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1、BS 8485:2007 Code of practice for the characterization and remediation from ground gas in affected developments ICS 91.120.99; 91.200 NO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAW BRITISH STANDARD Licensed Copy: London South Bank University, London South Bank University, Fri
2、 Nov 16 07:54:50 GMT+00:00 2007, Uncontrolled Copy, (c) BSI Publishing and copyright information The BSI copyright notice displayed in this document indicates when the document was last issued. BSI 2007 ISBN 978 0 580 56934 0 The following BSI references relate to the work on this standard: Committe
3、e reference I/-/2 Draft for comment 07/30149736 DC Publication history First published 31 October 2007 Amendments issued since publication Amd. no.DateText affected BS 8485:2007 Licensed Copy: London South Bank University, London South Bank University, Fri Nov 16 07:54:50 GMT+00:00 2007, Uncontrolle
4、d Copy, (c) BSI BSI 2007i BS 8485:2007 Contents Foreword ii Introduction 1 1Scope 2 2Normative references 2 3Terms and definitions 2 4Overview of ground gas characterization and assessment 3 5Site categorization 3 6Risk assessment objective Estimation of a site characteristic hazardous gas flow rate
5、 6 7Solutions choice 9 Annexes Annex A (informative) Estimation of underfloor ventilation and pressurization performance 13 Annex B (informative) Checklist of factors to take into consideration 19 Bibliography 22 List of figures Figure 1 Ground gas characterization and assessment flowchart 4 Figure
6、A.1 Performance assessment criteria of ventilation layer for methane hazard (from PiT 7) 16 List of tables Table 1 Characteristic gas situation by site characteristic hazardous gas flow rate 9 Table 2 Required gas protection by characteristic gas situation and type of building 10 Table 3 Solutions s
7、cores 12 Table A.1 Summary of gas dispersal characteristics of different ventilation media on idealized foundations 17 Table A.2 Comparison of PiT gas regime and CIRIA 665/BS 8485 calculated hazardous gas flow rate by gas screening value in l/hr 18 Table B.1 Variables and common factors to be consid
8、ered in the application of this code of practice Source variables 20 Table B.2 Variables and common factors to be considered in the application of this code of practice Pathway variables 20 Table B.3 Variables and common factors that should be considered in the application of this code of practice T
9、arget variables 21 Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, pages 1 to 22, an inside back cover and a back cover. Licensed Copy: London South Bank University, London South Bank University, Fri Nov 16 07:54:50 GMT+00:00 2007, Uncontrolled Copy, (c
10、) BSI BS 8485:2007 ii BSI 2007 Foreword Publishing information This British Standard is published by BSI and came into effect on 31 October 2007. It was prepared by Technical Committee I/-/2, Brownfield developments. A list of organizations represented on this committee can be obtained on request to
11、 its secretary. Information about this document This standard was developed to provide designers of developments on sites affected by ground gas with a structured method for risk-based solution choice. Use of this document As a code of practice, this British Standard takes the form of guidance and r
12、ecommendations. It should not be quoted as if it were a specification and particular care should be taken to ensure that claims of compliance are not misleading. Any user claiming compliance with this British Standard is expected to be able to justify any course of action that deviates from its reco
13、mmendations. Presentational conventions The provisions in this standard are presented in roman (i.e. upright) type. Its recommendations are expressed in sentences in which the principal auxiliary verb is “should”. Commentary, explanation and general informative material is presented in smaller itali
14、c type, and does not constitute a normative element. Contractual and legal considerations This publication does not purport to include all the necessary provisions of a contract. Users are responsible for its correct application. Compliance with a British Standard cannot confer immunity from legal o
15、bligations. Licensed Copy: London South Bank University, London South Bank University, Fri Nov 16 07:54:50 GMT+00:00 2007, Uncontrolled Copy, (c) BSI BSI 20071 BS 8485:2007 Introduction When building/developing on or adjacent to: brownfield sites, sites where degradable materials are present within
16、the ground, and in areas of mineworkings, there is a potential risk of the generation of ground gases and accumulation of these gases within buildings. Under adverse circumstances, methane and carbon dioxide gases can build up to hazardous concentrations within confined spaces giving rise to a poten
17、tial risk of explosion or asphyxiation. Indeed, there are documented cases of loss of life and damage to property resulting from ground gas accumulation. Guidance available up to the date of this British Standard has generally focused on the occurrence and methods of measurement of ground gases and
