Layers of Protection Analysis vs Hazop.pdf

Outlines the general philosophy, purpose & benefits of HAZOP & compares it with LOPA studies.

1. HazopvsLOPA
SLChakravorty

2. SLChakravorty

3. SLChakravorty

4. EVENT TREE ANALYSIS
SLChakravorty

5. SLChakravorty
Event Tree Analysis (ETA)

6. WHAT IS LOPA ( Layer of Protection Analysis)
•LOPA is a semi-quantitative method using
numerical categories to estimate the
parameters needed to calculate the
necessary risk reduction which corresponds
to the acceptance criteria.
•LOPA usually receives output from a HAZOP
or a hazard identification study (HAZID) &
often serve as input to a more thorough
analysis as a QRA.

7. * Safety protection of a facility or chemical plant is broken
down into layers.
*Seven layers are shown in Fig. 1 and are
generally applied beginning at the center of the diagram.
Layer 1: Process Design (e.g. inherently safer designs);
Layer 2: Basic controls, process alarms, and operator
supervision;
Layer 3: Critical alarms, operator supervision, and manual
intervention;
Layer 4: Automatic action (e.g. SIS or ESD);
Layer 5: Physical protection (e.g. relief devices);
Layer 6: Physical protection (e.g. dikes);
Layer 7: Plant emergency response; and not shown
Layer 8: Community emergency response[9].
EACH LAYER HAS TO BE INDEPENENT .
Concept of layers of protection( LOPA)

8. SLChakravorty

9. LOPA can be represented mathematically using the following
computational equation:
•Which multiplies the frequency of an initiating event (IEFi) by
the probabilities that each independent protection layer will
fail to perform( PFDs) its intended function:
•Frequency of Consequence is Given By:

10. •An initiating event is a failure that starts a
sequence of events that, if not interrupted by the
successful operation of a layer of protection,
results in a hazardous outcome.
Examples of common initiating events include
mechanical failure, operator error, and control
loop failure.
The initiating event frequency is considered
once every 10 years (IEFi is therefore 0.1/yr.)
(i) IEFi – Initiating event frequency

11. (ii) PFD - probability of failure upon demand of
Independent Layers
•Failure on demand occurs when a safety system is called upon to
act following an initiating event but fails to Act.
•Example: the reactor system has an emergency quench water
system piped to the reactor in the event of a runaway.
A runaway occurs, and the quench system is called upon to take
action. This is considered a demad.
•Further, it is established that this quench system will successfully
operate 9 times out of 10 times ,when demanded to act.
•This implies that it fails only one time out of 10
So PFD is 0.1
Success to act is 0.9

12. TAKE AN EXAMPLE - CASE STUDY FOR LOPA
Application to a batch reactor system
•Let's examine LOPA as applied to a batch reactor manufacturing
ortho-nitroaniline from ammonia and orthonitrobenzene.
•let’s imagine that we want to prevent a reactor rupture/ the
catastrophe incident.
•IEFi (Initiating event frequency)
•PFD (Probability of Failure on Deman) for each layer is given below:
Layer 1 Process design : PFD 1
Layer 2: Basic controls, process alarms, operator supervision: PFD2
Layer 3: Critical alarms, operator supervision, and manual intervention: PFD3
Layer 4: Automatic action SIS or ESD : PFD3
Layer 5: Physical protection (relief devices); : PFD 4
Layer 6: Physical protection (dikes) : PFD5
Layer 7: Plant emergency response : PFD6
Layer 8: Community emergency response: PFD7

13. Compare the resulted frequency with the risk
tolerance level .
In this case, the risk tolerance level for a runaway
reaction leading to vessel rupture is 10-5/yr
, , frequency of the consequence occurring for scenario.

15. LAYER OF PROTECTION ANALYSIS
LOPA
4x5x6x
7
IEFiPFD1 PFD2PFD3 8x9
SDV

16. Compare the resulted frequency,
with
the risk tolerance level (=10
−5
/yr)
, , , frequency of the consequence occurring for scenario.

17. What is Safety Integrity Level (SILs)?
•Safety Integrated Level (SIL) is a measure of reliability
& integrity for respective Safety instrumented system
when a process demand occurs.
SIL LEVEL PFD Integrity / Reliability of SIS
1 0.1 to 0.01 =10
−2
Lowest
2 0.01 to 0.001 = 10
−3
3 0.001 to 0.0001 = 10
−4
4 0.0001 to 0.00001 = 10
−5
Highest
The probability of failure of SIS will be lowest with highest level
of SIL as given below: