risk assessment for furnace oil storage tank...in such cases contents of the biggest vessel / tank...

QRA Study for Seshasayee Paper and Boards Limited, Erode of 18

RISK ASSESSMENT FOR FURNACE OIL STORAGE TANK:

Overview

Risk Analysis is proven valuable as a management tool in assessing the overall safety

performance of the chemical process industry and hazardous substance handling operations

at a specific location. Although management systems such as engineering codes, checklists,

and reviews by experienced engineers have provided substantial safety assurances, major

incidents involving numerous casualties, injuries and significant damage can occur - as

illustrated by recent world-scale catastrophes. Risk Analysis techniques provide advanced

quantitative means to supplement other hazard identification, analysis, assessment, control

and management methods to identify the potential for such incidents and to evaluate

control strategies.

Risk in general is defined as a measure of potential economic loss or human injury in terms

of the probability of the loss or injury occurring and magnitude of the loss or injury if it

occurs. Risk thus comprises of two variables; magnitude of consequences and the

probability of occurrence. The results of Risk Analysis are often reproduced as Individual and

groups risks and are defined as below.

Individual Risk is the probability of death occurring as a result of accidents at a plant,

installation or a transport route expressed as a function of the distance from such an

activity. It is the frequency at which an individual or an individual within a group may be

expected to sustain a given level of harm (typically death) from the realization of specific

hazards. Such a risk actually exists only when a person is permanently at that spot (out of

doors). The exposure of an individual is related to the following factors such as:

The likelihood of occurrence of an event involving a release and

Ignition of hydrocarbon,

The vulnerability of the person to the event,

The proportion of time the person will be exposed to the event (which is termed

'occupancy' in the QRA terminology).

The second definition of risk involves the concept of the summation of risk from events

involving many fatalities within specific population groups. This definition is focused on the

risk to society rather than to a specific individual and is termed 'Societal Risk'. In relation to


the process operations we can identify specific groups of people who work on or live close

to the installation; for example communities living or working close to the plant.

PHAST v6.7 and PHAST Risk Micro v6.7

The software developed by DNV is used for risk assessment studies involving flammable and

toxic hazards where individual and societal risks are also to be identified. It enables the user

to assess the physical effects of accidental releases of toxic or flammable chemicals.

PHAST v6.7 is used for consequence calculations and PHAST Risk Micro v6.7 is used for risk

calculations.

Risk Assessment Methodology

Hazard identification and risk assessment involves a series of steps as follows:

Step 1: Identification of the Hazard

Hazard Identification is a critical step in Risk Analysis. Many aids are available, including

experience, engineering codes, checklists, detailed process knowledge, equipment failure

experience, hazard index techniques, What-if Analysis, Hazard and Operability (HAZOP)

Studies, Failure Mode and Effects Analysis (FMEA), and Preliminary Hazard Analysis (PHA). In

this phase all potential incidents are identified and tabulated. Site visit and study of

operations and documents like drawings, process write-up etc are used for hazard

identification.

Step 2: Assessment of the Risk

Consequence Estimation is the methodology used to determine the potential for damage or

injury from specific incidents. A single incident (e.g. rupture of a pressurized flammable

liquid tank) can have many distinct incident outcomes, (e.g. Thermal radiation due to Pool

fire). Likelihood assessment is the methodology used to estimate the frequency or

probability of occurrence of an incident. Estimates may be obtained from historical incident

data on failure frequencies or from failure sequence models, such as fault trees and event

trees. In this study the historical data developed by software models and those collected by

CPR18E – Committee for Prevention of Disasters, Netherlands (Edition: PGS 3, 2005) are

used. Risks arising from the hazards are evaluated for its tolerability to personnel, the

facility and the environment. The acceptability of the estimated risk must then be judged

based upon criteria appropriate to the particular situation.


Step 3: Elimination or Reduction of the Risk

This involves identifying opportunities to reduce the likelihood and/or consequence of an

accident Where deemed to be necessary. Risk Assessment combines the consequences and

likelihood of all incident outcomes from all selected incidents to provide a measure of risk.

The risk of all selected incidents are individually estimated and summed to give an overall

measure of risk. Risk-reduction measures include those to prevent incidents (i.e. reduce the

likelihood of occurrence) to control incidents (i.e. limit the extent and duration of a

hazardous event) and to mitigate the effects (i.e. reduce the consequences). Preventive

measures, such as using inherently safer designs and ensuring asset integrity, should be

used wherever practicable. In many cases, the measures to control and mitigate hazards

and risks are simple and obvious and involve modifications to conform to standard practice.

