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Page 1
Quantitative Risk Assessment : Rule Set Page 1 of 3
Steps performed in Quantitative Risk Assessment (QRA) :
1. Hazard Identification
Hazard identification is done on the basis of experience, detail process knowledge etc.
1.1. HAZOP/ HazId Workshop
Scenario are considered for QRA which having risk ranking equal to or more than 2 from HAZOP study.
All Top Events from HazId which having ultimate consequences are considered for QRA study. If it is
piping or process release, refer section 1.2 and isolate that portion completely and consider separate
isolatable section for QRA.
1.2. Plant sectionalisation Method
By considering all possible remotely operating valves and in special cases Non-Return valve, Pump
suction, vessel/ tank are as isolation in the PFDs/ P&IDs. Mark each section such as it should be isolate
completely. This is isolatable section. Find out and mark all possible isolatable section in the process
plant using PFDs/ P&IDs. Each isolatable section is considered as separate scenarios.
List out all isolatable sections, corresponding/ representative stream nos., phase of the stream,
composition for the same, process temperature and pressure for the isolatable section/ representative
stream, major equipment covered in the isolatable section and pipeline size.
If isolatable section having both phases i.e. vapour and liquid, model both phase as different sub
scenario.
2. Volume Calculation
Calculate the volume of the isolatable section for major equipment covered in the isolatable section
and pipeline given as below.
2.1. Pipeline volume : calculate Piping volume using formula V = (D2/4)L for all possible diameter in
the isolatable section.
Where V : Volume of the pipeline
D : Diameter of pipeline
L : Length of the piping section (Length is considered as 1.5 times the straight distance
between two equipment from Unit plot plan provided.
2.2. Column Volume : 30% column volume is considered as vapour volume and 70% as liquid.
2.3. Vessel Volume : consider HHLL level to calculate liquid volume using equipment layout diagram
provided. If not consider entire vessel volume as liquid or vapour depending on the phase of the
isolatable section.
Quantitative Risk Assessment : Rule Set Page 1 of 3
Steps performed in Quantitative Risk Assessment (QRA) :
1. Hazard Identification
Hazard identification is done on the basis of experience, detail process knowledge etc.
1.1. HAZOP/ HazId Workshop
Scenario are considered for QRA which having risk ranking equal to or more than 2 from HAZOP study.
All Top Events from HazId which having ultimate consequences are considered for QRA study. If it is
piping or process release, refer section 1.2 and isolate that portion completely and consider separate
isolatable section for QRA.
1.2. Plant sectionalisation Method
By considering all possible remotely operating valves and in special cases Non-Return valve, Pump
suction, vessel/ tank are as isolation in the PFDs/ P&IDs. Mark each section such as it should be isolate
completely. This is isolatable section. Find out and mark all possible isolatable section in the process
plant using PFDs/ P&IDs. Each isolatable section is considered as separate scenarios.
List out all isolatable sections, corresponding/ representative stream nos., phase of the stream,
composition for the same, process temperature and pressure for the isolatable section/ representative
stream, major equipment covered in the isolatable section and pipeline size.
If isolatable section having both phases i.e. vapour and liquid, model both phase as different sub
scenario.
2. Volume Calculation
Calculate the volume of the isolatable section for major equipment covered in the isolatable section
and pipeline given as below.
2.1. Pipeline volume : calculate Piping volume using formula V = (D2/4)L for all possible diameter in
the isolatable section.
Where V : Volume of the pipeline
D : Diameter of pipeline
L : Length of the piping section (Length is considered as 1.5 times the straight distance
between two equipment from Unit plot plan provided.
2.2. Column Volume : 30% column volume is considered as vapour volume and 70% as liquid.
2.3. Vessel Volume : consider HHLL level to calculate liquid volume using equipment layout diagram
provided. If not consider entire vessel volume as liquid or vapour depending on the phase of the
isolatable section.
