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. London A Charitable Company Limited by Guarantee .. .e:_ I ~ LIB R A.._. rxsrrnrts . gPT .<. _. Cf. . _.RIA.". R'Y .INSTITUTE OF PETROLEUM: AREA CLASSIFICATION _... -._.. 2~d edition . August 2002 _. Published by The Institute of Petroleum. .. CODE FOR INSTALLATIONS -... .... HANDLING FLAIvTh1ABLE FLUIDS . WORl.....' . "PARTTS-" OF THE OF PETROLEUM MODEL CODE OF SAFE PRACTICE IN ~ PETROLEUM mDUSTRY .. '. _.
Exploration and Production: Ltd Stetoil (U$-) ~ TaliSman Energy (UK) Lid TotalFinaEIfExploration UK PLC TOtalFinaElfUK Ltd . UK Ltd Shell UK Oil Ptoduots Limited .: Shell Ux. Commerce Way. Copyright C 2002 by The Institute of Petroleum. Registered No.The In. Tel: +44 (0) 1206 796 351 email: sales@portland. UK.·sernces.stitute ofPetrolewn ptefil!l.com . Phillips ~etl'Ol"wn Co. Colchester CO2 8HP.»ncco Limited Concco UXLtd Enterprise Oil PLC ExxonMobil Inteiuational Ltd towar~ the scientific and Kerr-McGee North Sea (UK) Ltd Kuwait Petroleum International Ltd MUICOPetroleum Ltd Petroplus Relining Teeside Ltd . ISBN 0 85293 223 5 Published by The :Institute of Petroleum or translated into Further copies can be obtained from Portland Customer Services. or transmitted a machine language without the written permission of the publisher. Hess Ltd BGGroup BHP BiIliUln Limited BP Exploratimi Operating Co Ltd BP OilUKLrdChevron'Iexaco Ltd O. 135273. .All rights reserved No part oftbis book may be reproduced by any means.y aclo1owledges the financial contributions technicalprogrsmme from the following companies: Agip (UK) Ltd Amerada. Whitehall rndustrial Estate. England . London: A charitable company 1imited by guarantee.
10 '. . . 9 2... . .. ... .. .fication of common types of facilities in open areas Scope ' : . . .. . . .. ~'. . . . . . . . . .. 1.•••.•. . .. • . .. ... . 6 The technique of hazardous area classification .. .'. . .2-Area classificatiou.4 3. . .:':: 2. . .Classes 1. . .. . . .'.. . . .. . .. . . .3 3. ... .. . .. . ...limits. ..3 Application of this Code' . .4 Safety principles fimdamentalto area classification 1. . Point source release approach Apparatus sub-group and temperature class 9 10 ~ -. .7 3.. .Classes I.. .. . .. . . . Marine facilities andjetties .. . . . .. . . . . : 1.. . .2 2. . ... . .: . .. . .1 Introduction . .. . .' .. . .. . . ' .ll and ill . . .. . . . . . i1 . . .... . . . '.. . . . . . . xiii 1 1 1 2 2 3 3 5 Introduction . . . . . .. . . . . . ... .5 ine management of area classification 1. .. . . . . . : ' -. .2 3. . . . . ..6 3. . .. .6 KeyteIms 1. . 9 2. ' Storage tanks . . . . . of appliCability .. .. • • • . . . .. .:-. . . .. .. '.. .. : . . . ."'~""' .. ... .. . . : . . . .Classes I. .. " '... ..•.. . . .8 esample methcdfer classi. . . . . . . . . '.. .Classes 1.. . . .. . ..' ' :... . .. . . . . . . . . .• Road tanker loading . . . . . .... . . . .. ...Open air ventilation .5 -3.. . .1 Scope . ITand ID Filling and service stations 13 14 18 29 33 38 39 43 v . .ll and ill . .4 2..... . . . . " . . . ... . • .7 The area classification drawing 3 11 13 The direct 3. . . . .CONTENTS '. .. .Page '. .. . .. . . .Classes I. . . . ix : ... . . . . . . ... . ..5 2. . . 11 i ••••••••••••• ' ' .•... . . . . ..- .. . II and III _.. .. . .1 3. .. . xi Foreword Aclotowledgements Overview 1 .: _: Drum filling . ... ... . .ll and m " Rail car loading . . .7 Ventilation 1. .: . . 1. '" . . .. . 1. .. . .. . . ~.. . . . ... . ...:_ _ Road-tanker discharge .. . . .. . . . .3 2.. .. . . . .. . .& Buoyancy of release 2 .. .•... .. The direct eiaIirple approach.6 Data required for the assessment Application ""'... . . . .. . . ..... . . . .. . :: ~ -. .-.
