quantitative risk assessment of mounded bullet project€¦ · international r isk c ontrol a sia l...

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INTERNATIONAL RISK CONTROL ASIA LLP

[An ISO 9001:2015 Certified Company]

Quantitative Risk Assessment of

Mounded Bullet Project

For

Indian Oil Corporation Limited

Guwahati Refinery

Client’s Name: Indian Oil Corporation Limited (IOCL)

Project Title: QRA for Mounded Bullet Project at IOCL Guwahati Refinery

IRCA Document Number: IRCA-IOCL-QRA-20171808-02

2 12-07-2018 Revised, Incorporating

client comments Sufiyan Ansari R. Krishnan Rajneesh Kumar

1 21-05-2018 Revised, Incorporating

client comments Sufiyan Ansari R. Krishnan Rajneesh Kumar

0 04-04-2018 Issued for Review /

Comments Sufiyan Ansari R. Krishnan Rajneesh Kumar

Revision Issue Date Reason for Issue Prepared by Reviewed by Approved by IRCA

Mounded Bullet Project at IOCL Guwahati Refinery

Quantitative Risk Assessment

Report Number IRCA-IOCL-QRA-20171808-02 Rev 2 July 2018

Page | ii

Contents

1. INTRODUCTION ............................................................................................................................1.1

2. STUDY OBJECTIVE .......................................................................................................................2.1

3. PROCESS DESCRIPTION ..............................................................................................................3.1

4. STUDY METHODOLOGY .............................................................................................................4.1

5. STUDY INPUTS ..............................................................................................................................5.1

6. RISK ANALYSIS RESULTS ..........................................................................................................6.1

7. CONSEQUENCE ANALYSIS ........................................................................................................7.1

8. CONCLUSIONS & RECOMMENDATIONS .................................................................................8.1

Attachment I : QRA Assumption Sheets

Attachment II : Failure Cases Input to QRA

Attachment III : Consequence Analysis Graph




Page | iii

Executive Summary

Indian Oil Corporation Limited (IOCL), Guwahati, desires to install two nos. of 350 MT net storage

capacity mounded bullets at Guwahati Refinery for LPG. This corresponds to total net storage capacity

of 700 MT of LPG. The main intention of setting up this facility is to improve safety aspects and also to

replace/phase out existing refinery practice to store LPG in Horton Spheres/Bullets.

IOCL being an organization with high standards of safety, health and environment management, wishes

to ensure the process risks associated with the installation of new mounded bullets and LPG transfer

pumps are properly assessed to ensure that risk levels are kept as low as reasonably practicable. IOCL

has therefore engaged M/s International Risk Control Asia (IRCA), Mumbai, to carry out a Quantitative

Risk Analysis (QRA) for Mounded Bullet Project at Guwahati Refinery.

Individual Risk

The overall iso–risk contours representing location-specific individual risk (LSIR) for Mounded Bullet

Project at Guwahati Refinery are shown in Figure 1.

Figure 1: Overall iso-risk contours

The highest location-specific individual risk contour in mounded bullet area at Guwahati Refinery is of

10-5

per year.




Page | iv

The maximum LSIR in the units are listed in Table 1.

Table 1: Maximum Location-Specific Individual Risk (LSIR)

SR.

NO. AREA / UNIT

MAXIMUM LSIR

(PER YEAR)

1. LPG Transfer Pumps 3.4 E-05

2. Mounded Bullet Area 1.9 E-05

3. LPG Pump House (Existing) 1.5 E-06

4. Switch Gear Room 1.3 E-06

5. Compressor House 1.2 E-06

6. LPG Operator Room 1.0 E-06

7. Bulk Loading Control Room 1.1 E-07

Individual risk to worker

The Location-specific individual risk (LSIR) is risk to a person who is standing at that point 365 days a

year and 24 hours a day. The personnel in mounded bullet area are expected to work in 8 hour shift as

well general shift. The actual risk to a person i.e. “Individual Specific Individual Risk” (ISIR) would be

far less after accounting for the time fraction a person is expected to spend at a location.

ISIR Area = LSIR x (8/24)(8 hours shift) x (Time spend by an individual / 8 hours)




Page | v

The maximum ISIR in the units are listed in Table 2.

Table 2: Maximum Individual-Specific Individual Risk (ISIR)

SR.

NO. AREA / UNIT

MAXIMUM ISIR

(PER YEAR)






From the results shown above, the maximum individual risk to worker is estimated as 2.83 x 10-6

per

year.

ALARP Summary & Comparison of Individual risk with Acceptability Criteria

The objective of this QRA study is to assess the risk levels with reference to the defined risk

acceptability criteria and recommend measures to reduce the risk level to as low as reasonably

practicable (ALARP).

The comparison of maximum individual risk with the risk acceptability criteria is shown in Figure 2.

The individual risk of 2.83 x 10-6

per year for worker is in the Broadly Acceptable Level.




Page | vi

Figure 2: Individual Risk

Max. Individual Risk to Plant Personnel:

2.83 E-06 per year

(Negligible Risk) Max. Individual Risk to Public:

< 1.0 E-06 per year




Page | vii

Societal Risk

The Societal risk parameter is shown in Figures 3 in the form of an FN curve.

The results of FN curves show that the risk is in “Broadly Acceptable (Negligible Risk)” region.

Figure 3: FN Curve for Societal Risk




Page | viii

Top Risk Contributors (Group Risk)

The significant risk contributions from Mounded Bullet project based on results available from PHAST

RISK are shown in Table 3.

Table 3: Top Risk Contributors

SR.

NO. Area / Unit

Risk Contribution

(%)

1 LPG transfer Pump (P-103D) discharge -3 mm leak 19

2 LPG transfer Pump (P-103C) discharge -3 mm leak 14


4 Mounded Bullet (T-103D) liquid outlet to pump

suction – 50 mm leak 12

5 Mounded Bullet (T-103C) liquid outlet to pump








Page | ix

CONCLUSIONS & RECOMMENDATIONS

The maximum risk to persons working in the Mounded Bullet area is 2.83 x 10-6

per year which is in

Broadly Acceptable level (refer red band in risk acceptability criteria).

The risk to Public is in due to the proposed mounded bullet project is in “Broadly Acceptable level”.

Societal risk is also in “Broadly Acceptable Level”.

The high risk contributors in the unit are due to LPG pump discharge leakage followed by leakage from

pump suction side. Mounded bullets provide high level of safety for storage of LPG as they are not

susceptible to hazards of catastrophic failure and Fire ball / BLEVE.

The following recommendations are made to keep the risk level in broadly acceptable level.

Recommendations

1. It is necessary to provide extensive fire and gas detection system in the Mounded Bullets and

LPG transfer pump area. Philosophy for operation of fire and gas detection system to isolate the

relevant sections should be clearly defined and the operating personnel should be trained for

proper use of this safety system.

2. It is recommended to have necessary provision for emergency stop of LPG transfer pumps from

control room in the event of major leak / flash fire there should be an SOP established for clarity

of actions to be taken in case of fire / leak emergency.

3. The emergency response plan of the refinery to be updated to cover the new Mounded bullet

Project.

4. Liquid outlet line from the bottom of mounded bullet is shown with flanged ROV. In case of

leakage from downstream flange ROV can be closed to stop the leakage however if leakage from

upstream flange, leak duration is much longer and increasing the likelihood of jet /pool fire then

exposed the bullet to external fire thus defeating the purpose of mounded bullet. Therefore it is

recommended that ROV with flange end fitted in pipe line shall be Spiral Wound metallic gasket

or RTJ gasket as per OISD STD-150.




Page | 1.1

1. INTRODUCTION

Guwahati Refinery is the country’s first refinery of Indian Oil Corporation Limited (IOCL) serving the

nation since 1962. Built with Rumanian assistance, the Refinery with initial capacity of 0.75 MMTPA

was designed to process a mix of OIL and ONGC crude. The refining capacity was subsequently

enhanced to 1.0 MMTPA. With INDMAX, the pilot plant for in-house technology of IOCL, the ISOSIV

and Hydrotreater the Refinery was able to produce eco-friendly fuels.

