Methods of testing cement - Part 10: Determination of the water-soluble chromium (VI) content of cement

This European Standard specifies the method for the determination of the water-soluble chromium (VI) content of cement.
A reference method is described consisting of two stages, an extraction procedure and an analysis of the filtered extract. Guidance on other extraction procedures, suitable for screening tests, for factory production control or other purposes, is given but in case of dispute or failure to comply with a regulatory limit only the reference method is used. The reference method has alternatives whereby the filtered extract may be subjected to an oxidation step or not. The criteria by which the appropriate procedure is selected are set down. Other instrumental procedures may be used for the analysis of the filtered extract provided they are calibrated against the analysis of the filtered extract using the reference procedure. In the case of a dispute, only the reference method is used.
Annex A sets out a normative procedure to be followed in case this test method is used as the basis for evaluation of conformity of a cement with the regulatory limit in Directive 2003/53/EC.
This European Standard describes a method that applies to cements. It may have wider applicability but this would need to be verified by testing on a product-by-product basis. Guidance in the possible application of this European Standard to the determination of the water-soluble chromium (VI) content of cement-containing preparations is given in Annex B.
Annexes C and D provide information on other test procedures based on paste extraction and thus depart from the performance of cement in its normal conditions of use. They may be carried out with or without the oxidation process. Users should be aware that results using these methods might be significantly different to those obtained by the reference method. In the case of dispute or failure to comply with the regulatory limit only the reference method is used.

Prüfverfahren für Zement - Teil 10: Bestimmung des Gehaltes an wasserlöslichem Chrom (VI) in Zement

Diese Europäische Norm legt das Verfahren zur Bestimmung des Gehaltes an wasserlöslichem Chrom(VI) in Zement fest.
Es wird ein Referenzverfahren beschrieben, das aus zwei Schritten, d. h. aus einem Extraktionsverfahren und einer Analyse des abfiltrierten Extraktes, besteht. Hinweise zu anderen Extraktionsverfahren, die für Eignungsprüfungen, die werkseigene Produktionskontrolle und andere Zwecke geeignet sind, sind angegeben; in Streitfällen oder bei Überschreitung eines gesetzlich vorgeschriebenen Grenzwertes darf nur das Referenzverfahren angewendet werden. Das Referenzverfahren enthält alternative Verfahrensschritte, nach denen der filtrierte Extrakt wahlweise einem Oxidationsschritt unterzogen werden kann. Die Kriterien für die Wahl der geeigneten Vorgehensweise sind festgelegt. Andere instrumentelle Verfahren dürfen zur Analyse des abfiltrierten Extraktes verwendet werden, vorausgesetzt, dass sie gegen die Analyse des gefilterten Extraktes mit dem Referenzverfahren kalibriert sind. Im Streitfall darf nur das Referenzverfahren angewendet werden.
In Anhang A wird ein normatives Verfahren festgelegt, das bei Anwendung dieses Prüfverfahrens als Grundlage für die Bewertung der Übereinstimmung eines Zementes mit dem in der Richtlinie 2003/53/EG angegebenen Grenzwert anzuwenden ist.
Das in dieser Europäischen Norm beschriebene Verfahren gilt für Zemente. Die Anwendung auf andere Stoffe ist möglich; die Anwendbarkeit ist jedoch im Einzelfall zu verifizieren. Anhang B enthält Hinweise zur Anwendung dieser Europäischen Norm zur Bestimmung des Gehaltes an wasserlöslichem Chrom(VI) in zementhaltigen Zubereitungen.
Die Anhänge C und D enthalten Angaben zu anderen Prüfverfahren, die auf der Extraktion von Zementleim beruhen und daher von dem Verhalten von Zement unter den üblichen Gebrauchsbedingungen abweichen. Diese Prüfverfahren können mit oder ohne Oxidationsschritt durchgeführt werden.

Méthodes d'essai des ciments - Partie 10 : Détermination de la teneur du ciment en chrome VI soluble dans l'eau

Metode preskušanja cementa - 10. del: Določevanje vodotopnega kroma (VI) v cementu

General Information

Status
Withdrawn
Publication Date
31-Oct-2006
Withdrawal Date
16-Jun-2016
Current Stage
9900 - Withdrawal (Adopted Project)
Start Date
17-Jun-2016
Due Date
10-Jul-2016
Completion Date
17-Jun-2016

RELATIONS

Buy Standard

Standard
SIST EN 196-10:2006
English language
39 pages
sale 10% off
Preview
sale 10% off
Preview

e-Library read for
1 day

Standards Content (sample)

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Methods of testing cement - Part 10: Determination of the water-soluble chromium (VI) content of cementFHPHQWXMéthodes d'essai des ciments - Partie 10 : Détermination de la teneur du ciment en chrome VI soluble dans l'eauPrüfverfahren für Zement - Teil 10: Bestimmung des Gehaltes an wasserlöslichem Chrom (VI) in ZementTa slovenski standard je istoveten z:EN 196-10:2006SIST EN 196-10:2006en91.100.10Cement. Mavec. Apno. MaltaCement. Gypsum. Lime. MortarICS:SLOVENSKI

STANDARDSIST EN 196-10:200601-november-2006

EUROPEAN STANDARDNORME EUROPÉENNEEUROPÄISCHE NORMEN 196-10July 2006ICS 91.100.30 English VersionMethods of testing cement - Part 10: Determination of the water-soluble chromium (VI) content of cementMéthodes d'essai des ciments - Partie 10 : Déterminationde la teneur du ciment en chrome VI soluble dans l'eauPrüfverfahren für Zement - Teil 10: Bestimmung desGehaltes an wasserlöslichem Chrom (VI) in ZementThis European Standard was approved by CEN on 19 June 2006.CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this EuropeanStandard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such nationalstandards may be obtained on application to the Central Secretariat or to any CEN member.This European Standard exists in three official versions (English, French, German). A version in any other language made by translationunder the responsibility of a CEN member into its own language and notified to the Central Secretariat has the same status as the officialversions.CEN members are the national standards bodies of Austria, Belgium, Cyprus, Czech Republic, Denmark, Estonia, Finland, France,Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania,Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.EUROPEAN COMMITTEE FOR STANDARDIZATIONCOMITÉ EUROPÉEN DE NORMALISATIONEUROPÄISCHES KOMITEE FÜR NORMUNGManagement Centre: rue de Stassart, 36

B-1050 Brussels© 2006 CENAll rights of exploitation in any form and by any means reservedworldwide for CEN national Members.Ref. No. EN 196-10:2006: E

EN 196-10:2006 (E) 2 Contents Page Foreword.............................................................................................................................................................4 1 Scope......................................................................................................................................................6 2 Normative references...........................................................................................................................6 3 General requirements for testing........................................................................................................7 3.1 Number of tests.....................................................................................................................................7 3.2 Repeatability and reproducibility........................................................................................................7 3.3 Expression of masses, volumes, factors and results.......................................................................7 3.4 Blank determinations............................................................................................................................7 4 Reagents................................................................................................................................................8 5 Apparatus..............................................................................................................................................8 6 Preparation of a test sample of cement............................................................................................10 7 Extraction procedure..........................................................................................................................10 7.1 Principle...............................................................................................................................................10 7.2 Preparation of mortar.........................................................................................................................10 7.3 Filtration...............................................................................................................................................11 8 Determination of chromium (VI)........................................................................................................11 8.1 General.................................................................................................................................................11 8.2 Measurement of absorbance without oxidation..............................................................................12 8.3 Measurement of absorbance with oxidation....................................................................................12 9 Calculation and expression of results..............................................................................................13 9.1 Calculation...........................................................................................................................................13 9.2 Expression of results..........................................................................................................................14 10 Reporting of results............................................................................................................................14 11 Repeatability and reproducibility......................................................................................................14 Annex A (normative)

Evaluation of the compliance of cement with the regulatory limit in Directive 2003/53/EC on water-soluble hexavalent chromium content...........................................15 Foreword...........................................................................................................................................................15 A.1 Scope....................................................................................................................................................16 A.2 Normative references.........................................................................................................................16 A.3 Terms and definitions.........................................................................................................................16 A.4 Factory production control by the manufacturer............................................................................17 A.5 Tasks for the verification body..........................................................................................................19 A.6 Compliance criteria.............................................................................................................................22 A.7 Compliance assessment....................................................................................................................22 A.8 Actions in the event of non-compliance...........................................................................................24 A.9 Requirements for dispatching centres.............................................................................................25 Annex B (informative)

Guidance on the application of this European Standard to the determination of the water soluble chromium (VI) content of cement-containing preparations........................................................................................................................................26 B.1 Background.........................................................................................................................................26 B.2 Extraction procedure..........................................................................................................................26 B.3 Filtration procedure............................................................................................................................27 B.4 Calculation and reporting of results.................................................................................................27 B.5 Evaluation of compliance...................................................................................................................27

EN 196-10:2006 (E) 3 Annex C (informative)

Guidance on screening test method (1) using paste extraction - method based on DS 1020.................................................................................................................28 C.1 Object and field of application...........................................................................................................28 C.2 Principle...............................................................................................................................................28 C.3 Reagents..............................................................................................................................................28 C.4 Apparatus............................................................................................................................................29 C.5 Procedure............................................................................................................................................29 C.6 Calculation of results..........................................................................................................................30 C.7 Reporting result..................................................................................................................................30 C.8 Precision and accuracy......................................................................................................................30 C.9 Report...................................................................................................................................................30 Annex D (informative)

Guidance on screening test method (2) using paste extraction – method based on TRGS 613..............................................................................................................31 D.1 Significance and use..........................................................................................................................31 D.2 Basic principles of the method..........................................................................................................31 D.3 Apparatus............................................................................................................................................31 D.4 Materials...............................................................................................................................................32 D.5 Construction of a calibration curve..................................................................................................32 D.6 Sample preparation and analysis......................................................................................................33 D.7 Evaluation and Interpretation............................................................................................................33 D.8 Health and safety................................................................................................................................34 Annex E (informative)

Guidance on the photometric determination of chromium reduction capacity in cements..........................................................................................................35 Foreword...........................................................................................................................................................35 E.1 Summary..............................................................................................................................................35 E.2 Scope....................................................................................................................................................35 E.3 Apparatus............................................................................................................................................35 E.4 Reagents..............................................................................................................................................36 E.5 Procedure............................................................................................................................................37 E.6 Calculations.........................................................................................................................................37 E.7 Result...................................................................................................................................................38 E.8 Control of instrument.........................................................................................................................38 Bibliography.....................................................................................................................................................39

EN 196-10:2006 (E) 4 Foreword This document (EN 196-10:2006) has been prepared by Technical Committee CEN/TC 51 “Cement and building limes”, the secretariat of which is held by IBN/BIN. This European Standard shall be given the status of a national standard, either by publication of an identical text or by endorsement, at the latest by January 2007, and conflicting national standards shall be withdrawn at the latest by January 2007. This European Standard on the methods of testing cement comprises the following Parts: EN 196-1, Methods of testing cement — Part 1: Determination of strength EN 196-2, Methods of testing cement — Part 2: Chemical analysis of cement EN 196-3, Methods of testing cement — Part 3: Determination of setting time and soundness EN 196-5, Methods of testing cement — Part 5: Pozzolanicity test for pozzolanic cement EN 196-6, Methods of testing cement — Part 6: Determination of fineness EN 196-7, Methods of testing cement — Part 7: Methods of taking and preparing samples of cement EN 196-8, Methods of testing cement — Part 8: Heat of hydration — Solution method EN 196-9, Methods of testing cement — Part 9: Heat of hydration — Semi-adiabatic method NOTE A previous part, EN 196-21: Methods of testing cement — Part 21: Determination of the chloride, carbon dioxide and alkali content of cement, has been revised and incorporated into EN 196-2. Another document, ENV 196-4 Methods of testing cement — Part 4: Quantitative determination of constituents, has been drafted and will be published as a CEN Technical Report.

According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following countries are bound to implement this European Standard: Austria, Belgium, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.

