14, Number 1
A Gossman Consulting, Inc.
- Pros and Cons
In 1998 we published a GCI Tech
that summarized the HAZOP process. Recently I had the
to teach a class on performing HAZOPs to a group of safety
professionals in Shanghai, China. As a result of that
further information on the process of performing HAZOPs will be
presented in a new series of GCI Tech Notes starting with this issue.
A Hazard and Operability (HAZOP) study is a structured and systematic
examination of a planned or existing process or operation in order to
identify and evaluate problems that may represent risks to personnel or
equipment, or prevent efficient operation. The HAZOP
was initially developed to analyze chemical process systems, but has
later been extended to other types of complex systems including, as
examples, transportation systems and software systems. The
HAZOP process is just one of a large number of different
techniques available to the safety professional for analyzing systems
to identify and prevent hazards. It has the further advantage that it
also identifies and helps to prevent operational problems.
studies require more details regarding the systems under consideration,
but produce more comprehensive information on hazards and errors in the
system design. As with any of these processes there are pros
cons to using a specific technique for a particular circumstance.
HAZOPs are not the best technique for every circumstance and
is important to understand the benefits as well as the costs and
limitations of the method before making the decision to use it in a
- The HAZOP process is a systematic examination.
- The team approach to a HAZOP makes it a multidisciplinary
- The HAZOP team utilizes operational experience.
- The process covers safety as well as operational aspects.
- Solutions to the problems identified may be indicated.
- HAZOPs consider operational procedures.
- HAZOPs cover human errors.
- The HAZOP study led by independent person.
- HAZOP study results are recorded.
- For team members the process is easily learned and
- A HAZOP does not require considerable technical expertise
for technique formulation.
- As a systematic process it provides rigor for focusing on
system elements and hazards.
- The HAZOP process is a team effort with many viewpoints.
- Commercial software is available to assist in HAZOP
- A HAZOP focuses on single events rather than combinations
of possible events.
- The HAZOP focus on guide-words allows it to overlook some
hazards not related to a guide-word.
- Training is essential for optimum results, especially for
- HAZOPs are typically very time consuming and thus expensive.
HAZOP is a hazard identification technique which considers system parts
separately and systematically examines the effects of deviations on
each part. Sometimes a serious hazard will involve the interaction
between a number of parts of the system. In these cases the hazard may
need to be studied in more detail using techniques such as event tree
and fault tree analyses. Many systems are highly
and a deviation at one of them may have a cause elsewhere. Adequate
local mitigating action may not address the real cause and still result
in a subsequent accident. Many accidents have occurred
small local modifications had unforeseen knock-on effects elsewhere.
While this problem can be overcome by carrying forward the implications
of deviations from one part to another, in practice this is frequently
not done. As with any technique for the identification of
or operability problems, there can be no guarantee that all hazards or
operability problems will be identified in a HAZOP study. The study of
a complex system should not, therefore, depend entirely upon a HAZOP.
It should be used as a compliment to other suitable techniques. It is
essential that other relevant studies are coordinated within an
effective overall safety management system. The success of a
HAZOP study depends greatly on the ability and experience of the study
leader and the knowledge, experience and interaction between team
members. HAZOP only considers parts that appear on the design
representation. Activities and operations which do not appear on the
representation are not considered.
An important benefit of HAZOP studies is that the resulting knowledge,
obtained by identifying potential hazards and operability problems in a
structured and systematic manner, is of great assistance in determining
appropriate remedial measures. While a HAZOP is not
in all circumstances one of the major benefits that can be used to help
justify the cost and time investment is that it also helps to avoid
operating problems and can thus provide a clear return on the
investment beyond the reduction in hazards.