Quality LPG, Motor Spirit, Aviation Turbine Fuel, Superior Kerosene Oil, High Speed Diesel, Light

Diesel Oil and Raw Petroleum Coke are the products of this Refinery. With ISOM Project

commissioned in 2010, the MS produces here complies to BS-III specifications and so does the HSD,

thus meeting the Auto Fuel Policy of the Government of India.

Indian Oil Corporation Limited (IOCL), Guwahati, desires to install two nos. of 350 MT net storage

capacity mounded bullets at Guwahati Refinery for LPG. This corresponds to total net storage capacity

of 700 MT of LPG. The main intention of setting up this facility is to improve safety aspects and also to

replace/phase out existing refinery practice to store LPG in Horton Spheres/Bullets.

IOCL being an organization with high standards of safety, health and environment management, wishes

to ensure the process risks associated with the installation of new mounded bullets and LPG transfer

pumps are properly assessed to ensure that risk levels are kept as low as reasonably practicable. IOCL

has therefore engaged M/s International Risk Control Asia (IRCA), Mumbai, to carry out a Quantitative

Risk Analysis (QRA) for Mounded Bullet Project at Guwahati Refinery.

IRCA has carried out hazard and risk analysis studies for a large number of oil & gas installations and

chemical plants over the past eight years including 15 MMTPA Paradip Refinery Project of IOCL.

This document presents IRCA's report on QRA study of Mounded Bullet Project at Guwahati Refinery.




Page | 2.1

2. STUDY OBJECTIVE

This study aims for quantitative assessment of process risks at mounded bullet project at IOCL

Guwahati Refinery. The risk covered in this study is mainly risk to people due to release of material by

loss of containment resulting in fire, explosion or toxic dispersion. The risk to life is calculated as

“Individual Risk” and “Group Risk”.

Individual Risk: It is represented by iso-risk contours, which show the geographical distribution of risk

to an individual. It is assumed that the individual is continuously present at that location, out of doors

and does not shelter or try to escape.

Group Risk: it is represented by FN curves, which show the cumulative frequency distribution of

accidents causing different numbers of fatalities. The FN curve therefore indicates whether the Group

risk to the facility is dominated by relatively frequent accidents causing small numbers of fatalities or

low frequency accidents causing many fatalities.

The main objectives of this study are:

To establish the risk levels, compare them with appropriate risk acceptability criteria to

determine the suitability of the development, and suggest necessary risk reduction measures so

that the risk is as low as reasonably practicable.

To estimate the extent of potential damage due to fire, explosion or toxic release resulting from

credible leak scenarios so as to ensure that the necessary measures for damage reduction are

incorporated in the system design.

To provide necessary inputs for preparing on-site and off-site emergency plans

The scope of this QRA study is to cover all the new equipments coming under Mounded bullet projects

as shown in plot plan for LPG bullet and LPG pump house area Drawing No. PC000118-5111-07-0001

Rev 1.




Page | 3.1

3. PROCESS DESCRIPTION

The main intention of setting up this facility is to improve safety aspects and also to replace/phase out

existing refinery practice to store LPG in Horton Spheres/Bullets.

Mounded Bullets provide intrinsically passive & safe environment & eradicates the possibility of

Boiling Liquid Expanding Vapor Explosion (BLEVE), though LPG handling possess many challenges,

due to its inherent dangerous properties, modern state of art safety features has been taken into

consideration while designing the facilities using different OISD codes.

Net Capacity of each Mounded Bullet is 350MT and Total net Capacity is 700 MT.

Max Design filling rate is 18 m3/hr to each Mounded bullet and Max Pump Out rate is 60 m

3/hr of LPG.




Page | 4.1

4. STUDY METHODOLOGY

4.1 Quantitative Risk Analysis

The five normal components of a Quantitative Risk Assessment (QRA) study are:

Hazard, (or failure case) identification

Failure frequency estimation

Consequence calculations

Risk calculation (Risk Summation)

Risk assessment (using an acceptability criteria)

Figure 4.1 below shows the relationship of each step and the additional external data requirements.

Figure 4.1: Classical Approach of QRA

Plant

Data

Derive

Failure

Cases

Calculate

Frequencies

Calculate

Consequences

Generic

Failure Rate

Data

Meteorological

Data

Safety

Management

Factor

Calculate

Risks

Assess

Risks

Ignition

Data

Population

Data




Page | 4.2

This QRA study has been carried out by IRCA using the DNV software package PHAST RISK (earlier

known as SAFETI) current Version 6.7.

4.1.1 Collection of Data

The total data requirement can broadly be put in five categories as under:

Plant data

Generic failure rate data

Meteorological data

Population data

Ignition source data

The plant data are derived from the description of facilities (PFDs, P&IDs, Lay out plans etc.).

4.1.1.1 Failure Case Identification and Definition

The first stage in any QRA is to identify the potential accidents that could result in the release of the

hazardous material (oil & gas in this study) from its normal containment. This is achieved by a

systematic review of the facilities together with an effective screening process.

PHAST software can model toxic and flammable effects based on properties of the material.

Sectionalization For the purpose of defining the failure scenarios to be considered in risk analysis, the plant is divided

into sections containing significant inventory of hazardous material with defined isolation arrangement

(shut-down valve, remote operated valve, NRV, pump etc.). Averaged process conditions and

composition for the section will be used in the analysis. Where relevant (e.g. Separator), release of gas

and liquid from the section will be considered separately.

Defining process materials PHAST has provision to define mixtures of pure components. This feature is used to define mixtures to

represent the process streams relevant to the study for modelling releases from the sections.

Selection of leak sizes There is a possibility of failure associated with each mechanical component of the plant (vessels, pipes,

pumps or compressors). These are generic failures and can be caused by such mechanisms as weld

failure, corrosion, vibration or external impact (mechanical or overpressure).

The range of possible releases for a given component covers a wide spectrum, from a pinhole leak up to

a catastrophic rupture (of a vessel) or full bore rupture (of a pipe). It is both time-consuming and

unnecessary to consider every part of the range; instead, representative failure cases are generated. For a

given component these should represent fully both the range of possible releases and their total

frequency. The range of leak sizes considered for QRA is listed in Table 4.1.




Page | 4.3

Table 4.1: Representative Leak Sizes for QRA

Leak Type Representative hole Size (mm)

Small leak 3

Medium leak 10

Large leak 50

Rupture 100

For each identified failure case, the appropriate data required to define that case are input to the PHAST

RISK package. When the appropriate inputs are defined, PHAST RISK calculates the source terms of

each release, such as the release rate, release velocity, release phase and drop size. These source term

parameters then become inputs to the consequence modelling. Alternatively, PHAST RISK allows these

source terms to be input directly.

4.1.1.2 Failure frequency data

Leak frequency for each leak size will be estimated using generic leak frequency data available in the

latest publication ‘Risk Assessment Data Directory’ by International Association of Oil & Gas

Producers (OGP), UK. The database contains generic leak frequencies for various categories of pipes,

flanges, valves, pressure vessels, process equipment, instrument fittings etc. The leak frequencies are

available for different leak sizes.

First calculate the failure frequencies for each leak size and then create a table for each of the

failure case

For each case, count the number of each type of item (valve, flange, equipment etc.) in the plant

section from P&I diagrams and layout drawings.

Insert the failure frequencies for each type of item.

Multiply by the number of items to obtain the frequency for each item type and leak size.

Sum the frequencies for each leak size over all the items to give the case frequencies for each

leak size in the plant section.

4.1.1.3 Meteorological data

The following weather data are required for QRA.

Ambient temperature, relative humidity

Wind speed, wind direction and atmospheric stability in the form of wind rose data indicating the

annual probability distribution.

4.1.1.4 Population data

The quantitative risk assessment using PHAST RISK is concerned with risk of fatality due to exposure

to toxic and flammable effects following the accidental release of hazardous material from the plant.

In PHAST RISK, the population distribution in and around the plant is to be defined on the site map

drawing.




