1. Process system and safety laboratory
Chemical Process Risk Analysis Using Layer of Protection Analysis and a Study on the Establishment about Proper Protection Layers
Yunju Jung, Seungjune Choi, and En Sup Yoon
School of Chemical Engineering, Seoul National University
Process system and safety laboratory

2. Process system and safety laboratory
What is IPL?
IPL : Independent Protection Layer
Features of IPL
Criteria : Specificity, Independence, Dependability, Auditability
3D : Detect, Decide, Deflect
3E : Fast Enough, Strong Enough, Big Enough
Big I : Independent
All IPLs are safeguards, but not all safeguards are IPLs.
Process system and safety laboratory

3. Classification of IPLs
Passive IPLs : dike, underground drainage system, open vent(no valve), Fire proofing, blast wall/bunker, inherently safe design, flame/detonation arrestors
Active IPLs : relief valve, rupture disc, basic process control system, interlocks
sensor(instrument, mechanical, or human)
decision making process(logic solver, relay, mechanical device, human)
action(instrument, mechanical, or human)
Process system and safety laboratory

4. Protection Layers of the Process
Process system and safety laboratory

5. The safety Life Cycle New or Existing Process Perform PHA &
Risk Assessment
Apply Non-SIS Protection
Layers to Reduce Risk
Define Target SIL
SIS
Required
Develop Safety
Requirement Specs
SIS Installation
& Commissioning
Perform Detail SIS Design
Conceptual SIS Design
Specs Met?
Establish Operations &
Maintenance Process
Pre-Startup
Safety Review
Operations, Testing, &
Maintenance
Modify or
Decommission
Decommissioning
Facility Design
SIS Design
Operation & Maintenance
PHA
Installation
Yes No
Process system and safety laboratory

6. Process system and safety laboratory
What is LOPA?
LOPA : Layer of Protection Analysis
LOPA is a semi-quantitative methodology that can be used to identify safeguards that meet the independent protection layer (IPL) criteria.
LOPA provides specific criteria and restrictions for the evaluation of IPLs.
LOPA is limited to a single cause-consequence pair as a scenario.
Process system and safety laboratory

7. Process system and safety laboratory
Use of LOPA
LOPA is used all around the process life cycle.
Research, process development, process design, operations & maintenance modification, decommissioning
provide guidelines in process design
Decide the safety critical
Identify operator actions & responses
LOPA is typically applied after a qualitative hazard analysis has been completed.
It is cost effective that LOPA is used during or after the HAZOP review or revalidation.
Process system and safety laboratory

8. Process system and safety laboratory
Task of LOPA
How safe is safe enough?
How many protection layers are needed?
How much risk reduction should each layer provide?
LOPA
Providing rational, semi-quantitative, risk-based answers
Reducing emotionalism
Providing clarity and consistency
Documenting the basis of the decision
Process system and safety laboratory

9. The steps to the LOPA process
Step 1 : Identify the consequence to screen the scenario
Step 2 : Select an accident scenario
Step 3 : Identify the initiating event & determine the initiating event frequency
Step 4 : Identify the IPLs & estimate PFD of each IPL
Step 5 : Estimate the risk
Step 6 : Evaluate the risk
Process system and safety laboratory

10. Benefits of LOPA LOPA takes less time than quantitative risk analysis.
LOPA provides better risk decision basis.
LOPA is more defensible for more rigorous documentation and specific value than qualitative method.
LOPA identifies operations and practices.
LOPA is simple numerical qualitative methodology!
Process system and safety laboratory

11. Process system and safety laboratory
Case Study
Hexane Storage Tank Overflow – spill not contained by the dike
Initiating event
The inventory control system fails.
A truck arrives at the tank with insufficient space in the tank.
Probability : due to an error in ordering, or unit shutdown after the truck was ordered, once a year
Process system and safety laboratory

12. Case Study (Continued)
IPLs in place
Human action to check level prior to filling
(PFD for human response = 1X10-1)
This procedure is an IPL because it meets the criteria of:
Effectiveness – if it is performed correctly,
The level is read correctly
the operator does not initiate loading
an overflow will not occure
Independence, Auditability
Dike (PFD = 1X10-2)
Total PFD for the IPLs in place = 1X10-1 X1X10-2 = 1X10-3
Process system and safety laboratory

13. Case Study (Continued)
Safeguards that are not IPLs for LOPA
The BPCS level control loop
Human action other than response to a BPCS alarm is not an IPL
Process system and safety laboratory

14. Case Study (Continued)
IPLs proposed
BPCS and operators are involved with either the initiating event or existing IPLs.
Thus, additional equipment must be added to reduce the risk.
SIF(Safety Instrumented Function)
(PFD of SIF candidate = 1X10-2)
Total PFD for the IPLs in place = 1X10-1 X1X10-2 X 1X10-2 = 1X10-5
Process system and safety laboratory

15. Process system and safety laboratory
Discussion
LOPA is a methodology for hazard evaluation and risk assessment, and lies between simple qualitative and more elaborate quantitative analysis techniques.
In decision-making process, LOPA helps to decide the propriety of protection layers that exist or are suggested to prevent accidents, so ideally matches the risk-decision criteria of the company.
LOPA is a recognized technique that can establish a proper safety integrity level (SIL) of the process.
Using LOPA, we need to set up proper protection layers that evaluate, analyze, and decease the risk in chemical process.
Process system and safety laboratory