.... .. .5 Wirelining . ... . 4.5 Shape factors and hazard radii for pressnrised releases . ..... . .•.. . . . .. . . . .... ... . ..•• " .. 7. .. . .. . . ..7 Temperature class and gas ignition temperature .. ..' . 7.. .... . . ... 7.. ....' ..2 Open areas . . 4.4 Type of protection ' '.•.... ...• . ..4 Point sources .... ." •• " 7. .. .. . .. .. . . 71 73 73 75 76 79 81 81 83 83 83 84 85 85 85 86 87 87 88 6 Effect of ventilation on hazardous area classification 6.. SO 54 56 The area classification of drilling rigs.... ..... 7...3 Enclosed areas .. .. .2 Area classification for drilling. ... . ... . .. . .... .. ' .. .. .12 Installation ...... .18 Cathodic protection. .. installation....... . . .... .6 The effect ofloss of ventilation on the area classification ofan enclosed area 'Selection.. .. .. ... . . '" '.. .. . ... .... .. 4.." ' '.•.. . Classification of individual point sources . . .'.. . ~... . . .. 6.. .. . . . . . .. earthing and bonding 7 88 88 88 88 89 90 90 90 vi . .. .. ...3 Selection of Group II apparatus equipment . .. .. • .. . . ..... .10 Emergency systems..•.4 Gas vent hazardous area ..... .8 Enclosure ingress protection .. .. .. .. . 4..' . . . . . ..... ..•. 4.. • .. '. ...... . . .: '." ..2 Explanation of the 'point source' concept as used in this Code .•. .... .. .. .... . .. . . . . . .. . . ... . ... . ... .. 7.. . . .. 7..... . 5. . 5. .. .4 Sheltered or obstructed areas . maintenance ami use of eqllipment in hazardous areas 7.. . 4 Page 49 49 . . . . 6.. ' "... . . ... .... 4...•..1 Introduction . .2 Standards . . .. . .. ... . .. ' 5.. . .... ......'. . . .. . .. . .. .. .. .. .. 4............ .. . . . . ..' 7. .... . . .. . .. ... . ..•..... ... portable and transportable electrical apparatus and its connections 1. .. ... .' . .. 6.. .. . .. . .5 Effect of ventilation on the hazardous area classification of enclosed areas . .. "' ... . ... .. . . .' .. . .. .... .. . .•. .. •. . . . . .. . ...7 Other spaces .. .... . . 6.. ...Contents Cont . . ... .. .. . . ......6.. 7. ...... .. ... ... . 4. ... . . .. . ... .. ... .. .. . . .... .. ...11 Non-electrical SOUl'Ces f ignition o : . . ... 1...8 Well test systems . .3 Methodology :: · ' . 57 57 57 57 57 58 58 59 S9 59 59 5 61 .. ...13 Protection of electrical apparatus and cables from physical damage 7. 5. . " S.10Documentation .. . . . . • .. . .17 Battery rooms 1. .15 Mobile. .1 Introduction . . . . equipment and well operations 4.... . .16 Personal apparatus 7. . .1 Scope ... . .6 Apparatus sub-groups 7.. '. . :.9' Producing oil and gas wells on land .... .....14 Maintenance and inspection .. .. .. . . ... . . ..1 Introduction . .. ..3 Surface mud systems ..... ... . ..5 Selection according to hazardous zone : . . ..6 Miscellaneous sources 'of release . . ... . . . . ..... . .. . . .. .... .. ... . : . : .. ... . .... .. 7. . . 4. . . . .. " ' 7.. . ...•• .. ... . .. . .... . . . .9 Other requirements . workover and wireline operations in open areas ... 4... ..' . .11 Marking of apparatus ..
