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RISK ASSESSMENT STUDY FOR INDMAX UNIT:

[�� ] Page 1

EXECUTIVE SUMMARY

Introduction

IOCL Guwahati Refinery has plans to Revamp INDMAX Unit from 0.1MMTPA to 0.15

MMTPA at their existing refinery complex. INDMAX unit is installed to maximize LPG and

light olefin production from heavy petroleum fractions. INDMAX, Indane Maximization

Process, developed by Indian Oil Corporation Limited (IOCL) is similar to conventional FCC

process. In INDMAX, Coker Gasoline and heavy oils such as RCO, CFO are cracked to more

valuable light and middle distillates such as LPG, Gasoline and Diesel.

This document is prepared by Mantec Consultants Pvt. Ltd. for Risk Assessment (RA) of the

proposed revamp INDMAX Unit to identify the key hazards and risks. By conducting this

type of RA it should be emphasized that the focus is on the major, worst-case, hazards and

impacts from surrounding area of these units, essentially in order to prioritise the off-site

risks and potential impacts to the public.

Risk Criteria

Individual risks are the key measure of risk acceptability for this type of study, where it is

proposed that:

Risks to the public can be considered to be broadly acceptable (or negligible) if below 10-6

per year (one in 1 million years). Although risks of up to 10-4

per year (1 in 10,000 years)

may be considered acceptable if shown to be As Low As Reasonably Practicable (ALARP), it

is recommended that 10-5

per year (1 in 100,000 years) is adopted for this study as the

maximum tolerable criterion.

Risks to workers can be considered to be broadly acceptable (or negligible) if below 10-5

per

year and where risks of up to 10-3

per year (1 in 1000 years) may be considered acceptable if

ALARP.

Individual risk due to INDMAX revamp unit is below the ALARP regions.

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

INDMAX unit at Guwahati refinery are given in Figure-1.


[�� ] Page 2

Figure 1: Overall iso-risk Contours

The highest location-specific individual risk (LSIR) contour in INDMAX unit at Guwahati

refinery is of 1E-05 per year which is within the INDMAX unit.

The maximum LSIR in the units are listed in Table-1:

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

S. No. Unit Maximum LSIR

1. HDT/HGU field Operator room 6.57E-08

2. SRU block field Operator room 2.31E-08

3. INDMAX Field Operator room 1.14E-07

Individual risk to worker at INDMAX unit (ISIR):

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 INDMAX unit are expected to work 8

hour shift as well as 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 spent by and individual/8 hours)

The maximum ISIR in the units are listed in Table2.


[�� ] Page 3

Table-2: Maximum Individual Specific Individual Risk (ISIR) at INDMAX unit

S. No. Unit Maximum ISIR




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

unit is estimated as 3.8E-08 per year.

ALARP summary & comparison of Individual risk with acceptability criteria.

The objective of this QRA study is to assess the risk levels at INDMAX unit 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

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

unit is estimated as 3.8E-08 per year is lower part of ALARP region.


[�� ] Page 4

Figure-2: Individual risk at INDMAX unit

Societal risk criteria are also proposed, although these should be used as guidance only.

A criterion of 10-4

per year is recommended for determining design accidental loads for on-

site buildings, i.e. buildings should be designed against the fire and explosion loads that occur

with a frequency of 1 in 10,000 years.

The societal risk parameter for INDMAX unit is shown in Figure-3 in the form of FN curve.

The result from the FN curve show that the Societal risk due to INDMAX Unit is below the

ALARP Region which is broadly acceptable or negligible risk.

Figure-3: FN Curve for societal Risk at INDMAX unit at Guwahati Refinery

Top risk contributors (Group Risk):

The significant risk contributions from units in INDMAX unit based on result available from

PHAST are shown in Table-3.

Table -3 Top Risk contributors at INDMAX unit.

S.No. Scenario Societal risk

contribution (%)

1. Rupture in inlet line to stabilizer/Debutanizer C-06 52.09

2. Rupture from shell side of TCO CR/C2 Stripper Feed

Exchanger(E-06 A/B)

22.34


[�� ] Page 5

3. Leak from shell side of TCO CR/C2 Stripper Feed

Exchanger(E-06 A/B)

11.72

4. Rupture in TCO CR line to main fractionator column C-01 2.22

5. Leak in discharge line of LPG R/D Pump (P-15 A/B) 1.01

Conclusions and Recommendations

Although the results of this Risk analysis show that the risks to the public are broadly

acceptable (or negligible), they will be sensitive to the specific design and/or modeling

assumptions used.

The maximum risk to persons working in the INDMAX unit is 3.8x10-8

per year which is

below the unacceptable level and is in the lower part of ALARP triangle.

It is observed that the iso-risk contour of 1x10-5

per year is within the INDMAX unit and the

risk contour of 1x10-6

per year extended to the adjoining facilities on South East direction

which have storage tankage and SRU unit.

The high risk contributors in the INDMAX unit are Stabilizer/Debutanizer and TCO CR/C2

Stripper Feed exchanger (E-06A/B).

The major conclusions and recommendations based on the risk analysis of the identified

representative failure scenarios are summarized below:

� The individual risk from all scenarios is found below the ALARP region for Employee

and Public for INDMAX unit.

� The INDMAX unit of Guwahati refinery is covered in the process safety management

system of Guwahati refinery.

� Mitigate the risk by preventing toxic cloud travelling beyond the plant boundary in

South West side but the concentration of Hydrocarbons beyond the boundary is very

low, therefore no specific mitigation measures are required for that point.

� Smoking booths existing in non hazardous area.

� Gas detectors are provided at critical locations. Operators are well trained about the fire

and gas detection systems.

� Emergency stop of critical equipments are available in control room.

� CCTV coverage with perimeter monitoring available.

� The vehicles entering the refinery should be fitted with spark arrestors.

� Routine checks to be done to ensure and prevent the presence of ignition sources in the

immediate vicinity of the refinery (near boundaries).

� Clearly defined escape routes shall be developed for each individual plots and section of

the INDMAX unit taking into account the impairment of escape by hazardous releases

and sign boards be erected in places to guide personnel in case of an emergency.

� Well defined muster stations in safe locations shall be identified for personnel in case of

an emergency.

� Windsocks existing in all prominent locations with clear visibility.


[�� ] Page 6

� Identificatio of critical equipments done & inspection methodologies existing for

inspection during shutdown.

� The active protection devices like fire water sprinklers and other protective devices

shall be tested at regular intervals.

� SOP should be established for clarity of actions to be taken in case of fire/leak

emergency.

General Recommendations:

1. Nearest tank of INDMAX Unit is T-23, T-15, T-16 and T-28 TANK ON FIRE could

affect adjacent tanks in same dyke. Also heat radiations from the tank on fires will

slightly affect the INDMAX Unit but the intensity is not so high to cause major

damage to the unit. Fixed water sprays system is available on all nearest tanks,

irrespective of diameter where inter distances between tanks in a dyke and/or within

dykes are not meeting the requirements of OISD-STD-118.

2. Ensure that combustible flammable material is not placed near the Critical instrument

of the INDMAX Unit. These could include oil filled cloths, wooden supports, oil

buckets etc. these must be put away and the areas kept permanently clean and free

from any combustibles. Secondary fire probability would be greatly reduced as a

result of these simple but effective measures.

3. Sprinklers and foam pourers provided. Monitors & hydrants located at a distance

more than 15 meters.

4. ROSOV and Hydrocarbon detectors to be provided with the nearest tank of the

INDMAX unit.

5. Since Refinery operation is being done 24 Hrly. Lighting arrangements are available

in line.

**********

RISK ASSESSMENT STUDY FOR INDMAX UNIT

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Table of Contents

CHAPTER-1: INTRODUCTION ................................................................................................................. 5

1.1 Introduction ........................................................................................................................................ 5

1.2 Scope of Study .................................................................................................................................... 6

1.3 Execution Methodology ...................................................................................................................... 7

1.3.1 Kick off meeting with Mantec: .................................................................................................... 7

1.3.2 Study of IOCL operations ............................................................................................................ 7

1.3.3 Study of IOCL operating parameters ........................................................................................... 7

1.3.4 Identification of hazards............................................................................................................... 7

1.3.5 Consequence Effects Estimation .................................................................................................. 7

CHAPTER-2: PROJECT DESCRIPTION ................................................................................................... 8

2.1 Introduction ......................................................................................................................................... 8

2.2 INDMAX unit detail ........................................................................................................................... 8

2.3 Site Condition ..................................................................................................................................... 9

2.3.1 Site Location and Vicinity ........................................................................................................... 9

2.3.2 Population .................................................................................................................................. 10

2.3.3 Ignition Source ........................................................................................................................... 10

2.3.4 Meteorological Condition .......................................................................................................... 10

2.4 Tank detail ........................................................................................................................................ 14

CHAPTER: 3 IDENTIFICATION OF HAZARD AND SELECTION OF SCENARIOS ........................ 15

3.0 Hazard identification ......................................................................................................................... 15

3.1 Hazards associated with the refinery ................................................................................................ 16

3.2 Hazards Associated with Flammable Hydrocarbons ........................................................................ 16

3.2.1 Liquefied Petroleum Gas ........................................................................................................... 16

3.2.2 Hydrogen .................................................................................................................................... 17

3.2.3 Naphtha and Other Heavier Hydrocarbon...................................................................................... 18

3.3 Hazard Associated with Toxic/Carcinogenic materials .................................................................... 18

3.3.1 Hydrogen Sulfide ....................................................................................................................... 18

3.3.2 Chlorine ...................................................................................................................................... 19

3.3.3 Ammonia .................................................................................................................................... 19


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3.4 Selected Failure Cases ...................................................................................................................... 20

3.5 Hazard identification as per NFPA ................................................................................................... 24

3.6 Characterizing the failures ................................................................................................................ 26

3.7 Operating Parameters ........................................................................................................................ 26

3.7.1 Inventory .................................................................................................................................... 26

3.7.2 Loss of Containment .................................................................................................................. 27

3.7.3 Liquid Outflow from a vessel/ line ............................................................................................ 27

3.7.4 Vaporization ............................................................................................................................... 27

CHAPTER-4 RELEASE CONSEQUENCE ANALYSIS.......................................................................... 28

4.1 GENERAL ........................................................................................................................................ 28

4.2 Consequence Analysis Modeling ...................................................................................................... 28

4.2.1 Discharge Rate ........................................................................................................................... 28

4.2.2 Dispersion .................................................................................................................................. 28

4.2.3 Flash Fire ................................................................................................................................... 28

4.2.4 Jet Fire ........................................................................................................................................ 29

4.2.5 Pool Fire ..................................................................................................................................... 29

4.2.6 Blast Overpressures.................................................................................................................... 31

4.2.7 Toxic Release ............................................................................................................................. 32

4.3 Size and duration of release .............................................................................................................. 32

4.4 Damage Criteria ................................................................................................................................ 32

4.4.1 LFL or Flash Fire ....................................................................................................................... 33

4.4.2 Thermal Hazard Due to Pool Fire, Jet Fire ................................................................................ 33

4.4.3 Vapor Cloud Explosion .............................................................................................................. 33

4.5 Generic Failure Rate Data ................................................................................................................. 34

4.6 Plant Data .......................................................................................................................................... 35

4.7 Consequence analysis for INDMAX unit ......................................................................................... 36

4.7.1 Scenarios .................................................................................................................................... 36

CHAPTER- 5: RISK ANALYSIS .............................................................................................................. 47

5.1 Individual Risk .................................................................................................................................. 47

5.1.1 Individual risk acceptability criteria........................................................................................... 47

5.1.2 Location Specific Individual Risk (LSIR) ................................................................................. 51


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5.1.3 Individual Specific Individual Risk (ISIR) ................................................................................ 52

5.2 Societal Risk ..................................................................................................................................... 53

CHAPTER-6: COMPARISON AGAINST RISK ACCEPTANCE CRITERIA ........................................ 56

6.1 The ALARP Principle ....................................................................................................................... 56

CHAPTER-7: RECOMMENDATIONS FOR RISK REDUCTION ......................................................... 58

7.1 Conclusion and Recommendations ................................................................................................... 58

7.2 General Recommendations: ................................................................. Error! Bookmark not defined.

