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Cyan 100% Magenta 76% Yellow 0 Black 27% Wetstock Reconciliation at Fuel Storage Facilities. An Operator s Guide - PDF
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1 Cyan 100% Magenta 76% Yellow 0 Black 27% Wetstock Reconciliation at Fuel Storage Facilities An Operator s Guide2 Our vision: A country where worker safety, health and welfare and the safe management of chemicals are central to successful enterprise Acknowledgements & References Fairbanks Environmental Limited was commissioned by the Health & Safety Authority to prepare this Best Practice guide, which replaces previous H.S.A. Guidelines called Wetstock Inventory Control for Petrol Stations, now revoked. The Authority also wish to acknowledge the APEA / EI guide Design, construction, modification, maintenance and decommissioning of filling stations, 3rd Edition, also referred to as The Blue Book, in the development of the guide. Valuable advice and assistance was provided by a range of stakeholder technical experts, from the petroleum industry, Government and Local Authority bodies. Published in January 2013 by the Health & Safety Authority, The Metropolitan Building, James Joyce St., Dublin 1. 23 Wetstock Reconciliation at Fuel Storage Facilities An Operator s Guide Contents Acknowledgements & References...2 Chapter 1 Introduction to this guide...4 Chapter 2 The Basics of Wetstock Management...5 Chapter 3 How to Keep Accurate Data...7 3a) Daily Variance Calculations...7 3b) Cumulative Variance Calculations...8 Chapter 4 Establishing your Normal Variance Trend....9 Chapter 5 Detecting a change in Variance (Abnormal Variance Trend)...13 Chapter 6 Loss investigation...15 Chapter 7 Risk Assessment...17 Chapter 8 Levels of Leak Detection or Containment Systems (appropriate for the site) risk assessment classification Chapter 9 Summary...24 Appendices What Causes Variance? a) Variances through Tank Stock Measurement b) Variances through Sales c) Variances through Deliveries d) Variances through Vapour Recovery Systems (Stage 1b) e) Common Variances and their Solutions Quick guides a) Best Practice b) Troubleshooting Glossary of Terms Wetstock Reconciliation Worksheet4 Wetstock Reconciliation at Fuel Storage Facilities Chapter 1 Introduction to this guide This Best Practice document in Wetstock Inventory Control replaces the previous HSA Guidance on Wetstock Inventory Control for Petrol Stations and has been updated to include all types of fuel and incorporate current best practice. The purpose of the guidance is to assist petrol station operators to control fuel losses on their site in order to minimise any adverse impacts on safety, the local community and environment, to ensure compliance with the law, and save costs due to fuel losses, all of which are good for business. Efficient and effective wetstock management control will facilitate operators in complying with a range of legal requirements including Mineral Oil Regulations, and relevant safety and environmental legislation. Although primarily aimed at petrol inventory control, this guidance can be applied to all types of liquid fuels (including diesel, biofuel and kerosene) being stored and dispensed at retail & private petroleum stores. Note: The term petrol station used throughout the document can be taken to cover any type of retail fuel storage and dispensing station, petrol station being the most commonly used terminology. Objectives of this guide are to: > Help to understand the nature of wetstock and the risks involved > Outline how to keep accurate data (which is the basis of effective analysis) > Explain why variances (+/-) exist > Instruct how to establish your tanks normal variances > Instruct how best to accurately detect abnormal variances > Provide a guide for loss investigation > Provide guidance to current best practice in controlling risks due to fuel losses on your site, based on a risk assessment 4 Chapter 15 An Operator s Guide Chapter 2 The Basics of Wetstock Management What is Wetstock? Wetstock is the liquid fuel contained in controlled storage conditions. Wetstock management is important because of the risk presented by liquid fuels in the event of loss of containment. Petroleum spirit (petrol) is a highly volatile and flammable liquid, which means that at room temperatures it gives off flammable vapours which, when mixed with air, will burn with explosive force if ignited. Petrol vapour can find its way into basements of buildings and public drains with serious consequences, should the vapours come into contact with an ignition source. Petrol is also hazardous to the environment, injurious to aquatic life and presents a particular risk to drinking water supplies. Whenever petrol leaks or escapes from an underground storage tank or pipelines it can travel significant distances dependent on whether there is a high water-table or underground river in the vicinity. Although diesel and kerosene are not as flammable as petrol and therefore do not pose a significant inherent flammability risk, they are hazardous to the environment and any leakages of these fuels could pose a threat in particular to groundwater in the vicinity. The risks around wetstock storage As most fuel is stored in underground storage tanks, if there are leaks, it is easier for the fuel to enter the underground water system and pollute the groundwater which in many cases provides drinking water to local communities. Given the significant