The general hierarchy of risk reducing measures is:

Prevention (by distance or design)

Detection (e.g. fire and gas, Leak detection)

Control (e.g. emergency shutdown and controlled depressurization)

Mitigation (e.g. fire fighting and passive fire protection)

Emergency response (in case safety barriers fail)

The current study is limited to evaluation of risk associated with the Flammable inventory

in the furnace oil tank farm area.


Overview of Risk Assessment Methodology

Consequence Assessment:

Accidental release of flammable liquids can result in severe consequences. Delayed ignition

of flammable liquid results in pool Fire. Furnace Oil having very less vapour pressure i.e. less

tendency to evaporate. Considering this Flash fire and Explosion are not envisaged in case of

release of furnace oil.

The effect of fire on a human being is in the form of burns. There are three categories of

burn such as first degree, second degree and third degree burns. The consequences caused

by exposure to heat radiation are a function of:

The radiation energy onto the human body [kW/m2]; The exposure duration [sec]; The protection of the skin tissue (clothed or naked body). The lethality of a pool fire is assumed to be 100% for the people who are caught in

the flame. Outside the flame area, the lethality depends on the heat radiation distances.


The limits for 1% of the exposed people to be killed due to heat radiation, and for second-

degree burns are given in the table below (Reference from Guidelines for Hazard Evaluation

Procedures, Centre for Chemical Process Safety, American Institute of Chemical Engineers)

Exposure Duration Radiation energy

(1% lethality, kW/m2

Radiation energy for 2nd degree burns,

kW/m2

Radiation energy for first degree burns,

kW/m2

10 Sec 21.2 16 12.5

30 Sec 9.3 7.0 4.0

Table 1 – Damages to Human Life Due to Heat Radiation

Incident

Radiation

(kW/m2)

Type of Damage

0.25-0.7 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.

37.5 Heavy Damage to process equipments

Table 2– Effects Due To Incident Radiation Intensity

Meteorological Data:

The consequence of released flammable material is largely dependent on the prevailing

weather conditions. For the risk analysis of major scenarios the most important

meteorological parameters are wind speed, atmospheric stability, relative humidity, surface

roughness and temperature as they directly affect the atmospheric dispersion of the

released material. Risk analysis, modelling is based on the following weather categories as

derived from metrological data provided by client.


Windrose Diagram

Wind Speed

(m/s)

Stability

Class Description

1.5 F This is typical of during night time with low wind speed.

5 D This is typical of day time situation, with moderate wind

fluctuations

Table 3 – Wind Speed and Stability Class

Atmospheric Temperature : 33 C

Surface Roughness : 0.3m

Average Relative Humidity : 70%


Scenarios Considered for the Risk Estimations

The following scenarios have been considered for the consequence-distance calculations,

which have been computed for the accidental release and fire scenarios considered.

Leak of furnace oil from tank

Pool fire at furnace oil storage tank

Summary of assumptions considered in the modeling

Leak of tank containing solvent is for 10 minutes

1.5 F and 5D Weather condition is considered

All furnace oil storage tanks are at 1atm pressure and temperature of 30degC

Bund area considered for furnace oil storage tank is 182.25 m2

Bund height considered for the study 2 m

Population details inside SPB-PC Facility 1259

Population details outside SPB-PC Facility

Village Name Population

Odapalli 4879

Pudhupalayam 5704

Hazards Identification:

As per CPR 18E - Guidelines for Quantitative Risk Assessment, developed by the Committee

for the Prevention of Disasters, Netherlands, for each of scenario two leak sizes i.e., hole

sizes are considered for analysis,

Leak – Leak size 10 mm

Rupture – Catastrophic rupture of storage tanks

The following tables present the potential initiating events and credible accident scenarios

identified and quantitatively analysed:

Sr. No. Scenario Description Inventory (Kl)

Pressure (Bar)

Temperature ( C)

1 Leak of furnace oil storage tank (200 Kl) 200 Atmospheric 30

2 Rupture of furnace oil storage tank (200 Kl) 200 Atmospheric 30


Frequency Assessment:

For this study the failure data is taken from CPR 18E – Guidelines for Quantitative Risk

Assessment, developed by the Committee for the Prevention of Disasters, Netherlands.

Internal domino effects are not explicitly covered in QRA. An internal domino needs to be

considered only in case of a situation in which the failure of one component clearly leads to

the failure of another component. In Such cases contents of the biggest vessel / tank needs

to be taken for Instantaneous failure.

The failure frequencies, as per CPR 18E, are provided below

Sr. No. Scenario Description Frequency

(per annum)

1 Leak of furnace oil storage tank (200 Kl) 4.16E-06

2 Rupture of furnace oil storage tank (200 Kl) 2.08E-06

Event Tree:

A release can result in several possible outcomes or scenarios (fire, explosions, unignited

release etc.). This is because the actual outcome depends on other events that may or may

not occur following the initial release. Event tree analysis is used to identify potential

outcomes of a release and to quantify the risk associated with each of these outcomes.