List of Table

Table 1: Unit and their production capacity GR ........................................................................................... 5

Table 2: Population Detail around INDMAX unit ...................................................................................... 10

Table 3: wind speed and wind direction (%) April-14 to June-14 .............................................................. 10

Table 4: Percentage of No. of days wind from various direction ............................................................... 11

Table 5: Average mean wind speed (m/s) ................................................................................................... 11

Table 6: Pasquill stability classes................................................................................................................ 13

Table 7: Weather parameters for consequence analysis ............................................................................. 13

Table 8: Tank details around INDMAX unit .............................................................................................. 14

Table 9 Hazardous Properties of LPG ........................................................................................................ 17

Table 10 Hazardous Properties of Hydrogen .............................................................................................. 17

Table 11: Hazardous Properties of Naphtha ............................................................................................... 18

Table 12: Toxic effects of Hydrogen Sulfide .............................................................................................. 18

Table 13: Toxic effect of chlorine............................................................................................................... 19

Table 14: Toxic effects of Ammonia .......................................................................................................... 19

Table 15: Selected failure case for INDMAX unit ..................................................................................... 20

Table 16: NFPA for MS and LPG .............................................................................................................. 24

Table 17: Explanation of NFPA classification ........................................................................................... 25

Table 18: Leak size of selected failure scenario ......................................................................................... 32

Table 19: Duration of release ...................................................................................................................... 32

Table 20: Effects due to incident radiation intensity .................................................................................. 33

Table 21: Damage due to Overpressures .................................................................................................... 34

Table 22: Failure frequency (OGP Data) .................................................................................................... 35

Table 23: List of documents used in study ................................................................................................. 35

Table 24: Major contributing risk scenario consequence table .................................................................. 36

Table 25: Scenarios for the consequence analysis ...................................................................................... 36

Table 26: Major contributing risk scenario Consequence Analysis result .................................................. 39

Table 27: Consequence Analysis – Scenario result .................................................................................... 40

Table 28: Acceptable Risk Criteria of various countries ............................................................................ 47

Table 29: Maximum LSIR at INDMAX unit .............................................................................................. 51


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Table 30: Maximum ISIR at INDMAX unit ............................................................................................... 52

Table 31: Top Risk Contributors at INDMAX unit .................................................................................... 55

List of Figure

Figure 1: Risk Assessment methodology ...................................................................................................... 6

Figure 2: Wind Rose diagram of Guwahati refinery ................................................................................... 12

Figure 3: Overall ISO-Risk Contour ........................................................................................................... 49

Figure 4: Enlarged Iso-Risk Contours for INDMAX unit .......................................................................... 50

Figure 5: Enlarged Iso-Risk Contours for INDMAX unit .......................................................................... 51

Figure 6: ALARP summary of INDMAX unit ........................................................................................... 53

Figure 7: Societal Risk Criteria ................................................................................................................... 54

Figure 8: FN Curve for Group Risk at INDMAX unit................................................................................ 55

Figure 9: ALARP Detail ............................................................................................................................. 57


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CHAPTER-1: INTRODUCTION

1.1 Introduction

Guwahati Refinery is one of the eighth operating refineries owned by Indian Oil Corporation

Limited. The crude oil processing capacity of Guwahati refinery is 1 MMTPA. Unit and their

installation capacity of Guwahati refinery is given in Table-1.

Table 1: Unit and their production capacity GR

Units Installed Capacity (MMTPA)

CDU 1

DCU 0.33

NSF 0.13

HDT 0.66

HGU 10 TMTA

SRU 5 TPD

INDMAX 0.1

MSQ 0.05

The main products currently manufactured in Guwahati Refinery are:

� Liquefied Petroleum Gas (LPG)

� Motor Spirit (MS)

� Superior Kerosene Oil (SKO)

� Aviation Turbine Fuel (ATF)

� High Speed Diesel (HSD)

� Light Diesel Oil (LDO)

� Sulphur (S)

� Low Sulphur Heavy Stock (LSHS)

� Raw Petroleum Coke (RPC)

The other facilities consist of Crude oil, intermediate and product tanks, Captive Power Plant

(CPT) Hydrogen and Nitrogen storage bullets, tank wagon loading /unloading gantry, tank

truck loading/ unloading gantries, LPG storage and dispatch facilities. There is a well

equipped Laboratory and a modern effluent treatment plant besides fresh water supply from the

river Brahmaputra to the Refinery and other end users.


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1.2 Scope of Study

Mantec Consultants Pvt. Ltd, D-36, Sector-6, NOIDA (U.P.) is appointed for carrying out the

Quantitative Risk Analysis study. The objective of the Quantitative Risk Analysis study is to

identify vulnerable zones, major risk contributing events, understand the nature of risk posed to

nearby areas and form a basis for the Emergency Response Disaster Management Plan or

ERDMP. In addition, the Quantitative Risk Analysis study is also necessary to ensure

compliance to statutory rules and regulations. Risk assessment methodology is given in Figure-1.

Risk Analysis broadly comprises of the following steps:

� Project Description

� Identification of Hazards and Selection of Scenarios

� Effects and Consequence Calculations

� Risk Summation (Risk calculation)

� Risk assessment(using an acceptability criteria)

� Risk Mitigation Measures

Figure 1: Risk Assessment methodology


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1.3 Execution Methodology

The methodology adopted for executing the assignment is briefly given below:

1.3.1 Kick off meeting with Mantec:

This was used to set the study basis, objectives and related matters and also identify in detail the

facilities to be covered in the RA.

1.3.2 Study of IOCL operations

This was carried out for studying the risk assessment study at Guwahati Refinery.

1.3.3 Study of IOCL operating parameters

This involved collection of pertinent project information on the operation process details such as

P&ID’s, PFD and Plant Layout. Critical instruments their temperature and pressure and other

details. The data so collected would ensure a more realistic picture for the risks subsequently

identified and estimated.

1.3.4 Identification of hazards

This includes estimation of possible hazards through a systematic approach. It typically covers

identification and grouping of a wide ranging possible failure cases and scenarios. The scenario

list was generated through generic methods for estimating potential failures (based on historical

records based on worldwide and domestic accident data bases) and also based on IOCL’s

experience in operating the facilities.

1.3.5 Consequence Effects Estimation

This covers assessing the damage potential in terms of heat radiation.


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CHAPTER-2: PROJECT DESCRIPTION

2.1 Introduction

INDMAX is a high severity catalytic cracking process developed by IOC R&D to produce very

high yield of light olefins, high octane gasoline from various hydrocarbon fractions. Flow

scheme in the INDMAX unit is similar to that in a conventional Fluidized Catalytic Cracking

(FCC) unit. The unit was designed to process residual feed comprising of Reduced Crude Oil

(RCO), Coker Fuel Oil (CFO) and Coker Gasoline (CG). Since then, the unit is under normal

operation giving a tangible benefit to the refinery. This unit has been operated under both LPG

and gasoline mode as per the requirement.

2.2 INDMAX unit detail

INDMAX unit consists of the following sections:

� Feed Storage and Pumping Section

� Reaction and Regeneration Section

� Fractionation Section

� Gas Concentration Section

� LPG/ Gasoline Treatment Section

RCO and CFO will be preheated to 180-220 °C in heat exchanger with steam. Preheated feed

will contact catalyst at 700 °C in the riser. On contact with catalyst feed will get cracked to

lighter HC’s and the final temperature will be 585 °C. Cracked vapors will be separated from

catalyst in the riser and reactor cyclone. Vapors from riser cyclone will go to main column via

vapor line where separation of HC’s in the various streams will take place.

Main column over heads are separated into Gas, LPG and Gasoline in the Gas Concentration

section consists of wet gas compressor four columns and set of exchangers and vessels etc. LPG

and Gasoline are caustic washed to remove H2S and then water washed to remove entrained

caustic. Diesel withdrawn from the column goes to diesel pool as well as for flushing oil after

stripping in stripping column.

Main part of the main column bottom is recycled to column as quench and wash. Rest of the

bottom materials is clarified in either slurry settler or slurry filter and sent to tanks as clarified

oil.

Catalyst from reactor stripper after stripping out entrained HC’s gets back into the regenerator

through spent catalyst standpipe. Spent catalyst is regenerated in the regenerator by combustion

of coke formed on the catalyst with air. Specially designed air grid ensures uniform distribution

of air in the regenerator. Air blower supplies air for coke burning. Regenerated catalyst travels

back to riser through regenerated catalyst standpipe.


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Combustion gases form the regenerator at temperature of 730 °C with catalyst enters regenerator

primary and secondary cyclone to knock down the catalyst. Hot flue gases from regenerator

passes through Double Disc Slide Valve to the Orifice Chamber where the pressure of the gases

is reduced from 2.5 kg/cm2 to 0.2 kg/cm

2. Heat of hot flue is removed in WHB by generating HP

Steam.

Fresh and equilibrium catalyst are stored in two different hoppers with requisite loading

unloading provision. Apart from these two hoppers automatic catalyst loading system has been

installed from M/s Intercat for smooth catalyst handling and continuous catalyst loading. The

unit has a dedicated flushing oil system. Flushing oil is required during the normal operations as

well as during shutdown/ start up.

With the MS quality up gradation project, a 3-cut splitter was added in INDMAX unit as Object-

55. A combined feed stream of wild naphtha and INDMAX (FCCU) Gasoline is routed to 3-cut

splitter column located at eastern side of existing INDMAX unit, wherein the feed stream split

up into 3 fractions:

� Top Cut (Light Gasoline, TBP Boiling Range: C5-70 °C) High Octane and Low

Aromatics stream. The same is directly routed to MS pool.

� Middle Cut (Heart Cut, TBP Boiling Range: 70-90 °C rich in Benzene, Sulphur,

Aromatics and Olefins-hence, cannot be directly absorbed in Euro-III Grade MS pool.

This stream is routed to 56 units as feed for NHDT, followed by further treatment in

ISOM and DIH sections.

� Bottom Cut (Heavy Gasoline, TBP Boiling Range: 90-200 °C) can be absorbed in MS

pool or DHDT (Diesel Hydrotreater) feed.

IOCL Guwahati refinery plan to revamp INDMAX Unit form 0.1 MMTPA to 0.15 MMTPA.

2.3 Site Condition

This chapter depicts the location of IOCL Guwahati Refinery complex and population

distribution in and around the INDMAX unit installation. It also indicates the meteorological

data, which will be used for the Quantitative Risk Analysis study.

2.3.1 Site Location and Vicinity

The proposed project site is located within premises of Guwahati refinery of IOCL at Noonmati

in Kamrup district of Assam state. Geographically, the INDMAX unit site is located at

26º11’05.09”N, 91º48’30.24”E, at a distance of about 7 km from Guwahati railway station and

30 km from Guwahati International Airport. The general topography of the area is flat

surrounded by hilly regions and the general elevation of the site is 64 m amsl.


�� Page 10

2.3.2 Population

The population, which may be exposed to risk of hazards present in the refinery, is IOCL

personnel working in and around the INDMAX unit and the general population living in the

immediate vicinity of the complex.

Location wise population data inside the refinery, which has been considered for the study, is

indicated in below Table-2:

Table 2: Population Detail around INDMAX unit

General shift

(Elect. + Mach.) Shift A Shift-B Shift-C Shift Incharge Gen Shift

INDMAX field CR 14

3 3 3 3 1

SRU field CR 2 2 2 3

HDT/HGU field CR 8 4 4 4 6

2.3.3 Ignition Source

The ignition sources within and outside the refinery premise is a key factor in performing QRA

Study. The ignition sources, combined with their ignition probability, wind directional

probability and presence of flammable hydrocarbon is a key factor in determining the delayed

ignition probability of the cloud which further results in flash fire and overpressure scenarios.

The various ignition sources considered in the study includes but not limited to heaters,

Incinerators, smoking booth, canteen, traffic movement within the refinery and movement of rail

wagons for loading purpose.

2.3.4 Meteorological Condition

The consequences of released toxic or flammable material are largely dependent on the

prevailing weather conditions. For the assessment of major scenarios involving release of toxic

or flammable materials, the most important meteorological parameters are those that affect the

atmospheric dispersion of the releasing material. The critical variables are wind direction, wind

speed, atmospheric stability and temperature. Rainfall does not have any direct bearing on the

results of the risk analysis; however, it can have beneficial effects by absorption / washout of

released materials. Actual behavior of any release would largely depend on prevailing weather

condition at the time of release. Wind speed and Wind direction of the of the Guwahati refinery

April14 to June14 is given (%) in following Table-3:

Table 3: wind speed and wind direction (%) April-14 to June-14

Directions (degree) Wind Classes (m/s) Total


�� Page 11

0.5 - 2.1 2.1 - 3.6 3.6 - 5.7 5.7 - 8.8 8.8 - 11.1 >= 11.1

348.75 - 11.25 143 17 3 0 0 0 163

11.25 - 33.75 48 24 8 0 0 0 80

33.75 - 56.25 144 30 14 0 0 0 188

56.25 - 78.75 93 15 6 0 0 0 114

78.75 - 101.25 6 5 1 0 0 0 12

101.25 - 123.75 1 0 0 0 0 0 1

123.75 - 146.25 0 0 0 0 0 0 0

146.25 - 168.75 0 0 0 0 0 0 0

168.75 - 191.25 3 3 0 0 0 0 6

191.25 - 213.75 5 10 0 0 0 0 15

213.75 - 236.25 11 6 2 0 0 0 19

236.25 - 258.75 6 4 4 0 0 0 14

258.75 - 281.25 14 3 10 1 0 0 28

281.25 - 303.75 17 22 4 1 0 0 44

303.75 - 326.25 46 33 4 2 0 0 85

326.25 - 348.75 53 13 2 0 0 0 68

Sub-Total 590 185 58 4 0 0 837

Calms

518

Wind speed and Wind direction

The meteorological data considered for the study is based on the location Contain from the IMD.

The averages mean speed and the wind from various directions in percentage number of days is

as in Table-4 & 5 below.

Table 4: Percentage of No. of days wind from various direction

Day 7 22 14 2 4 3 4 3 43

Night 5 15 7 2 5 6 9 9 45

Table 5: Average mean wind speed (m/s)

Jan Feb March April May June July Aug Sep Oct Nov Dec

Speed 2.4 3.3 4.7 5.8 5.0 4.3 3.8 3.8 3.3 3.1 2.7 2.2

RISK ASSESSMENT

��

Figure 2: W

It is observed from the IMD dat

night and 30% in the day time. P

a maximum of 3.5 m/s. Predomin

The study of oktas (all clouds)

compared to November to March

Pasuill Stability

One of the most important charac

its tendency to resist vertical mo

influences the ability of atmosph

dispersion scenarios, the relevan


Wind Rose diagram of Guwahati refinery

data that calm weather is experienced for 20% o

. Predominant wind speed for Guwahati is in the r

inant wind direction for Guwahati is North and N

s) show that the months of June to September

ch where there sky is predominantly cloud less.

racteristics of atmosphere is its stability. Stability

motion or to suppress existing turbulence. This t

sphere to disperse pollutants released from the fa

ant atmospheric layer is that nearest to the gro

INDMAX UNIT

Page 12

of the time in the

e range of 1 m/s to

North East.

er are very cloudy

ty of atmosphere is

s tendency directly

facilities. In most

ground, varying in


�� Page 13

thickness from a few meters to a few thousand meters. Turbulence induced by buoyancy forces

in the atmosphere is closely related to the vertical temperature gradient.

Temperature normally decreases with increasing height in the atmosphere. The rate at which the

temperature of air decreases with height is called Environmental Lapse Rate (ELR). It varies

from time to time and place to place. The atmosphere is considered to be stable, neutral or

unstable according to ELR is less than, equal to or greater than Dry Adiabatic Lapse Rate

(DALR), which is a constant value of 0.98°C/100 meters.

Pasquill stability parameter, based on Pasquill – Gifford categorization, is a meteorological

parameter, which describes the stability of atmosphere, i.e., the degree of convective turbulence.

Pasquill has defined six stability classes ranging from `A' (extremely unstable) to `F' (stable).

Wind speeds, intensity of solar radiation (daytime insulation) and night time sky cover have been

identified as prime factors defining these stability categories.

The following table indicates the Pasquill stability classes.

Table 6: Pasquill stability classes

Surface Wind Day time solar radiation. Night time cloud cover

Speed(m/s) Strong Slight Slight Thin< 40% Medium Overcast >80%

< 2 A A-B B - - D

2-3 A-B B C E F D

3-5 B B-C C D E D

5-6 C C-D D D D D

>6 C D D D D D

When the atmosphere is unstable and wind speed is moderate or high or gusty, rapid dispersion

of pollutants will occur. Under these conditions, pollutant concentration in air will be moderate

or low and the material will be dispersed rapidly. When the atmosphere is stable and wind speed

is low, dispersion of material will be limited and pollutant concentration in air will be high.

Stability category for this study is identified based on the cloud amount, day time solar radiation

and wind speed.

Table 7: Weather parameters for consequence analysis

S.No. Wind Speed(m/s) Pasquill Stability

1. 2 F

2. 5 D


�� Page 14

2.4 Tank detail

Only four tank which containing class-B product are situated around the INDMAX unit. The

details of tank around INDMAX unit is given in Table

Table 8: Tank details around INDMAX unit

Tank No Service Capacity (KL) Roof Type Dia. (m) Ht. (m)

15 TCO 2000 FIXED ROOF 15.25 11.74

16 SKO 2000 FIXED ROOF 15.25 11.74

23 HSD 5000 FIXED ROOF 22.8 11.7

28 HSD 5000 FLOATING ROOF 22.9 13.6


�� Page 15

CHAPTER: 3 IDENTIFICATION OF HAZARD AND SELECTION OF

SCENARIOS

3.0 Hazard identification

A classical definition of hazard states that hazard is in fact the characteristic of

system/plant/process that presents potential for an accident. Hence all the components of a

system/plant/process need to be thoroughly examined in order to assess their potential for

initiating or propagating an unplanned event/sequence of events, which can be termed as an

accident.

In Risk Analysis terminology a hazard is something with the potential to cause harm. Hence the

Hazard Identification step is an exercise that seeks to identify what can go wrong at the major

hazard installation or process in such a way that people may be harmed. The output of this step is

a list of events that need to be passed on to later steps for further analysis.

The potential hazards posed by the facility were identified based on the past accidents, lessons

learnt and a checklist. This list includes the following elements. Catastrophic rupture of pressure

vessel. “Guillotine-Breakage” of pipe-work Small hole, cracks or instrument tapping failure in

piping and vessels. Flange leaks. Leaks from pump glands and similar seals.

Modes of Failure

There are various potential sources of large leakage, which may release hazardous chemicals and

hydrocarbon materials into the atmosphere. These could be in form of gasket failure in flanged

joints, bleeder valve left open inadvertently, an instrument tubing giving way, pump seal failure,

guillotine failure of equipment/ pipeline or any other source of leakage. Operating experience

can identify lots of these sources and their modes of failure. A list of general equipment and

pipeline failure mechanisms is as follows:

Material/Construction Defects

• Incorrect selection or supply of materials of construction

• Incorrect use of design codes

• Weld failures

• Failure of inadequate pipeline supports

Pre-Operational Failures

• Failure induced during delivery at site

• Failure induced during installation

• Pressure and temperature effects

• Overpressure

• Temperature expansion/contraction (improper stress analysis and support design)


�� Page 16

• Low temperature brittle fracture (if metallurgy is incorrect)

• Fatigue loading (cycling and mechanical vibration)

Corrosion Failures

• Internal corrosion (e.g. ingress of moisture)

• External corrosion

• Cladding/insulation failure (e.g. ingress of moisture)

• Cathodic protection failure, if provided

Failures due to Operational Errors

• Human error

• Failure to inspect regularly and identify any defects

External Impact Induced Failures

• Dropped objects

• Impact from transport such as construction traffic

• Vandalism

• Subsidence

• Strong winds

Failure due to Fire

• External fire impinging on pipeline or equipment

• Rapid vaporization of cold liquid in contact with hot surfaces

3.1 Hazards associated with the refinery

Refinery complex handles a number of hazardous materials like LPG, Hydrogen, Naphtha,

Benzene, Toluene and other hydrocarbons which have a potential to cause fire and explosion

hazards. The toxic chemicals like Benzene, Ammonia, Chlorine and Hydrogen sulfide are also

being handled in the Refinery. This chapter describes in brief the hazards associated with these

materials.

3.2 Hazards Associated with Flammable Hydrocarbons

3.2.1 Liquefied Petroleum Gas

LPG is a colorless liquefied gas that is heavier than air and may have a foul smelling odorant

added to it. It is a flammable gas and may cause flash fire and delayed ignition.

LPG is incompatible to oxidizing and combustible materials. It is stable at normal temperatures

and pressure. If it is released at temperatures higher than the normal boiling point it can flash

significantly and would lead to high entrainment of gas phase in the liquid phase. High

entrainment of gas phase in the liquid phase can lead to jet fires. On the other hand negligible


�� Page 17

flashing i.e. release of LPG at temperatures near boiling points would lead to formation of pools

and then pool fire. LPG releases may also lead to explosion in case of delayed ignition.

Inhalation of LPG vapors by human beings in considerable concentration may affect the central

nervous system and lead to depression. Inhalation of extremely high concentration of LPG may

lead to death due to suffocation from lack of oxygen. Contact with liquefied LPG may cause

frostbite. Refer to Table 7 for properties of LPG.

Table 9 Hazardous Properties of LPG

3.2.2 Hydrogen

Hydrogen (H2) is a gas lighter than air at normal temperature and pressure. It is highly

flammable and explosive. It has the widest range of flammable concentrations in air among all

common gaseous fuels. This flammable range of Hydrogen varies from 4% by volume (lower

flammable limit) to 75% by volume (upper flammable limit). Hydrogen flame (or fire) is nearly

invisible even though the flame temperature is higher than that of hydrocarbon fires and hence

poses greater hazards to persons in the vicinity. Constant exposure of certain types of ferritic

steels to hydrogen results in the embrittlement of the metals. Leakage can be caused by such

embrittlement in pipes, welds, and metal gaskets.

In terms of toxicity, hydrogen is a simple asphyxiant. Exposure to high concentrations may

exclude an adequate supply of oxygen to the lungs. No significant effect to human through

dermal absorption and ingestion is reported. Refer to Table 8 for properties of hydrogen.

Table 10 Hazardous Properties of Hydrogen

S.No. Properties Values

1. LFL (%v/v) 1.7

2. UFL (%v/v) 9.0

3. Auto ignition temperature (°C) 420-540

4. Heat of combustion (Kcal/Kg) 10960

5. Normal Boiling point (°C) -20 to -27

6. Flash point (°C) -60


1. LFL (%v/v) 4.12

2. UFL (%v/v) 74.2

3. Auto ignition temperature (°C) 500


5. Normal Boiling point (°C) -252

6. Flash point (°C) NA


�� Page 18

3.2.3 Naphtha and Other Heavier Hydrocarbon

The major hazards from these types of hydrocarbons are fire and radiation. Any spillage or loss

of containment of heavier hydrocarbons may create a highly flammable pool of liquid around the

source of release.

If it is released at temperatures higher than the normal boiling point it can flash significantly and

would lead to high entrainment of gas phase in the liquid phase. High entrainment of gas phase

in the liquid phase can lead to jet fires. On the other hand negligible flashing i.e. release at

temperatures near boiling points would lead to formation of pools and then pool fire. Spillage of

comparatively lighter hydrocarbons like Naphtha may result in formation of vapor cloud. Flash

fire/ explosion can occur in case of ignition. Refer to Table 9 for properties of Naphtha.

Table 11: Hazardous Properties of Naphtha

3.3 Hazard Associated with Toxic/Carcinogenic materials

3.3.1 Hydrogen Sulfide

Hydrogen sulfide is a known toxic gas and has harmful physiological effects. Accidental release

of hydrocarbons containing hydrogen sulfide poses toxic hazards to exposed population. Refer

Table 10 for hazardous properties of Hydrogen Sulfide.

Table 12: Toxic effects of Hydrogen Sulfide


1. LFL (%v/v) 0.8

2. UFL (%v/v) 5.0

3. Auto ignition temperature (°C) 228


5. Normal Boiling point (°C) 130-155

6. Flash point (°C) 38-42

S.No. Threshold Limits Concentration

(ppm)

1. Odor threshold 0.0047

2. Threshold Limit Value(TLV) 10 10

3. Short Term Exposure Limit (STEL)

(15 Minutes)

15

4. Immediately Dangerous to Life and

Health (IDLH) level (for 30 min

exposure)

100


�� Page 19

3.3.2 Chlorine

Chlorine is required in a refinery complex for water treatment. Chlorine tonner is therefore

located near the Cooling water system. Chlorine gas is not flammable but highly poisonous in

nature. Its routes of entry into the human body are through inhalation, ingestion, skin and eyes.

An exposure to chlorine can cause eye irritation, sneezing, restlessness. Exposure to high

concentration of chlorine can cause respiratory distress and violent coughing. Lethal effects of

inhalation depend not only on the concentration of the gas to which people are exposed, but also

on the duration of exposure. The toxic effects of chlorine are listed in Table 11.

Table 13: Toxic effect of chlorine

3.3.3 Ammonia

Ammonia may be release from failure of connection tube of ammonia cylinder used in

Atmospheric unit (AU). Ammonia is also likely to be present in sour gas produced from Sour

water stripper unit (SWSU). The hazard associated with ammonia is both toxic and flammable

hazards. Toxic hazards being more pronounced. Vapors of ammonia may cause severe eye or

throat irritation and permanent injury may result. Contact with the liquid freezes skin and

produces a caustic burn. Table 12 indicates the toxic properties of ammonia.

Table 14: Toxic effects of Ammonia


(ppm)

1. Short Term Exposure Limit

(STEL) (15 Minutes)

2

2. Immediately Dangerous to Life

and Health (IDLH) level (for 30

min exposure)

10


(ppm)

1. Threshold Limit Value (TLV) 25

2. Short Term Exposure Limit

(STEL) (15 Minutes)

35

3. Immediately Dangerous to Life

and Health (IDLH) level (for 30

min exposure)

300


�� Page 20

3.4 Selected Failure Cases

A list of failure cases was prepared based on process knowledge, engineering judgment,

experience, past incidents associated with such facilities and considering the general

mechanisms for loss of containment. The cases have been identified for the consequence

analysis is based on the following.

o Cases with high chance of occurrence but having low consequence:

Example of such failure cases includes two-bolt gasket leak for flanges, seal failure for

pumps, sample connection failure, instrument tapping failure, drains, vents, etc. The

consequence results will provide enough data for planning routine safety exercises. This

will emphasize the area where operator's vigilance is essential.

o Cases with low chance of occurrence but having high consequence (The example

includes catastrophic failure of lines, process pressure vessels, etc.)

This approach ensures at least one representative case of all possible types of accidental

failure events, is considered for the consequence analysis. Moreover, the list below

includes at least one accidental case comprising of release of different sorts of highly

hazardous materials handled in the refinery. Although the list does not give complete

failure incidents considering all equipments, units, but the consequence of a similar

incident considered in the list below could be used to foresee the consequence of that

particular accident.

Table 15: Selected failure case for INDMAX unit

Equipment Scenario Flow rate

(m3/hr)

Pressure

(Kg/cm2g)

Temp

(0

C)

Failure

Frequency

(per year)

Regenerator

Primary Cyclone

(CY-03)&

Secondary Cyclone

(CY-04)

1.Leak in inlet flue gas

line from Regenerator

cyclone to office

chamber V-20

13971.67 2.06 709 1.00E-05

2.Rupture in inlet flue

gas line form

Regenerator cyclone to

office chamber V-20

13971.67 2.06 709 1.00E-05

Cyclone CY-02 3.Leak in reactor

effluent stream from

Reactor Cyclone CY-

02

11641.71 1.84 555 2.50E-05


�� Page 21


(m3/hr)

Pressure

(Kg/cm2g)

Temp

(0

C)

Failure

Frequency

(per year)

4.Rupture in reactor

effluent stream from

Reactor Cyclone CY-

02

11641.71 1.84 555 5.00E-07

Mixed Feed

Nozzle Sp-10A/B

5.Leak in combined

feed line combined fed

line (CFO & RCO) to

Mixed Feed Nozzle

SP-10A/B

10.49 7.3 250 3.00E-05

6.Rupture in combined

feed line (CFO &

RCO) to Mixed Feed

Nozzle SP-10A/B

10.49 7.3 250 4.50E-06

Feed MCB

Exchanger (E-

01A/B)

7.Leak from shell side

of Feed/MCB

Exchanger (E-01A/B)

17.97 12 80 5.00E-04

8.Rupture from shell

side of Feed/MCB

Exchanger (E-01A/B)

17.97 12 80 2.50E-05

TCO-CR Pump

(P-06A/B)

9.Leak in discharge

line of TCO-CR Pump

(P06A/B)

34.64 10.2 194.91 1.50E-05

10.Rupture in

discharge line of TCO-

CR Pump (P-06A/B)

34.64 10.2 194.91 2.25E-06

TCO-CR Pump

(P-new)

11.Leak in discharge

line of HCO Cr Pump

(P-new)

29.82 6.8 309.51 1.50E-05

12.Rupture in

discharge line of HCO

CR Pump(P-mew)

29.82 6.8 309.51 2.25E-05

CLO PA Line 13.Leak in CLO PA

line to main

fractionators column

(C-01)

57.52 9 309.72 1.00E-05


�� Page 22


(m3/hr)

Pressure

(Kg/cm2g)

Temp

(0

C)

Failure

Frequency

(per year)

14.Rupture in CLO PA

line to Main

fractionators column

(C-01)

57.52 9 309.72 1.50E-06

Sponge Absorber

C-04

15.Leak in feed line to

Sponge Absorber C-04 145.71 15.53 38.32 1.00E-05

16.Rupture in feed to

Sponge Absorber C-04 146.71 15.53 38.32 1.50E-06

Dry Gas KO Drum

V-30

17.Leak in Outlet from

Dry Gas KO Drum V-

30

150.4 2.5 37.73 1.00E-06

18.Rupture in Outlet

line from Dry Gas KO

Drum V-30

150.4 2.5 37.73 1.50E-06

TCO CR/ C2

Stripper Feed

Exchanger (E-

06A/B)

19. Leak from shell

side of TCO CR/C2

Stripper Feed

Exchanger (E-06a/B)

110.26 16 71 5.00E-04

20.Rupture from shell

side of TCO CR/C2

Stripper Feed

Exchanger (E-06A/B)

110.26 16 71 2.50E-05

Main Fractionator

column C-01

21.Leak in TCO CR

line to C-01 31.87 2.63 139.7 2.00 -05

22.Rupture in TCO

CR line to C-01 31.87 2.63 139.7 3.00E -06

Feed RCO/FCO

Pump (P-01A/B/C)

23.Leek in section line

of Feed RCO/FCO

Pump P-01A/B/c

17.99 2 80 1.50E-05

24.Rupture in suction

line of Feed RCO/FCO 17.99 2 80 2.25e-06


�� Page 23


(m3/hr)

Pressure

(Kg/cm2g)

Temp

(0

C)

Failure

Frequency

(per year)

Pump P-01A/B/c

Feed CG (Coker

gas) Pump

25.Leak in suction line

of Feed CG (Coker

gas) Pump P-02A/B

4.87 2 80 1.20E-05

26.Rupture in suction

line of Feed CG

(Coker gas) Pump P-

02A/B 4.87

4.87 2 80 1.80E-06

Unstablized

gasoline pump

P05A/B


line of Unstable

gasoline pump P-

05A/B

7.88 15 34 1.80E-05

28.Rupure in discharge

line of Un stabilized

gasoline pump P-

05a/B

7.88 15 34 2.70E-06

HP separator V-05 29.Leak in outlet from

Hp separator V-05 254.31 16.03 40 2.00E-05

30.Rupture inlet line

form Hp separator V-

05

254.31 16.03 40 3.00E-06

LPG R/D Pump P-

15A/B


line of LPG R/D Pump

P-15a/B

8.88 23.7 23.2 1.60E-05

32.Rupture in

discharge line of LPG

R/D Pump P-15A/B

8.88 23.7 23.2 2.40E-06

Debutanizer C-06 33.Leak in inlet feed

line to Stabilizer

Debutanizer C-06

158.31 16.5 140 2.00E-05


�� Page 24


(m3/hr)

Pressure

(Kg/cm2g)

Temp

(0

C)

Failure

Frequency

(per year)

34.Rupture in inlet

feed line to Stabilizer

Debutanizer C-06

158.31 16.5 140 3.00E-06

Stabilizer Gasoline

Bottom Pump P-

16A/B


line from Stabilizer

Gasoline Bottom

Pump P-16a/B

9.75 11.53 30 1.70E-05

36.Rupture in

discharge line from

Stabilizer Gasoline

Bottom Pump P-

16A/B

9.75 11.53 30 2.55E-06

Wet gas

compressor K-01

37.Leak in inlet line to

Wet gas compressor

K-01

2887.98 1.89 34 1.50E-05

38.Rupture in inlet line

to Wet gas compressor

K-01

2887.98 1.89 34 2.25E-06

3.5 Hazard identification as per NFPA

The fire and health hazards are also categorized based on NFPA (National Fire Protection

Association) classifications, described below in Table-14.

Table 16: NFPA for MS and LPG

S. No PETROLEUM PRODUCT Nh Nf Nr

1. MS 1 3 0

2. LPG 1 4 0

Nh - NFPA health hazard factor


�� Page 25

Nf -NFPA flammability hazard factor

Nr -NFPA reactivity hazard factor

Evaluation of the hazard based on the F&E Index is done based on the following guidelines:

Table 17: Explanation of NFPA classification

Classification Definition

Health Hazard

4 Materials, which on very short exposure could cause death or major residual

injury even though prompt medical treatments were given.

3 Materials, which on short exposure could cause serious temporary or residual

injury even though prompt medical treatments were given.

2

Materials, which on intense or continued exposure could cause temporary

incapacitation or possible residual injury unless prompt medical treatment is

given.

1 Materials, which on exposure would cause irritation but only minor residual

injury even if no treatment is given.

0 Materials, which on exposure under fire conditions would offer no hazard

beyond that of ordinary combustible material.

Flammability

4

Materials which will rapidly or completely vaporize at atmospheric pressure and

normal ambient temperature, or which are readily dispersed in air and which

will burn readily.

3 Liquids and solids that can be ignited under almost all ambient temperature

conditions.

2 Materials that must be moderately heated or exposed to relatively high ambient

temperatures before ignition can occur.

1 Material that must be preheated before ignition can occur.

0 Materials that will not burn.

Reactivity


�� Page 26

4 Materials which in themselves are readily capable of detonation or of explosive

decomposition or reaction at normal temperature and pressures.

3

Materials which in themselves are capable of detonation or explosive reaction

but require a strong initiating source or which must be heated under

confinement before initiation or which react explosively with water.

2

Materials which in themselves are normally unstable and readily undergo

violent chemical change but do not detonate. Also materials which may react

violently with water or which may form potentially explosive mixtures with

water.

1

Materials which in themselves are normally stable, but which can become

unstable at elevated temperature and pressures or which may react with water

with some release of energy but not violently.

0 Materials which in themselves are normally stable, even under fire exposure

conditions, and which are not reactive with water.

3.6 Characterizing the failures

Accidental release of flammable or toxic vapors can result in severe consequences. Delayed

ignition of flammable vapors can result in blast overpressures covering large areas. This may

lead to extensive loss of life and property. Toxic clouds may cover yet larger distances due to the

lower threshold values in relation to those in case of explosive clouds (the lower explosive

limits). In contrast, fires have localized consequences. Fires can be put out or contained in most

cases; there are few mitigating actions one can take once a vapor cloud is released.

In a petroleum marketing installation such as the plant in question, the main hazard arises due to

the possibility of leakage of petroleum products during decanting (number of hose connections,

tank lorry movement etc.), storage, filling and transportation. To formulate a structured approach

to identification of hazards an understanding of contributory factors is essential.

3.7 Operating Parameters

3.7.1 Inventory

Inventory Analysis is commonly used in understanding the relative hazards and short listing of

release scenarios. Inventory plays an important role in regard to the potential hazard. Larger the

inventory of a vessel or a system, larger the quantity of potential release. A practice commonly

used to generate an incident list is to consider potential leaks and major releases from fractures of


�� Page 27

pipelines and vessels containing sizable inventories. Each section is then characterized by the

following parameters required for consequence modeling:

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

� Pressure, Temperature and composition of the material

� Hole size for release

3.7.2 Loss of Containment

Plant inventory can get discharged to Environment due to Loss of Containment. Various causes

and modes for such an eventuality have been described. Certain features of materials to be

handled at the plant need to the clearly understood to firstly list out all significant release cases

and then to short list release scenarios for a detailed examination.

3.7.3 Liquid Outflow from a vessel/ line

Liquid release can be either instantaneous or continuous. Failure of a vessel leading to an

instantaneous outflow assumes the sudden appearance of such a major crack that practically all

of the contents above the crack shall be released in a very short time. The flow rate will depend

on the size of the hole as well as on the pressure in front of the hole, prior to the accident. Such

pressure is basically dependent on the pressure in the vessel.

3.7.4 Vaporization

The vaporization of released liquid depends on the vapor pressure and weather conditions.

Such consideration and others have been kept in mind both during the initial listing as well as

during the short listing procedure. Initial listing of all significant inventories in the process

plants was carried out. This ensured no emission through inadvertence.

Based on the methodology discussed above a set of appropriate scenarios was generated to carry

out Risk Analysis calculations for Pool fire, fire ball, source strength, toxic threat zone,

flammability threat zone, overpressure (blast force) from vapor cloud explosion.


�� Page 28

CHAPTER-4 RELEASE CONSEQUENCE ANALYSIS

4.1 GENERAL

Consequence analysis involves the application of the mathematical, analytical and computer

models for calculation of the effects and damages subsequent to a hydrocarbon / toxic release

accident.

Computer models are used to predict the physical behavior of hazardous incidents. The model

uses below mentioned techniques to assess the consequences of identified scenarios:

� Modeling of discharge rates when holes develop in process equipment/pipe work.

� Modeling of the size & shape of the flammable/toxic gas clouds from releases in the

atmosphere.

� Modeling of the flame and radiation field of the releases that are ignited and burn as jet

fire, pool fire and flash fire.

� Modeling of the explosion fields of releases which are ignited away from the point of

release.

The different consequences (Flash fire, pool fire, jet fire and Explosion effects) of loss of

containment accidents depend on the sequence of events & properties of material released

leading to the either toxic vapor dispersion, fire or explosion or both.

4.2 Consequence Analysis Modeling

4.2.1 Discharge Rate

The initial rate of release through a leak depends mainly on the pressure inside the equipment,

size of the hole and phase of the release (liquid, gas or two-phase). The release rate decreases

with time as the equipment depressurizes. This reduction depends mainly on the inventory and

the action taken to isolate the leak and blow-down the equipment.

4.2.2 Dispersion

Releases of gas into the open air form clouds whose dispersion is governed by the wind, by

turbulence around the site, the density of the gas and initial momentum of the release. In case of

flammable materials the sizes of these gas clouds above their Lower Flammable Limit (LFL) are

important in determining whether the release will ignite. In this study, the results of dispersion

modeling for flammable materials are presented LFL quantity.

4.2.3 Flash Fire

A flash fire occurs when a cloud of vapors/gas burns without generating any significant

overpressure. The cloud is typically ignited on its edge, remote from- the leak source. The

combustion zone moves through the cloud away from the ignition point. The duration of the


�� Page 29

flash fire is relatively short but it may stabilize as a continuous jet fire from the leak source. For

flash fires, an approximate estimate for the extent of the total effect zone is the area over which

the cloud is above the LFL.

4.2.4 Jet Fire

Jet fires are burning jets of gas or atomized liquid whose shape is dominated by the momentum

of the release. The jet flame stabilizes on or close to the point of release and continues until the

release is stopped. Jet fire can be realized, if the leakage is immediately ignited. The effect of jet

flame impingement is severe as it may cut through equipment, pipeline or structure. The damage

effect of thermal radiation is depended on both the level of thermal radiation and duration of

exposure.

4.2.5 Pool Fire

A cylindrical shape of the pool fire is presumed. Pool-fire calculations are then carried out as

part of an accidental scenario, e.g. in case a hydrocarbon liquid leak from a vessel leads to the

formation of an ignitable liquid pool. First no ignition is assumed, and pool evaporation and

dispersion calculations are being carried out. Subsequently late pool fires (ignition following

spreading of liquid pool) are considered. If the release is bounded, the diameter is given by the

size of the bund. If there is no bund, then the diameter is that which corresponds with a minimum

pool thickness, set by the type of surface on which the pool is spreading.

While modeling cases of lighter hydrocarbons in the range of naphtha and MS wherein the

rainout fraction have been minimal (not leading to pool formation) due to the horizontal direction

of release, downward impingement has been considered for studying the effects of pool fire for

consequence analysis only.

Pool fires occur when spilled hydrocarbons burn in the form of large diffusion flames.

Calculating the incident flux to an observer involves four steps, namely

• Characterizing the flame geometry

• Estimation of the flame radiation properties

• Computation of the geometric view factors

• Estimation of flame attenuation coefficients and computation of geometric view factors

between observer and flame.

The size of the flame will depend upon the spill surface and the thermo chemical properties of

the spilled liquid. In particular, the diameter of the fire, the visible height of the flame, the tilt

and drag of the flame etc. The radioactive output of the flame will depend upon the fire size, the

extent of mixing with air and the flame temperature. Some fraction of the thermal radiation is

absorbed by the carbon dioxide and water vapor in the intervening atmosphere. In addition, large

hydrocarbon fires produce thick smoke which significantly obscure flame radiation.


�� Page 30

The calculations for radiation damage distances start with estimation of the burning velocity:

Y= 92.6 e – 0.0043TbMw10-7

/(� X 6)

Where y= burning velocity in m/s

Mw= molecular weight in kg/kg mol

Tb= normal boiling point

The next step involves calculation of the equivalent diameter for the spreading pool- this depends

upon the duration of the spill (continuous, instantaneous, finite duration etc.). This is calculated

using expressions like:

Deq. =2(V/3.142y)1/2

Where Deq. Is the steady state diameter of the pool in m

V= liquid spill rate in m3/s

Y= Liquid burning rate in m/s

In the absence of frictional resistance during spreading, the equilibrium diameter is reached over

a time given by:

Teq.= 0.949 Deq./(� y X Deq.)1/3

The visible flame height is given by;

Hflame= 42Dp ((BvD/Da(gDp)1/2)0.61

Where Hflame = flame height in m

D= density in kg/m3

Da= air density in kg/m3

g = gravitational acceleration or 9.81 m/s2

The emissive power of a large turbulent fire is a function of the black body emissive power and

the flame emissivity. The black body emissive power can be computed by Planck’s law of

radiation. The general equation used for the calculation is:

EP= -0.313Tb+117

Where Ep is the effective emissive power in kw/m2

Tb= normal boiling point of the liquid in °F

Materials with a boiling point above 30 °F typically burn with sooty flames-the emissive power

from the sooty section is about 20 kW /m2. The incident flux at any given location is given by the

equation:

Qincident = EP * t * V F

Where Qincident = incident flux in kw/m2

t= transmitivity (a function of path length, relative humidity and flame temperature) often taken


�� Page 31

as 1 and the attenuation of thermal flux due to atmospheric absorption ignored.

VF= geometric view factor

The view factor defines the fraction of the flame that is seen by a given observer.

V F= 1.143 (Rp/X) 1.757

Where X= distance from the flame center in m

Rp= pool radius in m

Based on the radiation received, the fatality levels are calculated from Probit equation, which for

protected clothing is given by:

Pr.= -37.23 + 2.56 ln (t X Q4/3

)

Where Pr. = Probit No.

t= time in seconds

Q heat radiation in w/m2

4.2.6 Blast Overpressures

Blast Overpressures depend upon the reactivity class of material and the amount of gas between

two explosive limits. MS could give rise to a VCE due to their vapor pressures - however, as the

results will indicate, the cloud flammable masses are quite small due to the high boiling point

and low vapor pressures. In addition, unless there is sufficient extent of confinement, it is

unlikely to result in any major explosion. Examples where flammable mixtures could be found

are within storage tanks and road tankers. Open-air explosions are unlikely. As a result, damage

would be limited

Equations governing the formation of overpressures in an explosion are given later. Blast

overpressures are calculated based on comparison of combustion energy per unit mass of a vapor

cloud with that of TNT and taking into account that only a fraction of the energy will contribute

to the explosion. Overpressure data compiled from measurements on TNT are used to relate

overpressure data to distance from explosions. The equivalent mass of TNT is calculated using

the equations:

MTNT= (Mcloud X (�Hc.)/1155 X Yf)

Where MTNT is the TNT equivalent mass (lb)

�Hc = Heat of combustion is in Kcals/kg

Mcloud is mass in cloud in lbs

Yf is the yield factor

The distance to a given overpressure is calculated from the general equation:

X=MTNT 1/3 exp (3.5031-0.7241 ln (Op) + 0.0398 (ln Op))2

Where X is the distance to a given overpressure in feet


�� Page 32

Op is the peak overpressure

4.2.7 Toxic Release

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

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

e.g. H2S, chlorine, etc was undertaken to the Immediately Dangerous to Life and Health

concentration (IDLH) limit to determine the extent of the toxic hazard created as the result of

loss of containment of a toxic substance.

4.3 Size and duration of release

Leak size considered for selected failure cases are as listed below:

Table 18: Leak size of selected failure scenario

Failure Description Leak Size

Pump seal failure 6 mm hole size

Flange gasket failure 10 mm hole size

Instrument tapping failure 19 mm hole size

Small hole 20 mm hole size

Large hole 50 mm hole size

Catastrophic failure Complete rupture of pressure vessels

The duration of release is a very important input to the consequence analysis as this directly

dictates the quantity of material released. General basis for deciding the duration of release is

given in the Table- 17.

Table 19: Duration of release

Blocking system configuration Isolation

Time(m)

Fully automatic blocking system( including automatic detection and closure of

block valves) 2

For remote operated blocking systems (detection is automatic, but control room

operator must validate alarm signal and close block valve remotely) 10

For hand-operated blocking systems (detection is automatic, but control room

operator must validate alarm, go to field and manually close block valve) 30

The discharge duration is taken as 10 minutes for continuous release scenarios as it is considered

that it would take plant personnel about 10 minutes to detect and isolate the leak.

4.4 Damage Criteria

In order to appreciate the damage effect produced by various scenarios, physiological/physical

effects of the blast wave, thermal radiation or toxic vapor exposition are discussed.


�� Page 33

4.4.1 LFL or Flash Fire

Hydrocarbon vapor released accidentally will spread out in the direction of wind. If a source of

ignition finds an ignition source before being dispersed below lower flammability limit (LFL), a

flash fire is likely to occur and the flame will travel back to the source of leak. Any person

caught in the flash fire is likely to suffer fatal burn injury. Therefore, in consequence analysis,

the distance of LFL value is usually taken to indicate the area, which may be affected by the

flash fire.

Flash fire (LFL) events are considered to cause direct harm to the population present within the

flammability range of the cloud. Fire escalation from flash fire such that process or storage

equipment or building may be affected is considered unlikely.

4.4.2 Thermal Hazard Due to Pool Fire, Jet Fire

Thermal radiation due to pool fire, jet fire or fire ball may cause various degree of burn on

human body and process equipment. The following table details the damage caused by various

thermal radiation intensity.

Table 20: Effects due to incident radiation intensity

Incident Radiation

(kW/m2)

Type of Damage

0.7 Equivalent to Solar Radiation

1.6 No discomfort for long exposure

4.0 Sufficient to cause pain within 20 sec. Blistering of skin (first

degree burns are likely)

9.5 Pain threshold reached after 8 sec. Second degree burns after 20

sec.

12.5 Minimum energy required for piloted ignition of wood, melting

plastic tubing etc.

25 Minimum energy required to ignite wood at indefinitely long

exposure

37.5 Sufficient to cause damage to process equipment Source: Major Hazard Control, ILO

4.4.3 Vapor Cloud Explosion

In the event of explosion taking place within the plant, the resultant blast wave will have damaging effects

on equipment, structures, building and piping falling within the overpressure distances of the blast. Tanks,

buildings, structures etc. can only tolerate low level of overpressure. Human body, by comparison, can

withstand higher overpressure. But injury or fatality can be inflicted by collapse of building of structures.

The following table illustrates the damage effect of blast overpressure.


�� Page 34

Table 21: Damage due to Overpressures

Peak Overpressure Damage Type

12.04 psi Total Destruction

4.35 psi Heavy Damage

1.45 psi Moderate Damage

0.44 psi Significant Damage

0.15 psi Minor Damage

4.5 Generic Failure Rate Data

Generic leak frequency data published by International Association of Oil and 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 reported in the Table 22.


�� Page 35

Table 22: Failure frequency (OGP Data)

Equipment overall failure frequency(per year)

Equipment Name Minor

Leak

Medium Leak Major Leak Full bore

Rupture

Total

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

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” 3.70.E-

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” 4.40 E-

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”

3.30 E-

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 1.90-03 1.20E-03 8.00E-04 7.2 E-3

Compressor -

Reciprocating

4.50E-02 1.70E02 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

4.6 Plant Data

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

the INDMAX unit. These documents are given in Table-23.

Table 23: List of documents used in study

S. No Documents/Drawing Documents Drawing No. Document Name

1. Facilities Description Provided by IOCL

2. Process Flow Diagram IOC R&D/GR/INDMAX/PFD/01 Catalyst handling /

Regenerator Section

3. Process Flow Diagram IOC R&D/GR/INDMAX/PFD/01 Reactor and WHR Section


�� Page 36

4. Process Flow Diagram IOC R&D/GR/INDMAX/PFD/03 Fractionator Section

5. Process Flow Diagram IOC R&D/GR/INDMAX/PFD/04 Gas concentration Section

6. P&I Diagram IOC R&D/GR/INDMAX/P&ID/02 Feed section

7. P&I Diagram IOC R&D/GR/INDMAX/P&ID/03 Main Fractionator

8. P&I Diagram IOC R&D/GR/INDMAX/P&ID/03 TCO Stripper

9. P&I Diagram IOC R&D/GR/INDMAX/P&ID/05 Gas concentration section

10. Plot plan/Equipment

layout

053 MAX-LOL-001 Plot plan for INDMAX unit

11. Layout plan of Guwahati

refinery

TS-00-150 Layout plan of Guwahati

Refinery

4.7 Consequence analysis for INDMAX unit

4.7.1 Scenarios

Major contribution Risk scenario consequence analysis has been identified as listed in Table-24

Table 24: Major contributing risk scenario consequence table

S.No. Description Jet

Fire

Pool

Fire

Flash

Fire

VCE

1. Rupture in inlet feed line to Stabilizer Debutanizer C-

06 √ √ √ √


Exchanger (E-06A/B) - √ √ √


Exchanger (E-06a/B) √ √ √ √

4. Rupture in TCO CR line to C-01 √ √ √ √

5. Leak in discharge line of LPG R/D Pump P-15a/B √ - √ √

The scenarios for consequence analysis has been identified as listed in Table-25

Table 25: Scenarios for the consequence analysis


Fire

Pool

Fire

Flash

Fire

VCE

1. Leak in inlet flue gas line from Regenerator cyclone to

office chamber V-20 - - - -

2. Rupture in inlet flue gas line form Regenerator cyclone

to office chamber V-20 - - - -


�� Page 37


Fire

Pool

Fire

Flash

Fire

VCE

3. Leak in reactor effluent stream from Reactor Cyclone

CY-02 √ - - -

4. Rupture in reactor effluent stream from Reactor

Cyclone CY-02 √ - - -

5. Leak in combined feed line combined fed line (CFO &

RCO) to Mixed Feed Nozzle SP-10A/B √ - √ -

6. Rupture in combined feed line (CFO & RCO) to Mixed

Feed Nozzle SP-10A/B √ - √ √

7. Leak from shell side of Feed/MCB Exchanger (E-

01A/B) √ √ - √

8. Rupture from shell side of Feed/MCB Exchanger (E-

01A/B) √ √ - √

9. Leak in discharge line of TCO-CR Pump (P06A/B) √ - √ √

10. Rupture in discharge line of TCO-CR Pump (P-06A/B) √ - √ √

11. Leak in discharge line of HCO Cr Pump (P-new) √ - √ √

12. Rupture in discharge line of HCO CR Pump(P-mew) √ - √ -

13. Leak in CLO PA line to main fractionators column (C-

01) √ - √ -

14. Rupture in CLO PA line to Main fractionators column

(C-01) √ - √ √

15. Leak in feed line to Sponge Absorber C-04 √ - √ -

16. Rupture in feed to Sponge Absorber C-04 √ - √ √

17. Leak in Outlet from Dry Gas KO Drum V-30 √ - - -

18. Rupture in Outlet line from Dry Gas KO Drum V-30 √ - √ -


Exchanger (E-06a/B) √ √ √ √


Exchanger (E-06A/B) √ √ - √

21. Leak in TCO CR line to C-01 √ - √ √

22. Rupture in TCO CR line to C-01 √ √ √ √

23. Leek in section line of Feed RCO/FCO Pump P-

01A/B/c √ √ √ √


�� Page 38


Fire

Pool

Fire

Flash

Fire

VCE

24. Rupture in suction line of Feed RCO/FCO Pump P-

01A/B/c √ √ - √

25. Leak in suction line of Feed CG (Coker gas) Pump P-

02A/B √ √ - √

26. Rupture in suction line of Feed CG (Coker gas) Pump

P-02A/B 4.87 √ √ - √

27. Leak in discharge line of Unstable gasoline pump P-

05A/B √ - √ √

28. Rupture in discharge line of Un stabilized gasoline

pump P-05a/B √ - √ √

29. Leak in outlet from Hp separator V-05 √ - √ √

30. Rupture inlet line form Hp separator V-05 √ - √ √

31. Leak in discharge line of LPG R/D Pump P-15a/B √ - √ √

32. Rupture in discharge line of LPG R/D Pump P-15A/B √ - √ √

33. Leak in inlet feed line to Stabilizer Debutanizer C-06 √ - √ √

34. Rupture in inlet feed line to Stabilizer Debutanizer C-

06 √ √ √ √

35. Leak in discharge line from Stabilizer Gasoline Bottom

Pump P-16a/B √ √ - √

36. 36.Rupture in discharge line from Stabilizer Gasoline

Bottom Pump P-16A/B √ √ √ √

37. Leak in inlet line to Wet gas compressor K-01 √ - - -

38. Rupture in inlet line to Wet gas compressor K-01 √ - - -

Consequence analysis results

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

Table-27 and major contributing risk scenario consequence analysis given in Table-26. Major

contributing Scenario to societal risk from INDMAX unit consequence analysis graph are

attached as ANNEXURE-A


�� Page 39

Table 26: Major contributing risk scenario Consequence Analysis result

Scenario Weather

Condition

Flash fire (m) Pool Fire(m) Jet Fire(m) Overpressure (m)

LFL ½

LFL

4

kW/m2

12.5

kW/m2

37.5

kW/m2

4

kW/m2

12.5

kW/m2

37.5

kW/m2

2psi 3psi 5psi

1. Rupture in inlet line to

Stabilizer/Debutanizer D-5 m/s 255.48 287.38 222.58 214.09 204.56 218.41 222.17 77.37 257.34 227.27 203.15

F-2 m/s 223.87 231.71 137.39 124 114.72 210.41 218.17 70.37 248.92 215.21 185.52

2. Rupture from shell of Leak

from shell side of TCO CR/

C2 Stripper Feed Exchanger

(E-06A/B)

D-5 m/s 134.82 192.32 102.32 42.4 NR NR NR NR 240.49 220 206.94

F-2 m/s 117.90 156.16 81.24 42.41 NR NR NR NR 251.04 228.05 207.18

3. Leak from shell side of

TCO CR/ C2 Stripper Feed

Exchanger (E-06A/B)

D-5 m/s 24.21 47.92 44.5 42.47 41.14 31.02 29.30 28.06 54.36 51.11 48.14

F-2 m/s 38.23 74.89 43.03 35.5 27.86 25.05 21.86 17.84 90.92 86.17 81.85

4. Rupture in TCO CR line to

C-01 D-5 m/s 148.96 215.63 127.84 119.12 107.38 87.16 186.3 NR 254.25 234.19 224.91

F-2 m/s 117.4 170.24 70.27 62.09 54 87.16 186.3 NR 247.13 225.1 207.77

5. Leak in discharge line of

LPG R/ D Pump P -15A/B D-5 m/s 19.26 48.34 NA NA NA 26.86 24.52 22.95 51.56 48.94 46.55

F-2 m/s 25.09 70.76 NA NA NA 30.18 22.45 16.33 85.04 81.04 78.03


�� Page 40

Table 27: Consequence Analysis – Scenario result

Equipment Scenario Weather

Condition


LFL ½

LFL

4

kW/m2

12.5

kW/m2

37.5

kW/m2

4

kW/

m2

12.5

kW/m2

37.5

kW/m2

2psi 3psi 5psi

Regenerator

Primary

Cyclone

(CY-03)&

Secondary

Cyclone

(CY-04)

1.Leak in inlet

flue gas line

from

Regenerator

cyclone to

orifice chamber

V-20

D-5 m/s (IDLH 26.55m),

SO2=100ppm NA NA NA NA NA NA NA NA NA NA NA

F-2 m/s (IDLH 36.28m),


2.Rupture in inlet

flue gas line

from

Regenerator

cyclone to orifice

chamber V-20

D-5 m/s (IDLH 65m)


F-2 m/s (IDLH 73.25m)


Cyclone

CY-02

3. Leak in reactor

effluent stream

from Reactor

Cyclone CY-02.

D-5m/s 1.19 2.23 NA NA NR NR NR NR NR NR NR

F-2 m/s 1.29 2.53 NA NA NA NR NR NR NR NR NA

4. Rupture in

reactor effluent

stream from

Reactor Cyclone

CY- 02

D-5 m/s 47.87 101.11 NA NA NA 212.7

7 91.05 NR

197.0

9 162

130.5

8

F-2 m/s 35.56 56.17 NA NA NA 221.5

1 102.98 NR

193.3

7

158.6

5

126.9

3

Mixed Feed

Nozzle SP-

10A/B

5.Leak in

combined feed

line

(CFO&RCO) to

mixed Feed

Nozzle SP-

D-5m/s 3.09 4.95 NA NA NA 6.28 NR NR NR NR NR

F-2m/s 3.59 5.82 NA NA NA 6.37 NR NR NR NR NR


�� Page 41


Condition


LFL ½

LFL

4

kW/m2

12.5

kW/m2

37.5

kW/m2

4

kW/

m2

12.5

kW/m2

37.5

kW/m2

2psi 3psi 5psi

10A/B

6.Rupture in

combined feed

line

(CFO&RCO) to

Mixed Feed

Nozzle SP-

10A/B

D-5m/s 9.17 17.84 NA NA NA 58.91 27.78 NR 43.19 35.68 28.82

F-2m/s 6.56 8.75 NA NA NA 55.67 24.45 NR NR NR NR

Feed MCB

Exchanger

(E-01A/B)

7.Leak from

shell side of Feed

MCB Exchanger

(E-01A/B)

D-5 m/s 22..56 44.34 37.89 37.04 36.59 NA NA NA 47.69 50.49 53.57

F-2 m/s 38.65 68.56 33.55 28.79 24.53 NA NA NA 71.91 76.26 81.02

08 .Rupture from

shell side of Feed

MCB Exchanger

(E-01A/B)

D-5 m/s 72.79 105.79 54.76 24.14 NR NA NA NA 131.6

5

119.9

5

110.1

9

F-2 m/s 60.06 79.21 45.21 18.64 NR NA NA NA 135.0

5

120.3

3

100.8

7

TCO CR

Pump

9.Leak in

discharge line of

TCO-CR Pump

(P-06A/B)

D-5 m/s 9.85 24.38 NA NA NA 25.21 21.14 17.70 27 25.42 23.97

F-2 m/s 12.53 31.35 NA NA NA 24.44 18.57 12.35 38.24 36.37 34..6

7

10. Rupture in

discharge line of

TCO-CR Pump

(P-06A/B)

D-5 m/s 45.79 115.79 NA NA NA 237.8

9 121.71 22.72

166.4

3

135.5

5

109.9

3

F-2 m/s 28.91 118.59 NA NA NA 237.8

9 121.71 22.72

151.9

3

132.0

7

104.7

8

HCO-CR

Pump

11.Leak in

discharge line of D-5 m/s 2.59 4.65 NA NA NA 5.36 NR NR NR NR NR


�� Page 42


Condition


LFL ½

LFL

4

kW/m2

12.5

kW/m2

37.5

kW/m2

4

kW/

m2

12.5

kW/m2

37.5

kW/m2

2psi 3psi 5psi

HCO-CR Pump

(P-new) F-2 m/s 3.04 5.21 NA NA NA 5.39 NR NR NR NR NR

12.Rupture in

discharge line of

HCO-CR Pump

(P-new)

D-5 m/s 10.14 16.98 NA NA NA 64.56 30.37 NR 50.41 41.26 32.9

F-2 m/s 7.41 9.78 NA NA NA 60.24 28.32 NR NR NR NR

CLOPA

Line

13.Leak from

CLO PA line to

main

fractionators

column (C-01)

D-5 m/s 3.15 5.02 NA NA NA 6.58 NR NR NR NR NR

F-2 m/s 3.03 6.15 NA NA NA 6.71 NR NR NR NR NR

14.Rupture in

CLO PA line to

main

fractionators

column (C-01)

D-5 m/s 13.46 21.15 NA NA NA 94.77 46.42 NR 59.49 48.78 38.41

F-2 m/s 10.3 13.95 NA NA NA 92.23 43.35 NR 60.13 48.78 38.41

Sponge

Absorber

C-04

15.Leak in feed

line to sponge

Absorber C-04


F-2 m/s 4.43 7.44 NA NA NA 6.95 NR NR NR NR NR

16.Rupture in

Feed line to

Sponge Absorber

C-04

D-5 m/s 15.88 24.69 NA NA NA 126.7

7 65.49 17.44 73.33 61.26 50.23

F-2 m/s 12.41 17.29 NA NA NA 122.2

4 62.21 16.23 65.64 53.04

41..5

4

Dry Gas KO

DrumV-30

17.Leak in outlet

line from Dry

Gas KO Drum

V-30

D-5 m/s 1.35 2.50 NA NA NA NA NR NR NR NR NR

F-2 m/s 1.47 2.82 NA NA NA NR NR NR NR NR NR


�� Page 43


Condition


LFL ½

LFL

4

kW/m2

12.5

kW/m2

37.5

kW/m2

4

kW/

m2

12.5

kW/m2

37.5

kW/m2

2psi 3psi 5psi

18.Rupture in

Outlet line from

Dry Gas KO

Drum V-30

D-5 m/s 9.86 26.07 NA NA NA 47.84 17.0 NR 44.09 36.37 29.32


TCO CR/

C2 Stripper

Feed

Exchanger

(E-06A/B)

19.Leak from

shell side of

TCO CR/ C2

Stripper Feed

Exchanger

(E-06A/B)

D-5 m/s 24.21 47.92 44.5 42.47 41.14 31.02 29.30 28.06 54.36 51.11 48.14

F-2 m/s 38.23 74.89 43.03 35.5 27.86 25.05 21.86 17.84 90.92 86.17 81.85

20.Rupture from

shell of Leak

from shell side of

TCO CR/ C2

Stripper Feed

Exchanger

(E-06A/B)

D-5 m/s 134.82 192.32 102.32 42.4 NR NR NR NR 240.4

9 220

206.9

4

F-2 m/s 117.90 156.16 81.24 42.41 NR NR NR NR 251.0

4

228.0

5

207.1

8

Main

fractionators

column

C-01

21.Leal in TCO

CR Line to C-01 D-5 m/s 8.92 21.57 NR NR NR 19.14 17.92 NR 26.89 25.33 23.9

F-2 m/s 14.62 40.95 24.45 23.05 22.17 16.66 13.22 NR 49.73 47.53 45.52

22.Rupture in

TCO CR line to

C-01

D-5 m/s 148.96 215.63 127.84 119.12 107.38 87.16 186.3 NR 254.2

5

234.1

9

224.9

1

F-2 m/s 117.4 170.24 70.27 62.09 54 87.16 186.3 NR 247.1

3 225.1

207.7

7

Feed

RCO/FCO

Pump (P-

01A/B/C)

23.Leak in

suction line of

Feed RCO/FCO

Pump P-

01A/B/C

D-5 m/s 11.32 24.57 44.63 28.83 NR 31.02 29.30 28.06 54.36 51.11 48.14

F-2 m/s 25 37.51 43.36 28.83 NR NA NA NA 40.17 37.86 35.76


�� Page 44


Condition


LFL ½

LFL

4

kW/m2

12.5

kW/m2

37.5

kW/m2

4

kW/

m2

12.5

kW/m2

37.5

kW/m2

2psi 3psi 5psi

24.Rupture in

suction line of

Feed RCO/FCO

Pump P-

01A/B/C

D-5 m/s 60.27 88.36 54.27 20.27 NR NA NA NA 110.6

2 99.67 91.64

F-2 m/s 53.14 57.36 45.96 17.55 NR NA NA NA 118.5

6

105.3

1 93.19

Feed

RCO/FCO

Pump (P-

02A/B)

25.Leak in

suction line of

Feed CG (Coker

gas) Pump P-

02A/B

D-5 m/s 8.67 20.49 35.11 25.55 13 NA NA NA 27.89 26.11 24.47

F-2 m/s 19.82 33.33 34.21 22.09 11.84 NA NA NA 39.22 37.14 35.23

26.Rupture in

suction line of

Feed CG

(Cooker gas)

Pump P-02 A/B

D-5 m/s 37.19 57.49 36.68 21.99 8.33 NA NA NA 69.64 62.93 57.67

F-2 m/s 31.71 40.85 34.18 17.21 8.05 NA NA NA 70.15 61.79 55.97

Unstablised

gasoline

pump P-

05A/B

27.Leak in

discharge line of

unstablised

gasoline pump P-

05A/B

D-5 m/s 21.35 40.91 NA NA NA 31.24 29.51 28.27 55.53 62.02 48.08

F-2 m/s 15.15 28.38 NA NA NA 25.12 22.42 19.88 67.42 63.48 59.88

28.Rupture in

discharge line of

unstablised

gasoline pump P-

05A/B

D-5 m/s 27.54 44.18 NA NA NA 46.15 35.11 33.2 58.3 47.3 37.38

F-2 m/s 20.73 55.79 NA NA NA 39.68 28.43 24.67 72.34 65.43 62.24

HP

separator V-

05

29.Leak in outlet

line from HP

separator v-05



30.Rupture in

inlet line from D-5 m/s 22.73 38.11 NA NA NA 174.1

4 90.65 26.94

111.3

6 90.68 71.79


�� Page 45


Condition


LFL ½

LFL

4

kW/m2

12.5

kW/m2

37.5

kW/m2

4

kW/

m2

12.5

kW/m2

37.5

kW/m2

2psi 3psi 5psi

HP separator V-

05 F-2 m/s 17.15 23.58 NA NA NA 171.3

3 86.25 24.33

109.1

1 88.94 70.51

LPG R/D

Pump P-

15A/B

31.Leak in

discharge line of

LPG R/ D Pump

P -15A/B

D-5 m/s 19.26 48.34 NA NA NA 26.86 24.52 22.95 51.56 48.94 46.55

F-2 m/s 25.09 70.76 NA NA NA 30.18 22.45 16.33 85.04 81.04 78.03

32.Rupture in

discharge line of

LPG R/ D Pump

P -15A/B

D-5 m/s 81.63 137.24 NA NA NA 164.0

2 86.29 29.32

147.9

3

139.3

5

131.8

7

F-2 m/s 52.89 96.85 NA NA NA 164.0

2 86.29 29.32

119.1

6

110.2

3

103.3

8

Debutanizer

C-06)

33.Leak in inlet

feed line to

Stabilizer/Debuta

nizer C-06

D-5 m/s 17.59 44.29 NR NR NR 26.56 24.54 23.31 51.37 48.79 46.44

F-2 m/s 24.83 68.64 32.4 31.21 30.49 27.88 21.36 15.54 75.52 72 68.79

34.Rupture in

inlet line to

Stabilizer/Debuta

nizer

D-5 m/s 255.4

8

287.3

8 222.58

214.0

9

204.5

6

218.4

1

222.1

7 77.37

257.3

4

227.2

7

203.1

5

F-2 m/s 223.8

7

231.7

1 137.39 124

114.7

2

210.4

1

218.1

7 70.37

248.9

2

215.2

1

185.5

2

Stablizer

Gasoline

Bottom

Pump P-

16A/B

35.Leak in

discharge line

from Stablizer

Gasoline Bottom

Pump

P-16A/B

D-5 m/s 16.74 35.42 48.9 23.19 NR NR NR NR 55.04 44.85 35.53

F-2 m/s 13.71 26.32 41.7 18 NR NR NR NR 57.46 46.72 36.9

36.Rupture in

discharge line

from Stablizer

Gasoline Bottom

Pump

D-5 m/s 26.29 37.14 64.6 53.98 40.34 29.86 28.26 NR 44.98 41.59 38.49

F-2 m/s 20.31 48.88 54.31 37.43 28.67 23.82 22.04 20.08 57.32 53.39 49.81


�� Page 46


Condition


LFL ½

LFL

4

kW/m2

12.5

kW/m2

37.5

kW/m2

4

kW/

m2

12.5

kW/m2

37.5

kW/m2

2psi 3psi 5psi

P-16A/B

Wet gas

compressor

K-01

37.Leak in

inletline to Wet

gas compressor

K-01

D-5 m/s 1.83 2.97 NA NA NA NR NR NR NR NR NR

F-2 m/s 2.03 3.73 NA NA NA NR NR NR NR NR NR

38.Rupture in

inlet line to Wet

gas compressor

K-01

D-5 m/s 38.16 141.27 NA NA NA NR NR NR NR NR NR

F-2 m/s 25.41 218.72 NA NA NA 158.2

2 72.01 NR

141.4

3

116.2

1 95.58


�� Page 47

CHAPTER- 5: RISK ANALYSIS

5.1 Individual Risk

The results of Risk Analysis are often reproduced as Individual Risk. Individual Risk is the

probability of death occurring as a result of accidents at a fixed installation or a transport route

expressed as a function of the distance from such an activity.

There are no specified risk acceptance criteria as yet in our country for Individual Risk levels. A

review of risk acceptance criteria in use in other countries indicates the following:

• For fixed installations Official Individual Risk Criteria have been developed by various

countries and the review indicates that Individual Risk of fatality to the members of the

public outside the installation boundaries may be adopted as higher 10-5

per year (in

populated areas) for intolerable risk and lower than 10-6

per year for negligible risk. The

region in between is the so-called ALARP region where risk is acceptable subject to its

being As Low As Reasonably Practicable (the ALARP principle).

• The individual risk results show the geographical distribution of risk. It is the frequency

at which an individual may be expected to sustain a given level of harm from the

realization of specified hazards and is normally taken as risk of death (fatality). It is

expressed as risk per year.

• Individual risk is usually presented in the form of Individual Risk Contours, which are

also commonly known as ISO Risk Curves. This is the risk to a hypothetical individual

being present at that location continuously there for 24 hours a day and 365 days a year.

5.1.1 Individual risk acceptability criteria

As per IS15656:2006 Indian Standard code of practice on hazard identification & Risk analysis,

in many countries the acceptable risk criteria has been defined for the industrial installations and

are shown in below Table

Table 28: Acceptable Risk Criteria of various countries

Authority and Application Maximum tolerable risk (per

year)

Negligible risk(per

year)

VROM, the Netherlands (New) 1 x 10-6

1 x 10-8

VROM, the Netherlands (Existing) 1 x 10-5

1 x 10-8

HSE, UK (Existing hazardous

industries)

1 x 10-4

1 x 10-6


�� Page 48

HSE, UK (Nuclear power station) 1 x 10-5

1 x 10-6

HSE, UK (Substance transport) 1 x 10-4

1 x 10-6

HSE, UK (New Housing near plants) 3 x 10-5

3 x 10-7

Hong Kong Government (new plants) 1 x 10-5

Not Used

Since there are no guidelines on the tolerability of fatality risk sanctioned in India to date, to

demonstrate the risk to employee and public the following are considered.

� If the average expectation of life is about 75 years, then the imposition of an annual

risk of death to individual is 0.01 (one in one hundred years), it seems unacceptable.

Hence 1 in 1000 years, it may not be totally unacceptable if the individual knows of

the situation, has been considered as upper limit of the ALARP triangle for people

working inside the Refinery complex.

� Lower limit of ALARP triangle is taken as 1 x 10-5

per year for people working inside

the Refinery complex.

� Upper limit of tolerable risk to a member of general public is taken as 1 x 10-3

per

year.

� Similarly, 1 x 10-6 per year (Negligible risk) is considered for public to demonstrate

the risk. This is the lower limit of the ALARP triangle.

The Individual Risk per Annum levels discussed above is demonstrated graphically in the so

called “ALARP triangle” represented in Figure-9. In the lower region, the risk is considered

negligible, provided that normal precautions are maintained. The upper region represents an

intolerable risk must be reduced. The area between these two levels is the “ALARP Region (As

Low As Reasonably Practicable)” in which there is a requirement to apply ALARP principle.

Any risk that lies between intolerable and negligible levels should be reduced to a level which is

“As Low As Reasonably Practicable”.

For Transportation facilities, the Risk tolerability criteria as set in the ACDS Transport Hazards

Report published by the HSE of the UK adopts fatality risk 10-3

per year as ‘intolerable’ while

fatality risk of 10-6

per year is adopted as ‘broadly acceptable’. The ALARP principle then

implies that if the fatality risk from a particular transport activity lies between 10-6

per year and

10-3

per year, then efforts should be made to reduce to it to as low a level as reasonably

practicable.

The individual risks from an activity are the result of the cumulative of risks connected with all

possible scenarios.


�� Page 49

The individual risk results show the geographical distribution of risk. It is the frequency at which

an individual may be expected to sustain a given level of harm from the realization of specified

hazards and is normally taken as risk of death (fatality). It is expressed as risk per year.

In case of INDMAX unit, the Individual Risk Contours run close to the Refinery.

Figure 3: Overall ISO-Risk Contour


�� Page 50

Figure 4: Enlarged Iso-Risk Contours for INDMAX unit


�� Page 51

Figure 5: Enlarged Iso-Risk Contours for INDMAX unit

5.1.2 Location Specific Individual Risk (LSIR)

The highest location-specific individual risk (LSIR) contour in INDMAX unit at Guwahati

refinery is of 1E-05 per year which is within the INDMAX unit.

The maximum LSIR in the unit are listed in Table below

Table 29: Maximum LSIR at INDMAX unit

S. No. Unit Maximum LSIR

1. HDT/HGU Field Operator Room 6.57E-08

2. SRU block Field Operator Room 2.31E-08



�� Page 52

5.1.3 Individual Specific Individual Risk (ISIR)

Individual risk to worker at INDMAX unit is calculated as 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 risk acceptability criteria is given in Figure: 6

HDT/HGU Field Operator Room

The maximum LSIR in HDT/HGU Field Operator Room unit is 6.57E-08 per year. The person

in this area work 8 hour shift. During the shift, an individual person is expected to be present in

the room for all the 8 hours. The individual specific individual risk(ISIR) is estimated as follows.

ISIR operator room = 6.57x10-8

x (8/24) x (8/8) = 2.19 x 10-8

per year

SRU block Field Operator Room

The maximum LSIR in SRU block Field Operator Room is 2.31E-08 per year. The person in this

area work 8 hour shift. During the shift, an individual person is expected to be present in the

room for all the 8 hours. The individual specific individual risk (ISIR) is estimated as follows.


x (8/24) x (8/8) = 7.7 x 10-9

per year

INDMAX Field Operator room

The maximum LSIR in INDMAX Field Operator Room is 1.14E-07 per year. The person in this

area work 8 hour shift. During the shift, an individual person is expected to be present in the

room for all the 8 hours. The individual specific individual risk (ISIR) is estimated as follows.


x (8/24) x (8/8) = 3.8 x 10-8

per year

Table 30: Maximum ISIR at INDMAX unit

S. No. Unit Maximum ISIR





�� Page 53

From the results shown above, the maximum individual risk to plant personnel at INDMAX unit

is estimated as 3.8E-08 per year. This is below the unacceptable individual risk criteria (10-3

per

year) as follow in the lower part of the ALARP region.

Figure 6: ALARP summary of INDMAX unit

5.2 Societal Risk

It is the risk experience in a given time period by the whole group of personnel exposed,

reflecting the severity of the hazard and the number of people in proximity to it. It is defined as

the relationship between the frequency and the number of people suffering a given level of harm

(normally taken to refer to risk of death) from the realization of the specified hazards It is

expressed in the form of F-N curve.

Societal risk acceptability criteria

A formal risk criterion is used at all for societal risk; the criterion most commonly used is the FN

curve. Like other forms of risk criterion, the FN curve may be cast in the form of a single

criterion curve or of two criterion curves dividing the space in to three regions – where the risk is

unacceptable, where it is negligible and where it requires further assessment. The latter approach

corresponds to application to societal risk of the ALARP principle. Risk criteria for the

Netherlands have been considered for the present study and it is represented in Figure given

below


�� Page 54

Figure 7: Societal Risk Criteria


�� Page 55

Figure 8: FN Curve for Group Risk at INDMAX unit

Top risk contributors (Societal risk)

The table given below presents major contributing scenarios to societal risk form INDMAX unit.

Table 31: Top Risk Contributors at INDMAX unit

S.

No.

Scenario Societal risk

contribution (%)

1. Rupture in inlet line to stabilizer/Debutainizer C-06 52.09

2. Rupture from shell side of TCO CR/C2 Sripper Feed

Exchanger(E-06 A/B)

22.34

3. Leak from shell side of TCO CR/C2 Sripper Feed

Exchanger(E-06 A/B)

11.72

4. Rupture in TCO CR line to main fractionators column C-01 2.22

5. Leak in discharge line of LPG R/D Pump (P-15 A/B) 1.01


�� Page 56

CHAPTER-6: COMPARISON AGAINST RISK ACCEPTANCE CRITERIA

A risk analysis provides a measure of the risks resulting from a particular facility or activity. It

thus finds application as a decision making tool in situations where judgment has to be made

about the tolerability of the risk posed by an existing/proposed activity. However, risk analysis

produces only numbers, which themselves provide no inherent use. It is the assessment of those

numbers that allows conclusions to be drawn and recommendations to be developed. The normal

approach adopted is to relate the risk measures obtained to risk acceptance criteria.

Risk criteria, if they are to be workable, recognizes the following:

• There is a level of risk that is so high that it is considered unacceptable or intolerable

regardless of the benefits derived from an activity.

• There is also a level of risk that is low enough as to be considered negligible.

• Levels of risk in between are to be considered tolerable subject to their being reduced As

Low As is Reasonably Practicable (ALARP). (The meaning of ALARP is explained in

the following sub-section.)

• The above is the formulation of the, now well-established, three tier structure of risk

criteria and risk control.

• The risk criteria simply attempt to establish whether risk is “tolerable”. Below is a list of

words generally in use and their meaning.

ACCEPTABLE RISKS: Since risks in general are unwelcome no risk should be called

“acceptable”. It might be better to say that the activity may be acceptable generally, but the risks

can only ever be tolerable.

TOLERABLE RISKS: are risks the exposed people are expected to bear without undue

concern. A subtle difference is made out here between Acceptable Risks and Tolerable Risks

though these terms are sometimes used interchangeably.

NEGLIGIBLE RISKS: are risks so small that there is no cause for concern and there is no

reason to reduce them.

6.1 The ALARP Principle

The ALARP (As Low As is Reasonably Practicable) principle seeks to answer the question

“What is an acceptable risk?” The definition may be found in the basis for judgment used in

British law that one should be as safe as is reasonably practicable. Reasonably practicable is

defined as implying “that a computation must be made in which the quantum of risk is placed on

scale and the sacrifice involved in the measures necessary for averting the risk (whether in

money, time, or trouble) is placed on the other, and that, if it be shown that there is a gross


�� Page 57

disproportion between them – risk being insignificant in relation to the sacrifice – the defendants

discharge the onus upon them” The ALARP details are represented in the Figure below

Figure 9: ALARP Detail

ALARP summary: The Individual and Societal risk per year of INDMAX unit is lower of

ALARP region.


�� Page 58

CHAPTER-7: RECOMMENDATIONS FOR RISK REDUCTION

7.1 Conclusion and Recommendations

Although the results of this Risk analysis show that the risks to the public are broadly acceptable

(or negligible), they will be sensitive to the specific design and/or modeling assumptions used.

The maximum risk to persons working in the INDMAX unit is 3.8x10-8

per year which is below

the unacceptable level and is in the lower part of ALARP triangle.

It is observed that the iso-risk contour of 1x10-5

per year is within the INDMAX unit and the risk

contour of 1x10-6

per year extended to the adjoining facilities on South East direction which have

storage tankage and SRU unit.

The high risk contributors in the INDMAX unit are Stabilizer/Debutanizer and TCO CR/C2

Stripper Feed exchanger (E-06A/B).

The major conclusions and recommendations based on the risk analysis of the identified

representative failure scenarios are summarized below:

� The individual risk from all scenarios is found below the ALARP region for Employee and

Public for INDMAX unit.

� The INDMAX unit of Guwahati refinery is covered in the process safety management

system of Guwahati refinery.

� Mitigate the risk by preventing toxic cloud travelling beyond the plant boundary in South

West side but the concentration of Hydrocarbons beyond the boundary is very low,

therefore no specific mitigation measures are required for that point.

� Smoking booths existing in non hazardous area.

� Gas detectors are provided at critical locations. Operators are well trained about the fire and

gas detection systems.

� Emergency stop of critical equipments are available in control room.

� CCTV coverage with perimeter monitoring available.

� The vehicles entering the refinery should be fitted with spark arrestors.

� Routine checks to be done to ensure and prevent the presence of ignition sources in the

immediate vicinity of the refinery (near boundaries).

� Clearly defined escape routes shall be developed for each individual plots and section of

the INDMAX unit taking into account the impairment of escape by hazardous releases and

sign boards be erected in places to guide personnel in case of an emergency.

� Well defined muster stations in safe locations shall be identified for personnel in case of an

emergency.

� Windsocks existing in all prominent locations with clear visibility.

� Identificatio of critical equipments done & inspection methodologies existing for

inspection during shutdown.


�� Page 59

� The active protection devices like fire water sprinklers and other protective devices shall be

tested at regular intervals.

� SOP should be established for clarity of actions to be taken in case of fire/leak emergency.

General conclusion and Recommendations:

1. Nearest tank of INDMAX Unit is T-23, T-15, T-16 and T-28 TANK ON FIRE could

affect adjacent tanks in same dyke. Also heat radiations from the tank on fires will

slightly affect the INDMAX Unit but the intensity is not so high to cause major damage

to the unit. Fixed water sprays system is available on all nearest tanks, irrespective of

diameter where inter distances between tanks in a dyke and/or within dykes are not

meeting the requirements of OISD-STD-118.

2. Ensure that combustible flammable material is not placed near the Critical instrument of

the INDMAX Unit. These could include oil filled cloths, wooden supports, oil buckets

etc. these must be put away and the areas kept permanently clean and free from any

combustibles. Secondary fire probability would be greatly reduced as a result of these

simple but effective measures.

3. Sprinklers and foam pourers provided. Monitors & hydrants located at a distance more

than 15 meters.

4. ROSOV and Hydrocarbon detectors to be provided with the nearest tank of the INDMAX

unit.

5. Since Refinery operation is being done 24 Hrly. Lighting arrangements are available in

line.

**********

Annexure-A

1. Rupture in inlet feed line to stabilizer/debutanizer C-06- Pool Fire

2. Rupture in inlet feed line to stabilizer/debutanizer C-06- Jet Fire

3. Rupture in inlet feed line to stabilizer/debutanizer C-06- Flash Fire

4. Rupture in inlet feed line to stabilizer/debutanizer C-06- VCE

5. Rupture from shell side of TCO CR/C2 stripper feed exchanger (E-06 A/B)- Pool Fire

6. Rupture from shell side of TCO CR/C2 stripper feed exchanger (E-06 A/B)-Flash fire

7. Rupture from shell side of TCO CR/C2 stripper feed exchanger(E-06 A/B)-VCE

8. Leak from shell side of TCO CR/C2 stripper feed exchanger(E-06 A/B)- Pool fire

9. Leak from shell side of TCO CR/C2 stripper feed exchanger(E-06 A/B)- Jet fire

10. Leak from shell side of TCO CR/C2 stripper feed exchanger(E-06 A/B)- Flash fire

11. Leak from shell side of TCO CR/C2 stripper feed exchanger(E-06 A/B)- VCE

12. Rupture in TCO CR line to main fractionators column C-01- Pool Fire

13. Rupture in TCO CR line to main fractionator column C-01- Jet Fire

14. Rupture in TCO CR line to main fractionator column C-01- Flash Fire

15. Rupture in TCO CR line to main fractionator column C-01- VCE

16. Leak in discharge line of LPG R/D pump (p-15A/B)- Jet Fire

17. Leak in discharge line of LPG R/D pump (p-15A/B) - Flash Fire

18. Leak in discharge line of LPG R/D pump (p-15A/B) – VCE

TANK- 23 HSD

SOURCE STRENGTH: Tank No. 23 HSD

Leak from hole in vertical cylindrical tank

Flammable chemical escaping from tank

Tank Diameter: 22.8 meters

Tank Length: 11.7 meters

Internal Temperature: Equal to ambient

Tank is 80% full

Circular Opening Diameter: 10 centimeters

Opening is 1 meters from tank bottom

THREAT ZONE: Toxic area of vapour cloud.

Red: 40 meters --- (7.9 ppm = PAC-3)

Note: Threat zone was not drawn because effects of near-field patchiness make dispersion

predictions less reliable for short distances.

Orange: 1.3 kilometers --- (0.031 ppm = PAC-2)

Yellow: 5.1 kilometers --- (0.0028 ppm = PAC-1)

Scenario: Toxic area of vapour cloud T-23 HSD Tank is near to INDMAX unit.

Thermal radiation from pool fire, Tank 23, HSD

THREAT ZONE: Thermal radiation from fire ball (BLEVE)

(INDMAX UNIT nearest tank T-23 explodes)

Threat Modeled: Thermal radiation from fireball Red: 1.7 kilometers (10.0 kW/(sq m) =

potentially lethal within 60 sec), Orange: 2.3 kilometers (5.0 kW/(sq m) = 2nd degree burns

within 60 sec), Yellow: 3.6 kilometers (2.0 kW/(sq m) = pain within 60 sec)

SOURCE STRENGTH: Tank No.15 (TCO)


Flammable chemical escaping from tank




Tank is 80% full



Toxic area of vapour cloud

Red : 40 meters --- (7.9 ppm = PAC-3)



Orange: 1.3 kilometers (0.031 ppm = PAC-2),

Yellow: 5.1 kilometers (0.0028 ppm = PAC-1)

Toxic area of vapour cloud Tank- 15 (TCO)

Thermal radiation from pool fire. T-15 (TCO)


(INDMAX UNIT nearest tank T-15 explodes)

THREAT ZONE: Threat Modeled: Thermal radiation from fireball Red : 1.3 kilometers (10.0

kW/(sq m) = potentially lethal within 60 sec), Orange: 1.8 kilometers- (5.0 kW/(sq m) = 2nd

degree burns within 60 sec), Yellow: 2.8 kilometers- (2.0 kW/(sq m) = pain within 60 sec)

SOURCE STRENGTH: Tank- 16(SKO)




Tank Capacity: 2000KL


Tank is 80% full



Threat Zone:

Red : 40 meters --- (440 ppm = PAC-3)



Orange: 72 meters --- (20 ppm = PAC-2)

Note: Threat zone was not drawn because dispersion predictions are unreliable for lengths less

than the maximum diameter of the puddle.

Maximum diameter of the puddle: 80 meters Yellow: 482 meters --- (1.9 ppm = PAC-1)

Toxic area of vapour cloud T-16( SKO)

Thermal radiation from pool fire, T-16 SKO


(INDMAX UNIT nearest tank T-16 explodes) Threat Modeled: Thermal radiation from

fireball

Red-1.3 kilometers (10.0 kW/(sq m) = potentially lethal within 60 sec), Orange: 1.8 kilometers

(5.0 kW/(sq m) = 2nd degree burns within 60 sec),Yellow: 2.8 kilometers (2.0 kW/(sq m) = pain

within 60 sec)

Toxic area of vapour cloud. Tank No. 28 HSD.

SOURCE STRENGTH:

Leak from hole in vertical cylindrical tank -28 HSD

Flammable chemical is burning as it escapes from tank



Tank Capacity 5000KL


Tank is 80% full



THREAT ZONE:

Threat Modeled: Thermal radiation from pool fire

Red: 27 meters (10.0 kW/(sq m) = potentially lethal within 60 sec)

Orange: 36 meters (5.0 kW/(sq m) = 2nd degree burns within 60 sec)

Yellow: 54 meters (2.0 kW/(sq m) = pain within 60 sec)

Thermal radiation from pool fire: Tank -28 HSD