Page | 4.4

4.1.1.5 Ignition source data

The following ignition sources are generally encountered in process plants.

Fired heaters, boilers

Ordinary electrical equipment such as transformers, switchgear room

High voltage transmission lines

Transportation – roads and railway lines

Workshops, garages, restaurants etc.

Residential buildings

Data on the ignition sources in and around the plant are based on the plot plan and site map drawings.

4.1.2 Risk Calculation

The final estimation of risk is carried out by PHAST RISK package based on the input data detailed

above. Each failure case is analysed to determine its impact (in terms of fatalities). Effect zone

information generated by consequence analysis is combined with meteorological, ignition source and

population data. Event tree conditional probabilities leading to a particular outcome and frequency

information, extracted from the original failure case description, are used to determine the level of risk

for the specific failure case under analysis.

PHAST RISK generates the required standard forms of risk measure. It calculates both individual risk at

grid points and the societal group risk of each incident outcome.

To calculate group or societal risk, the total number of fatalities for each release case, event tree

outcome, weather type and wind direction must be calculated. The frequencies of all those combinations

contributing to the same number of fatalities must be added. The PHAST RISK package allows these

results to be presented in the form of an FN group risk curve. An FN curve is a graph, which plots the

frequency of N or more fatalities per year (F) against the number of fatalities (N). It is conventional that

this information is presented on a log-log plot.




Page | 4.5

4.1.3 Risk Presentation

The risk levels associated with the facilities will be presented in the following standard forms:

Individual risk contours which show the geographical distribution of risk to an individual.

Group risk (FN) curves which show the cumulative frequency (F) distribution of accidents

causing different numbers (N) of fatalities. The FN curve therefore indicates whether the societal

risk to the facility is dominated by relatively frequent accidents causing small numbers of

fatalities or low frequency accidents causing many fatalities.

4.1.3.1 Risk Assessment

The final, and most significant, step in the process is the assessment of what the calculated risk levels

portray. Risk assessment is a process by which the results of a risk analysis are used to make judgments,

either through relative risk ranking of risk reduction strategies or through comparison with risk targets

(criteria). Where risk criteria have been issued by the regulatory authority, it is possible for interested

parties to assess the calculated risk levels against these criteria. The risk assessment stage determines

whether the risks are tolerable, or if risk mitigation measures are required to reduce the risk to a level,

which can be considered to be as low as reasonably practicable (ALARP).

4.1.3.2 Risk Tolerability Criteria

A risk analysis provides measures of the risk resulting from a particular facility or activity. However, the

assessment of the acceptability or otherwise of that risk is left to the judgement and experience of the

people undertaking and/or using the risk analysis work. The normal approach adopted is to relate the

risk measures obtained to acceptable risk criteria.

A quantitative risk analysis produces only numbers, which in themselves provide no inherent use. It is

the assessment of those numbers that allows conclusions to be drawn and recommendations to be

developed. The assessment phase of a study is therefore of prime importance in providing value from a

risk assessment study.

Individual risk Criteria

The risk acceptability criteria published by UK HSE is applied when judging the tolerability of risk to

persons for IOCL facilities, sites, combined operations or activities. The same is graphically expressed

as in Figure 4.2. It broadly indicates as follows:

a) Individual risk to any worker above 10-3 per annum shall be considered intolerable and

fundamental risk reduction improvements are required.

b) Individual risk below 10-3 for worker but above 10-6 per annum for any worker shall be

considered tolerable if it can be demonstrated that the risks are as low as reasonably practicable.

c) Individual risk below 10-6 per annum for any worker shall be considered as broadly acceptable

and no further improvements are considered necessary provided documented control measures

are in place and maintained




Page | 4.6

d) Individual risk to any member of the general public as a result of CIL Businesses activities shall

be considered as intolerable if greater than 10-4 per annum, broadly acceptable if less than 10-6

per annum and shall be reduced to as low as reasonably practicable between these limits.

Figure 4.2: Individual Risk Criteria for IOCL

(Negligible Risk)




Page | 4.7

Group Risk Criteria – FN Curves

When considering the risks associated with a major hazard facility, the risk to an individual is not

always an adequate measure of total risks; the number of individuals at risk is also important.

Catastrophic incidents with potential multiple fatalities have little influence on the level of individual

risk but have a disproportionate effect on the response of society and impact on company reputation.

Group risk is the relationship between frequency of an event and the number of people affected. Societal

risk from a major hazard facility can thus be expressed as the relationship between the number of

potential fatalities N following a major accident and the frequency F at which N fatalities are predicted

to occur. Minimum criteria for societal risk based on F-N curves are presented in Figure 4.3.

Figure 4.3: Societal Risk Criteria for IOCL

(Negligible Risk)




Page | 4.8

4.2 Consequence Analysis

Consequence analysis has been carried out using the DNV PHAST software latest version 6.7. PHAST

is a software package developed by DNV, which provides a standard and validated suite of consequence

models which can be used to predict the effects of a hydrocarbon release.

Consequence analysis provides quantitative information about the flammable effects and toxic gas

dispersion resulting from release of material due to loss of confinement.

Flammable effects

When the dispersing cloud containing flammable material above LFL concentration comes into contact

with ignition source, there is potential for the following.

Jet fire

Pool fire

Flash fire

Vapour cloud explosion

Jet Fires

Jet fires are usually associated with releases of gas. They have high momentum and high heat flux

radiation levels. At high release rates, the jet becomes highly turbulent, entrains more air and burns

hotter. The flame will stabilize on or near the point of release and will have a torch or fan-like

appearance, depending on the type of release. The primary method for controlling jet fires is by isolation

and blow-down of the inventory to starve the fire of fuel, with passive fire protection, as appropriate, to

prevent escalation.

Pool Fires

Pool fires may occur in any area where flammable liquids are stored. It should be noted that the fuel

pool is not necessarily static and can spread or contract with respect to the leak rate of the hydrocarbon

and its burning rate, and according to any slope of the underlying surface. Leaking liquid hydrocarbons

will be removed from the immediate area by the hazardous open drains system, reducing the available

fuel inventory and therefore reducing the potential size and duration of any pool fire.

Pool fires have little or no momentum and lower heat fluxes than jet fires. They may be adequately

controlled using a solution of firewater and fire fighting foam. A pool fire cannot be quickly eliminated

by isolating the fuel supply alone.

Flash Fires

Where a gas cloud develops in an unconfined environment and where ignition is delayed, a flash fire can

occur where rapid combustion occurs through the cloud similar to an explosion, but with little

overpressure. The speed of combustion is also much less than in an explosion.




Page | 4.9

4.3 Explosions

Delayed ignition of a gas cloud can result into explosion. The overpressures generated by explosion

have the potential to damage buildings/structures and cause secondary fires.

Toxic Gas Dispersion

Release of toxic compounds (H2S & Chlorine) resulting in a toxic vapour cloud, before it becomes

sufficiently diluted to no longer be considered toxic.

4.3.1 Event Identification

There are a large number of fire, explosion and toxic dispersion events that could occur. The

consequence analysis has focused on those events that would have a significant effect on the safety of

personnel and assets.

4.3.2 Inventory Identification

The process and storage units are sub-divided into discrete isolatable systems.

The approach used was to review the process and relevant utility P&IDs and to identify the sections

containing large inventory of hazardous material that can be isolated by operation of valves.

Each section is then characterized by the following parameters required for consequence modelling:

Mass of flammable material in the process/ storage section (oil/ gas)

Pressure, temperature and composition of the material

Hole size for release

4.3.3 Release Size Definition

Releases from process equipment can be of any size from very small releases (1 mm flange leak) to

large releases (catastrophic rupture of a large pressure vessel or flow line).

In order to obtain only the results of consequence analysis for specific release scenarios, it is necessary

to model these cases directly in PHAST. For example, consequence analysis using leak sizes of 50.8

mm (2 inches) and normally prevailing weather conditions are used for review of layout, emergency

escape routes, location of emergency systems etc. taking into account the effects of fire and explosion

due to accidental releases. Performing consequence analysis using PHAST provides graphical results

plotted on site map in addition to tabular results.

