RISK ANALYSIS REPORT

Transcription

1 RISK ANALYSIS REPORT OF LPG PLANT, DURGAPUR OF BHARAT PETROLEUM CORPORATION LTD OCTOBER 2015

2 INDEX INDEX SL NO SECTION SUBJECT PAGE No 1 Section 1 Introduction 1-1 to Section -2 Executive summary 2-1 to Section -3 Hazard Identification 3-1 to Section -4 Description & Properties 4-1 to Section -5 Maximum credible Accident analysis 5-1 to Section -6 Hazard of LPG Spillage/ Escape from containment 6-1 to Section -7 History of Past Accident 7-1 to Section -8 Consequence Analysis 8-1 to Section -9 Recommendation 9-1 to Anx - 1 Material Safety Data sheet of LPG Attachment 1

3 Risk Analysis for BPCL LPG Bottling INTRODUCTION 1.0 INTRODUCTION SECTION I INTRODUCTION M/s Bharat Petroleum Corporation Ltd., one of the leading oil marketing companies in Public Sector is engaged in bottling of LPG Cylinders for domestic as well as industrial purposes. Since the demand of LPG is growing day by day, refineries are increasing their capacities for production of more LPG along with other Oil products. Since LPG is highly inflammable and is stored under pressure in substantial quantities, there is potential for damage to property and injury in the event of release of significant quantity of LPG. Bharat Petroleum Corporation Limited,. Vide purchase order No dated entrusted Sonar Bharat Environment & Ecology Pvt. Ltd., (SBEE) to carry out a Comprehensive Risk Analysis of the Durgapur LPG Plant. Our team of experts had visited Durgapur LPG Plant to collect relevant data. For the purpose of obtaining specification of different onsite facilities, pipe lines, pump Capacity as well as off site facilities, a detailed questionnaire was prepared. During visit of our team members, they had collected the required information s in the format. Pertinent documents like lay out plan., P&I diagram, were collected from the Plant. Our team members along with the staffs of the station had gone round the Plant. Besides operational aspect, the team was also apprised of the organizational set up, existing system of handling Emergency Situation, available fire fighting system SBEE wants to put on record the excellent co operation they had received from the respective In charge of the station and his team during entire course of their study. We extend our thanks especially to Mr. Nirmalya Chakraborty and Mr. Krishno Kanto Saaha for their excellent support in preparation of the report. Page 1

4 Risk Analysis for BPCL LPG Bottling INTRODUCTION Scope of work includes the following Identification of vulnerable sections of the plant, which are likely to cause damage to the plant, operating staff and the surrounding communities due to accidental release of LPG from the LPG Plant. Assessment of overall damage potential of the hazardous events in relation to Plant and environment. Assessment of total individual risk for activities in the plant. This is an expansion project for increasing the storage capacity by installation of 2 nos of Mounded bullet of 300 mt each. Capacity of existing storage of LPG Plant is 450 MT (150MT x 3).After the proposed enhancement of storage capacity by 600 MT. Aggregate storage capacity of the LPG plant shall stand at 1050 MT. Page 2

5 Risk Analysis for BPCL LPG Bottling EXECUTIVE SUMMARY SECTION II EXECUTIVE SUMMARY 2.0 INTRODUCTION Durgapur LPG Bottling Plant of M/s Bharat Petroleum Corporation Limited (BPCL) is located at Rajbandh Chatty, Durgapur, West Bengal. Durgapur Rajbandh is located 11 km away from Durgapur City & 500 mtrs from NH- 2. The land area is 25 acres. Nearest facilities are follows SL,NO FACILITIES NAME KM 1 Railway Station Rajbandh 6 km 2 Air Port Andal 20 km 3 Bus Stand Rajbandh 3 km 4 Police Station Kanksa 4 km 5 Fire Station Durgapur 5 km 6 Hospital D.S.P Hospital Durgapur 10 km 7 National Highway HH km The plant premise is bounded by the following North South East West BPCL Retail Installation, Small village, Vacant Land HPCL Rajbandh IRD Rajbandh station Page 1

6 Risk Analysis for BPCL LPG Bottling EXECUTIVE SUMMARY 2.1 PROCESS DESCRIPTION Bulk LPG is received from Haldia Refinery. Road tankers are decanted at Tank lorry Gantry. Four Nos. of tank Lorries can be unloaded simultaneously. Proposed project envisages addition of two bays in the in gantry. LPG from the tank Lorries is transferred to the storage vessels through LPG Compressors by differential pressure method LPG from bullets is transferred through a pipeline to filling manifolds of carousal with the help of centrifugal pumps. The empty LPG cylinders brought into premises by Lorries are received and stored in the empty shed. They are fed to conveyor system after due inspection and are carried to the filling machines in the filling shed. The filling is cut off as soon as the weight of LPG in the cylinder reaches the desired weight.. After filling these cylinders are counter checked for correct weight, tested for leaks from valves and body, capped and sealed before sending them to the filled cylinder shed. Any defective cylinder is emptied for product LPG recovery. The filled cylinder are dispatched for distribution.through distributors. 2.2 PLANT FACILITY RECEIVING Bulk petroleum LPG is received by Road tankers of 18 MT capacity. About 8 Nos of Tankers per day supply bulk LPG to the bottling Plant. There are 4 bays for unloading the tankers. 2 more bays are proposed to be added for unloading. Bulk LPG is received from Haldia Refinery by Road tankers is decanted at Tank lorry Gantry., LPG from the tank lorries is transferred to the storage vessels through LPG Compressors by pressure differential method. Page 2

