rise
to the more interest into the deeper water platforms
[1].
Risk Assessment Approaches for Offshore Structures
M. Shouman
1
, N.I. Ghoneim
2
& M. El-Khatib
3
1
Arab Academy for Science, Technology & Maritime Transport, Alexandria, Egypt
2
International Maritime College Oman, Falaj Al Qabail, Sultanate of Oman
3
Pharos University in Alexandria, Alexandria, Egypt
ABSTRACT: Risk assessment and management was established as a scientific field some 30–40 years ago.
Principles and methods were developed for how to conceptualize, assess, and manage risk. These principles
and methods still represent largely the foundation of this field today, but many advances have been made,
linked to both the theoretical platform and practical models and procedures. The purpose of the thesis is to
perform a review of these advances, with a special focus on the fundamental ideas and thinking on which these
are based. We have looked for trends in perspectives and approaches, and we reflect on where further
development of the risk field is needed and should be encouraged. The present study is written for readers with
different types of background, not only for experts on risk.
However, there is a conflict between the cost impact and safety aspect. E&P managers as well as government
supervisor authorities are constantly faced with decisions to be made regarding of safety. In order to ensure
comparability and to set priorities application of QRA is a useful tool to justify choices made with regard to
personnel safety, environmental protection, asset damage and business reputation, it is recommended to apply
the systematic cause analysis method and develop the risk management models which contains an integral
approach toward the health, safety and environmental aspect.
http://www.transnav.eu
the International Journal
on Marine Navigation
and Safety of Sea Transportation
Volume 15
Number 2
June 2021
DOI: 10.12716/1001.15.02.18
402
In general, an offshore platform can have around
30~50 wellheads that are located on the platform, and
directional drilling allows reservoirs to be accessed at
both different depths and remote positions up to
10~15km from the platform. The remote subsea wells
are connected to the platform by flow lines and by
umbilical connections and these subsea solutions
consist of single wells or of a manifold centre (i.e.
consisting of orbits whose behavior around the
equilibrium point is not controlled by either the
attraction of the stable manifold or the repulsion of
the unstable manifold) for multiple wells [2].
1.2. Offshore structure problems
Engineers in the offshore construction industry must
face a multiplicity of risks. Uncertainties are
magnified for offshore structures compared to on-
land structures owing to the relative severity and
unfamiliarity of the ocean environment, the scarcity of
data about loads and materials, and the expense of
data gathering. In this section a brief review of
methods for assessing risks which are primarily
technical in nature; that is, risks attributable to either
natural or accidental loads, structural materials, or
foundation deficiencies. Such risks yield in varying
degrees to quantitative treatment and can generally be
reduced by engineering effort and appropriate
expenditure of funds [3].
The term risk is synonymous with probability of
"failure" within a given time period, where "failure"
means that the structure, its foundation system, or one
of its components reaches a "limit state." The "limit
state" may relate to the behavior of the entire structure
(e.g., collapse, excessive elastic deformation, excessive
permanent deformation); to a structural component
(e.g., exceeding yield limit or ultimate strength); or to
the foundation (e.g., instability, excessive settlement,
excessive differential settlement, or soil liquefaction).
Many different approaches to engineering risk
assessment for offshore structures are possible,
ranging from entirely subjective and implicit risk
evaluation to application of formal methods of
applied probability. The appropriate level of
treatment of uncertainty depends on such factors as
the specific purpose of the risk assessment; the type,
amount and quality of data available; the degree to
which the phenomenon at hand lends itself to
probabilistic modeling; and the importance of (and
the funds involved in) the decision situation which
calls for the risk assessment [4].
2 RISK ASSESSMENT METHODS
2.1 Choice of Approach
2.1.1 Introduction
The terminology for risk studies is:
− Risk analysis - the estimation of risk from the basic
activity “as is”.
− Risk assessment - a review as to acceptability of
risk based on comparison with risk standards or
criteria, and the trial of various risk reduction
measures.
− Risk management - the process of selecting
appropriate risk reduction measures and
implementing them in the on-going management
of the activity
− These basic approaches are illustrated in Fig.1. The
figure shows that hazard identification (HAZID) is
an essential component of all three types of study.
Figure 1. Risk Assessment Approaches
Table 1. Classification of the offshore platforms
__________________________________________________________________________________________________
Shallow water offshore platforms Deepwater offshore platform
__________________________________________________________________________________________________
A. Fixed platforms: Concrete offshore platforms, offshore A. Semi-submersibles: Operating range: 1000~2250m.
steel platforms, and concrete-steel Offshore platforms. B. Drill-ships: Operating range: 2250m onwards.
Operating range: up to 600m. C. Tension leg offshore platforms: Operating range:
Concrete-steel offshore platforms: Normally unmanned 1000~2000m.
offshore platforms and Offshore conductor platforms D. Spar offshore platforms: Operating range: 1500~2500m.