. . Glossary.. . .. . . . . . Page 91 91 91 . . ... . . . . . . . . .. .. . . ' .. .. . .. . . . . . .4 Area classification during maintenance work . . . .. . . .. . ... .... . . . . . .. Part 1: Procedure for establishment of appropriate release frequency level Part 2: Background to risk-based approach. ... . .. . . . . . . .... . .' Small-scale operations (laboratories and pilot plants) Types of protection and electrical apparatus that may have an internal source of release Safeguards on fired process heaters : ~. . . .1 Introduction 8. . . . . .. Releases within buildings associated external hazardous areas : ' . . . . . .' . . . . . .. . Are!_!classification forhydregen Calculation of hazard radii .. . . . .. ...2 Ignition sources 8. . .. . .. . . . . . . .. . .. .. .. .. .. 8. . . . .. . 101 105 107 109 115 11"9 123 127 AnnexD AnnexE AnnexF AnnexG AnnexH Annex I and 129 135 137 References '.. . ...... . 99 ANNEXES AnnexA Annex B AnnexC Classification and categorisation of petroleum and flammable fluids. .. . . . . .. .. .. ... . ' ... . .. . .... . . . . . Part 3: Background to the calculation of hazard radii in Chapter 5 . . . . . . ... 97 . . .. . . . . ..3 Use of gas detectors in hazardous areas 8. . . . . . . 141 . . . . . . . . '. . g Non-electrical ignition sources. .. ... . . .Contents Cont . .. . . .. . .. .. . . .' . .. ... .. . . . . .. . . . . . .
The former approach made a distinction between heavier and lighter than air materials but this is no longer valid. classification ofhazardous areas in. taking into account variables ..FOREWORD Part 15 ofth~ lP Code' of Safe Practice i~ a well-~stablished. for damage or loss. The Code also provides a risk-based approach for specifying hazardous areas from' secondary point source releases. or alleged damage or loss.. since the new methodology used takes account of both the composition of the material released and its release conditions including the release pressure. the pettbleliri! :industry. updated. the full methodology is provided in a separate publication: IP A rislc-b_ased approach to area classification..internationally-accepted Code for: the . which has broadened the applicability of the Code to all installations handling flammable fluids. arising or otherwise occurring as a result of the application of this Code. Whilst the Code" includes the basis of the Risk-Based Approach. ' will ix . The Code applies current dispersion methodology to the calculation of hazard radii. .hoped and anticipated that this publication assist those involved in the area classification of installations handling flammable fluid's. the Institute of Petro Ierim cannot accept any respoasibility. demoristrable ' methodology for specifying hazard radii. The second-edition provides a:b. such as pressure of release and the effect of mist or spray formation. allowing further flexibility in specifying 'hazard radii. Moder Although it is . of whatsoever kind.
Ltd.Marathon Oil U.tu~ of Petroleum' s Area TheImniute wishes to record its appreciation of the work carried out by themembers of the Working Group. Institute of Petroleum .K. BP KCA-Deutag Ltd. and te'~'M\gnise the contribution made by those individuals. ~erek Stirling .ACKNOWLEDGEMENTS This Part of the Modet'Code of Safe Practice was prepared Classification Working Group: Institute of Petroleum BP Chemicals Ltd..1 Consultant Advantica Technology Ltd. t xi .eehnieal review. companies and organisations that provided comments d~ . Alia Alavi Howard Crowther Phil Cleaver Kieran Glynn 'Peter Nichols ·Andrew Sangster by members· of the Insti.~ Tyldesley_ Health and safety Executive 't<4iGkWansborough Shell UK Oil Products Ltd.