The sample event tree is shown below

Initiating Event

Frequency

Probability of

Immediate Ignition

Probability of Delayed

Ignition

Explosion Probability

Outcome Frequency Event Outcome

Yes 0.01 FF Immediate Pool Fire Explosion

FF 0.4 FF Explosion Yes 0.7 No

0.99 0.6 FF Flash Fire/ Late Pool Fire

No 0.3 FF No Ignition

Please refer Annexure 1 for event tree Analysis.

Consequence Results for Pool Fire:

Sr. No. Scenario Description

Consequence Modeling Results : Pool Fire Weather Condition : 1.5F Weather Condition : 5D

4 kW/m2

12.5 kW/m2

37.5 kW/m2

4 kW/m2

12.5 kW/m2

37.5 kW/m2

1 Leak of furnace oil storage tank (200 Kl) 60 34 14 67 44 21

2 Rupture of furnace oil storage tank (200 Kl) 85 49 21 92 60 31

Analysis of the results

Maximum damage due to pool fire radiations will be caused by Rupture of furnace oil

storage tank (200 Kl), at a weather condition of 1.5F. The pool fire radiation of 37.5 kW/m2

(corresponding to 100% fatality) will reach up to a distance of 21 m at 1.5F weather

condition. The pool fire radiation of 12.5 kW/m2 will reach up to a distance of 49 m at 1.5F

weather condition. The equipments within a distance of 49 m will be subjected to major

damage or piloted ignition of wood, melting of plastics tubings etc is possible within this

distance. The pool fire radiation of 4 kW/m2 will reach up to a distance of 85 m at 1.5F


weather condition. First degree burns may be caused for persons who are within 85 m

distance.

S.No. Facilities

Approximate distance for the facilities (m)

from furnace oil storage tank as per the

layout

Pool Fire

Damage

Distance (m) for

12.5 kW/ m2

1 11Kv transformer yard 12 49

2 Proposed PCC plant 40 49

3 WBL tank 9 49

4 Primary mud washer 20 49

In case of pool fire effect in the furnace oil storage tank, heat radiation level of 12.5 KW/m2

will prevail up to a distance of 49m at 1.5F weather condition. From the above pool fire

consequence values all the nearby existing and proposed facilities like 11Kv transformer

yard, Proposed PCC plant, WBL tank and primary mud washer near to Furnace oil storage

tank are falling under 12.5Kw/m2 heat radiation level region.

Hence it is recommended to provide concrete blocks of 355 mm thickness or of R.C.C. of 200

mm thickness shall be constructed between 11Kv transformer yard transformers, WBL tank

and furnace oil storage tanks.

These walls shall be extended horizontally 600 mm beyond the extremities of the furnace oil

tank and vertically 600 mm above the highest point of the tank.

Estimated Heat Radiation Levels due to Furnace oil Accidental Fires

Heat Radiation Level (KW/m2)

Heat Radiation Distance for Furnace oil storage tank Fire (Pool Fire Scenario) (meters)

Leak 200 Kl Rupture 200 Kl 37.5 14 21 25.0 20 30 12.5 34 49 9.5 40 57 4 60 85

1.6 90 126

Pool fire contours


1. Leak of furnace oil storage tank (200 Kl)

A) 1.5F Weather Condition

B) 5D Weather Condition


2. Rupture of furnace oil storage tank (280 Kl)

A) 1.5F Weather Condition

B) 5D Weather Condition

Legends Heat Radiation Level (KW/m2) 37.5 25 12.5 9.5 4 1.6

Colour


Risk Assessment:

Population Data:

It is necessary to know the population exposure in order to estimate the consequences and

the risk resulting from an incident. The exposed population is often defined using a

population density. Population densities are an important part of a QRA for several reasons.

The most notable is that the density is typically used to determine the number of people

affected by a given incident with a specific hazard area. Sometimes, population data are

available in sketchy forms. In the absence of specific population data default categories can

be used.

The population density can be averaged over the whole area that may be affected or the

area can be subdivided into any number of segments with a separate population density for

each individual segment.

Population details inside SPB-PC Facility 1259

Population details outside SPB-PC Facility

Village Name Population

Odapalli 4879

Pudhupalayam 5704

Individual Risk and Societal Risk:

The Individual Risk per annum (IRPA) measure expresses the risk exposure to any Individual

who is continuously present in a particular area for the whole year. The risk exposure is

calculated for all relevant hazards and summed to give the overall risks for area of the

installation.