(offshore satellite platforms). Operating range: up to 500m. For economic reasons, both semi-submersible and
drillship are designed to have capacities for production
B. Floating platforms: Compliant offshore platforms and and storage (for semi-submersible the design capacity is
jack-up offshore platforms. Operating range: 600~1000m. low, but for drillship it is high).
Operating range: For drilling and storage at the
moderately deeper water, (water depth < 2250m) semi-
submersible is and will remain an attractive option.
However, for ultra-deepwater (water depth > 3500m)
large size drillships will become the more favourable
option in future.
__________________________________________________________________________________________________
Floating offshore production systems: FPSO (floating production, storage, and offloading system) offshore ship, FSO
(floating storage and offloading system) offshore ship, and FSU (floating storage unit) offshore ship.
__________________________________________________________________________________________________
Shallow water depths: less or equal than 1000m, deep-water depths: more than 1000m.
__________________________________________________________________________________________________
403
Figure 2. ISO 17776 Risk Matrix
2.1.2 Types of Risk Assessment
Risk assessment can be applied in approaches
described as Qualitative, Semi-Quantitative and
Quantitative, and the project manager needs to decide
which the right approach for the job is. The basic aim
is risk reduction and the key test is one of reasonable
practicability. In general, qualitative approaches are
easiest to apply (least resource demands and least
additional skill sets required) but provide the least
degree of insight. Conversely quantitative approaches
(QRA) are most demanding on resources and skill
sets, but potentially deliver the most detailed
understanding and provide the best basis if significant
expenditure is involved. Semi-quantitative
approaches lie in between these extremes. Thus, a
coarse hazard identification can support both
qualitative and semi-quantitative risk assessments,
whereas a detailed hazard identification can support
any level of risk assessment [5].
2.2 Risk Matrix Methods
Risk matrices provide a traceable framework for
explicit consideration of the frequency and
consequences of hazards. This may be used to rank
them in order of significance, screen out insignificant
ones, or evaluate the need for risk reduction of each
hazard. A risk matrix uses a matrix dividing the
dimensions of frequency (also known as likelihood or
probability) and consequence (or severity) into
typically 3 to 6 categories. To illustrate this, three
different risk matrix approaches are presented below
[11].
In each case, a list of hazards is generated by a
structured HAZID technique, and each hazard is
allocated to a frequency and consequence category
according to qualitative criteria. In the terms of this
guide, this does not constitute quantification (semi or
full) and the technique is still classed as qualitative
[13].
2.2.1 Defense Standard Matrix
A risk matrix that has been applied to marine
activities derives from Defence Standard 00-56 “Safety
Management Requirements For Defense Systems Part
1: Requirements” (1996). This sets out a 6 x 4 risk
matrix based on frequency and consequence
definitions as follows. A more detailed version is also
provided in Part 2 of the standard, which applies
more to reliability of technical systems .
The severity categories are defined as:
Table 2.
_______________________________________________
Category Definition
_______________________________________________
Catastrophic Multiple deaths
Critical A single death; and/or multiple severe
injuries or severe occupational illnesses
Marginal A single severe injury or occupational illness;
and/or multiple minor injuries or minor
occupational illness
Negligible At most a single minor injury or minor
occupational illness
_______________________________________________
The frequency categories are defined as:
Table 3.
_______________________________________________
Accident Occurrence
Frequency (During operational life considering all
instances of the system)
_______________________________________________
Frequent Likely to be continually experienced
Probable Likely to occur often
Occasional Likely to occur several times
Remote Likely to occur some time
Improbable Unlikely, but may exceptionally occur
Incredible Extremely unlikely that the event will occur
at all, given the assumptions recorded about
the domain and the system
_______________________________________________
There are four decision classes:
Table 4.
_______________________________________________
Risk Class Interpretation
_______________________________________________
A Intolerable
B Undesirable and shall only be accepted when
risk reduction is impracticable
C Tolerable with the endorsement of the Project
Safety Review Committee
D Tolerable with the endorsement of the
normal project reviews
_______________________________________________
The actual risk matrix (with the decision classes
shown) is as follows:
404
Table 5.
_______________________________________________
Catastrophic Critical Marginal Negligible
_______________________________________________
Frequent A A A B
Probable A A B C
Occasional A B C C
Remote B C C D
Improbable C C D D
Incredible C D D D
_______________________________________________
2.3 ISO Risk Matrix
An alternative, more up-to-date approach is given in
the draft international standard 17776 (ISO 1999). This
provides a 5 x 5-risk matrix with consequence and
likelihood categories that are easier for many people
to interpret (Figure 2). The ISO 17776 matrix uses four
types of consequence category: people, assets,
environment, and reputation reflecting current good
practice in integrating safety and environmental risk
decision-making [14].
