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Hazard Analysis Methodologies
Hazards analysis can get pretty sophisticated and go into much detail. Where the
potential hazards are significant and the possibility for trouble is quite
real, such detail may well be essential. However, for many processes
and operations — both real and proposed — a solid look at the operation
or plans by a variety of affected people may be sufficient. The easiest
and possibly most effective method is using the step-by-step process of
the Job Hazard Analysis (JHA). JHA, sometimes referred to as a Job
Safety Analysis (JSA), is covered in good detail in the
Job Hazard Analysis, OSHA Publication 3071.
However, if you are faced with fairly sophisticated and complex risks with a reasonable
probability of disaster if things go wrong, you may want some help with
some of the other hazards analysis methodologies. What follows is
a very brief look at the common ones. If you decide to try
one of the approaches, check with your local OSHA Consultation office or call an engineering firm which specializes in hazards analysis.
WHAT - IF Checklist: The what - if checklist
is a broadly-based hazard assessment technique that combines the creative
thinking of a selected team of specialists with the methodical focus of
a prepared checklist. The result is a comprehensive process hazards
analysis that is extremely useful in training operating personnel on the
hazards of the particular operation.
The review
team is selected to represent a wide range of disciplines — production,
mechanical, technical, safety. The team is then provided with basic information on hazards
of materials, process technology, procedures,
equipment design, instrumentation control, incident experience, previous
hazard reviews, and so on. A field tour of the process is also conducted
at this time, assuming the process is in operation.
The review
team methodically examines the process from receipt of raw materials to
delivery of the finished product to the customer's site. At each
step the group collectively generates a listing of what - if
questions regarding the hazards and safety of the operation.
When the review team has completed listing its spontaneously-generated
questions, it systematically goes through a prepared checklist to stimulate
additional questions.
Subsequently,
answers are developed for each question. The review team then works
to achieve a consensus on each question and answer. From these answers,
a listing of recommendations is developed specifying the need for additional
action or study. The recommendations, along with the list of questions
and answers, become the key elements of the hazard assessment report.
Hazard
and Operability Study (HAZOP): HAZOP is a formally
structured method of systematically investigating each element of a system
for all of the ways in which important parameters can deviate from the
intended design conditions to create hazards and operability problems.
The hazard and operability problems are typically determined by a study
of the piping and instrument diagrams (or plant model) by a team of personnel
who critically analyze the effects of potential problems arising in each
pipeline and each vessel of the operation.
Pertinent
parameters are selected — for example, flow, temperature, pressure, and
time. Then the effect of deviations from design conditions of each
parameter is examined. A list of key words such as more of,
less of, none of, part of, are selected for use in describing each
potential deviation.
The system
is evaluated as designed and with deviations noted. All causes of
failure are identified. Existing safeguards and protection are identified.
An assessment is made weighing the consequences, causes, and protection
requirements involved.
Failure
Mode and Effect Analysis (FMEA): The failure mode and effect
analysis is a methodical study of component failures. This review
starts with a diagram of the process that includes all components which
could fail and conceivably affect the safety of the process. Typical
examples are instrument transmitters, controllers, valves, pumps, and
rotometers. These components are listed on a data tabulation sheet
and individually analyzed for the following:
- Potential mode of failure ... open, closed, on, off, leaks, etc..
- Consequence of the failure.
- Effect on other components.
- Effect on whole system.
- Hazards
class ... high, moderate, low.
- Probability
of failure.
- Detection
methods.
- Compensating
provision/remarks.
Multiple
concurrent failures are also included in the analysis. The last
step is analysis of the data for each component or multiple component
failure and development of a series of recommendations appropriate to
risk management.
Fault Tree Analysis:
A fault tree
analysis is a quantitative assessment of all of the undesirable outcomes,
such as a toxic gas release or explosion, which could result from a specific
initiating event. It begins with a graphic representation (using
logic symbols) of all possible sequences of events that could result in
an incident. The resulting diagram looks like a tree with many branches —
each branch listing the sequential events (failures) for different
independent paths to the top event. Probabilities (using failure
rate data) are assigned to each event and then used to calculate the probability
of occurrence of the undesired event. A simple example of a fault
tree analysis chart is shown below.
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This
technique is particularly useful in evaluating the effect of alternative
actions on reducing the probability of occurrence of the undesired event.
Other
Hazard Evaluation Procedures:
Additional
information on the hazard evaluation procedures outlined above and descriptions
of other hazard evaluation procedures, as well as information concerning
the selection of an appropriate procedure, are contained in Guidelines
for Hazard Evaluation Procedures, prepared by The Center
for Chemical Process Safety of the American Institute of Chemical Engineers.
Routine Hazard Analysis:
Even simple
processes are complex — they are impacted by human behavior, workplace
variables, other business and natural forces, raw material variables,
normal wear and tear, and more.
It's a given —
jobs once designed for safety may now have hazards or improper operations.
The hazards
analysis process — called a Job Hazards Analysis (JHA) or Job Safety Analysis
(JSA) — pulls processes back on the safety track periodically.
Done for
every job, a JHA or JSA ensures safe steps, teaches new workers, eliminates
or controls hazardous materials, and much more.
- Some companies have work teams complete JHAs or JSA on every job or process and then
use them as the guide for how to do the job
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