1 can be used to assess the level ofventiletioa for given situations. CHAPTER. both onshore and offshore with the aid of type diagrams. where extremesofvcHatility. Describes the area olassification drawing. temperature class. A risk-based approach is also provided for determining the extent of Zone 2 areas where release hole sizes are not specified apriori. with diagrams. and allows for variations in release rates and-operational pressure. CHAPTER CHAPTER 4: Provides guidance for the classification of drilling rigs.Figure 1.~' . Methods of artificial ventilation and the effect ofloss ofventilation on the area classification are discussed. andto consider all sources of ignition. Indicates a: means of defining flammable fluids for area classification purposes by their flash point and.Chapter 5 for variable releases such as tank vents. xiii . 3: Provides examples. Open areas. These are based on current dispersion methodology as detailed in IF Calculations in support of IP 15.OVERVIEW CHAPTER 1: Establishes the scope and appli~ability of the code and defines key terms. CHAPTER 6: Provides guidance on the effect of ventilation in non-open areas. . distances are specific to the conditions given. 5: The point source methodology is described in this chapter and provides the basis for the hazard radii specified.1 provides a step-by-step guide to claSsifying hazardous areas using the Code. CHAPTER 7: Gives guidance onselection of electrical equipment according to hazard zane. This chapter considers the igaitionrisks associated with non-electrical equipment. . "temperature and pressure occur. CHAPTER 2: Identifies the information required to classify an area and explains the technique of hazardous area classification by use of either the direct example or the point source approach. apparatus group and enclosure ingress protection (IP). sheltered areas and enclosed areas are defined and the applicationef area classification to each situation is: described. The different levels of ventilation are described and Figure 6. CHAPTERS: New Iegislation requires users to carry out a hazardous area classification. the chapter also refers to the point source methodology in.basis for selecting equipment. by fluid category. to use this as It. However. which can be used to classify typical facilities. although distances are derived with greater reference to the pamt source methodology given in Chapter 5. type of protection.
. It is intended that ¢. refrigerated or cryogenic fluids nor does it address the assessment Certain locations handling only small quantities . distribution. the hazards of draining Standardization.(CENELEC). Guidance as to the recommended fixed sources of ignition in those areas. definitions and explanations of terms relating to area classification. In such cases tbroughoutthis Code where appropriate (summarised in due precautions must be taken to prevent ignition Annex I). determining layout. including sources of considered when introducing and using any temporary ignition. production and retail sectors. spacings between equipment and public classification zoning restrictions should also be boundaries and to other facilities.text of area General guidance as to the main. followed nationally by gasoline from a vehicle fuel tank in an enclosed garage bodies such as. be classified as 'non-hazardous'. 1 . 'flnids sirriiliii . For instance..Blectrotecbnical Commission (lEC) and in fluid samples. aspects of area and provides a basis for both the correct selection of classification may be considered -in . in· 30 m then the size of the release is generally larger than that considered for area classification purposes and processing..possible to set a cut-off point. However. It is not..1 Small scale operations industries. the British space or a below-ground inspection pit necessitate strict Standards Institution.-.in physical characteristics to those occurring ill the petroleum. as this must be judged according to the Europe by the Buropean Committee for Electrotechnical circumstances. consideration should be given to modifying the facility The application of this Code is limited to flammable to minimise the size-of the release. generating a source of ignition_ .1 --INTRODUCTION. will be found in other lP codes referenced in electrical equipment or mobile equipment..e guidance given in this Code Nate: ~ a resulting hazard radius is greater than is applicable internationally to installations. This may apply to laboratories for testing small petroleum classificationhasalsobeensetoutiD.1 SCOPE 1.. in the United Kingdom. determining fixed electrical equipment arid the location of other separation distances. 1.temationallybythe Iatemational. References to standards and avoidance of all sources of ignition and only Zone 1 guidance issued. principles. It does not cover ignitable dusts._ .. by these bodies are provided electrical equipment should be permitted. for example.. capable of Annex I.2. flammable fluids can. in the con. petrochemical and allied ~.of of health risks due to the handling of flammable fluids. Area safety . .2 AREA CLASSIFICATION LJMITS OF APPLICABILITY This Code gives guidance on the classification of areas Area classification should not be used as a prime tool in around equipment handling or storing flammable fluids.