The ISO risk matrix uses more factual likelihood
terminology (“has occurred in operating
2.4 Risk Ranking Matrix
A risk matrix has been proposed for a revision of the
IMO Guidelines on FSA (IMO 1997) to assist with
hazard ranking. It uses a 7 x 4 matrix, reflecting the
greater potential variation for frequencies than for
consequences.
The severity index (SI) is defined as:
Table 6.
_______________________________________________
SI Severity Effects on Effects on S
Safety Ship (Fatalities)
_______________________________________________
1 Minor Single or minor Local equipment 0.01
injuries damage
2 Significant Multiple or Non-severe ship 0.1
severe injuries damage
3 Severe Single fatality Severe casualty 1
or multiple
severe injuries
4 Catastrophic Multiple Total loss 10
Fatalities
_______________________________________________
The frequency index (FI) is defined as:
Table 7.
_______________________________________________
FI Frequency Definition F
(per ship year)
_______________________________________________
7 Frequent Likely to occur once per month 10
on one ship
5 Reasonably Likely to occur once per year in a 0.1
probable fleet of 10 ships, i.e. likely to occur
several times during a ship’s life
3 Remote Likely to occur once per year in a 10
-3
fleet of 1000 of ships, i.e. 10% chance
of occurring in the life of 4 similar ships
1 Extremely Likely to occur once in 100 years in 10
-5
remote a fleet of 1000 ships, i.e. 1% chance
of occurring in the life of 40 similar
ships
_______________________________________________
Intermediate indices may be chosen if appropriate.
Non-integer values may be used if data that is more
specific is available. If risk is represented by the
product frequency x consequence, then an index of log
(risk) can be obtained by adding the frequency and
severity indices. This gives a risk index (RI) defined
as:
RI = FI + SI
E.g., an event rated “remote” (FI=3) with severity
“moderate” (SI=2) would have RI=5. The risk matrix is
as follows (risk indices in bold):
Table 8.
_______________________________________________
FI Frequency Severity (SI)
1 2 3 4
Minor Moderate Serious Catastrophic
_______________________________________________
7 Frequent 8 9 10 11
6 7 8 9 10
5 Reasonably 6 7 8 9
probable
4 5 6 7 8
3 Remote 4 5 6 7
2 3 4 5 6
1 Extremely 2 3 4 5
remote
_______________________________________________
The risk index may be used to rank the hazards in
order of priority for risk reduction effort. In general,
risk reduction options affecting hazards with higher
RI are considered most desirable [15].
3 CONDUCTING A RISK ASSESSMENT
3.1 Selection of Risk Assessment Approach
It is prudent that the selection of risk assessment
approach reflects the technical and operational
challenges that the facilities are faced with ISO
standard 17776 (ISO 1999) suggests four levels of
approach to risk assessment:
− Experience/judgement
− Checklists
− Codes/standards
− Structured review techniques.
These approaches are listed in order of complexity,
implying that experience and judgement may be
sufficient for very simple facilities, whereas structured
review techniques (including risk analysis studies) are
supposed to be used for the complex facilities and
operations. This book only addresses the structured
review techniques, whereas the ISO17776 standard
addresses the top three approaches mainly. In
selecting the appropriate risk assessment tools and
techniques, the nature and scale of the installation [6].
3.2 Quantitative or Qualitative Risk Assessment?
The purpose of risk assessment is primarily to decide
on risk reducing measures in the context of a
structured, systematic, and documented process. The
documentation requirements for the safety case under
UK legislation are in this respect the most explicit,
when they require documentation of the outcome of
405
the decision making process for risk reduction
measures based on a risk assessment.
This overall purpose is often forgotten, in the sense
that companies may think that the purpose of risk
assessment is to document that the risk level is
tolerable. Even worse, a risk assessment may
sometimes be conducted in order to demonstrate that
it is acceptable to deviate from regulatory
requirements or common industry practice. This is
what is referred to as ‘misuse of risk analysis’. The
next question is to what extent the risk assessment
needs to be quantitative. This question is very often
repeated, it is sometimes argued that qualitative risk
assessment is better, because the numbers are often
rather uncertain [7].
The majority’s opinion is further that
quantification improves the precision when a study is
carried out. A qualitative study will discuss various
factors, but will often not perform a detailed trade-off
between the factors. When quantification is needed,
such a trade-off is needed as part of the quantification,
and a more precise answer is produced. The approach
in ISO17776 is thus fundamentally wrong in many
cases, as quantification should be used in the majority
of projects, not as the least alternative as the ISO17776
suggests. The proper attention to evaluation of
uncertainty and evaluation of model sensitivity is
extremely crucial in quantitative studies [8].