7 Risk Analysis for BPCL LPG Bottling EXECUTIVE SUMMARY STORAGE 3 Nos. Bullets having a safe filling capacity of 3 x 150 MT and 2 nos of Mounded Bullet having capacity 2 x 300 MT are proposed to be installed. On top of the Bullet two nos. of safety relief valves are provided, one valve is set at 13.6kg/cm 2 and other is set at 14.2 kg/cm 2. All bullets are provided with two independent level indicators and high level alarm. Remote operated valves are provided in liquid and vapour lines of each storage vessels. Technical details of the Bullets are as under : BULLET NOS 1.2 & 3 SL,NO ITEM TECHNICAL DETAILS 1 Bullet no. 1,2 & MT 2 Design Pressure 16 kg/cm 2 at 55 0 C 3 Operating Pressure 14.2 kg/cm 2 at 55 0 C 4 Hydro testing Pressure kg/cm 2 5 Corrosion Allowance 1.6 mm BULLET NOS 4 & 5 (Mounded Bullet) SL,NO ITEM TECHNICAL DETAILS 1 Bullet no. 4&5 300 MT 2 Design Pressure 16.5 kg/cm 2 at 55 0 C 3 Operating Pressure 14.2 kg/cm 2 at 55 0 C 4 Hydro testing Pressure 21 kg/cm 2 5 Corrosion Allowance 1.5 mm FILLING OPERATION LPG from bullet is pumped to the filling plant for bottling through 24 station carousel. The system is capable of bottling various capacity of cylinders. The filling system can turn out 50TMT per anum on single shift of 8 hrs. The sequence of filling operation starts with the receipts of empty cylinders and the fallowing operation are carried out: Page 3

8 Risk Analysis for BPCL LPG Bottling EXECUTIVE SUMMARY Visual checking for defects and tare weight De-capping Filling Electronic weight checking Correction of overfilled and under filled cylinder Valve leak / O ring checking Cylinder body and bung leak checking Capping and sealing Loading in trucks Empty cylinders are unloaded from Lorries and manually placed over Telescopic chain conveyor. As they move on the conveyor, the empty cylinder is to be checked visually for defects and markings. Defective cylinders are to be segregated. There are provission for storing about kg empty cylinders in the empty cylinders storage shed. The cylinders after de-capping are moved on to the filling machine for filling and will be filled automatically at a rate of approximately 26 cylinders per minute. Filled cylinders automatically come out of the carousel and continue to travel in the conveyor for weight checking. The under / over filled cylinders are separated for weight correction. Cylinders with correct weight are to be subjected to valve leak check, O Ring leak and body and bung leak check as they move on the conveyor. Cylinder found defective on the above checks will be sent for replacement of Valve in online valve changing machine and replacement of O Ring. Sound cylinder move on for capping and sealing the valves. Cylinders will then be loaded on to Lorries or will be stored in the storage shed which can store about 5000 nos of filled cylinders. Page 4

9 Risk Analysis for BPCL LPG Bottling EXECUTIVE SUMMARY AUTOMATIC FILLING PROCESS FUNCTIONAL DESCRIPTION LPG is pumped to the carousal from which the cylinders of different sizes are filled under pressure The system described is intended for filling standard domestic & LPG cylinder for industrial use, with a minimum number of operations, with process, production and monitoring function carried out with the help of sophisticated equipment and control system. VAPOUR EXTRACTION The Vapour extraction system will facilitate extraction of any leakage of LPG from around the carousel and other leak prone areas and discharge the same at suitable elevation above the roof level of shed. The system will be completed with exhaust fan and necessary ducting EVACAUTION AND VALVE CHANGE Cylinder found defective in valves, bung or body will be evacuated of their contents using a vapor compressor and the evacuated LPG will be sent back to the bullets. Leaky valves will be removed and fitted with new valves. Cylinders that require hot work will be sent to the authorized repair shops PURGING FACILITY Purging will be required in the following cases: New cylinder received are required to be air evacuated and LPG purged before the same are filled. Repaired cylinders which have been hydro tested with water are subject to evacuation for removal of moisture and air before refilling. An online purging system has been provided. Page 5

10 Risk Analysis for BPCL LPG Bottling EXECUTIVE SUMMARY 2.3 PLANT UTILITIES Air compressor/ Receiver/ Dryer Air compressor along with air receiver and dryer are provided to cater to the requirement of instrument air for carousel, pneumatic ROVs, fire protection system Compressed air is required for the following purpose Pneumatic actuation of different on-line instruments like ROV and control valve. Instrument actuation in LPG filling system. For compressed air requirement, 1 no. of 198 CFM 7.0 kg/sq cm capacity and 2 no. 100 CFM 7.0 kg/sq cm capacity air compressors have been installed. ELECTRICAL SYSTEM The total power demand of the LPG filling plant is in the region of 200 KVA. Client s battery limit has been considered as the incoming HT supply at 11 KV and through the two-pole structure / substation would be brought into 11 KV transformers for further onward LT distribution. Incoming supply is taken from the state electricity board at 11 KV TRANSFORMER 500 KVA Air cooled transformer is installed in the plant. STANDBY POWER SUPPLY 1X380 KVA, 1X250 KVA, 1X125 KVA & 1X7.5 KVA DG sets. ELECTRICAL FITTINGS All electrical fitting in the sensitive area are of flameproof / intrinsically safe type. Page 6

11 Risk Analysis for BPCL LPG Bottling EXECUTIVE SUMMARY 2.4 SAFETY RELATED TYPES OF UTILITIES Some of the general safety features for the storage & handling of LPG provided in the complex are discussed below DESIGN The main feature of the plant is the safe design of the equipment & pipelines.equipment are designed, inspected stage wise tested & certified by statutory authorities such as CCOE (Chief Controller of Explosives) & third party in accordance with relevant codes & standards. The main codes & standards used in the LPG bottling plant are ASME VUl or IS or BS-5500 or equivalent duly approved by CCOE for pressure vessels. Materials of Construction (MOC) used are SA 516 Gr. 70. Full radiography, stress relieving & hydro-test is carried out for the vessels & all critical drawings /documents are certified & approved by the competent authority. All critical LPG piping is seamless carbon steel of 300 rating with piping designed in accordance with ASTM, ANSI & equivalent codes & standards within built margin of safety. Intrinsic safety is largely built in into the design itself through use of time tested standards & codes which inherently incorporate a good margin of safety. Apart from the equipment design & selection (only well known reputed vendors with proven safe & trouble free track record in similar service are selected ) there are other features related to safety in the layout.operation, shutdown systems etc FIRE WATER STORAGE Two Above Ground Tanks having capacity 2 X 2700 KL (5400KL).. FIRE WATER PUMP & JOCKEY PUMP Diesel driven 3 nos. of 616Kl/Hr. 2X10Kl/Hr Page 7

12 Risk Analysis for BPCL LPG Bottling EXECUTIVE SUMMARY LPG PUMP 2 nos. of 50 Kl/Hr. FIRE HYDRANT SYSTEM Fire hydrants have been provided to be located as per requirements specified in OISD-144 to cover the entire plant area and Tank Lorry Parking area. Double Headed Hydrants - 25 Nos Single Headed Hydrants - 5 Nos. Water Monitors - 16 Nos SAFETY RELIEF SYSTEM Relief system adequately designed and provided as per OISD 144 guidelines. Two sets of safety relief valves are provided on each vessel, each relief valve having the required design, relieving capacity. Other routed locally but to safe location There is a locking arrangement to prevent inadvertent closing of the isolation valves, thus rendering the tank unprotected. Relief valves are always kept locked in open position. Relief valves are tested once a year and calibrated, if necessary. Page 8

13 Risk Analysis for BPCL LPG Bottling HAZARD IDENTIFICATION SECTION III HAZARD IDENTIFICATION 3.0 ENUMERATION & SELECTION OF INCIDENTS Effective management of a Risk Analysis study requires enumeration & selection of incidents or scenarios. Enumeration attempts to ensure that no significant incidents are overlooked, selection tries to reduce the incident outcome cases studied to a manageable number. These incidents can be classified under either of two categories: loss of containment of material or loss of containment of energy. Unfortunately, there is an infinite number of ways (incidents) by which loss of containment can occur in either category. For example, leaks of process materials can be of any size, from a pinhole up to a severed pipeline or ruptured vessel. An explosion can occur in either a small container or a large container and in each case, can range from a small "puff" to a catastrophic detonation. A technique commonly used to generate an accident list is to identify potential leaks & major releases from fractures of all process pipelines & vessels. This complication should include all pipe work & vessels in direct communication, as these may share a significant inventory that cannot be isolated in an emergency. The data generated is as shown below. Vessel number description & dimensions Materials present Vessel conditions ( phase, temperature & pressure) Inventory & connecting pining dimensions The goal of selection is to limit the total number of incident outcome cases to be studied to a manageable size without introducing bias or losing resolution through overlooking significant incidents or incident outcomes. The purpose of incident selection is to construct an appropriate set of Sonar Bharat Environment & Ecology Pvt Ltd Page 1

14 Risk Analysis for BPCL LPG Bottling HAZARD IDENTIFICATION incidents for study from the Initial List that has been generated by the enumeration process. An appropriate set of incidents is the minimum number of incidents needed to satisfy the requirements of the study & adequately represent the spectrum of incidents enumerated. 3.1 CHARACTERISING THE FAILURE Accidental release of flammable or toxic vapours can result in severe consequences. Delayed ignition of flammable vapours can result in blast overpressures covering large areas. This may lead to extensive loss of life & 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 gets released. Major accident hazards arise, therefore, consequent upon the release of flammable or toxic vapors or BLEVE in case of pressurized liquefied gases. In an LPG bottling plant such as the plant in question the main hazard arises due to the possibility of leakage of LPG during decanting (large number of those connections etc), storage, cylinder filling & storage & transportation. The various operations where leakage is more likely include during compression. To formulate a structured approach to identification of hazards and understanding of contributory factors is essential. 3.2 BLAST OVER PRESSURES Blast over Pressures depends upon the reactivity class of material & the amount of gas between two explosive limits. LPG is expected to give rise to a vapor cloud on release. Sonar Bharat Environment & Ecology Pvt Ltd Page 2

15 Risk Analysis for BPCL LPG Bottling HAZARD IDENTIFICATION 3.3 OPERATING PARAMETERS Potential vapor release for the same materials depends significantly on the operating conditions. Since LPG is being handled at atmospheric temperature & in pressurized conditions, LPG releases have been considered for release scenario based on their pressure & temperature condition. 3.4 INVENTORY Inventory analysis is commonly used in understanding the relative hazards & short of release scenarios. Inventory plays an important role in regard to the potential hazard. Larger the inventory of a vessel or a system, larger is the quantity of potential release. A practice commonly used to generate an accident list is to consider potential leaks & major releases from fractures of pipelines & vessels containing sizable inventories. The potential vapor release (source strength) depends upon the quantity of liquid release, the properties of the materials & the operating conditions (pressure, temperature) 3.5 LOSS OF CONTAINMENT Plant inventory can get discharged to Environment due to loss of containment. Various causes & 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 & then to short release scenarios for a detailed examination. Liquid release can be either instantaneous or continuous. Failure of a vessel to an instantaneous outflow assumes the sudden appearance of such major crack that practically all of the contents above the crack shall release in a very short time. The more likely event is the case of liquid release from a hole in a pipe connected to the vessel. The flow rate will depend on the size of the hole as well as on the pressure in front of the Sonar Bharat Environment & Ecology Pvt Ltd Page 3

16 Risk Analysis for BPCL LPG Bottling HAZARD IDENTIFICATION hole, prior to the accident. Such pressure is basically dependent on the pressure in the vessel. Vaporization of released liquid depends on the vapour pressure & weather conditions. Such consideration & others have been kept in mind both during the initial listing as well as the short listing procedure. Initial listing of all significant inventories in the process plants was carried out This ensured no omission through inadvertence. Based on the methodology discussed above a set of appropriate scenarios was generated to carry out Risk Analysis calculation, as listed below S.NO ITEM EVENT 1 Catastrophic Rupture of 150 MT Bullet Immediate Ignition, BLEVE MT (each) LPG Bullets Vapour Side VCE rupture 3 Failure of bottom line of LPG Bullet Delayed Ignition, VCE 4 Failure of LPG Compressor Delayed Ignition, VCE 5 Failure of LPG Pump Delayed Ignition, VCE 6 Flange joint leakage in LPG Pipeline Delayed Ignition, VCE 7 Tank Truck Vessel Failure BLEVE 8 Electrical Fire 9 Hygiene Events Earthquake, extreme Wind, Aircraft Impact 10 Rupture of filled 5,14.2, 19, 35 & 47.5 kg Immediate ignition and cylinder BLEVE Civil Disorder, strikes etc can lead to any of these releases scenarios & it would result in similar consequences. However, these events have been considered in the probability estimation for the release scenarios, wherever would have significant impact. Sonar Bharat Environment & Ecology Pvt Ltd Page 4

17 DESCRIPTION AND PROPERTIES SECTION IV DESCRIPTION AND PROPERTIES 4.0 INTRODUCTION LPG is a mixture of commercial propane & commercial Butane which may also contain small quantity of unsaturated hydrocarbons. LPG market in India is governed by IS 4776 & Test methods by IS LPG being highly flammable may cause fire & explosion. It, therefore calls for special attention during its handling. PHYSICAL PROPERTIES DENSITY LPG at atmospheric pressure & temperature is a gas which is 1.5 to 2.0 times heavier than air. It is easily liquefied under moderate pressure. The density of liquid is approximately half that of water and ranges from to 0.58 m 3. Since LPG vapour pressure is heavier than air, it normally settle down at ground level/low lying areas. This accumulation of LPG vapour gives rise to potential fire and explosion. VAPOUR PRESSURE The pressure inside a LPG storage vessel is corresponding to the temperature in storage vessel. This vapour pressure is dependent on temperature as well as percentage composition of the mixture of hydrocarbons present in LPG. Beyond liquid full condition in cylinders any further expansion of the liquid will increase the cylinder pressure by 7 8 kg/ m 2. For each degree centigrade rise in temperature. This clearly indicates the hazardous situation which may arise due to overfilling of cylinder or any storage vessel. Page 1

18 DESCRIPTION AND PROPERTIES FLAMMABILITY LPG has an explosive limit range or 1.8% to 9.5% by volume of the gas in air. This is an considerably narrower than other common gaseous fuel. AUTO-IGNITION TEMPERATURE. The auto ignition temperature of LPG is around C & will not ignite on its own at normal temperature. COMBUSTION Combustion of LPG increases the volume of products in addition to generation of heat. LPG requires about 24 to 30 times its own for complete combustion & yields 3 4 times of its own volume of Co 2. The heat of combustion is about 10,900 kcal.kg COLOUR LPG is colorless both in liquid and vapour phase. During leakage and vaporization of LPG cools the atmosphere & condenses the water vapour contained in it forming a white fog. This makes possible to see & escape of LPG VISCOSITY LPG has a low viscosity (around 0.3 at 45 0 C) & can leak when other petroleum products cannot. This properly demands a high degree of integrity in the pressurized systems handling LPG to avoid Leakage. ODOUR LPG has a very faint smell & as such for detecting leakage of LPG ethyl mercaptan is generally added in the ratio approx 1 kg for mercaptan per 100 ft 3 of Liquid LPG (20 ppm) Page 2

19 DESCRIPTION AND PROPERTIES TOXICITY LPG is slightly toxic. Although it is not poisonous in vapour phase, it suffocates when present in large concentration due to displacement of Oxygen. IDLH value of LPG is generally taken as PPM PYROFORIC IRON Highly inflammable pyroforic iron Sulphide is formed due to reaction of loose iron / iron oxide with Sulphur or its compounds. Formation of, Pyrophoric Iron Sulphide is prevented by totally eliminating H 2 S, limiting the total volatile Sulphur to 0.2% by mass & reducing loose iron oxide by thoroughly cleaning the storage vessels internally during outage. However, pyrophoric Iron Sulphide will spontaneously ignite in a sphere or a cylinder due to high concentration of LPG which is much above the upper flammable limit. When these vessels are aired (during opening The saturation vapour pressure, flammability range, toxicity data of Propane- Butane mixtures as well as pure compounds are listed below Propane (%) Butane (%) S.V. Process at 50C kg/cm 2 Flammability (Range (%) Toxicity IDLH (PPM) Odour Threshold (PPM) N/A N/A N/A N/A N/A N/A N/A - Page 3