The Refinery complex involves the handling and processing of both flammable and toxic materials. Loss

of containment of pressurized flammable gases could lead to fire or a vapour cloud explosion. Whilst a

loss of containment of toxic materials such as hydrogen sulphide on site could lead to health risks

associated with toxic exposure.




Page | 4.10

Release of flammable or toxic materials to the atmosphere can lead to one of the following:

Immediate ignition of released vapour resulting in a Jet Fire.

Spreading of flammable vapour with the wind until its lower flammability limit is reached or an

ignition source found, which will result in a Flash Fire or explosion.

Spillage of flammable liquid on the ground resulting in formation of a pool of liquid, which will

evaporate taking heat from the ground surface thereby forming a flammable atmosphere above

the pool. Ignition of this atmosphere will result in a pool fire.

Explosion of a confined/unconfined vapour cloud will generate over-pressure.

Release of toxic compounds resulting in a toxic vapour cloud, before it becomes sufficiently

diluted to no longer be considered toxic.

4.4 Damage Criteria

Flash Fire

Flammable vapour, after loss of containment, will normally spread in the direction of the wind. If it

finds an ignition source before being dispersed to below its Lower Flammability Limit (LFL), a Flash

Fire is likely to result and the flame may travel back to the source of the release. Any person caught in a

Flash Fire is likely to suffer fatal burn injuries. Therefore, in this consequence analysis, the distance at

which LFL is achieved is calculated to indicate the area which may be affected by a Flash Fire.




Page | 4.11

Thermal Radiation

Thermal radiation due to a pool fire or jet fire may cause various degrees of burns on human bodies or

damage to objects, such as piping or equipment. Table 4.2 tabulates thermal radiation intensities and

their damage effect in case of an incident.

Table 4.2: Damage due to incident radiation intensities

Intensity

Radiation

(kW/m²)

Type of Damage

37.5 Sufficient to cause damage to process equipment

32 Maximum allowable radiation intensity on thermally protected

and pressurised storage tank

25 Minimum energy required to ignite wood at infinitely long

exposure (non-piloted)

12.5 Minimum energy required for piloted ignition of wood, melting

of plastic etc.

8 Maximum allowable radiation intensity on thermally

unprotected and pressurised storage tank

4

Sufficient to cause pain to personnel if unable to reach cover

within 20 seconds; however, blistering of skin (1st degree burn)

is unlikely

1.6 Intensity insufficient to cause discomfort for long exposures

0.7 Equivalent to Solar Radiation

Thermal hazard distances to 37.5 kW/m², 12.5 kW/m² and 4 kW/m² radiation intensity are considered in

consequence analysis.

For thermal hazards over 37.5 kW/m² escalation may occur.

For thermal hazards of 12.5 kW/m² or higher combustibles on buildings may spontaneously ignite.

For thermal hazards of 4 kW/m² or higher personnel injury may occur.

Storage tank farm

The possible damage effect from the Tank Farm may manifest itself in the following ways:

Damage due to thermal radiation from tank fire and dyke fire

Damage due to Flash Fire owing to flammable spill in dyke

These may affect people and property within and outside the facilities.




Page | 4.12

Although 37.5 kW/m² incident radiation intensity level is hazardous for adjacent tanks, while deciding

the layout for tank spacing consideration, a maximum of 32 kW/m² radiation intensity is permitted on

adjacent thermally protected tanks (e.g. with water sprinklers or insulation etc.) and a maximum of 8

kW/m² is permitted on adjacent thermally unprotected tanks.

For this study, it is assumed that for a tank fire, the peak level of radiation intensity is not reached

suddenly. It will take some time for a tank fire to grow to full size. For fixed roof tanks, the roof will

have to be blown off before the full diameter fire can develop. Similarly, for floating roof tanks, a fire

initially starts as a rim fire. If this can be sensed and tackled immediately, spreading into a large fire can

be avoided. However, for the purpose of this study, a full tank fire has been considered.

Incident radiation intensity of 4 kW/m² on a public road beyond the perimeter of the facility has been

specified as the criterion to judge the acceptability of the current layout under this scenario.

Explosion In the event of a flammable gas cloud being ignited, an explosion can occur. The resultant blast wave

will have damaging effects on plant and buildings failing within the overpressure contours. The human

body, can by comparison, withstand higher overpressure. However, injury can occur from collapse of

buildings or structures.

Explosion overpressure damage effects relating to building type are shown in Table 4.3.

Table 4.3: Damage effects of blast overpressure

Building type Overpressure

(psig)

Consequences

B1: Wood-frame trailer or

Shack

0.2 Onset of serious damage

1.0 Isolated building overturned; temporary building

complexes partially destroyed.

B2: Steel Frame / metal

siding or pre-engineered

building

>1.5 Sheeting is ripped off. Internal walls damaged.

>2.5 Cladding & walls damaged, but building frame

stands.

>5.0 Complete building collapse.

B3: Un-reinforced

masonry bearing wall

building

1.0 Walls collapse.

1.5 Total building collapse.

B4: Steel or concrete

framed with reinforced

masonry infill or cladding

1.0 Wall damage.

2.0 Roof slab may collapse.

2.5 Total building collapse.

B5: Reinforced concrete or

masonry shear building

2.0 Very minor damage.

4.0 Roof and walls will deflect under loading and internal

wall damage.

6.0 Major damage and possible collapse.




Page | 4.13

Damage effects due to 5 psi, 3 psi, 1 psi and 0.5 psi in terms of distance from the overpressure source

are used in this consequence analysis.

For overpressures of 5 psi or greater blast resistance will be required for buildings that are required to

survive the event (e.g. buildings providing refuge or performing shutdown/ emergency functions).

Buildings potentially experiencing pressures greater 0.5 psi should not have external glass.

Buildings located within the zone between the 5 psi overpressure and the 1 psi overpressure contours

may require some degree of blast protection. This should be assessed on a case by case basis by the

relevant building designer.

Toxic Release

The aim of the toxic risk study is to determine whether the operators in the plant, people in occupied

buildings and the public are likely to be affected by toxic substances. Toxic gas cloud dispersion to the

Immediately Dangerous to Life and Health Concentration (IDLH) limit is normally considered to

determine the extent of the toxic hazard created as the result of loss of containment of a toxic substance.

The IDLH values available in current NIOSH publication are used for consequence analysis.

In addition, the short term exposure limits currently specified in the Second Schedule of Factories Act,

“Permissible Levels of Certain Chemical Substances in Work Environment” are also considered in

consequence analysis mainly to identify the areas where awareness to the toxic hazard is to be

developed.

The toxic materials and concentrations used in consequence analysis are shown in Table 4.4.

Table 4.4: Toxicity values

Chemical

IDLH

Concentration

(ppm)

STEL

Concentration

(ppm)

Ammonia (NH3) 300 35

Carbon monoxide (CO) 1200 400

Chlorine (Cl2) 10 3

Hydrogen sulphide (H2S) 100 15

Sulphur dioxide (SO2) 100 5

In the scope of the present study for mounded bullet project, toxic gas dispersion is not significant.




Page | 4.14

Consequence Analysis General Input to PHAST

Consequence analysis is carried out using the current version 6.7 of PHAST software package of DNV.

The study file for consequence analysis will be basically the same as that used for QRA by PHAST

Risk. The input data for materials and process conditions will be the same for the models.

Weather parameters considered for consequence analysis are listed in Table 4.5.

Table 4.5: Weather Parameters for Consequence Analysis

Wind speed, m/s 3 5

Atmospheric stability class D D

Ambient temperature, C 30 30

Relative humidity, % 80 80

Results of consequence analysis such as intensity radii for jet fire and pool fire, flash fire envelope,

explosion overpressure radii and toxic cloud footprint are plotted on the site map. In addition, tabular

results are also provided as output from PHAST.




