Industrial safety unit iv ppt

1. INDUSTRIAL SAFETY
Ms. V.KANNAGI
Associate Professor/ECE
R.M.K. College of Engineering and Technology

2. UNIT IV
HAZARD ANALYSIS
System Safety Analysis
Different Techniques
Fault Tree Analysis (FTA)
Failure Modes and Effects Analysis (FMEA)
HAZOP analysis
Risk Assessment

3. HAZARD ANALYSIS
Analysing their
potential causes
Process of
recognizing
hazards that may
arise from a system
or its environment
First step
in a process
used to
assess risk
Result - the
identification of
different type of
hazards
Hazard
Analysis

5. System Safety Analysis
Techniques
A number of different methods can be used for conducting
detailed analyses. The most widely used of these are as follows:
 Failure mode and effects of analysis (FMEA)
 Hazard and operability review (HAZOP)
 Human error analysis (HEA)
 Technique of operations review (TOR)
 Fault tree analysis (FTA)
 Risk analysis

6. Fault tree analysis (FTA)
Fault Tree Analysis was originally developed
in1962 at Bell Laboratories by H.A. Watson.
FTA is a deductive analysis approach for
resolving an undesired event into its causes.
Logic diagrams and Boolean Algebra are used to
identify the cause of the top event.
A logic diagram called Fault tree is constructed
to show the event relationship.
Probability of occurrence values are assigned to
the lowest events in the tree in order to obtain
the probability of occurrence of the top event.

7. Why FTA is Carried Out?
 Identify the cause of a failure.
 Monitor and control safety performance of a
complex system.
 To identify the effects of human errors .
 Minimize and optimize resources.

8. Fault tree
Fault tree is the logical model of the relationship
of the undesired event to more basic events.
The top event of the Fault tree is the undesired
event.
The middle events are intermediate events and
the basic events are at the bottom.
The logic relationship of events are shown by
logic symbols or gates.

9. Basic Fault Tree Structure

10. Events of a Fault tree
 Basic Event: A lower most event that can not be
further developed.
 Intermediate Event: This can be a intermediate event
(or) a top event. They are a result logical combination
of lower level events.
 Undeveloped Event: An event which has scope for
further development but not done usually because of
insufficient data.
 External Event: An event external to the system which
can cause failure.

11. Basic Gates Of a Fault tree
 OR Gate: Either one of the bottom event results in
the occurrence of the top event.
 AND Gate: For the top event to occur all the
bottom events should occur.
 Inhibit Gate: The top event occurs only if the
bottom event occurs and the inhibit condition is
true.

12. Sample Fault Tree

13. Functions of FTA
 analyze failure reasons of the top events combined with
the system architecture;
 quantify the probabilities of the top events;
 allocate the safety requirements of the top events to the
lower level events;
 assess the effects of the development errors through the
combination of qualitative and quantitative methods;
 assess the effects of single and combined failures;

14. Functions of FTA
 assess the effects of the exposure time of the hidden
failures on the system safety;
 assess the source of common cause failures;
 assess the nature of fail-safe design (fault tolerance and
error tolerance);
 assess the effects of design change on safety;

15. Advantages of Fault tree
analysis
The fault tree can serve in all phases of the
machinery life cycle because it can help to
determine possible causes of undesirable events.
FTA may be used to evaluate competing designs
by revealing qualitative and quantitative event
interdependencies.

16. Disadvantages of FTA
No effective formal control against overlooking
of events or the neglect of operating or
environmental conditions.
Lack of reliable and relevant failure rate data as
well as the probabilities of events.
Construction of fault trees can demand a lot of
effort and may become expensive.

17. Failure Mode and Effect
Analysis
 Process that identifies all the possible types of failures
that could happen to a service and potential
consequences of those failures
 A structured approach to:
Identify the ways in which a process can fail
Estimate risk associated with specific causes
Prioritize the actions that should be taken to reduce
risk
Evaluate design validation plan (design FMEA) or
current control plan (process FMEA)

18. What Is A Failure Mode?
A Failure Mode is:
Things that could go wrong
The way in which the steps and / or the process
could fail to perform its intended function
Failure modes may be the result of upstream
operations or may cause downstream operations to
fail

19. Uses of FMEA
Methodology that facilitates process
improvement
Improve internal and external customer
satisfaction
Focuses on prevention
FMEA may be a customer requirement
Identifies and eliminates concerns early in the
development of a process or design
FMEA may be required by an applicable Quality
Management System Standard

20. Sample FEMA form

21. Contents of FEMA form
Compensating provisions
Probability of occurrence
Failure classification
 Safe
 Marginal
 Critical
 Catastrophic

22. Advantages of FMEA
• Risk index/RPN enables prioritization of faults
• Explicitly documents modes of control/
mitigation
• Format useful for tracking action items
• Easily constructed using hand-written
spreadsheets or computer-based software tools

23. Disadvantages of FMEA
 Failure and reliability rates are particularly difficult to
estimate when human performance is involved
 Difficult to assess combination of event/complex
interactions ( unless explicitly documented)
 Severity and occurrence ratings are often difficult for
individuals or teams to estimate. Much time can be spent
in discussion.
 Sometimes can be conservative. With each fault isolated,
failure to consider combinational events (as do fault
trees) may lead to the false conclusion that every item
requires explicit mitigation.