20 DESCRIPTION AND PROPERTIES CHEMICAL PROPERTIES Sl.No 1 Formula C 3 -C 4 mixture 2 Molecular Weight Kg/KMol 3 Boiling Temperature at 1 bar ( 0 K) K 4 Critical Temperature ( 0 K) K 5 Critical Pressure (bar) 40 bar 6 Density ( liquid) at 45 0 C E+01 Kg/M 3 7 Boiling Temperature E+01 Kg/M 3 8 Density ( Gas) at 1 Bar & 45 0 C 1.93 E + 00 Kg/M 3 9 At Boiling Temperature 2.44 E + 00 Kg/M 3 10 Heat capacity ( Gas) at 45 0 C E+ 02 J/Kg/k 11 Heat of Vapourisation at 45 0 C (J/Kg) E + 04 J/Kg/K 12 Boiling Temperature E/ + 02 J/Kg/K 13 Heat Combustion (J/Kg) E+06 J/ Kg/K 14 Vapour Pressure at 45 0 C 9.74 bar 15 Ratio of Spec heats (cp/cv) Thermal Conductivity ( Gas) at 45 0 C 1.97E-02 W/M/K 17 Boiling Temperature 0.00 E-00 W/M/K 18 Thermal Conductivity ( Liquid) at 45 0 C 8.33 E -02 W/M/K 19 At Boiling Temperature 12.17E -02 W/M/K 20 Stoichiometric Ratio 0.036M 3 /M 3 21 Lower Flammability Limit (% V/V) Upper Flammability Limit (% V/V) IDLH Valve (PPM) E (+,- numerals) = Means Power of ten of the coefficients Page 4

21 DESCRIPTION AND PROPERTIES THE PHYSICAL CHEMICAL PROPERTIES OF LPG WHICH MAKE LPG HAZARDOUS ARE AS FOLLOWS : LPG liquid is lighter than water and hence floats on water and evaporates LPG vapor is heavier than Air LPG can be stored at ambient temperatures only at higher that atmospheric Pressure Pressure and the actual pressure depends on the percentage of propane in LPG LPG is highly inflammable and forms explosive mixtures with air LPG liquid expands to vapor phase by about 250 times LPG has a fairly good burning velocity and explosive potential The flame temperature is quite high and has a potential to endanger steel structure. With high moisture. LPG can form solid hydrates which can Plug pipelines, valves, regulators and other devices at lower temperatures. Vapour pressure increases steeply with increasing temperature. Frost bites, can occur when LPG in liquid phase comes into contact with skin Page 5

22 Risk Analysis for BPCL LPG Bottling MAXIMUM CREDIBLE ACCIDENT ANALYSIS (MCAA) APPROACH SECTION-V MAXIMUM CREDIBLE ACCIDENT ANALYSIS (MCAA) APPROACH 5.1 INTRODUCTION A Maximum Credible Accident (MCA) can be characterized, as an accident with a maximum damage potential, which is still believed to be probable. MCA analysis does not include quantification of probability of occurrence of an accident. Moreover, since it is not possible to indicate exactly a level of probability that is still believed to be credible, selection of MCA is somewhat arbitrary. In practice, selection of accident scenarios representative for a MCA- Analysis is done on the basis of engineering judgment and expertise in the field of risk analysis studies, especially accident analysis. Major hazards posed by flammable storage can be identified taking recourse to MCA analysis. This encompasses certain techniques to identify the hazards and calculate the consequent effects in terms of damage distances of heat radiation, toxic releases, vapor cloud explosion etc. A host of probable or potential accidents of the major units in the complex arising due to use, storage and handling of the hazardous materials are examined to establish their credibility. Depending upon the effective hazardous attributes and their impact on the event, the maximum effect on the surrounding environment and the respective damage caused can be assessed. As an initial step in this study, a selection has been made of the processing and storage units and activities, which are believed to represent the highest level of risk for the surroundings in terms of damage distances. For this selection, following factors have been taken into account: Type of compound viz. flammable or toxic Quantity of material present in a unit or involved in an activity and Page 1

23 Risk Analysis for BPCL LPG Bottling MAXIMUM CREDIBLE ACCIDENT ANALYSIS (MCAA) APPROACH Process conditions such as temperature, pressure, flow, mixing and presence of incompatible material In addition to the above factors, location of a unit or activity with respect to adjacent activities is taken into consideration to account for the potential escalation of an accident. This phenomenon is known as the Domino Effect. The units and activities, which have been selected on the basis of the above factors, are summarized, accident scenarios are established in hazard identification studies, whose effect and damage calculations are carried out in Maximum Credible Accident Analysis Studies. 5.2 METHODOLOGY Following steps are employed for visualization of MCA scenarios: Chemical inventory analysis Identification of chemical release and accident scenarios Analysis of past accidents of similar nature to establish credibility to identified scenarios; and Short-listing of MCA scenarios 5.3 COMMON CAUSES OF ACCIDENTS Based on the analysis of past accident information, common causes of accidents are identified as: Poor house keeping Improper use of tools, equipment, facilities Unsafe or defective equipment facilities Lack of proper procedures Improvising unsafe procedures Failure to follow prescribed procedures Jobs not understood Lack of awareness of hazards involved Page 2

24 Risk Analysis for BPCL LPG Bottling MAXIMUM CREDIBLE ACCIDENT ANALYSIS (MCAA) APPROACH Lack of proper tools, equipment, facilities Lack of guides and safety devices, and Lack of protective equipment and clothing 5.4 FAILURES OF HUMAN SYSTEMS An assessment of past accidents reveal human factor to be the cause for over 60% of the accidents while the rest are due to other component failures. This percentage will increase if major accidents alone are considered for analysis. Major causes of human failures reported are due to: Stress induced by poor equipment design, unfavorable environmental conditions, fatigue, etc. Lack of training in safety and loss prevention Indecision in critical situation; and Inexperienced staff being employed in hazardous situation Often, human errors are not analyzed while accident reporting and accident reports only provide information about equipment and/or component failures. Hence, a great deal of uncertainty surrounds analysis of failure of human systems and consequent damages. 5.5 MAXIMUM CREDIBLE ACCIDENT ANALYSIS (MCAA) Hazardous substances may be released as a result of failures or catastrophes, causing possible damage to the surrounding area. This section deals with the question of how the consequences of release of such substances and the damage to surrounding area can be determined by means of models. It is intended to give an insight into how the physical effects resulting from release of hazardous substances can be calculated by means of models and how vulnerability models can be used to translate the physical effects in terms of injuries and damage to exposed population and environment. A disastrous Page 3

25 Risk Analysis for BPCL LPG Bottling MAXIMUM CREDIBLE ACCIDENT ANALYSIS (MCAA) APPROACH situation in general is due to outcome of fire, Vapor Cloud explosion in addition to other natural causes, which eventually lead to loss of life, property and ecological imbalance. Major hazards posed by flammable storage can be identified taking recourse to MCA analysis. MCA analysis encompasses certain techniques to identity the hazards and calculate the consequent effect in terms of damage distances of heat radiation, toxic release, vapor cloud explosion etc. A host of probable or potential accidents of the major units in the complex arising due to use, storage and handling of the hazardous materials are examined to establish their credibility. Depending upon the effective hazardous attributes and their impact on the event, the maximum effect on the surrounding environment and the respective damage caused can be assessed. The MCA analysis involves ordering and ranking various sections in terms of potential vulnerability. 5.6 PHYSICAL EFFECTS AND CONSEQUENCES Using the failure case data developed the program undertakes consequences calculation for each indentified incident or failure case. The software initially models the dispersion of the released material irrespective of whether it is flammable or toxic. For flammable materials the software then proceeds to determine the effect zones for the various possible outcomes of such release. The risk analysis must account for all these possible outcomes. The possible consequences include. Fireball / BLEVE Heavy Cloud Dispersion Jet Fire Vapor Cloud Explosion The particular outcomes modeled depend on the behavior of the release and the dilution regimes which exist. This can be quite complex. The program Page 4

26 Risk Analysis for BPCL LPG Bottling MAXIMUM CREDIBLE ACCIDENT ANALYSIS (MCAA) APPROACH undertakes these calculations for the representative meteorological condition as suitable for the meteorological condition in the area. Consequential effects of the accidental release of a chemical are: Intensity of heat radiation due to a fire or a fireball or BLEVE as a function of the distance of source Energy of vapor cloud explosion as a function of the distance of the exploding cloud. Concentration of gaseous material in the atmosphere due to the dispersion of the evaporated material. The letter can be either an explosive or a toxic material. A release can ignite as the result of the event, which causes it, or can ignite close to the source before the flammable cloud has travelled away from the source. Immediate ignition can result in a fireball or a BLEVE or pool fire depending on the nature and spread of release. A fireball can occur when there is a specific type of fireball resulting raises the internal pressure and weakens the vessel shell unit it bursts open and releases its entire contents as large and very intense fireball. If the material does not ignite immediately, allowing spill / release to form a liquid pool a flammable gas cloud may be formed thorough evaporation of the pool due to combination of solar heat, ground heat and heat from the neighbouring environment and it can ignite at a number of points downwind if its path is such that it goes across ( for example, a road an area where people are present or other ignition sources). Delayed ignition can result in wide spread damaging vapor cloud explosion of high energy or minor flash fire of limited energy depending on the quantity of flammable vapor. The accident scenarios are normally divided into the following categories of the chemicals according to their physical state / phase, pattern of release, nature of dispersion, physical effects and damage: Page 5

27 Risk Analysis for BPCL LPG Bottling MAXIMUM CREDIBLE ACCIDENT ANALYSIS (MCAA) APPROACH a. Release of a gas ( Flammable or toxic or both ) b. Release of a liquid ( Flammable or toxic or both ) c. Release of a liquefied gas ( Flammable or toxic or both ) Event trees are the simplified schemes of consequence, which show the possible evolution of effects after the release of the material. Such trees are very effective in determining the possible consequences. 5.7 CONSEQUENCE MODELLING Accidental release of' flammable or toxic vapors can result in severe consequences. Delayed ignition of flammable vapors can result in blast overpressures covering larger areas. This may lead to extensive loss of life & property. Toxic clouds may cover yet a larger distance 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 gets released If LPG is released into the atmosphere, it may cause damage due to resulting BLEVE, fires or vapor cloud explosion of the evaporated LPG. To formulate a structured approach to identification of hazards and understanding of contributory factors is essential. These factors have been described in detail. DAMAGE CRITERIA In consequence analysis, use is made of a number of calculation models to estimate the physical effects of an accident (spill of hazardous material) & to predict the damage (lethality, injury, material destruction) of the effects. The calculations can roughly be divided in three major groups: Page 6

28 Risk Analysis for BPCL LPG Bottling MAXIMUM CREDIBLE ACCIDENT ANALYSIS (MCAA) APPROACH a) Determination of the source strength parameters. b) Determination of the consequential effects. c) Determination of the damage or damage distances. The basic physical effect models consist of the following SOURCE STRENGTH PARAMETERS Calculation of the outflow of liquid, vapors or gas out of a vessel or a pipe, in case of rupture. Also two-phase outflow can be calculated Calculation, in case of liquid outflow, of the instantaneous flash evaporation & of the dimensions of the remaining liquid pool. Calculation of the evaporation rate, as a function of volatility of the material, pool dimensions & wind velocity Source strength equals pumps capacities, etc in came cases. CONSEQUENTIAL EFFECTS Dispersion of gaseous material in the atmosphere as a function of source strength, relative density of the gas, weather conditions & topographical situation of the surrounding area. Intensity of heat radiation ( KW/M2) due to fire or a BLEVE, as a function of distance of the source Energy of vapor cloud explosions [in N/M 2 ], as a function of the distance to the distance of the exploding cloud Concentration of gaseous material in the atmosphere, due to the dispersion of evaporated chemical. The tatter can be either explosive or toxic. Page 7

29 Risk Analysis for BPCL LPG Bottling MAXIMUM CREDIBLE ACCIDENT ANALYSIS (MCAA) APPROACH It may be obvious, that the types of models that must be used in a specific risk study strongly depend upon the type of material involved Gas, vapor, liquid, solid? Inflammable, explosive, toxic combustion products? Stored at high /low temperatures or pressure? Controlled outflow (Pump Capacity) or catastrophic failure? SELECTION OF DAMAGE CRITERIA The damage criteria give the relation between extent of the physical effects (exposure) & the percentage of the people that will be killed or injured due to those effects. The knowledge about these relations depends strongly on the nature of the exposure. For instance, much more is known about the damage caused by heat radiation, than about the damage due to toxic exposure, & for these toxic effects, the knowledge differs strongly between different materials. In consequences Analysis studies, in principle three types of exposure to hazardous effects are distinguished: Effects are distinguished I. Heat radiation from a jet, pool fire, a flash or a BLEVE II. Explosion III. Toxic effects, from toxic material or toxic combustion products In a LPG bottling plant as there are no toxic chemicals handled. In the next two paragraphs, the chosen damage catena are given & explained for heat radiation & vapor cloud explosion HEAT RADIATION The consequences of exposure to heat radiation are a function of: The radiation energy into the human body ( KW/M 2 ) The exposure duration [sec] The protection of the skin tissue ( clothed or naked body) Page 8

30 Risk Analysis for BPCL LPG Bottling MAXIMUM CREDIBLE ACCIDENT ANALYSIS (MCAA) APPROACH The limits for 1% of the exposed people to be killed due to heat radiation & for second degree bums are given in the table below DAMAGES TO HUMAN LIFE DUE TO HEAT RADIATION Since in practical situations, only the own employees will be exposed to heat radiation in cases of a fire, it is reasonable to assume the protection by clothing. It can be assumed that people would be able to find a cover or a shield against thermal radiation 10 sec time. Furthermore, 100% lethality may be assumed for all people suffering from direct contact with flames, such as the pool fire, a flash fire or a jet flame. The effects relatively lesser incident radiation intensity is given below: EFFECTS DUE TO INCIDENT RADIATION INTENSITY THERMAL 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 (1ST DEGREE BURNS ARE LIKELY) 9.5 PAIN THRESHOLD REACHED AFTER 8 SEC 2ND DEGREE BURN AFTER 20 SEC 12.5 MINIMUM ENERGY REQUIRED FOR PILOTED IGNITION OF WOOD, MELTING PLASTIC TUBING ETC The actual results would be less severe due to the various assumptions made in the models arising out of the flame geometry, emissivity, angle of incidence, view factor & others. Upon ignition, a spilled liquid hydrocarbon would be burn in Page 9

31 Risk Analysis for BPCL LPG Bottling MAXIMUM CREDIBLE ACCIDENT ANALYSIS (MCAA) APPROACH the form of a large turbulent diffusion flame the size of the flame would be depend upon the spill surface & the thermo - chemical properties of the spilled liquid. In particular, the diameter of the fire (if not confined to a dyke), the visible height of the flame, the tilt & drag of the flame due to wind can be correlated to the burning velocity of the liquid. The radiative output, of the flame would be dependent upon the fire size, extent of mixing with air & the flame temperature. Some fraction of the radiation is absorbed by carbon dioxide & water vapor in the intervening atmosphere. In addition, large hydrocarbon pool fires produce thick smoke, which can significantly obscure flame radiation. Finally the incident flux at an observer location would depend upon the radiation view factor.which is a function of the distance from the flame surface, the observer's orientation & the flame geometry Estimation of the thermal radiation hazards from the pool fires essentially involves 3 steps; characterization of flame geometry, approximation of the radiative properties of the fire & calculation of safe separation distances to specified levels of thermal radiation EXPLOSION In case of vapor cloud explosion, two physical effects may occur A flash fire over the whole length of the explosive gas cloud. A blast wave, with typical peak overpressures circular around ignition source As explained above, 100% lethality is assumed for all people who are present within the cloud proper. For the blast wave the lethality criterion is based on A peak overpressure of 0.1 bar will cause serious damage to 10% of the housing / structures Falling fragments will kill one of each eight persons in the destroyed buildings The following damage criteria may be distinguished with respect to the peak overpressures resulting from the blast wave: Page 10

32 Risk Analysis for BPCL LPG Bottling MAXIMUM CREDIBLE ACCIDENT ANALYSIS (MCAA) APPROACH DAMAGE DUE TO OVERPRESSURES PEAK OVERPRESSURE DAMAGE TYPE 0.83 BAR TOTAL DESTRUCTION 0.30 BAR HEAVY DAMAGE 0.10 BAR MODERATE DAMAGE 0.03 BAR SIGNIFICANT DAMAGE 0.01 BAR MINOR DAMAGE From this it may be concluded that p=0.17 E+5 pa corresponds approximately with 1% lethality. Furthermore it is assumed that everyone inside an area in which the peak overpressure is greater than 0.17 E+5 pa will be wounded by mechanical damage. For the gas cloud explosion this will be inside a circle with the ignition source as its center EXTERNAL EVENTS External events can initiate & contribute to potential incidents considered in a Risk Analysis. Although the frequency of such events is generally low, they may result in a major incident. They also have the potential to initiate common cause failures that can lead to escalation of the incident. External events can be subdivided into two main categories. Natural hazards : Earthquakes, Floods, Tornadoes, extreme temperature, lightening etc Man induced events : Aircraft crash, missile, nearby industrial activity, sabotage etc Page 11

33 Risk Analysis for BPCL LPG Bottling MAXIMUM CREDIBLE ACCIDENT ANALYSIS (MCAA) APPROACH TECHNOLOGY Normal design codes for gas/chemical plants have sufficient safety factors to allow the plant to withstand major external events to a particular level (e.g. intense loading of say 120 mph). Quantitative design rules usually used for seismic events, flooding, tornadoes & extreme wind hazards as follows SEISMIC The design should withstand critical ground motion with an annual Probability of 10-4 or less FLOODING The design should withstand the efforts of worst flooding occurrence in 100 year period WINDS - The design should withstand the most critical combination of Wind velocity & duration having a probability of or less in a 50 year period (annual probability of 10-4 or less). DAMAGE DUE TO INCIDENT RADIATION INTENSITY INCIDENT RADIATION (KW/M2) TYPE OF DAMAGE 62.0 Spontaneous Ignition Of Wood & Sufficient To Cause Damage To Process Equipments 37.5 Minimum energy required to ignite wood at infinitely long exposure ( Non plastic ) 12.5 Minimum energy required for piloted ignition if wood, melting plastic tubing, etc 4.5 Sufficient to cause pain to personal if unable to reach cover within the 20 seconds. However blistering of skin ( 1st degree burn is likely) 1.6 Will cause no discomfort to long exposure. 0.7 Equipment to solar radiation. Page 12

34 Risk Analysis for BPCL LPG Bottling MAXIMUM CREDIBLE ACCIDENT ANALYSIS (MCAA) APPROACH PHYSIOLOGICAL EFFECTS OF THRESHOLD THERMAL DOSES DOSE THRESOLD EFFECT CONSEQUENCES (KW/M 2 ) RD DEGREE BURN INVOLVE WHOLE OF DPIDERMIS AND DERMIS; SUB- CUTANEOUS TISSUES MAY ALSO BEDAMAGED ND DEGREE BURN INVOLE WHOLE OF EPIDERMIS OVER THE AREA OF THE BURN PLUS SOME PORTION OF DERMIS ST DEGREE BURN INVOLE ONLY EPIDERMES, BLISTER MAY OCCUR, EXAMPLE SUNBURNS. DAMAGE EFFECTS OF BLAST OVERPRESSURE BLAST OVER PRESSURE (Bar) DAMAGE LEVEL 0.3 Major structure damage ( assumed fatal to people inside building or within the other structures 0.1 Storage failure 0.01 Eardrum Rupture 0.03 Repairable damage, pressure Vessels light structure collapse Page 13

35 Risk Analysis for BPCL LPG Bottling MAXIMUM CREDIBLE ACCIDENT ANALYSIS (MCAA) APPROACH POSSIBLE RELEASE SCENARIO OF LPG PIPELINE RELEASE RUPTURE OF VESSEL BLEVE VAPOR LIQUID OUTFLOW JET FIRE DISPERSION OUTFLOW MODEL TWO PHASE OUTFLOW DELAYED IGNITION NO IGNITION JET FIRE LIQUID SPREADING AND EVAPORATION VCE/ FLASH FIRE SAFE DISPERSION DISPERSION POOL FIRE DELAYED IGNITION NO IGNITION VCE/ FLASH FIRE SAFE DISPERSION Page 14

36 HAZARDS OF LPG SPILLAGE / ESCAPE FROM CONTAINMENT 6.0 General SECTION-VI HAZARDS OF LPG SPILLAGE / ESCAPE FROM CONTAINMENT When LPG is released from a storage vessel or a pipeline, a fraction of LPG vaporizes immediately and the other portion forms a pool if the released liquid quantity is more. LPG from the pool vaporizes rapidly entrapping some liquid as droplets as well as considerable amount of air forming a gas cloud. The gas cloud is relatively heavier than air and forms a thin layer on the ground. The cloud flows into trenches and depressions and in this way travels a considerable distance. As the cloud formed in the area of spill moves downwind under influence of wind, it gets diluted. A small spark, when the vapour cloud is within the flammability limit can cause flash fire, explosion and if the liquid pool still exist and remains in touch of cloud under fire it can ignite the whole mass of liquid. However in case of non existence of any source of ignition there will be no occurrence of hazardous event and the cloud may get diluted to such a level that the mixture is no longer explosive. However, it can cause asphyxiation due to displacement of oxygen. Different types of combustion reactions. associated in case of. release of LPG from the containment are listed in the following sections. JET FIRE Escaping jet of LPG from pressure vessels / piping, if ignited cause a jet flame. The jet flame direction and tilt depend on prevailing wind direction and velocity. Damage, in case of such type of jet fires, is restricted to within the- plant boundary. However, the ignited jet can impinge on other vessels and equipment carrying LPG and cause domino effect. 1

37 HAZARDS OF LPG SPILLAGE / ESCAPE FROM CONTAINMENT POOL FIRE The liquid pool, if ignited, causes a "Pool Fire". In the pool fire, LPG burns with long smoky flame throughout the pool diameter radiating intense heat which creates severe damage to the adjoining buildings, structures, other vessels and equipment causing secondary fires. The flame.may tilt under influence of wind and may get propagated / brown several pool diameters down wind. Damage, in case of such fires,is restricted within the plant area and near the source of generation. UNCONFINED VAPOUR CLOUD EXPLOSION (UVCE) Clouds of LPG vapour mixed with air (within flammability limit) may cause propagating flames when ignited. In certain cases flame take place within seconds the thermal radiation intensity is severe depending on the total mass of LPG in the cloud and may cause secondary fires. When the flame travels very fast it explodes high over pressures or blast effects causing heavy damage at considerable distance from the release point. Such explosions are called unconfined vapour cloud explosion. BOILING LIQUID EXPANDING VAPOUR EXPLOSION (BLEVE) This phenomenon occurs when pressure inside a storage vessel increases above the design pressure due to a fire in the adjacent area. Due to impingement of flame or due to radiant heat, temperature in the vapour portion of the storage vessel increases rapidly compared to the portion filled with liquid. Increase in temperatures softens and weakens the metal wall of the shell. With the rise in vapour pressure and inadequate vapour space for expansion, the shell of storage tanks bursts causing fragments of the shell flying like projectiles with release of whole mass of pressurized boiling liquid. The released liquid flashes and atomies immediately often resulting a large fire ball in contact with 2