Page | 5.1

5. STUDY INPUTS

The total data requirement for QRA can broadly be put in five categories as under:

Plant data

Generic failure rate data

Population data

Meteorological data

Ignition source data

5.1 Plant Data

QRA study conducted is based on the data available from current engineering documents developed for

the Mounded Bullet Project in IOCL Guwahati Refinery. These documents are listed in Table 5.1.

Table 5.1: Reference Documents

Sr. No Document / Drawing Document Drawing No.

1 Facilities Description Provided by IOCL

2 Process Flow Diagrams PC00118-07-0045 Rev-0

3 Material Balance ---

4 Piping & Instrumentation Diagrams PC118-07-0021 Rev-0

5 Plot plan/ Equipment Layout PC000118-5111-07-0001 Rev-1

6 Layout Plan of Guwahati Refinery TS-00-150 Rev-19




Page | 5.2

5.2 Generic Failure Rate Data

Generic leak frequency data published by International Association of Oil & Gas Producers (OGP) are

used in this QRA study. An extract from OGP Risk Assessment Data Directory - Report No. 434 (March

2010) used in present study is reproduced in the Table 5.2.

Table 5.2: Failure Frequencies (OGP Data)

Equipment Overall Failure Frequency [per year]

Equipment/ Item

Minor Leak Medium Leak Major Leak Full bore

Rupture Total

[ 3 mm] [10 mm] [25 mm] [100 mm] [>100 mm]

Process Pipe < 2" 9.00E-05 3.80E-05 2.70E-05 1.6 E-4

Process Pipe < 6" 4.10E-05 1.70E-05 7.40E-06 7.60E-06 7.3 E-5

Process Pipe < 12" 3.70E-05 1.60E-05 6.70E-06 1.40E-06 5.90E-06 6.7 E-5

Flanges < 2" 4.40E-05 1.80E-05 1.50E-05 7.7 E-5

Flanges < 6" 6.50E-05 2.60E-05 1.10E-05 8.50E-06 1.1 E-4

Flanges < 12" 9.60E-05 3.90E-05 1.60E-05 3.20E-06 7.00E-06 1.6 E-4

Manual Valves < 2" 4.40E-05 2.30E-05 2.10E-05 8.8 E-5

Manual Valves < 6" 6.60E-05 3.40E-05 1.80E-05 1.10E-05 1.3 E-4

Manual Valves < 12" 8.40E-05 4.30E-05 2.30E-05 6.30E-06 7.80E-06 1.6 E-4

Actuated Valves < 2" 4.20E-04 1.80E-04 1.10E-04 7.1 E-4

Actuated Valves < 6" 3.60E-04 1.50E-04 6.60E-05 3.30E-05 6.1 E-4

Actuated Valves < 12" 3.30E-04 1.40E-04 6.00E-05 1.30E-05 1.80E-05 5.6 E-4

Instrument Connections 3.50E-04 1.50E-04 6.50E-05 5.7 E-4

Process (Pressure) Vessels 9.60E-04 5.60E-04 3.50E-04 2.80E-04 2.2 E-3

Pumps - Centrifugal 5.10E-03 1.80E-03 5.90E-04 1.40E-04 7.6 E-3

Pumps - Reciprocating 3.30E-03 1.90E-03 1.20E-03 8.00E-04 7.2 E-3

Compressor-Reciprocating 4.50E-02 1.70E-02 6.70E-03 2.00E-03 7.1 E-2

Heat Exchanger 2.20E-03 1.10E-03 5.60E-04 2.60E-04 4.1 E-3

Coolers 1.00E-03 4.90E-04 2.40E-04 1.10E-04 1.8 E-3

Filters 2.00E-03 1.00E-03 5.20E-04 2.60E-04 3.8 E-3




Page | 5.3

5.2.1 The Approach to Calculate Failure Frequency

First calculate the failure frequencies for each leak size and then create a table for each of the

failure case

For each case, record the number of each type of item.

Insert the failure frequencies for each type of item.

Multiply by the number of items to obtain the frequency for each item type and leak size.

Sum the frequencies for each leak size over all the items to give the case frequencies.

For this study the whole plant is divided into number of sections. The philosophy is to consider

isolatable sections. Once the items counts are completed, frequency analysis is performed for different

hole sizes envisaged in each process section.

The Assumption Sheet summarizing the parameters forming basis for this QRA study is presented in

Attachment-I.

Details of the failure cases with estimated leak frequencies are presented in Attachment-II titled

“Failure Cases Input to PHAST RISK”.

Section No.

Section description

Material

Process conditions (pressure, temperature)

Inventory

Leak frequency for selected hole sizes




Page | 5.4

5.3 Meteorological Data

The consequences of releases of flammable materials into the atmosphere are strongly dependent upon

the rate at which the released material is diluted and dispersed to safe concentrations. The rate of

dispersion is dependent on the meteorological conditions prevailing at the time of release, particularly

the wind speed and the degree of turbulence in the atmosphere. The wind direction is also of importance

as it determines the direction in which the cloud of material will travel. Meteorological data are thus

required at two stages of the risk analysis. Firstly, various parts of the consequence modelling require

specification of wind speed and atmospheric stability. Secondly, the impact calculations require wind-

rose frequencies for each combination of wind speed and stability specified.

The primary requirement is to choose a suitable number of combinations of wind speed ranges and

stabilities for the dispersion modelling and thermal radiation calculations. These combinations must

reflect the full range of observed variations in these quantities; at the same time it is neither necessary

nor computationally efficient to consider every combination observed. The procedure used is therefore

to group these combinations into representative weather classes which together cover all conditions

observed. The classes chosen must be sufficiently different to produce significant variations in

dispersion modelling. These critical conditions are, in general, for short-duration releases, high wind

speed and, for long duration releases, low wind speed with stable stratification.

Whilst speed and direction are clear in definition, stability is not a widely used term. Stability is

determined by the temperature gradient in the lowest tens of metres of the atmosphere; this in turn

depends on the heating (in the day) or cooling (at night) at the ground and on the mean wind speed. The

stability determines the degree of turbulence in the atmosphere and hence of mixing-in of air to a

released gas cloud by ambient turbulence: very unstable conditions (occurring in the middle of a calm,

sunny day) lead to much turbulence and hence rapid dispersion while very stable conditions (occurring

on a clear night) inhibit turbulence and hence dispersion. Stability is conventionally classified by

Pasquill stability classes, denoted A to F.

Table 5.3 shows the typical split of Pasquill Stability categories according to surface wind speed and

atmospheric conditions.

Table 5.3: Definition of Pasquill Stability Classes

Surface Wind

Speed (m/s)

Insolation Day

Time

Night Sky

Strong Modera

te

Thinly

Overcast

<3/8

Cloud

< 2 A A/B - -

2-3 A/B B E F

3-5 B B/C D E

5-6 C C/D D D

> 6 C D D D




Page | 5.5

Atmospheric stability categories A (very unstable), D (neutral) and F (stable) are described below.

Category A (very unstable) occurs typically on a warm sunny day with light winds and almost cloudless

skies when there is a strong solar heating of the ground and the air immediately above the surface.

Bubbles of warm air rise from the ground in thermals. The rate of change (decline) of temperature with

height (lapse rate) is very high.

Category D (neutral) occurs in cloudy conditions or whenever there is a strong surface wind to cause

vigorous mechanical mixing of the lower atmosphere.

Category F (stable) occurs typically on a clear, calm night when there is a strong cooling of the ground

and the lowest layers of the atmosphere by long wave radiation. There is a strong inversion of

temperature (i.e. warm air over cold air).

The wind rose diagram for Guwahati is shown in Figure 5.1.

Figure 5.1: Wind Rose Diagram for Guwahati Refinery

The distribution of wind direction and wind speed established for this study is shown in Table 5.4.

Table 5.4: Meteorological Data (Day/Night)

Wind

speed Stability

Class

Temp RH Wind Direction (From)

(m/s) C % N NNE NE ENE E ESE SE SSE S SSW SW WSW W WNW NW NNW

1.5 D 30 80 0.04 0.03 0.12 0.02 0.03 0.00 0.00 0.00 0.03 0.03 0.02 0.01 0.04 0.01 0.03 0.01

3 D 30 80 0.01 0.02 0.09 0.02 0.01 0.00 0.00 0.00 0.01 0.01 0.01 0.00 0.03 0.01 0.01 0.00

Total 0.05 0.05 0.21 0.04 0.04 0.00 0.00 0.00 0.04 0.04 0.03 0.01 0.07 0.02 0.04 0.01




Page | 5.6

5.4 Population Data

This QRA study covers the fatality risk to people by exposure to flammable and toxic hazards.

The data for distribution of people in the plant area have been provided by IOCL. The population

distribution considered for Mounded Bullet Project QRA is shown in Table 5.5.

Table 5.5: Distribution of People in and around Mounded Bullets

S. No. Description No. of Persons

Day Night

1. Shift-in-Charge 1 1

2. Panel Operator - -

3. Field Operator 2 2

4. General Shift Officer 1 -

Outside Mounded Bullet Unit

5. LPG Pump House - -

6. Bulk Loading Control Room 2

7. Compressor House - -

8. L.P.G. Office - -

9. L.P.G. Operator Room 2 2

10. Switch Gera Room - -

11. Separator Area west side of Mounded

bullet area 1 1




Page | 5.7

Ignition Source Data

If a flammable release is not ignited immediately, then its chance of ignition is dependent upon the

presence of ignition sources that may be in the vicinity. The probability of immediate ignition, however,

is normally due to the nature of the release (e.g. a release due to external impact is likely to be ignited

immediately due to heat caused by friction). If an ignition source is not reached, or the ignition source is

insufficient to ignite the release, then the release will have no impact.

In order to address delayed ignition, PHAST RISK requires information about the distribution of

ignition sources in the vicinity of the plant, together with information about their ignition strength.

Several different types of ignition source are possible, such as fired heaters, boilers, workshops

(welding), motor vehicles and people.

Other ignition sources must be individually defined. Each source can be defined as a point source (e.g. a

boiler), an area source (e.g. a workshop) or a line source (e.g. a road). For every source the probability

of it being present at any given time must be defined along with its ignition strength. For example, a

fired heater in a refinery would be continuously present and would have a high probability of igniting a

flammable cloud as soon as the cloud passed over it.

The ignition sources defined in the Mounded Bullet area are shown in Table 5.6.

Table 5.6: Ignition Sources at Mounded Bullet area

Description

Ignition

Probability

(Fraction)

Operating

Probability

(Fraction)

Sub-Stations 0.4 1

Railway line 0.4 1

Switch Gear Room 0.4 1




Page | 6.1

6. RISK ANALYSIS RESULTS

6.1 Individual Risk

Figure 6.1.1 shows the iso–risk contours representing Location specific individual risk (LSIR) due to

Mounded Bullet project and its associated facilities on the next pages.

The highest risk contour in Mounded Bullet area is of 10-5

per year. However, this does not mean that

there is an intolerable risk to the workers in the above units. In fact the actual risk to any one worker will

be far less than the maximum in this area considering the fraction of time the individual is present there.




Page | 6.1

Figure 6.1.1: Iso-Risk Contours for Mounded Bullet Project – Overall




Page | 6.2

Figure 6.1.1a: Iso-Risk Contours for Mounded Bullet Project – Enlarge view




Page | 6.1

It is seen in the above figures that contour for 10-6

per year due to Mounded Bullet Project does not

extend beyond the refinery boundaries. As such, individual risk to members of the public is found to be

in ‘Broadly Acceptable (Negligible Risk)’ level.

The highest location-specific individual risk contour in Mounded Bullet area at IOCL Guwahati

Refinery is of 10-5

per year.

The maximum LSIR in this area are listed in Table 6.1.1.

Table 6.1.1: Maximum Location-Specific Individual Risk (LSIR) at Mounded Bullet area

SR.

NO. AREA / UNIT

MAXIMUM LSIR

(PER YEAR)






6. LPG Operator Room 1.0 E-06

7. Bulk Loading Control Room 1.1 E-07




Page | 6.2

6.1.1 ALARP Summary & Comparison of Individual Risk with Acceptability Criteria

The Location Specific Risk (LSIR) i.e. risk to a person who is standing at that point 365 days a year and

24 hours a day. The people in plant are expected to work in 8 hour shift as well general shift. The actual

risk to a person “Individual Specific Individual Risk” (ISIR) would be far less after accounting the time

fraction a person spent at location.

ISIR Area = LSIR x (8/24)(8 hours shift) x (Time spend by an individual / 8 hours)

The comparison of maximum individual risk with the risk acceptability criteria is shown in Figure 4.1.

LPG Transfer Pump Area (New):

The maximum LSIR in this area is 3.4 x 10-5

per year. The personnel in this area work on 8 hour shift.

During the shift, an individual person is expected to be present close to the pump area for about 2 hours

on the average. The individual-specific individual risk (ISIR) is estimated as follows.

ISIR LPG Pump area = 3.4 x 10-5

x (8/24) x (2/8) = 2.83 x 10-6

per year

This is below the acceptable individual risk criteria (10-5

per year) and falls in the Broadly Acceptable

region.

Mounded Bullet Area:



During the shift, an individual person is expected to be present close to the mounded bullet area for

about 2 hours on the average. The individual-specific individual risk (ISIR) is estimated as follows.

ISIR Mounded Bullet area = 1.9 x 10-5

x (8/24) x (2/8) = 1.58 x 10-6

per year



region.

LPG Pump House (Existing):



During the shift, an individual person is expected to be present close to the pump area for about 2 hours

on the average. The individual-specific individual risk (ISIR) is estimated as follows.

ISIR LPG pump area = 1.5 x 10-6

x (8/24) x (2/8) = 1.25 x 10-7

per year



region.




Page | 6.3

Switch Gear Room:



During the shift, an individual person is expected to be present close to the switch gear room for about 2

hours on the average. The individual-specific individual risk (ISIR) is estimated as follows.

ISIR LPG pump area = 1.3 x 10-6

x (8/24) x (2/8) = 1.08 x 10-7

per year



region.

Compressor House:



During the shift, an individual person is expected to be present close to the compressor house for about 2

hours on the average. The individual-specific individual risk (ISIR) is estimated as follows.

ISIR Compressor house = 1.2 x 10-6

x (8/24) x (2/8) = 1.0 x 10-7

per year



region.

The maximum ISIR in the units are listed in Table 6.1.2.

Table 6.1.2: Maximum Individual-Specific Individual Risk (ISIR)

SR.

NO. AREA / UNIT

MAXIMUM ISIR

(PER YEAR)






From the results shown above, the maximum individual risk to plant personnel at Mounded Bullet

Project is estimated as 2.83 x 10-6

per year. This is below the acceptable individual risk criteria (10-5

per

year) and falls in the Broadly Acceptable region.




Page | 6.4

ALARP Summary & Comparison of Individual Risk with Acceptability Criteria

The objective of this QRA study is to assess the risk levels due to Mounded Bullet project with reference

to the defined risk acceptability criteria and recommend measures to reduce the risk level to as low as

reasonably practical (ALARP).

The comparison of maximum individual risk with the risk acceptability criteria is shown in Figure 6.1.2.

The individual risk to members of the public is in middle part of Broadly Acceptable region (Negligible

Risk)

The individual risk of 2.83 x 10-6

per year for plant personnel at Mounded Bullet is in the Broadly

Acceptable region.

Figure 6.1.2: Individual Risk

Max. Individual Risk to Worker: 2.83 E-06 per year

Max. Individual Risk to Public: < 1.0 E-06 per year

(Negligible Risk)




Page | 6.5

6.2 Societal Risk

The Societal Risk parameter for Mounded Bullet Project is shown in Figures 6.4 in the form of an FN

curve.

The results of FN curves show that the risk is in “Broadly Acceptable (Negligible Risk)” region.