e.3. the risk to an individual should be assessed.4 SAFETY PRINCIPLES FUNDAMENTAL TO AREA CLASSIFICATION 1. releases of flammable materials under -catastroPhic failure of plant. This is referred to as the 'direct example approach' and is presented in. E. The incidence of such releasesmust be kept within acceptable limits by correct design. . In certain circumstances. . which rapid escape would be difficult.Capacity thresholds above which area classification is required Flammable liquid at a temperatnre above its flash point 25litres Gas: Volume corrected to 1 Bar pressure Inside Outside 50 lines Liquefied Flammable Gas 5litres 100 lines 1000 litres 200 litres from any type of ignition source (see Chapter 8). In making such a judgement.3 . the rupture of a pressure vessel or pipeline. As prescribed by the Intematienal Blectrotechnical Commission (lEe 600-79-10).APPLICATION OF '!'f!!S CODE . level the probability of coincidence of a flammable atmosphere and an electrical or other source of ignition.1 . Where this is the case. maintenance and operation of facilities. constructed.AREA CLASSlF1CATION CODE FOR INSTALLATIONS HANDLING FLAMMABLE FLUIDS Table 1. Chapters 3 and 4.4. as in processing plant.1 Facility of common type Certain facilities of standard layout anddesign:handling flammable fluids can be classified directly·from typical examples. of a mist or spray. Such materials. has a very low probability of occurrence.g.3. Each vessel containing flammable fluids should be considered individually. normally regarded as non-hazardous. as in a relatively confined location frOID. possibilities 1.3. of design and operation technique described here The area classification assumes that the facilities to which it is applied are designed. ignition of quite small quantities of flammable gas/vapour mixed with air can cause danger to anyone in the immediate vicinity. a more rigorous calculation methodology is used. .1. should be treated as hazardous when they are pumped or under pressure and are capable cfproducing a inistdf spraydue tothe possibility'of areleasefrom a small hole or flange leak They should be regarded as a Category C fluid generating a hazardous area as appropriate.4.2 Good standard For process streams ofless uniform volatility and where there are extremes in temperature and pressure. 1.1 which summarises the steps needed to conduct an area classification. 1. This methodology is presented :in Chapter 5. 1. 1. The application oftrus Code and the relevance of each chapter are shown in Figure 1.1 Avoidance oUire and explosion 1. with consideration of the surroundings and where people need to move about As a rough guide. in properly run facilities. it is not the aim of area classification to guard against the ignition of major . construction.3 :Mists and sprays Flammable atmospheres may also be formed where flammable fluids handled below their flash points' are released in the form. The approach is to reduce to an acceptable minimum.2 Other facilities The aim of area classification is to avoid ignition ofthose releases that may occur from time to time in the operation of faoilities handling·flammable liquids and vapours. hazardous area classification may not be needed if the maximum amounts of material that could be released are below the quantities given in Table 1. maintained and operated in 2 . orthe cold failure of a tank which. referred to as the 'point source' methodology. Further information on the application of area classi:fication to small-scale facilities is given in Annex. area-classification may be needed down to quite small quantities offluid.
Areas are subdivided into zones based on This is. In other 1. 'flammable' atmosphere is preferable and should be used because the term 'explosive' is a special continually reviewed and kept updated. a specific legal the likelihood 'of occurrence and duration of a requirement under the AT~ directive (1999!92!EC). 1. the procedure subdivision of the hazardous areas into zones. process systems and equipment.6. though they should always be reviewed and drawings modified. vapours. when the cloud is: ignited. if may. fluids . as appropriate. offlammable substances . can be simplified by adopting a standardized area classification diagram. regarding good operational and maintenance practice should also be followed. as will be shown in Chapter 2.4 and IP The company operating a facility has the prime Design. construction and operation of distribution. .6 KEY TERMS 1. personnel. in which. 8. carried out by persons who have full knowledge of the . it will bum when . At this special precautions for the control of potential ignition stage. (Chapters 3 and 4). Examples include petroleum distribution installations (see also section. The' work. 1. ignited. as follows: Where a facility has been designed !IUd built on a 3 . under special controls. under atmospheric conditions. ISO 13702). cases. A hazardous area. combustion rapidly spreads safety. after ignition has occurred. The term. . The area classification areas are non-hazardous in this context.release of flammable fluid present In Area classification is the assessed division of a facility into hazardous areas and non-hazardous areas. with0ut any further admixture. loss prevention and electrical engineering to the entire unburned mixture. is -defined as a three-dimensional In classifying a new facility or a modification. All other improvements at little cost. Agreements reached on the area classification should be formally recorded. Records. temperature class as covered in Chapter 7.6. responsibility to ensure that area classification has been installations) and offshore production installations (see carried out on installations handling flammable fluids. identified and be competent ill this field.lNTRODUCITON accordance with good industry practice so as to reduce releases to a minimum.2 Area classification In principle. on completion or' design and before any area -wjthin the facility in which all work is carried out change is made to existing plants handling flammable.5 THE MANAGEMENT OF AREA These terms are consistent with the usage and principles in IEC 60079-10.6. flammable gases or vapours with air insuch proportion co-ordination af the -area classification -should he that. the plant designers should have carried out such a study.1 Flammable atmosphere CLASSIFICATION Area classification should be incorporated into a A flammable atmosphere is defined as a mixture of company's Health. it may be possible to make considerable sources including fixed electrical equipment. in part or whole. within the European Union. The recommendations of the IP Model Codes (Annex 1) or their equivalents. should include case of 'fJ. such as drawings andlortabulated data sheets. form part of a wider restricted necessary. Safety and Environmental Management System. turnkey basis. should be An.. the classification of an area entails consideration of all the actual sources and potential sources of . and the practice..3 Hazardous area and zone. sub-group and . 1. The person responsible for the . in consultation with in the form of gases. mists or dusts. explosive atmosphere is a mixture with air. which requires an interdisciplinary approach. the procedure of considering individual point sources will be necessary and this is detailed in Chapter 5. flammable atmosphere. the space in which a: flammable atmosphere may be area classification should be carried out before the expected to be present at such frequencies as to require design and layout of equipment are finalized. Equipment and piping should be designed to international standards or national equivalents.ammable' where' either congestion or details as to the type of protection selected to meet the confinement leads to the generation of over-pressure zone requirements and the apparatus. and should have passed it over with oilier documentation to the owners at the end of commissioning.
E FLUIDS 1:63. Although continuous. Also some sources ..FOR INSTALLATIONS HANDLING FLAMMABJ.may be considered to have a dual grade of release with a small continuous or . The grade of release is dependent solely on the frequency and duration of the release.de of !e!~e js not always obvious and will require experienced engineering and operational judgement Events which occur regularly but briefly should be classified as primary grade sources giving rise to a Zone 1 area unless carried out under permit-to-work circumstances. in any event. Continuous grade normally leads to Zone O. in operating procedures.6. primary and secondary grade releases will normally result in Zones ·0.AREA CLASSIFICATION CODF. In operating procedures.3. or the characteristics of the fluid. likelihood of leaks remaining undetected. the following quantities !I!esuggested. routine sampling points) they should be regarded as primary grade releases. Where releases are likely to be present for less than 10 hours per year but are anticipated in normal operation (e.nonhazardous. 1.il 'nornlal operation and. A release that is continuous or nearly so. For example. will do so only in:frequentlyand for short periods ie. under unrestricted 'open air' conditions a direct relationship between tb:e grade of release and the type of zone to which it gives rise.4). this may not always be true.ossaxy. 1 and 2 respectively. ifit occurs. Primary grade release: A release that is likely to occur periodically or occasionally in normal operation i. although these factors determine the extent of vapour travel and in consequence the dimensional limits of the hazardous zone. vapour or liquid may be released into the atmosphere.-Areas that do not fall into any.2 Zone 1 That part of a hazardous area in which a flammable .4. 1.' A rel~aSe that "is ~ely to occur i.5 ::Relationshipbetween grade of release and class of zone There is.1 Zone 0 That part of a hazardous area in which a flammable atmosphere is continuously present or present for long periods. in most cases. That part of a hazardous area in which a flammable atmosphere is not likely to oCCUr in normal operation and.es. 1. and thereby zonal identification. is not anticipated into account.4 Non-hazardous areas .he.4 Source and grade of release . primary grade and a larger secondary grade (see section 5. 1. Secondary grade normally leads to Zone 2. Examples of this are a vent with dual-purpose process requirements or a pump seal. The allocation of the grade of release should be reviewed in the course of the design stages to determine if practicable and economical design or engineering improvements can be made to reduce the number of OOJltinueus8:l:l4.3 Zone 2 .gql.. with high ventilation provision. will exist only for a short period.6.e. it should be noted that the terms 'Grade of Release' and 'Zone' are not synonymous. the degree ofventilation. It is completely independent. primary and secondary grade sources normally occur on typical equipment may be found in Chapters 3 and 4. 1. Examples where continuous. or that occurs frequently and for short periods.3. the converse will.already been taken For the purpose of area classification a source of release is defined as a point from _ which a flammable gas. To assist understanding of the boundaries of the definitions of the different grades of release.. Three grades of release are defined in terms of their likely frequency and duration: Continuous grade release: . This assessment should take account of any.6. of the above -are . be true (see Chapter 6). poor ventilation may result in a more stringent zone while.3. have.g. A release ~hould be 4 . However.6. Secondary grade release. is anticipated to occur.regarded as continuous grade if it is likely to be present for more than lOOOhours per year and primary grade if it is likely to be present for between 10 and 1000 hours per year.6. a release which.pr:b:gary grade r~eas. . A release likely to be present for less than 10 hours per year and for short periods only should be regarded as secondary grade. to occur. of the rate and quantity of the release. It should be noted that the respective grades of release. as definedin tne-gJ. Assessment of 1. Primary gradenonaally Ieads to' Zone 1.e.atmosphere is likely to occur in normal operation. i. a release which.
supplemental to the general classification by flash point.·«· <. This system is used througholrtthe type examples inChapter 3: In other situations in which extremes of fluid volatility. _. on release.3 .7 Fluid category The need.G(iJ.. B C G(i) A flammable liquid.. its volatility in relation to the conditions of temperature and pressure at which a potential release might take place is an essential factor. whilst a Zone I area will often be surrounded by alarger Zone 2 area. . 1. presentation of many cases of point source release covered in Chapter 5 uses a base parameter designated the 'hazard radius' which is defined as 'the largest horizontal extent of the hazardous area that is generated by the source when situated in an open area' .< point. 1. Inaddition to the standard terminology used throughout this Code. terms The glossary at the end of this Code should be consulted for the definition of other terms.6. have been introduced. these fluid categories are defined in Annex A and 1.4. It should also be noted that.Hazard radius Where the flammable fluid is ~ liquid. 'j\-' • . and their application is outlined in section 5. with its further subdivision of Classes ITand Ill into sub-classes (1) and (2) according to whether the liquids are handled at temperatures above or below the flash point (see Annex A).2. 1.6. not in Category A. but which can.class. which would require a larger Zone 2 area.2. in accordance withtheInstitute of Petroleum. A flammable liquid.. . not in Categories A or B. but at a temperature sufficient for boilingto occur on release.) . . there is no specific requirement for this. as shown in Table 1.3. Annex A). should be considered. when classifying the more extreme and varied flammable fluid conditions that may be encountered in "thepoint source method of Chapter 5. would vaporise rapidly and substantially. or form a flammable mist or spray. the classification of the flammable fluid by flash point . will be adequate for this purpose. for the extension of the 1P general classification based on closed cup flash point has led to the definition of the supplementary criteria by fluid category for flammable fluids. In many of the commonly encountered types of facilities. A typical methane-rich natural gas. FUrther explanation of how this parameter is derived may be found in Annex C (part 1). be at a temperature above its flash.the hazard radius in conjunction withfluid category and the release conditions is described in section 5. The use of .6. This category includes: (a) Any liquefied petroleum gas or lighter flammable liquid (b) Any flammable liquid at a temperature sufficient to produce.8 Specialterminology. . _.< . ..6 Classification of flammable fluids 1. Where a Zone I area is not part of a larger Zone 2 then the possibility of any large but infrequent release. since it will determine the extent of rapid vapour formation from that release. four categories of fluid condition. on release.6. classification (see Table A3. on release.- .2 -Fluid categories Fluid Category A Description A flammable liquid that._ .!NTRODUCTION Table 1.. . such as those referred to in section 2.7. temperature and pressure occur under typical processing conditions and the procedure of Chapter 5 is to be applied. . 1.6. .7 VENTILATION Ventilation comprises the movement of air within and through a volume to achieve the introduction of fresh 5 .9 Other. Refinery hyd!ogen". more than about 40% vol vaporisation with no heat input other than from the surroundings.
' 3. than 0.very short distance of the release point. than in a true open area.5 Sheltered or obstructed area methane were released as a non-pressurised cloud or An area within or adjoining an open area (which may 'bubble'. its dispersion would need to be specifically include a partially open building or structure) where.2 Artificial ventilation open areas. the volume and the mixing of air and contaminants within the volume. sumps andpools etc.7.7.7.7. in~-relationsbip of the types. The degree of openness of a region is an important factor in determining the adequacy of ventilation. temperatures: and. Some common situations where the releases are not the absence of artificial ventilation. Where'areas are sheltered 1.7. Similar .) If a 'lighter-than-arr gas such as hydrogen or 1. The shapes of these zones dependprimariIy enclosure).1 Natural areas such as pits and trenches and areas within tank bunds may be subject to restricted ventilation and therefore fall into tbiscategory. degree of openness and-Ievel:ofventilation: 1. It applies to enclosed areas only. The 'level' helps define the extent of any hazardous area and the zone number. Previous editions oftbis and other Area Classification Codes have made a distinction between 'heavier-thanVentilation caused by wind or convection effects.. types and levels should be assessed. Further. with the same zonal number as for the same source in an open area. . Where natural ventilation is adequate.'. natural and artificial. the air movement will be limited and any flammable atmosphere will not pressurised are given in the direct examples in Chapter be dispersed naturally. but these are-all where 'heavier-than-air' vapours exist (e. Two boundary cases and an intermediate case are defined in 1. room or enclosed space within which. Where the degree of obstruction is.g. Chapter 6 provides guidance on how.. so that convection. It is a key factor in determining area classification. as defined below. the shape of the mechanical means (such as fans or extractors) that may hazardous region isnorrelated t()'therel~tive density of be applied generally (throl:l~out the whole of aa. However..7. The extent of the hazard zone may be enlarged as a result.3 Open area and the jet momentum determine the initial direction of the flammable cloud. the diluting mixture in An area that is open-air without stagnant regions where air attains a density very similar to that of air within a vapours are rapidly dispersed by wind and natural . ventilation 6 . below-grade and these are discussed in Annex B.o. the obstruction can be classified as a sheltered area. would be buoyant by virtue of their. and the effect on the severity of ZOnenumbers be assessed on the basis of the artificial ventilation to be provided.7. A distinction between 1.7.AREA CLASSIFICATION CODE FOR INSTALLATIONS HANDLING FLAMMABLE FLUIDS air into. fer the majority of Ventilation caused by air purge or by assisted releases from pressnrised sources. assessed. or locally (to deal with a local release or a on the angle of the' release and how close the release stagnant region). and removal of contaminated air from.such that natural ventilation is less than adequate.4 and 1.5 is provided by the criterion of adequate ventilation given in section 6.5. Figure 6.f the. as described in Chapter 6.1 provides a summary . special reference should be made to the conditions in Chapter 6 since lighter-than-air releases A:4y building. This is because a turbulent jet dispersion mechanism prevails and the angle of release' 1. in conjunction with Chapter 5. Two main 'types' are recognised.8 BUOYANCY OF RELEASE': '': . Differing 'levels' of ventilation adequacy (adequate. special considerations apply to owing to obstruction. openroad-tankerfill covers. natural ventilation may be less hydrogen because of its low minimum ignition energy . air velocities will rarely be less buoyancy effects are not a significant factor. In addition. For example.3.7. point is to the ground. Typically. it should be classified as an enclosed area.5 metres per second and will frequently be above considerations apply to fluids which are released athigh 2 metres per second.3-1. corresponding low densities. in may accumulate at high level. dilution and over-pressure ventilation) are categorised under the main types.4 Enclosed area or enclosed.1. recent work (IP Calculations in support of !Pi 5) has shown that. 1. thefluid. air' and 'lighter-than-air' gases and vapours in determining the shape profile of a hazardous region in 1.
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