Some risk assessments are used in order to
establish design accidental loads, such as the
structural resistance to impact and/or hat loads. It is
not possible to understand how qualitative risk
assessments can be used in such cases. However, it
should also be realised that there are some examples
of use of quantitative risk assessments that are as far
from trustworthy as more or less possible. One final
overall aspect of quantification may be added; the best
use of such studies is often to use ‘‘quantitative
studies in a qualitative manner’’. Put differently, the
quantification is not the goal itself, but just a means to
achieve better decision-making [9].
3.3 Risk Assessment Approach
There has been considerable focus in the past few
years on models for risk assessment in various
industries, not the least the offshore oil and gas
industry. The most commonly used approach is the
ISO31000 standard: Risk management, principles and
guidelines on implementation (ISO 2009). The same
approach has also been adopted in the NORSOK Z-
013 standard: Risk and emergency preparedness
analysis (Standard Norway 2010). The same approach
is also adopted by the petroleum regulations in
Norway, issued by PSA. The main elements of the
model for risk assessment according to ISO31000 are
presented in Fig. 3 [10].
The core of the process, in the yellow box, is
consistent with common practice for many years, in
the offshore petroleum industry. The elements outside
this core are new elements; establishing the context,
monitoring and review as well as communication and
consultation. The ISO17776 standard (ISO 1999) is not
at all consistent with ISO31000, and for several years,
it has been completely overlooked. The most extensive
and explicit standard for offshore risk assessment is
NORSOK Z-013. There is an ongoing effort to revise
ISO17776. The outcome of this work is unknown, and
this book is based on the current contents of the
relevant standards, not what may be the result of a log
process with uncertain outcome. Each of the main
elements of this process is outlined in Sects. 6.4–6.10
[12].
Figure 3. Risk assessment process according to ISO31000
4 CASE STUDY
All data used in the matrix is from the Accidents from
1970 to 2007 Worldwide
Table 9. Data for risk matrix from 1980 to 2012
_______________________________________________
ID Event Repetition Fatalities count
_______________________________________________
BL Blowout 2 13
CL Collision 15 0
CN Contact 23 0
CR Crane accident 476 45
EX Explosion 7 0
FA Falling Load 266 23
FI Fire 163 1
HE Helicopter accident 1 0
LE Leakage 1 0
LG Spill/release 1171 26
TO Towing accident 47 1
ST Structural damage 3 0
WP Well problem 170 1
_______________________________________________
_______________________________________________
Catastrophic Critical Marginal Negligible
_______________________________________________
Frequent CR LG FA WP FI
Probable BL
Occasional CN TO CL
Remote EX
Improbable HE LE ST
_______________________________________________
_______________________________________________
Defense Interpretation
Risk Class
_______________________________________________
A Intolerable
B Undesirable and shall only be accepted when
risk reduction is impracticable
C Tolerable with the endorsement of the Project
Safety Review Committee
D Tolerable with the endorsement of the normal
project reviews
_______________________________________________
406
4.1 Recommendations
All major company must engage in collaborative
effort to guaranty all possible risks, their causes and
impacts on offshore platforms are effectively
identified and properly recorded.
There must be proper guarantees for researchers to
have access to the above-mentioned records in order
to facilitate safety and decision-making.
Operators are to further establish more acceptable
ways of improving management of safety information
in conjunction with regulatory bodies and researchers.
The major company within the industry and
regulatory agencies need to have better collaboration
and corporation and come up with programme design
to attract researchers to participate in efforts to
achieve a more efficient safety management.
This programme may also involve enforcement
agencies to ensure that researchers have some level of
unrestricted and timely access to industry safety data
for research purposes.
The operators need to create an enabling
environment to guarantee improved data
management as well as access to such information for
research purposes.
Risk information still require further efforts by
both the operators and regulators in order to achieve
harmonies system of recording safety and other
related information for the industry. This will be
achieved if all the major company including
regulatory agencies must to be involved in kind of
joint-partnership for the purpose of establishing
necessary programme specifically for this.
Researchers require solid support from the
industry regulators to guarantee them the right to
preserve the independence of their findings.
Inherent risks remain major impediments to the
safety of offshore oil and gas industry. Therefore, the
need to increase efforts towards mitigation of these
safety challenges must be accorded high priority and
all the major industry company must remain
committed and support these efforts in order to
achieve improved safety within the industry.
5 CONCLUSIONS AND RECOMMENDATIONS
The risks generated from normal operation of offshore
facility shall be adequately identified and controlled
by a standard Formal Safety Assessment. For this
purpose, risk assessment methods are carried out to
assess the different parameter of risk exposed to
facility personnel. Individual and societal risks are
identified, quantified and compared to acceptance
criteria to ensure all risk exposed are identified and
control within As Low As Reasonably Practicable
(ALARP) level. It is shown that the main increase in
risk is from immediate effects. This is mitigated by
leak and fire detection, isolation, blowdown or control
of ignition sources. Besides, the PFP should be
provided to avoid the potential domino effects from
ignited events.
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