Figure 6.2.1: FN Curve for Group Risk at Mounded Bullet




Page | 6.6

6.2.1 Top Risk Contributors (Group Risk)

The significant risk contributions from equipment in the Mounded Bullet project based on results

available from PHAST Risk are shown in Table 6.2.1.

Table 6.2.1: Top Risk Contributors

SR.

NO. Area / Unit

Risk Contribution

(%)






5 Mounded Bullet (T-103C) liquid outlet to pump








Page | 7.1

7. CONSEQUENCE ANALYSIS

7.1 Scenarios

The scenarios for consequence analysis have been identified as listed in Table 7.1.1.

Table 7.1.1: Scenarios

Case

No. Description Jet Fire

Pool

Fire

Flash

Fire VCE

1. LPG Mounded Bullets - Inlet

Piping – 25mm Leak

2. LPG Mounded Bullets - to LPG

pump Suction piping – 25mm Leak

3. LPG Transfer Pumps discharge –

25mm Leak

4. Mounded bullet Inlet / Outlet line

valve flange leak – 10 mm Leak

Consequence Analysis Results

Results of the consequence analysis for the scenarios covered in this study are summarized in Table

7.1.2. The Consequence analysis Graph are placed in Attachment-III




Page | 7.1

Table 7.1.2 Consequence Analysis - Scenario Result

Case

No. Case Description

Wind

speed &

Pasquill

stability

Flash fire

distance

Jet fire Thermal radiation

distances (m)

Pool fire Thermal

radiation distances (m) Overpressure distances (m)

(m) 37.5

kW/m2

12.5

kW/m2

4

kW/m2

37.5

kW/m212.5

kW/m24

kW/m2 0.5 psi 1 psi 3 psi 5 psi

1

LPG Mounded

Bullets - Inlet Piping

– 25mm Leak

3D 44.33 9.19 13.50 23.68 14.27 20.37 30.65 16.25 10.60 - -

5D 38.83 8.77 13.38 23.59 15.66 20.99 30.00 15.36 10.16 - -

2

LPG Mounded

Bullets - to LPG

pump Suction piping

– 25mm Leak

3D 74.95 19.42 25.60 44.10 20.61 30.67 47.35 17.69 11.31 - -

5D 61.81 18.16 25.38 43.89 22.60 31.78 46.77 17.14 11.04 - -

3

LPG Transfer Pumps

discharge – 25mm

Leak

3D 73.50 18.32 24.41 42.18 16.03 23.26 35.33 17.36 11.15 - -

5D 60.91 17.13 24.21 42.00 17.69 24.16 34.90 16.87 10.91 - -

4

Mounded bullet Inlet /

Outlet line valve

flange leak – 10 mm

Leak

3D 38.44 3.0 10.33 18.44 13.94 19.84 29.79 16.34 10.54 - -

5D 34.01 6.14 10.26 18.40 15.06 20.04 28.54 15.06 10 - -




Page | 8.1

8. CONCLUSIONS & RECOMMENDATIONS

The maximum risk to persons working in the Mounded Bullet area is 2.83 x 10-6

per year which is in

Broadly Acceptable level (refer red band in risk acceptability criteria).

The risk to Public is in due to the proposed mounded bullet project is in “Broadly Acceptable level”.

Societal risk is also in “Broadly Acceptable Level”.

The high risk contributors in the unit are due to LPG pump discharge leakage followed by leakage from

pump suction side. Mounded bullets provide high level of safety for storage of LPG as they are not

susceptible to hazards of catastrophic failure and Fire ball / BLEVE.

The following recommendations are made to keep the risk level in broadly acceptable level.

8.1 Recommendations

1. It is necessary to provide extensive fire and gas detection system in the Mounded Bullets and

LPG transfer pump area. Philosophy for operation of fire and gas detection system to isolate the

relevant sections should be clearly defined and the operating personnel should be trained for

proper use of this safety system.

2. It is recommended to have necessary provision for emergency stop of LPG transfer pumps from

control room in the event of major leak / flash fire there should be an SOP established for clarity

of actions to be taken in case of fire / leak emergency.

3. The emergency response plan of the refinery to be updated to cover the new Mounded bullet

Project.

4. Liquid outlet line from the bottom of mounded bullet is shown with flanged ROV. In case of

leakage from downstream flange ROV can be closed to stop the leakage however if leakage from

upstream flange, leak duration is much longer and increasing the likelihood of jet /pool fire then

exposed the bullet to external fire thus defeating the purpose of mounded bullet. Therefore it is

recommended that ROV with flange end fitted in pipe line shall be Spiral Wound metallic gasket

or RTJ gasket as per OISD STD-150.

Attachment – I

Assumption Sheets

GUWAHATI REFINERY –

QUANTITATIVE RISK ASSESSMENT

Document Number IRCA-IOCL-QRA-20171808-02 Rev 0 Jan 2018

Page 1 of 11

QRA ASSUMPTION SHEET

Project No: 20171808 Project Title: Guwahati Refinery – Mounded Bullet Project

Assumption No: QRA-001 Subject: Study basis

STUDY BASIS

Drawings and Documents The QRA study is based/or referenced on the following drawings/ Documents.

Sr. No Document / Drawing Document/ Drawing No.

1 Facilities Description Provided by IOCL

2 Process Flow Diagrams PC00118-07-0045 Rev-0

3 Material Balance ---

4 Piping & Instrumentation Diagrams PC118-07-0021 Rev-0

5 Plot plan/ Equipment Layout PC000118-5111-07-0001 Rev-1

6 Layout Plan of Guwahati Refinery TS-00-150 Rev-19

Justification/ Comments:

Approvals

CONTRACTOR Representative R. Krishnan, Principal Engineer, IRCA

OWNER Representative




Page 2 of 11



Assumption No: QRA-002 Subject: Software tools

SOFTWARE TOOLS Following software tools are used for this QRA

PHAST RISK - 6.7 (DNV Software, UK) for Onshore QRA Software

PHAST – 6.7 (DNV Software, UK) for Consequence analysis

Justification/ Comments: IRCA has the current version PHAST 6.7 under AMC with DNV Software.

Approvals






Page 3 of 11



Assumption No: QRA-003 Subject: Generic Database for leak frequency and leak sizes

LEAK FREQUENCY Following leak frequency database is used for this QRA

OGP Risk Assessment Data Directory - Report No. 434 (March 2010) LEAK SIZE

Leak Type Representative hole Size (mm)

Small leak 3

Medium leak 10

Large leak 50

Rupture 100

Justification/ Comments: The leak sizes considered for QRA are aligned with the leak sizes available in OGP Risk Assessment Data Directory - Report No. 434 (March 2010) The above leak sizes correspond to Pin hole leak, Flange leak, Large leak and Rupture.

Approvals






Page 4 of 11



Assumption No: QRA-004 Subject: Impact criteria for thermal radiation from jet fire/ pool fire & Impact criteria for explosion overpressure

THERMAL RADIATION CRITERIA

Event Description

Thermal radiation intensity

Effect

Jet fire / Pool fire 4 kW/m2 Heat instantly in areas where emergency actions lasting several minutes may be required by the personnel without shielding but appropriate clothing.

12.5 kW/m2 Significant chances of fatality for extended exposure. High chance of injury

37.5 kW/m2 Significant chances of fatality for people exposed instantaneously.

Flash fire LFL concentration Fatal for the people in the flammable cloud path.

EXPLOSION ANALYSIS CRITERIA

Event Description

Overpressure value

Effect

Explosion overpressure

0.5 psi Breakage of glass windows

1 psi Wall damage.

3 psi Cladding & walls damaged, but building frame stands.

5 psi Major damage and possible collapse.

TOXIC EXPOSURE CRITERIA The probability of death at toxic levels greater than the Toxic Damage Threshold (TDT) is assumed to be 1.0. The probability at toxic level less than the TDT is assumed to be 0.


Approvals






Page 5 of 11



Assumption No: QRA-005 Subject: Release rate, Release orientation and Elevation of release

RELEASE RATE Release rate for various releases will be calculated by the software based on the process data and leak size input. RELEASE ORIENTATION For liquid release orientation will be down impinging on ground and for gas it will be horizontal ELEVATION OF RELEASE As applicable (will be taken from vessel elevation drawing)


Approvals






Page 6 of 11



Assumption No: QRA-006 Subject: Ignition sources & ignition probability

IGNITION SOURCES The following ignition sources will be defined from site plan

1. Points such as fired heaters 2. Areas such as electrical substations/ transformers 3. Electrical lines such as HT overhead lines) 4. Transportation lines such as roads, railway lines

IMMEDIATE IGNITION PROBABILITY When modeling in PHAST, the probability of immediate ignition will be specified as “Use Event Trees”.

Justification/ Comments: Ignition sources will be strictly controlled in the refinery. As the specific sources of ignition in the site plan, flammable effects will be realistically modelled by using event trees in PHAST.

Approvals






Page 7 of 11



Assumption No: QRA-007 Subject: Ignition Probabilities for QRA

IGNITION PROBABILITIES FOR HYDROCARBON RELEASES TO BE USED IN QRA

Release rate (kg/s)

Ignition Probability

LPG, Propane, Propylene, Hydrogen etc.

Naphtha/ Gasoline StorageDiesel/ Kerosene/ Fuel Oil/

Crude Storage

Release of flammable gas, vapour or liquid significantly above normal boiling point

in large outdoor plants

Release of flammable liquid not having significant flash fraction if released in large

outdoor tank farm

Release of combustible liquid at ambient conditions (e.g. diesel, fuel oil) in large

outdoor tank farm & low pressure transfer system

1 0.0025 0.0020 0.0010

5 0.0125 0.0030 0.0010

10 0.0250 0.0040 0.0020

20 0.0500 0.0070 0.0030

50 0.1250 0.0200 0.0030

100 0.2500 0.0300 0.0030

200 0.5000 0.0500 0.0030

The ignition probabilities listed in Table above are total ignition probabilities, which can be considered as sum of probabilities of immediate ignition and delayed ignition. The probability of immediate ignition included in the above data is 0.001. For release in process units, probability of immediate ignition is considered as 0.01 based on the value specified in DNV Phast software. Event tree model option will be selected in Phast software with the definition of ignition sources in the plant layout.

Justification/ Comments: The ignition probabilities listed are taken from the following Data sheets available in the Report No. 434-6.1 dated March 2010 titled “Ignition Probabilities” published by International Association of Oil & Gas Producers (OGP).

Approvals






Page 8 of 11



Assumption No: QRA-008 Subject: Risk Criteria

RISK CRITERIA

Individual Risk Criteria The tolerability criteria for Individual Risk for use in QRA are proposed as follows:

1. Boundary between tolerable risk and unacceptable risk for members of the public: 1.0E-04 per year

2. Boundary between tolerable risk and unacceptable risk for workers: 1.0E-3 per year

3. Boundary between broadly acceptable risk and tolerable risk for members of public: 1.0E-06 per year

4. Boundary between broadly acceptable risk and tolerable risk for workers : 1.0E-05 per year

The criteria for individual risk are shown in the following diagram.

(Negligible

Risk)




Page 9 of 11

RISK CRITERIA

Societal Risk Criteria The tolerability criteria for Societal Risk for use in QRA are proposed as :

Justification/ Comments: The proposed criteria for individual risk and societal risk are those specified by UK Health & Safety Executive (UK-HSE) in their following documents:

Reducing Risks, Protecting People – HSE’s decision-making process (known as R2P2 document) – Please refer to paragraphs 130, 132 and 136.

Guidance on ALARP decisions in control of major accident hazards (SPC/Permissioning/12) - Please refer to paragraphs 18, 19, 35 and 36.

According to UK-HSE guideline available in the above documents, the upper boundary between Unacceptable and ALARP region passes through the point represented by N = 50 and F = 2.0E-04, and has slope of (-)1. The lower boundary between ALARP and Broadly Acceptable region is 2 orders of magnitude below the upper boundary.

Approvals



(Negligible

Risk)

(Negligible Risk)




Page 10 of 11



Assumption No: QRA-009 Subject: Weather/ Meteorological Data for QRA

WEATHER AND WIND ROSE DATA FOR GUWAHATI REFINERY TO BE USED IN QRA

Wind

speed Stability

Class

Temp RH Wind Direction (From)

(m/s) C % N NNE NE ENE E ESE SE SSE S SSW SW WSW W WNW NW NNW

1.5 D 30 80 0.04 0.03 0.12 0.02 0.03 0.00 0.00 0.00 0.03 0.03 0.02 0.01 0.04 0.01 0.03 0.01

3 D 30 80 0.01 0.02 0.09 0.02 0.01 0.00 0.00 0.00 0.01 0.01 0.01 0.00 0.03 0.01 0.01 0.00

Total 0.05 0.05 0.21 0.04 0.04 0.00 0.00 0.00 0.04 0.04 0.03 0.01 0.07 0.02 0.04 0.01


Approvals






Page 11 of 11



Assumption No: QRA-010 Subject: Population outside the INDAdeptG unit area

The data for distribution of people in the plant area have been provided by IOCL. The population distribution considered for Mounded Bullet Project is as follows

S. No. Description No. of Persons

Day Night

1. Shift-in-Charge 1 1

2. Panel Operator - -

3. Field Operator 2 2

4. General Shift Officer 1 -

Outside Mounded Bullet Unit

5. LPG Pump House - -

6. Bulk Loading Control Room 2

7. Compressor House - -

8. L.P.G. Office - -

9. L.P.G. Operator Room 2 2

10. Switch Gera Room - -

11. Separator Area west side of Mounded

bullet area 1 1


Approvals



Attachment – II

Failure Cases Input to QRA

Mounded Bullet Project:-

Section

No. Section Name Section Description Material Phase

Pressure

kg/cm2 g

Temperature

˚C

Inventory

(m3)

Failure Frequency

3mm

Leak

10mm

Leak

50mm

Leak

100 mm

Leak

1 LPG Mounded Bullets -

Inlet Piping 07-T-103C/D LPG Liquid 15 30 0.5 5.04E-04 1.59E-04 4.48E-05 -

2 LPG Mounded Bullets - to

LPG pump Suction piping 07-T-103C/D LPG Liquid

Sat.

Liquid 30 1.5 5.35E-04 1.70E-04 4.96E-05 1.70E-07

3 LPG Transfer Pumps

discharge 07-P-103C/D LPG Liquid 15 40 0.5 9.00E-04 2.74E-04 6.17E-05 7.50E-06

Attachment – III

Consequence Analysis Graph

1

QRA Report for Mounded Bullet Project at IOCL Guwahati Refinery

Consequence Analysis Results – Graphs

Scenarios

Case No. Description

1. LPG Mounded Bullets - Inlet Piping -

25 mm Leak (Liquid)

2. LPG Mounded Bullets - to LPG pump

Suction piping - 25 mm Leak (Liquid)

3 LPG Transfer Pumps discharge - 25 mm

Leak (Liquid)

4 Mounded bullet Inlet / Outlet line valve

flange leak – 10 mm Leak

Weather Parameters:

Wind Speed 3 m/s; Stability D

Wind Speed 5 m/s; Stability D

2

1: LPG Mounded Bullets - Inlet Piping - 25 mm Leak (Liquid)

Weather: Wind speed 3 m/s; Stability D

Flash Fire on map

Intensity radii for jet fire on map

3

Pool fire on Map

Explosion overpressure on map

4


Flash Fire on map


5

Pool Fire on Map


6

2: LPG Mounded Bullets - to LPG pump Suction piping - 25 mm Leak

(Liquid)


Flash Fire on map


7

Intensity radii for Pool fire on map


8


Flash Fire on map


9



10

3: LPG Transfer Pumps DISCHARGE


Flash Fire on map


11



12


Flash Fire on map


13



14

4: LPG Mounded bullet Inlet / Outlet line valve flange leak – 10 mm Leak


Flash Fire on map


15

Pool fire on Map


16


Flash Fire on map


17

Pool Fire on Map
