The document compares Layer of Protection Analysis (LOPA) and Hazard and Operability Study (HAZOP), highlighting LOPA as a semi-quantitative method for estimating risk reduction through independent safety layers. It details the layers of protection in a facility, each with specific probabilities of failure and illustrates the application of LOPA in a batch reactor scenario. Additionally, it defines Safety Integrity Levels (SILs), which measure the reliability of safety systems based on their probability of failure on demand.

1. Hazop vs LOPA
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4. EVENT TREE ANALYSIS
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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: Automaticaction (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)

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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
IEFi PFD1 PFD2 PFD3 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: