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TRANSCRIPT
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RISK ASSESSMENT STUDY FOR INDMAX UNIT:
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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.
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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.
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Table-2: Maximum Individual Specific Individual Risk (ISIR) at INDMAX unit
S. No. Unit Maximum ISIR
1. HDT/HGU field Operator room 2.19E-08
2. SRU block field Operator room 7.7E-09
3. INDMAX Field Operator room 3.8E-08
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.
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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
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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.
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� 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.
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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.
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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
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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
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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
RISK ASSESSMENT STUDY FOR INDMAX UNIT
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
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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
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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
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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)
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• 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
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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
S.No. Properties Values
1. LFL (%v/v) 4.12
2. UFL (%v/v) 74.2
3. Auto ignition temperature (°C) 500
4. Heat of combustion (Kcal/Kg) 28700
5. Normal Boiling point (°C) -252
6. Flash point (°C) NA
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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
S.No. Properties Values
1. LFL (%v/v) 0.8
2. UFL (%v/v) 5.0
3. Auto ignition temperature (°C) 228
4. Heat of combustion (Kcal/Kg) 10100
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
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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
S.No. Threshold Limits Concentration
(ppm)
1. Short Term Exposure Limit
(STEL) (15 Minutes)
2
2. Immediately Dangerous to Life
and Health (IDLH) level (for 30
min exposure)
10
S.No. Threshold Limits Concentration
(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
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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
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Equipment Scenario Flow rate
(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
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Equipment Scenario Flow rate
(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
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Equipment Scenario Flow rate
(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
27.Leak in discharge
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
31.Leak in discharge
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
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Equipment Scenario Flow rate
(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
35.Leak in discharge
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
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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
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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
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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.
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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
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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.
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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
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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
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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.
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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.
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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.
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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
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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 √ √ √ √
2. Rupture from shell side of TCO CR/C2 Stripper Feed
Exchanger (E-06A/B) - √ √ √
3. Leak from shell side of TCO CR/C2 Stripper Feed
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
S.No. Description Jet
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 - - - -
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S.No. Description Jet
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 √ - √ -
19. Leak from shell side of TCO CR/C2 Stripper Feed
Exchanger (E-06a/B) √ √ √ √
20. Rupture from shell side of TCO CR/C2 Stripper Feed
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 √ √ √ √
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S.No. Description Jet
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
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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
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Table 27: Consequence Analysis – Scenario result
Equipment 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
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),
SO2=100ppm NA NA NA NA NA NA NA NA NA NA NA
2.Rupture in inlet
flue gas line
from
Regenerator
cyclone to orifice
chamber V-20
D-5 m/s (IDLH 65m)
SO2=100ppm NA NA NA NA NA NA NA NA NA NA NA
F-2 m/s (IDLH 73.25m)
SO2=100ppm NA NA NA NA NA NA NA NA NA NA NA
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
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Equipment 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
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
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Equipment 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
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
D-5 m/s 4.01 6.04 NA NA NA 6.68 NR NR NR NR NR
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
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Equipment 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
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
F-2 m/s 6.72 22.76 NA NA NA 45.24 16.33 NR NR NR NR
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
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Equipment 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
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
D-5 m/s 4.16 6.25 NA NA NA 7.35 NR NR NR NR NR
F-2 m/s 4.54 7.6 NA NA NA 7.63 4.92 NR NR NR NR
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
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Equipment 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
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
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Equipment 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
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
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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
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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.
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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
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Figure 4: Enlarged Iso-Risk Contours for INDMAX unit
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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
3. INDMAX Field Operator room 1.14E-07
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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.
ISIR operator room = 2.31x10-8
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.
ISIR operator room = 1.14x10-7
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
1. HDT/HGU field Operator room 2.19E-08
2. SRU block field Operator room 7.7E-09
3. INDMAX Field Operator room 3.8E-08
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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
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Figure 7: Societal Risk Criteria
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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
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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
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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.
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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.
RISK ASSESSMENT STUDY FOR INDMAX UNIT
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� 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)
Leak from hole in vertical cylindrical tank
Flammable chemical escaping from tank
Tank Diameter: 15.25 meters
Tank Length: 11.74 meters
Internal Temperature: Equal to ambient
Tank is 80% full
Circular Opening Diameter: 10 centimeters
Opening is 1 meters from tank bottom
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)
Toxic area of vapour cloud Tank- 15 (TCO)
Thermal radiation from pool fire. T-15 (TCO)
THREAT ZONE: Thermal radiation from fire ball (BLEVE)
(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)
Leak from hole in vertical cylindrical tank
Tank Diameter: 15.25 meters
Tank Length: 11.74 meters
Tank Capacity: 2000KL
Internal Temperature: Equal to ambient
Tank is 80% full
Circular Opening Diameter: 10 centimeters
Opening is 1 meters from tank bottom
Threat Zone:
Red : 40 meters --- (440 ppm = PAC-3)
Note: Threat zone was not drawn because effects of near-field patchiness make dispersion
predictions less reliable for short distances.
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
THREAT ZONE: Thermal radiation from fire ball (BLEVE)
(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 Diameter: 22.9 meters
Tank Length: 13.6 meters
Tank Capacity 5000KL
Internal Temperature: Equal to ambient
Tank is 80% full
Circular Opening Diameter: 10 centimeters
Opening is 1 meters from tank bottom
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