18、the incorporation of protection measures into buildings to mitigate the risk of building on sites affected by ground gas. The issue of how to undertake assessment of gas monitoring data in order to determine suitable parameters to be used in the design of protection measures has, until recently, not
19、 been developed to any significant degree and, as a result, design solutions often lack a rigorous assessment of data and have often resulted in overly conservative solutions or insufficient measures being adopted. This standard is intended to provide a framework in line with CLR 11 1 that will allo
20、w designers to judge the adequacy of ground gas and related site investigation data, and provides an approach to determine appropriate ground gas parameters that can be used to identify a range of possible construction solutions that will mitigate against the presence of ground gas on a development
21、site. Importantly, it allows the identification of those sites where gas protection measures are not required. The framework is not prescriptive and judgement may be made as to the acceptability of risk and whether there is a cost benefit in undertaking more rigorous site assessment or adopting cons
22、ervative measures in design. Emphasis is placed on the justification and recording of risk assessments and design decisions throughout the process. This standard is intended to be used by designers of gas protection measures and regulators involved in the assessment of design solutions. It recognize
23、s that there are a number of factors requiring consideration which affect the sensitivity of the development to the effects of ground gas, and that there are a range of solutions available for different situations. In this regard it is anticipated that specialist advice will be required in the asses
24、sment of the ground gas data and in the risk assessment phase. Licensed Copy: London South Bank University, London South Bank University, Fri Nov 16 07:54:50 GMT+00:00 2007, Uncontrolled Copy, (c) BSI BS 8485:2007 2 BSI 2007 1 Scope This British Standard gives recommendations and describes methods f
25、or the investigation and assessment of the ground gases methane and carbon dioxide during new development of affected sites, and is not intended for the assessment of completed developments. It details a process that can be used to effectively demonstrate that risks posed by the potential presence o
26、f ground gas have been adequately considered and addressed. It presents the assessment and decision making stages in the form of a process flowchart, accompanying information and explanatory guidance and, where appropriate, references to other guidance and information. The standard does not consider
27、 ground gases other than methane and carbon dioxide. NOTEOther gases might require specific risk assessments and have to be considered separately. 2 Normative references The following referenced documents are indispensable for the application of this document. For dated references, only the edition
28、cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. BS 10175:2001, Investigation of potentially contaminated sites Code of practice Card G, Hutchings H, Mallett H, Oliver S, Wilson S. CIRIA C665, Assessing risks posed by hazardous
29、ground gases for buildings. CIRIA. 2007. (Formerly issued as C659.) BRE Report 414. Johnson R. Protective measures for housing on gas contaminated land. 2001. 3 Terms and definitions For the purposes of this document the terms and definitions in CLR 11 1 and the following apply. NOTE These terms are
30、 not to be confused with similar terms in other referenced documents. 3.1ground gas potentially hazardous gas, generated below ground NOTEThe most common ground gases are methane and carbon dioxide. 3.2measured flow rate q total gas flow from a borehole measured in volume per unit time (typically li
31、tres per hour) 3.3measured hazardous gas concentration Chg concentration of a specific hazardous gas measured as a percentage of the total gas volume from a borehole Licensed Copy: London South Bank University, London South Bank University, Fri Nov 16 07:54:50 GMT+00:00 2007, Uncontrolled Copy, (c)
32、BSI BSI 20073 BS 8485:2007 3.4calculated hazardous gas flow rate Qhg calculated flow rate of a specific hazardous gas from a borehole reading, i.e. 3.5site characteristic hazardous gas flow rate Qhgs flow rate representative of a site or zone, derived from empirical borehole data and other influenci
33、ng factors, in accordance with a conceptual model NOTE 1This figure is derived using professional judgement. NOTE 2Also known as “gas screening value”, e.g. in CIRIA C665. 4 Overview of ground gas characterization and assessment The process of assessing the appropriate treatment of ground gas in an
34、affected site should follow the flowchart in Figure 1. 5 Site categorization 5.1Desk Study COMMENTARY ON 5.1 The main objectives of the desk study are to start the process of constructing a conceptual model of the likely gas sources on or near the site, the likely migration pathways and receptors. T
35、his will inform further site investigation which will in turn revise and augment the conceptual model. Relevant guidance on the requirements and objectives of a desk study can be found in BS 10175:2001. Site investigations ought to be designed in accordance with BS 5930 and published guidance such a
36、s the AGS Guidelines for Good Practice in Site Investigation 2. Detailed advice on investigation of ground gas can be found in CIRIA C665. The primary requirements and objectives of the desk study should all be met, which are as follows. a)Have all potential gas sources been identified or discounted
37、? The assessment should include identification of natural geological sources, mine workings, waste materials, landfills, and an understanding of the nature of the gas generation processes involved. b)Have the site history and current use been evaluated and any likely gas sources, migration pathways
38、and receptors arising from site uses been identified? c)Is there a clear understanding of the geology and hydrogeology of the site, and the presence of contamination, and how it might affect gas sources and gas migration? This includes the effect of groundwater level variations, including tidal vari
39、ations (and how these can affect gas sources and gas migration). d)Have all potential pathways been identified or discounted? This includes natural geological pathways, services, underground structures and mine workings. e)Have potential receptors, both on and off site, been identified and their sen
40、sitivity assessed? Qhg Chg 100 - -q= Licensed Copy: London South Bank University, London South Bank University, Fri Nov 16 07:54:50 GMT+00:00 2007, Uncontrolled Copy, (c) BSI BS 8485:2007 4 BSI 2007 Figure 1Ground gas characterization and assessment flowchart Undertake desk study Develop conceptual
41、model Have potential gas sources been identified? Design and undertake ground gas investigation Refine conceptual model (CM) Does CM indicate there is a gas risk? Is the dataset adequate ? Derive site characteristic flow rate in accordance with best practice - can include site zoning, selection of r
42、epresentative gas data Have hazardous gas flow rates been calculated? Site characterization and selection of characterestic gas regime/hazard polution Determination of gas design regime Remediation method selection, remediation design Could the remedial costs be significantly reduced by improving th
43、e data quality to “comprehensive“ and reducing characterestic emission rates? Implement remediation Undertake appropriate validation IMPLEMENTATION OF REMEDIATION STRATEGY Consideration of external factors (Table 3) Data adequate Select worse case gas flow rate for site characterization Assume worst
44、 case gas flow rate for site conceptual model No further action Are the data sufficient to demonstrate there is no gas risk? Adequate/comprehensive datasets where there is a well supported conceptual model Either/or Yes Yes Yes Are desk study and existing ground investigation data sufficient to dete
45、rmine there is no gas hazard? No further action Yes Yes Yes No No No No Either/or No No No RISK ASSESSMENT See notes for the minimum reqirements to obtain gas flow rate See notes on inadequate, adequate and comprehensive datasets OPTIONS APPRAISAL Desk study should provide sufficient information on
46、sources, pathways and receptors for these to be investigated. (5.1) Data are inadequate Data are inadequate See notes for recommendation to compare output with expectations from desk study (6.2) Yes Licensed Copy: London South Bank University, London South Bank University, Fri Nov 16 07:54:50 GMT+00
47、:00 2007, Uncontrolled Copy, (c) BSI BSI 20075 BS 8485:2007 5.2Walk over (reconnaissance) The desk study should be supplemented with a site walk-over study as recommended in BS 10175:2001, 6.2.2. 5.3Site investigation Data derived from the main site investigation should be used to assess the risk of
48、 gassing and to design remediation measures. The key elements of the site investigation should be as follows. a)The investigation should be designed to confirm the geology and hydrogeology of the site, the presence of made ground, contamination, identification of the source and the nature of the mec
49、hanism of gas generation, from borehole/trial pit logs, and where appropriate sampling, testing and analysis. b)Where appropriate, the use of geophysical/remote sensing techniques should be used to help delineate the extent of landfill or made ground and the location of the methogenic material. c)Monitoring installations: are the type and depth of monitoring installations adequate to identify gas sources and migration pathways, and to determine whether receptors are likely to be impacted? d)Distribution
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