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SEMI S10-1103 © SEMI 1996, 2003 12 R2-2 Summary of Risk Assessment Techniques R2-2.1 Work Safety Analysis — A checklist is used to check the working place on criteria suc h as environm ent, ergonomics, and or ganization.…

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SEMI S10-1103 © SEMI 1996, 2003 11
RELATED INFORMATION 2
HAZARD ANALYSIS TECHNIQUES
NOTICE: This related information is not an official part of SEMI S10 and is not intended to modify or supersede
the official guideline. It has been derived from practical application by the task force members. Publication is
authorized by the vote of the responsible committee April 2, 2003.
R2-1 Hazard Analysis Techniques
R2-1.1 Introduction
R2-1.1.1 This related information gives an overview of several hazard analysis techniques that can be used. Each
technique has its own limitation or is developed for a special type of risk assessment. For each technique a short
description of the technique and a reference, if available, is given. Of course, it is not possible to list all techniques
in this overview.
R2-1.1.2 Analysis techniques: the choice of analysis technique depends upon the goal of the analysis. Two basic
types of techniques exist:
R2-1.1.2.1 Top-down (deductive) techniques are suitable for determining the initiating events that can lead to
identify top events, and calculating the probability of top events from the probability of the initiating events. They
can also be used to investigate the consequences of identified multiple failures. An Example of top-down techniques
is Fault Tree Analysis (FTA, see IEC 61025).
R2-1.1.2.2 Bottom-up (inductive) techniques are suitable for investigating the consequence of identified single
failures. Examples of bottom-up techniques are Failure Modes and Effects Analysis (FMEA, see IEC 812) and
Failure Modes, Effects and Criticality Analysis (FMECA, see MIL-STD-1629A).
Table R2-1 Overview of Analysis Techniques and Area of Use
When to use Where to Use
Technique
Before
malfunction
After
malfunction
Process Work place Machine Organization
Work Safety analysis X - - X - -
What-If X - X X X -
MORT X X - - - X
Checklists X X X X X X
Action Error Analysis X - - - X -
HAZOP X - X - X -
FMEA X - X - X -
Event Tree Analysis X - X X X -
Fault Tree Analysis X X X X X -
Circuit Logic Analysis X X X - - -
Interface Analysis X - X - X -
Mapping X - - - X -
Procedure Analysis X X - X - X
Contingency Analysis X - - X - X
Mathematical Malfunction analysis X - X X X -
Work Space analysis X - X - X
Task Analysis X X - X X -
SEMI S10-1103 © SEMI 1996, 2003 12
R2-2 Summary of Risk Assessment
Techniques
R2-2.1 Work Safety Analysis — A checklist is used to
check the working place on criteria such as
environment, ergonomics, and organization. On all the
criteria of the checklist a rating is given. The overview
of the ratings gives the “comfort” of the working place.
R2-2.2 MORT: Modified Fault Tree Analysis — Used
for detection of organization and policy errors being the
root causes of incidents. MORT uses a systematic
control list. MORT was developed as a safety
management program.
R2-2.3 Checklists — List of questions which is used as
guidance for the assessment. Almost every technique
uses a checklist. Checklists can be developed for
generic or specific situations (e.g., EN 1050 safety
checklist).
R2-2.4 Action Error Analysis — The consequences of
correct and incorrect actions are evaluated. Very much
based on handling of the person and the controls used.
R2-2.5 HAZOP — Hazard and Operability study:
Small team of experts of the machine/process which,
using a systematic checklist, checks for realistic
failures.
R2-2.6 FMEA — Failure Modes, Effects Analysis
(FMEA) is a tabulation of the system/plant equipment,
failure modes, and each failure mode' s effect on the
system/plant equipment. The failure mode is a
description of how equipment fails (e.g., open, closed,
on, off, leaks). The effect of the failure mode is the
system response or accident resulting from the
equipment failure. FMEA identifies single failure
modes that either directly result in or contribute
significantly to an important accident. Human/operator
errors are generally not examined in FMEA, although
the effects of a mis-operation are usually described by
an equipment failure mode. FMEA is not efficient for
identifying combinations of equipment failures that lead
to accidents. The FMEA can be performed by two
analysts or a multi-disciplinary team of professionals. A
Failure Modes, Effects and Criticality Analysis
(FMECA) is an FMEA with criticality rankings (Based
on MIL-STD-1629A).
R2-2.7 What-if — Possible failures are checked on
possible consequences. A checklist, suited for the
equipment to evaluate, may be used.
R2-2.8 Event Tree Analysis — Event tree analysis is a
technique for evaluating potential accident outcomes
resulting from a specific equipment failure or human
error known as an initiating event. Event tree analysis
considers operator response or safety system response
to the initiating event in determining the potential
accident outcomes. The results of the event tree
analysis are accident sequences, a chronological set of
failures or errors that define an accident. These results
describe the possible accident outcomes in terms of the
sequence of events (successes or failures of safety
functions) that follow an initiating event. Event tree
analysis is well suited for operations that have safety
systems or emergency procedures in place to respond to
specific initiating events.
NOTE R2-1: This technique is also known as Fault Hazard
Analysis.
R2-2.9 Fault Tree Analysis — Fault Tree Analysis
(FTA) focuses on one particular accident event and
provides a method for determining causes of that
accident event. The fault tree itself is a graphic model
that displays the various combinations of equipment
faults and failures that can result in the accident event.
The solution of the fault tree is a list of the sets of
equipment failures that are sufficient to result in the
accident event of interest. The strength of FTA as a
qualitative tool is its ability to break down an accident
into basic failures. This allows the safety analyst to
focus preventive measures on these basic causes to
reduce the probability of an accident.
R2-2.10 Circuit Logic Analysis — Logic of an
electrical circuit is checked by making a logic diagram.
Possible errors are reviewed for their consequences.
R2-2.11 Interface Analysis — Check how process,
equipment and systems are connected to each other.
Identify the risks of each connection.
R2-2.12 Mapping — The first step in determining a
risk profile is to develop a checklist of the areas of risk.
These factors can be evaluated quantitatively (as
accurate measurements) or qualitatively (as levels or
descriptive states). The second step is carrying out
sensitivity analyses for the quantitatively assessed
factors.
R2-2.13 Procedure Analysis — Procedures are
reviewed and checked if hazards occur in the steps or
sequence of steps.
R2-2.14 Contingency Analysis — Contingency
analysis is a method of treating uncertainty that
explores the effect on the alternatives of change in the
environment in which the alternatives are to function.
This is a “what-if” type of analysis, with the what-ifs
being external to the alternative.
R2-2.15 Mathematical Malfunction Analysis —
Identification of malfunctions, deviations in design are
made and the effect calculated. This technique is widely
used for rotating equipment.
SEMI S10-1103 © SEMI 1996, 2003 13
R2-2.16 Work Space Analysis — In this technique, the
position of the person performing a task is evaluated.
All external and task related circumstances are
evaluated and their risks are identified.
R2-2.17 Task Analysis — Task analysis is the
systematic examination of a task to identify all loss
exposures related to the task. A task will be reviewed in
the step-by step manner. Task Analysis should be done
during design and on final design. Task analysis is also
known as Job Safety Analysis (JSA). Verification of the
task analysis should be done by a Task Observation or
Job Safety Observation (JSO).