risks to health & safety of people and the environment, the storage of petrol at retail & private stores is controlled by specific legislation which requires such storage to be licenced (in the case of petroleum spirits only) and such licence conditions generally require all practicable steps to be taken to prevent accident by fire, explosion or escape of petrol. Similarly the Prevention of Pollution of Groundwater Regulations, S.I. 9 of 2010, prohibits the input of hazardous substances into groundwater. The level of risk from the storage and dispensing of motor fuels increases when petrol stations are located in urban areas, as they are surrounded by private or commercial premises. Therefore the need for consistent and accurate monitoring of petrol delivered, stored and dispensed at any petrol station in order to detect leaks from each underground tank and connected pipeline system, is essential. These best practice guidelines will provide practical advice and information to help you to develop and maintain an effective Wetstock Inventory Management System for your site(s), and to comply with legislative requirements as all petrol station operators will be required to carry out a risk assessment for their operation and ensure that adequate controls are put in place. All petrol station operators will be expected to meet a minimum standard of wetstock control in order to detect possible leaks, particularly from underground storage tanks. The method of controlling wetstock levels is called Wetstock Reconciliation. Chapter 2 56 Wetstock Reconciliation at Fuel Storage Facilities Wetstock Reconciliation Wetstock Reconciliation is the management of liquid stock, stored on the site, e.g. petrol, diesel, kerosene etc. It is based on the same theory of any stock control system, that is, measuring the amount of stock delivered into the storage tanks, subtracting the amount sold, and measuring what is left in stock. Any variances from what is expected to be in stock may be due to losses (leaks, evaporation, or theft of fuel). To reduce the risks from petrol leaking from an underground tank or pipeline it must be detected at the earliest possible time and any further escape prevented. For new or recently refurbished petrol stations, automatic detection systems can be incorporated into the installation of the underground tank and pipeline in order to monitor for leaks and raise an alarm. However, for older petrol stations this is not always feasible and some other method must be adopted to provide a similar level of leak detection. These guidelines are intended to outline a manual system of leak detection suitable for use in older petrol stations as well as outlining alternative systems which may be considered. The more accurate the Wetstock Management System is, the quicker a leak can be detected and action taken to prevent pollution or fire/explosion, as well as saving costs due to fuel losses. Where the risk of leakage is classed as medium or high then you should give consideration to the use of an approved third party company which uses a SIR (Statistical Reconciliation Inventory) system. Such systems will help you to detect leaks much more quickly and when the leakage rate is much lower, thereby minimising losses/damage to the environment/safety risks, as well as providing a robust means of generating fuel stock data all of which can be used to demonstrate compliance with the law. Typically you would submit your daily wetstock data to the third party company and their sophisticated, statistics based analysis would detect unusual losses or gains and start an investigation on your behalf. For the highest level of protection, SIR systems can be enhanced by real time analysis involving the reconciliation of every customer sale transaction. For further information on SIRs please see Chapter 8. 6 Chapter 27 An Operator s Guide Chapter 3 How to Keep Accurate Data 3a) Daily Variance Calculations This section will show you how to calculate wetstock figures for your site, and more importantly, how to get maximum benefit from them. We recommend you record them on a worksheet (A blank form is provided at the back of this booklet). However, it is advisable to use an electronic spread sheet as this will make calculations easier for you, as well as allowing graphs to be produced. Now here s where wetstock figures originate from and how they relate to your site and tanks: Site Trading Day (24 hour period) 10:00 pm 10:00 pm Opening stock: Delivery Sales Closing stock: Previous day s actual closing Measured stock level at the end of the day WETSTOCK RECONCILIATION WORKSHEET TANK: 2 CAPACITY: 33,400 PUMPS: 1,2,3,4 GRADE: Unleaded MONTH: April YEAR: 2013 DAILY Opening Book Closing Variance Date Day Stock Deliveries Sales Stock Stock Loss(-ve) Book Stock A B C D E F Opening Stock + Deliveries Sales = Book Stock (=A+B-C) (=E-D) = Mon = Tue Wed Thu Fri Sat Sun Variance Closing Stock Book Stock = Variance = = +43 Chapter 3 78 Wetstock Reconciliation at Fuel Storage Facilities 3b) Cumulative Variance Calculations Daily data calculations are useful for spotting major leaks or data errors. However, there are many issues that can be hard to see in the daily data but that can have a large impact over the long term. This is where cumulative calculations are extremely useful. Adding up the daily data over time can show us a tank s trend. The Cumulative columns in our worksheet are highlighted in yellow below. These figures are used to provide a Cumulative Percentage Variance which will give a better indication overall of a tank s variance trend over time. Cumulative Variance = Cumulative Variance from day before + daily variance for that day. e.g (-3) = -11 Cumulative Sales = Cumulative Sales from day before + daily Sales for that day. e.g = 5223 Cumulative Variance Cumulative % Variance = Cumulative Sales e.g x 100 x 100 = A Best Practice Tip: Dipping your tank for closing stock amounts Are you a non-24 hour site? No problem. Take accurate readings when you close and record them. 24 hour Site? Not so easy! Close half your site (e.g. at 10pm) take accurate readings then do the other half. 8 Chapter 39 An Operator s Guide Chapter 4 Establishing your Normal Variance Trend Normal variance trend can be the result of many causes such as evaporation, delivery errors, tank calibration etc. some of which can be controlled to reduce loss; others such as evaporation are however, unavoidable (for further details and common variances see appendix 1e). The Daily Variances we calculated in our worksheet will clearly show the losses and gains each day based on your book stock for that particular tank. The Cumulative Percentage Variances we calculated, however, will show losses and gains as a percentage of sales over time, indicating the variance trend of the tank for the period. This will allow us to identify change in variance trend and most importantly potential leaks. Plotting the Cumulative Percentage Variances onto a graph (as shown below) will allow you to see the trend more easily. A gradual increase of losses over the 20 days is more visible in the cumulative % column and the trend highlighted easier in the graph below. The cause for the losses seen in this example was a low level leak from a suction pipe. Cumulative Percentage Variance Cumulative Percentage Variance for period Date Best Practice Tip: Producing Charts of your data Using a spread 0sheet to record your Wetstock figures will make it easy to produce charts like the one seen here. Chapter 4 910 Wetstock Reconciliation at Fuel Storage Facilities Without good Wetstock reconciliation procedures the previous leak could have gone undetected for a long time and larger fuel amounts lost, resulting in serious pollution, high clean-up costs and possible legal proceedings. So could you notice a leakage like this by looking at your current Wetstock records? As little as 10 litres per day will release over 3,600 litres of fuel to ground per year! What is the normal wetstock variance of each of your storage tanks? You need to determine what is normal so that you can detect when an excessive or abnormal variance occurs. Here are some important points to take into account > The normal variance for each tank is unique to that tank and may be different to other tanks on your site. > Variance may be significantly different for petrol grades as for diesel grades. > Variance will change on each tank month by month, winter to summer. > Variance for each fuel grade should be similar to that of other stations in the same part of the country and supplied from the same terminal or depot. > Variances on your petrol grades will change if you have Stage 2 vapour recovery activated. By returning petrol vapour into your storage tanks you should notice a reduction in wetstock loss although it is difficult to quantify. > Variances will change if you install automatic temperature compensation (ATC) on your dispensers. For example in winter when the fuel temperature is colder and below 15 degrees C, you will dispense less fuel for a given quantity shown on the customer display (readout volume corrected to 15 degrees C) than if ATC was not fitted. This will result in a reduction in wetstock loss or may even result in a wetstock gain. However in summer if the fuel temperature in your tanks is warmer than 15 degrees C then you will have the opposite result. Once ATC is installed it should remain activated in both winter and summer. 0Best Practice Tip: Interpreting and reviewing your Wetstock data trends As well as recording and calculating your daily data, the site owner MUST review the loss/gain trends daily for variances from the usual trend of the tank and for any loss or gain exceeding acceptable levels based on deliveries, sales for that day and seasonality. 10 Chapter 411 An Operator s Guide The normal variance should be recorded on a monthly basis as well as over a longer length of time up to a 12 month period as shown below. Table 4.1 Normal monthly Variance % (Figures are for illustration purposes only) Normal monthly variance % Unleaded Diesel High Octane Unleaded* Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec *High Octane Unleaded (Super Unleaded) The charts below show the normal monthly % variance and the cumulative % variance trend over one year for all of the 3 tanks above within the same site. See how the High Octane Unleaded (Super Unleaded) fuel has a higher loss and is more erratic than the higher selling grades. This is because any wetstock variances on a low selling grade will be accentuated e.g. a 5 litre loss on a tank selling 1000 litres per day is a 0.5% loss, whereas on a tank selling 100 litres a day a 5 litre loss is a 5% loss. Chart 4.2 Normal Monthly % Variance Trend Normal Trend Monthly % Variance Period loss/gain % Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Date Key: Super Diesel Unleaded Chapter 4 1112 Wetstock Reconciliation at Fuel Storage Facilities Chart 4.3 Normal Cumulative % Variance Trend Normal Trend Cumulative % Variance Cumulative loss/gain % Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Key: Super Diesel Unleaded It is recommended that you establish the normal variance for each tank on a month by month basis. If you have accurate, reliable data for the previous year (with no events/ variance problems as described in appendix 1), then use this as your benchmark. Alternatively, you could use data for other sites in your area supplied by the same terminal or depot if you are able to access it. If you do not, then start now and in one years time you will have data you can use. 12 Chapter 413 An Operator s Guide Chapter 5 Detecting a change in Variance (Abnormal Variance Trend) Once you establish a normal variance trend for your tanks, accounting for any seasonal variation, you can quickly see if a tank deviates from its trend. If an abnormal variance is noticed (as below) you should investigate the cause immediately. Staff at the site must be trained to know what to do if an abnormal variance is noticed and records of staff training must be kept at the site as part of the safety management documentation. Chart 5.1 Abnormal Cumulative % Variance Trend Abnormal Trend Cumulative % Variance Trend Cumulative loss/gain % ec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Key: Super Diesel Normal Variance Unleaded Abnormal Variance Unleaded By comparing the monthly variance with your normal variance benchmark you will be able to detect when a change (an increase in wetstock loss) is significant and is increasing. Ways to compare A When you only have a single tank for that grade on your site then compare this year to last year and check for changes (as shown in Chart 5.2 next). B If you have multiple tanks of the same grade or other sites you can compare against them for a change in variance. Chapter 5 1314 Wetstock Reconciliation at Fuel Storage Facilities Chart 5.2 Year on Year comparison Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Deciding if the change in variance is significant It is not easy (or safe) to say how much of an increase makes it significant. It is no longer appropriate to use a single quantity (in litres or in %) that can be used by every site for each fuel grade and for each month. For example: If the normal variance is % (loss) and on that month you record a loss of % and your average daily sales are 200 litres, this increase is much less than 1 litre per day, which is insignificant. However if your average daily sales is 10,000 litres then the loss is equal to 10 litres per day or 3,650 litres per year, which is very significant. 0Best Practice Tip: Deciding on how significant a change is. In the absence of greater experience or expert help you may wish to use this. A significant change in variance could be: 1. An increase of 0.1% from the monthly normal variance. 2. An increase of 10 litres per day over a month. 3. An increase in monthly loss of more than 300 litres. 14 Chapter 515 An Operator s Guide Chapter 6 Loss investigation What to do if you detect a significant change in variance. If you are sure that you have accounted for all of the factors highlighted in appendix 1, there remain two possibilities the fuel may have been stolen or you may have a leak. What to do and what appropriate measures to take if a leak is suspected? If you think that you have a leak, as soon as practicable, you must inform your Petroleum Licensing Authority (Local Authority Fire Department) as that is a condition of your licence, and take any action necessary to minimise the Health & Safety risk. You must also inform the Environment section of your local authority, as they will identify any action necessary to protect the environment. Your site should have a written procedure detailing what to do in the event of a suspected leak. This is sometimes called an Escalation Procedure. It should contain details of what action you should take and how to carry out the relevant actions. It should contain details of how to: > Investigate the cause of the loss > Contact the Local Authority petroleum licencing and environmental sections > Take any necessary Health & Safety actions > Prevent any further leakage > Quantify the volume of product lost > Identify the leaking tank or pipework > Repair the leak or decommission the equipment in agreement with your licensing/ environmental officer > Remediate any pollution caused in agreement with the Local Authority Important It is vital that you tell the Local Authority as quickly as possible as they can provide advice on what to do in order to minimise the Health & Safety risks and protect the environment. This advice may include seeking help from specialist wetstock management companies, petrol station contractors, or environmental / oil industry consultants. Chapter 6 1516 Wetstock Reconciliation at Fuel Storage Facilities Leak investigation What to do Checklist This is not an exhaustive list and you should take expert advice as appropriate. 3 Carry out a visual inspection of all dispensers and tank manholes for signs of leakage. 3 For single wall tanks carry out a static tank test, either via the automatic tank gauge (ATG) if you have one or by a qualified contractor using a precision test method. 3 For suction pipework systems, check if there have been reports of dispensers losing prime. This is an indication that the pipeline may be leaking. If so, have it tested. 3 For pressurised pipework systems, check that any leak detection device is operational. 3 If any other leak sensors are fitted, have them checked. 0Best Practice Tip: Escalation Procedure Draw up an escalation procedure for your site and make sure all staff are informed and appropriately trained. 16 Chapter 617 An Operator s Guide Chapter 7 Risk Assessment Good management of your wetstock on your site is important for two reasons: 1. Fuel products can cause serious pollution of local streams and rivers and can contaminate large volumes of groundwater in aquifers and land below a site. 2. Fuel products are flammable and pose significant health and safety risks to both staff and the local community. Site operators have a duty to comply with all Health and Safety legislation that applies to the site. It is therefore important that any risk is managed. Central to the risk management of health and safety, is the ability to carry out risk assessments i.e. the ability to estimate the likelihood or chance of a loss or an injury occurring due to the hazards identified on the site and hazards that could arise due to work carried out on the site. By hazard we mean anything that has the potential to cause harm, i.e. human injury or ill-health. The risk of the hazard considers the severity (i.e. high, medium, and low) and the chance (how likely it is that an accident may happen). Carrying out a Risk Assessment is the recommended way to help you decide whether your current methods of leak detection are sufficient or whether you need to increase your level of protection. Risk assessment is fundamental to good health and safety management. All employers regardless of the size of business are required by law to carry out a risk assessment at their place of work and to keep a written record of that risk assessment. People are often put off by the idea of Risk Assessment because they think it is over complicated, difficult to complete and unnecessary. Risk Assessment is simply looking closely at what, in your place of work or about your work activities, could cause harm to your employees and visitors to your workplace (e.g. customers, suppliers, sales representatives etc.) and determining the control measures you can implement to minimise the risk. Chapter 7 1718 Wetstock Reconciliation at Fuel Storage Facilities There are 3 basic steps to Risk Assessment: 1. Identify the hazards (i.e. anything that has the potential to cause harm, in terms of human injury, ill-health or damage to property). For example; working with petroleum products or dangerous equipment. 2. Identify the level of risk for each hazard (i.e. the chance/likelihood of harm occurring, coupled with how severe the harm or ill health could be). Decide who could be harmed and how, giving consideration to vulnerable groups (e.g. young persons, the elderly, pregnant employees, shift workers etc.). 3. Identify the controls or improvements that need to be put in place to avoid or reduce the risk. Your control measures are the most significant part of the risk assessment, as they set out the steps that must be followed to protect people and the environment. Some control measures may already be in place. You will need to decide if additional measures are needed. Risk assessments will help you prioritise the high risk hazards first. More information on Hazards and Controls, including an explanation of the Hierarchy of Controls can be found within the Learn More section of BeSMART, the free, easy-to-use, online tool for Risk Assessments and Safety Statements from the HSA. See HSA web site for further details at and For a comprehensive guide to risk assessing your petrol station and adopting the appropriate leak protection system, a very good form of reference is the APEA/EI guide Design, construction, modification, maintenance and decommissioning of filling stations, 3rd Edition also referred to as The Blue Book. The guidance offered in this document is generally in agreement with the Blue Book. 18 Chapter 719 An Operator s Guide Guide to risk assessing your petrol station Risk assessment should, firstly, be viewed in terms of the severity of impact or how much damage would be incurred in the event of a leakage; and secondly how likely a leakage is to occur. Determine the severity of impact and the likelihood of leakage from the tables below Table Severity of impact of Leakage Aspect High Medium Low The presence of a basement, culvert or tunnel Within or adjacent to the site In proximity to the site and connected via drains, cable ducting or highly permeable soil No below ground features could be impacted by a leak Annual fuel sales in litres More than 5 million Between 500,000 and 5 million Less than 500,000 Number of people potentially affected by a fire or explosion (including staff, customers and neighbours More than 100 Between 10 and 100 Less than 10 Impact on surface water or groundwater Located on a principal aquifer, within 50m of a well or borehole or directly connected to a watercourse Located on a secondary aquifer No impact possible Impact on protected habitats or species Could have a direct impact on a nationally designated site Could have an indirect impact on a nationally designated site No possible impact Table Likelihood of leakage Aspect High Medium Low Site known to have had a previous leak incident or an integrity test failure With an element or elements of the failed system still remaining It is not known whether a leak has occurred There has been no leakage from the current system Tank and pipework construction Any element is single walled steel The system is non metallic but with some buried joints The entire system is non metallic with no buried joints Results of a soil survey if carried out Indicates a high likelihood of ground movement or corrosion of metallic components The survey shows no ground movement likely and no corrosion of metallic components likely Chapter 7 1920 Wetstock Reconciliation at Fuel Storage Facilities Using Table 7.1 and 7.2: In each case the highest category established must be used when determining the classification of the site from Table 7.3, e.g. in Table 7.1, if your site is low in four cases and medium in one case, you must use medium in Table 7.3 Then use the following table to determine whether your site has a classification of A (High risk), B (Medium risk) or C (Low risk) Table Site Classification Table High B A A Likelihood Medium C B A Low C B A Low Medium High Severityof impact 20 Chapter 721 An Operator s Guide Chapter 8 Levels of Leak Detection or Containment Systems (appropriate for the site) Risk Assessment Classification Also refer to the Blue Book tables 11.6 and 11.7 for suggested systems dependent on the types of tanks, pipework and physical leak detection devices existing on your site. Classification C Minimum Risk Level All petrol stations must meet at least this minimum level, which is the accurate daily recording of wetstock and the calculation and analysis of cumulative data (see Chapter 3). This may be achieved by following the guidance provided and by the appropriate use of manual dipstick(s) for each storage tank or compartment and the use of paper records (provided in the appendix back pages) and/ or the use of spread sheets or other 3rd party systems. It should be noted that meeting this minimum standard can still be challenging for sites with manual systems and procedures which are vulnerable to human error and work practices which are not well controlled. If an excessive loss is suspected, it can still incur considerable time and expense to find the cause of the loss and to stop it. It is therefore worth considering the merits of adopting a higher level of protection such as an SIR system as described under Classification B. The inevitable upfront and on-going running costs incurred in a higher level system should be considered in terms of the real costs incurred with the minimum risk level system, this is primarily your time and effort which, when costed fully, may not be dissimilar to that of some higher level systems. Classification B Medium Risk Level Petrol stations with a medium risk of causing loss and damage should ensure they have adequate measures to control the risk without incurring undue cost of system replacement or upgrade. Examples of adequate measures include: 1. A remotely monitored ATG system which has certified leak detection capability covering all parts of the tank and pipework system. 2. A Statistical Inventory Reconciliation (SIR) system which has a certified leak detection capability covering all parts of the tank and pipework system. Chapter 8 2122 Wetstock Reconciliation at Fuel Storage Facilities SIR (Statistical Inventory Reconciliation) This involves analysing your daily reconciliation data to establish a statistical variance (loss or gain) trend for each of your tanks, which takes into account all the cause factors explained earlier. When a leak or other unacceptable variance occurs an alarm condition is raised which is then validated and investigated. Using this service can greatly increase the accuracy of the leak detection because it can compare a single site against many sites using the same supply depot and therefore you can see how your site s tanks perform with regards to their peers. Classification A High Risk Level Petrol stations with a high risk of a leak, causing extensive loss and damage, should ensure that they have in place adequate measures to minimise the risk. Examples of adequate measures include: 1. Secondary containment of the storage tanks, the suction or pressure system pipework and the remote or offset fill pipework. 2. Electronic sensors which directly detect fuel loss which is contained underneath dispensers or within tank manhole chambers. 3. Remotely monitored ATG systems which have certified leak detection capability covering all parts of the tank and pipework system. 4. A Statistical Inventory Reconciliation (SIR) system enhanced by real time data analysis which has certified leak detection capability covering all parts of the tank and pipework system. 5. For pressurised pipework systems, a certified electronic line leak detection system which will shut down the pumping system upon detection of a leak (indicated by pressure drop). Measures 1 and 2 should prevent a leak to ground, whereas measures 3, 4 and 5 will detect a leak to ground, so it is vitally important that the detection time is minimised and therefore, it is recommended that these systems are capable of detecting a leak with a threshold equivalent to 9 litres per day and before 150 litres has been released to the ground. 22 Chapter 823 An Operator s Guide Real-Time Analysis This method involves the detailed reconciliation of fuel sales and the corresponding tank stock level change for every customer sales transaction, which makes it possible to diagnose the cause of a loss much more quickly and sometimes without the need to undertake extensive on-site inspections and tests. This method can be provided by qualified 3rd party service providers and you can seek advice about such providers and identify them via your petroleum regulatory authorities, trade representative groups, industry consultants or via the petrol station trade media. Table Wetstock Reconciliation (leak detection) Methods Risk Classification Method Requirements High A SIR with real time analysis An ATG Med B SIR An ATG is preferred but manual dipping is acceptable Low C Daily reconciliation in accordance with this Guide Can be paper- based but spread sheet-based or other back office system is preferred Manual dipping is acceptable Chapter 8 2324 Wetstock Reconciliation at Fuel Storage Facilities Chapter 9 Summary Now, with the aid of this guide you are able to measure and track the normal variance of your tanks. Starting with the basic calculations and using them cumulatively to see trends you can spot leaks, faulty equipment, theft and many other issues sooner and more accurately. The guidance notes discussed above will help increase the likelihood of earlier leak detection. However, small gradual leaks, which are very difficult to identify by visual inspection of your daily records may still be present on your site. For medium or high risk sites to spot these often more damaging leaks you may require a higher level of wetstock reconciliation analysis. Subject to the result of your risk assessment if your site is deemed to be of medium risk then you should adopt a more advanced approach which is SIR. In the case where your site is at a high risk that a leak could occur and cause significant damage then you should adopt an enhanced form of SIR which uses real time data analysis. 24 Chapter 925 An Operator s Guide Appendix 1 What Causes Variance? To benefit from carrying out good practice Wetstock Reconciliation, it is important to minimise the recording of incorrect stock readings, sales and delivery amounts and to know how to account for some of the many causes of variances seen. This section aims to give guidance on minimising inaccurate stock readings, sales and delivery data and provide an understanding of the common causes and effects of variances on Wetstock Reconciliation. 1a) Variances through Tank Stock Measurement It is advised to take readings at the same time every day using either a dipstick or tank gauge. If using a dipstick, slowly and gently lower the dipstick until it touches the bottom of the tank (i.e. protective plate), quickly raise the dipstick and read the fuel level in litres. If your dipstick is in gallons you will need to use a gallon to litre table to convert your measurements to litres. Fuel finding paste can make it easier to read the dipstick. Safety note; for tanks which are direct fill (the tanker delivery hose is connected directly to the tank top fill pipe), the dipstick should be stored and used within the fill pipe. Where the dipstick is stored in a separate dipping tube, there is a significant risk of spillage during a delivery if the dip cap has not been secured. It is therefore highly recommended that a separate dip tube is not used. In the case of tanks which are offset (remote) filled, manual dipping is not permitted and a tank contents gauge system should be installed. Appendix 1 2526 Wetstock Reconciliation at Fuel Storage Facilities 1a) i. Dipstick measuring Tank is wider in the middle Dipstick middle of tank Volume increments narrow in the middle of the dipstick 6000 Protective Plate Dipstick bottom of tank litres 100 litres 200 litres Short dipstick: The correct dipstick on the left reads the fuel level as 100 litres whereas the short dipstick wrongly reads 200 litres. 100 litres Short dipstick 26 Appendix 127 An Operator s Guide Scenario: short dipstick example > The bottom 5cm of the dipstick is missing, therefore the dipstick sits 5cm lower in the tank than it should. > At the bottom of the tank our 5cm scale is equivalent to 1 division on the dipstick. > 1 division represents 1 unit of volume; so here, 1 division is equal to 100 litres. > Now instead of reading the first 100 litres, the dipstick would read 200 litres because the short dipstick is actually starting its reading from the first division rather than at zero. > The matter gets worse when measuring at the middle of the tank because 5cm is now equivalent to 5 divisions and therefore measure 5 units of fuel more (i.e. 500 litres more). > Wetstock records will have incorrect readings because the amount of fuel will be overestimated, by varying amounts, depending on the volume in the tank. 0Best Practice Tips & Important points - Using your Dipsticks: > Ensure your dipstick measurements start at the bottom, from zero. > Check there are no signs of wear on the dipstick. > Tanks using dipsticks must have a protective plate above the base of the tank to prevent damage to the tank from the dipstick. > Each division on the dipstick represents a volume of fuel. > Divisions at the middle of the tank are smaller than those at the bottom or top (as shown previously). > Each dipstick is specific to the dimensions of an individual tank; check you have the correct dipstick. > Ensure the dipstick sits in the middle of the tank. > Dipstick readings can be affected by Vapour Recovery Systems (see section 1d). Appendix 1 2728 Wetstock Reconciliation at Fuel Storage Facilities 1a) ii. Tank Contents Gauges Hydrostatic Tank Gauges Description Hydrostatic Gauges based on pressure can have a similar accuracy as a dipstick. The pressure applied to the fuel in the tank to read the measurement is dependent on the volume of fuel i.e. the deeper the fuel the more pressure applied. Problems > The gauges can become unbalanced and give incorrect readings > As with dipsticks this system has problems accounting for the effects of Vapour Recovery due to the increased and decreased pressure from Vapour (Section 1d) Digital Gauges Magnetostrictive probes Description These probes come in different sizes and use 2 magnetic floats to take readings. The top float will measure fuel, the other water, and will rise and fall when stock levels change. Problems > A build-up of deposit and the float sticking > Float can get jammed following an overfill > Inaccurate calibration or failure to recalibrate the probe following a fuel grade change Digital Gauges Capacitance probes Description The Capacitance probe comprises a series of capacitor segments which detect the liquid level in a vessel. Problems > Poor initial Calibration > Probe can become contaminated > Electronic drift during life of probe 28 Appendix 129 An Operator s Guide 1a) iii. Water > It is important to check for water in each tank and record the results weekly or, ideally, on a daily basis. > To check for water, water-finding paste may be used, the paste changes colour when it comes into contact with water. The results should be recorded on your Weekly Loss / Gain Sheet. > Gaining variances in your Wetstock Reconciliation Data can indicate a possible water ingress problem and therefore it is good practice to check for water in the tank if gains are seen. 1b) Variances through Sales > It is important to record accurate sales amounts in your Wetstock Reconciliation Worksheet to allow you to identify any lost fuel that may not be accounted for in the sales record. Variances can occur if amounts are incorrect or simply missing from the records. > How accurately your fuel pump meters are performing will have an impact on the fuel dispensed and sold. It is possible that you could be giving fuel away on each sale made and, depending on how poor the meter readings are, it is possible you could be working outside legal tolerances. So it is recommended to get meters checked annually and reset to strike (zero) if required. See part 1e: Common variances and their solutions. Appendix 1 2930 Wetstock Reconciliation at Fuel Storage Facilities 1c) Variances through Deliveries > It is important to record accurate delivery amounts on your Wetstock Reconciliation Worksheet following fuel delivery to allow you to identify any lost fuel. > It is important that you check all fuel deliveries have gone into the correct tank. > Fuel which is warmer on delivery than the ambient in-tank temperature will shrink; likewise, fuel which is cooler on delivery than the ambient in-tank temperature will expand. This will help to explain why you may have losses or gains. > You MUST use the ticketed fuel amount (i.e. the fuel amount on the bill of loading /invoice i.e. whichever you pay for). This may be volume measured at either ambient temperature or converted to the volume of the fuel if it were at standard 15 degrees (standard temperature accounting). You should note on your records which measurement method is used. > As a check, it is good practice to take readings before and after the delivery (allow 5 minutes to settle) to calculate that the delivery amount matches roughly to the ticketed amount. > If you identify an excessive variance as a result of a delivery then you should firstly check this is not normally the case on all deliveries. Then contact your supplier to check if the correct quantity was delivered. If all the recommended checks have not resolved the discrepancy and your tanks are offset filled, you should consider the possibility of a leak in the offset fill pipework and have it tested. See part 1e: Common variances and their solutions. Motor spirits: with every 1 C increase in temperature there is an approx. 0.11% increase in volume and vice versa 30 Appendix 131 An Operator s Guide 1d) Variances through Vapour Recovery Systems (Stage 1b) Vapour recovery systems introduce pressure differences inside your tank, the increase and decrease of pressures in the tanks ullage space has an adverse effect on dipstick measurements and pressure based unmodified tank gauges (Hydrostatic/Analogue) effecting the readings of the tanks stock levels. Vapour recovery stage 1b the basics Tanker delivers fuel into tank. Vapour extracted from ullage space in the tank and taken through the vapour recovery system. Vapour deposited into tanker. Following Delivery: Pressure builds in the tank Compressed vapour in the tank forces the fuel to rise up the fill pipe. Any Tank Gauge or Dipstick located in the fill pipe will overestimate the amount of fuel in the tank. As Fuel is sold: The pressure drops and a partial vacuum can be created causing the fuel level in the fill pipe to drop. Any Tank Gauge or Dipstick located in the fill pipe will under- estimate the amount of fuel in the tank. Potential overfill danger when contents under-estimated. A Pressure Relief Valve as shown can be installed on dipstick or unmodified hydrostatic systems. This will help to take more accurate readings. The valve is opened before taking a dip and before deliveries to balance the pressure. The handle is pulled down on the valve to allow pressure in the tank to equalize by allowing vapour to be vented. Appendix 1 31 View more
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