Risk Summary

Sr. No. Scenarios Individual Risk (Avg. per Year)

Societal Risk (Avg. per Year)

1 Leak of furnace oil storage tank (200 Kl)

1.33E-06 9.28E-07

2 Rupture of furnace oil storage tank (200 Kl)

1.13E-06 1.10E-06


Individual Risk and Societal Risk Presentation:

1. Leak of furnace oil storage tank (200 Kl)

Individual Risk: 1.33E-06 per avg year

Societal Risk: 9.28E-07 per avg year


2. Rupture of furnace oil storage tank (200 Kl)

Individual Risk: 1.13E-06 per avg year

Societal Risk: 1.10E-06 per avg year


Risk Acceptance Criteria:

The IS 15656 HSE criteria have been proposed for application to average individual risk as

follows:

Authority and Application Maximum Tolerable

Risk (Per Year)

Negligible Risk

(Per Year)

VROM, The Netherlands (New) 1.0E-06 1.0E-08

VROM, The Netherlands (existing) 1.0E-05 1.0E-08

HSE, UK (existing hazardous industry) 1.0E-04 1.0E-06

HSE, UK (New nuclear power station) 1.0E-05 1.0E-06

HSE, UK (Substance transport) 1.0E-04 1.0E-06

HSE, UK (New housing near plants) 3 x 1.0E-06 3 x 1.0E-07

Hong Kong Government (New plants) 1.0E-05 Not used

Table 1 – Risk Criteria

UK HSE Criteria for existing hazardous industry, highlighted in the above table is used for the

study.

Plant workers are working in the Industry on 10 times higher Risk than Social people.


Conclusion:

It is concluded from the above study that Individual Risk and Societal risk curve (F-N Curve) were falls within the tolerable and acceptable region. In case of pool fire effect in the furnace oil storage tank, heat radiation level of 12.5 KW/m2 will prevail up to a distance of 49m at 1.5F weather condition. From the above pool fire consequence values all the nearby existing and proposed facilities like 11Kv transformer yard, Proposed PCC plant, WBL tank and primary mud washer near to Furnace oil storage tank are falling under 12.5Kw/m2 heat radiation level region. Hence it is recommended to provide concrete blocks of 355 mm thickness or of R.C.C. of 200 mm thickness shall be constructed between 11Kv transformer yard transformers, WBL tank and furnace oil storage tanks. These walls shall be extended horizontally 600 mm beyond the extremities of the furnace oil tank and vertically 600 mm above the highest point of the tank. Risk Control Measures

Mitigation measures should also aim at minimizing the quantity of release that may get released during major releases, detection of such leaks and minimizing the consequences due to such incidents. Proposed Facilities to be provided as per Pre feasibility report

Extension of existing plant hydrant network (with augmentation of pumps, if required) for new project facilities will be done.

Further, it will consist of fire alarm systems for control room, MCC room and cable alleys.

Portable extinguishers at strategic locations in the plant will be provided. Risk Control Measures Suggested

1. As per OISD 129, ensure that regular internal inspection along with ultrasonic thickness survey for storage tanks to be done in intervals of every ten years and external inspection for storage tanks to be done in intervals of every three years.

2. Provide concrete blocks of 355 mm thickness or of R.C.C. of 200 mm thickness shall be constructed between 11Kv transformer yard transformers, WBL tank and furnace oil storage tanks.

3. Onsite Emergency Response & Disaster Management Plan should be developed for the facility.

4. Ensure that bunds provided at the tank farm have proper drainage system. 5. Ensure that all the storage tanks are to be earthed separately as per IS 3043-1966. 6. Ensure that fire extinguisher and its components are inspected at regular intervals. 7. Ensure that fire alarms are tested at least once in a week. 8. Ensure that spill Management Kits are available and it should be maintained

properly. 9. To carry out adequacy check of fire water system for the upgraded facility.


ANNEXURE – 1: EVENT TREE ANALYSIS

Leak of furnace oil storage tank

Initiating Event

Frequency

Probability of

Immediate Ignition


Ignition

Explosion Probabilit

y

Outcome Frequenc

y Event Outcome

Yes 0.01 1.00E-06 Immediate Pool Fire Explosion

1.00E-04 0.4 2.77E-05 Explosion Yes 0.7 No

0.99 0.6 4.16E-05 Flash Fire/ Late Pool Fire

No 0.3 2.97E-05 No Ignition

Rupture of furnace oil storage tank

Initiating Event

Frequency

Probability of

Immediate Ignition


Ignition

Explosion Probabilit

y

Outcome Frequenc

y Event Outcome

Yes 0.01 5.00E-08 Immediate Pool Fire Explosion

5.00E-06 0.4 1.39E-06 Explosion Yes 0.7 No

0.99 0.6 2.08E-06 Flash Fire/ Late Pool Fire

No 0.3 1.49E-06 No Ignition

risk assessment for furnace oil storage tank...in such cases contents of the biggest vessel / tank...

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