EN 196-10:2006 (E) 5 Introduction This European Standard specifies the reference method for the determination of water-soluble chromium (VI) content of cement that consists of two stages, an extraction procedure and an analysis of the filtered extract. This European Standard test method has adopted the principle that extraction is carried out under conditions approximating as closely as possible to those during the commercial use of cement. Consequently extraction is by standard mortar and subsequent filtration. Other extraction procedures based on paste extraction have traditionally been used and are included in Annexes C and D for use as screening tests, in factory production control or laboratories not having access to equipment specified in EN 196-1 for the production of mortar. The use of paste extraction is outside the normal conditions of use of cement.. This European Standard test method has adopted the principle of analysis by spectrophotometry. The procedures set down generally permit the analysis to be carried out without the need for an oxidation step. On rare occasions some cements may contain reducing species, not controlled by the routine method, that interfere with the analysis and require an oxidation step. Inter-laboratory testing has demonstrated that it is necessary to include an ‘initial assessment test’ in order to observe the effects on the analysis. By comparing the results obtained from the method with and without the oxidation step, it can be determined whether, for that cement, the reference method should include the oxidation step. Other instrumental procedures may be used for the analysis of the filtered extract provided they are calibrated against the analysis of the filtered extract using the reference procedure. In case of dispute or failure to comply with a regulatory limit only the reference method shall be used. This European Standard test method has drawn heavily on the Danish Standard DS 1020 and the extraction procedure developed by the French cement industry association ATILH. Careful consideration has been given to the details of the German TRGS 613 method developed by Germany’s Hazardous Materials Committee in support of Industrial Regulations for Hazardous Materials. Notice was also taken of the British Cement Association ‘inherent colour’ method; the draft method produced by CEN/TC 193/WG1, reference N680, for cement-based adhesives; European Standard method EN 420 for protective gloves; and to the method, reference ID-215, developed by the Occupational Safety and Health Administration, Salt Lake, USA. The USA Portland Cement Association, Research and Development report Serial No. 2554 “Review and evaluation of analytical methods for the determination of hexavalent chromium in hydraulic cements and clinker” by Waldemar A. Klemm was found to be most helpful in resolving technical issues. The final draft by CEN/TC292 of CEN/TR 14589 confirmed that chromium species and solubilities are sensitive to pH and redox conditions and care has been taken to address these in this European Standard by controlling sample exposure to air, by adding the indicator to the alkaline filtered extract and by precisely specifying the pH for the analytical procedure. This European Standard test method was developed in order to provide a reference test method for use in the evaluation of compliance of cement with the requirements in Directive 2003/53/EC of the European Parliament and of the Council of 18 June 2003 amending for the 26th time Council Directive 76/769/EEC relating to restrictions on the marketing and use of certain dangerous substances and preparations (nonylphenol, nonylphenol ethoxylate and cement). A system for the evaluation of compliance of cement is set out in Annex A.

EN 196-10:2006 (E) 6

1 Scope This European Standard specifies the method for the determination of the water-soluble chromium (VI) content of cement. A reference method is described consisting of two stages, an extraction procedure and an analysis of the filtered extract. Guidance on other extraction procedures, suitable for screening tests, for factory production control or other purposes, is given but in case of dispute or failure to comply with a regulatory limit only the reference method is used. The reference method has alternatives whereby the filtered extract may be subjected to an oxidation step or not. The criteria by which the appropriate procedure is selected are set down. Other instrumental procedures may be used for the analysis of the filtered extract provided they are calibrated against the analysis of the filtered extract using the reference procedure. In the case of a dispute, only the reference method is used. Annex A sets out a normative procedure to be followed in case this test method is used as the basis for evaluation of conformity of a cement with the regulatory limit in Directive 2003/53/EC. This European Standard describes a method that applies to cements. It may have wider applicability but this would need to be verified by testing on a product-by-product basis. Guidance in the possible application of this European Standard to the determination of the water-soluble chromium (VI) content of cement-containing preparations is given in Annex B. Annexes C and D provide information on other test procedures based on paste extraction and thus depart from the performance of cement in its normal conditions of use. They may be carried out with or without the oxidation process. Users should be aware that results using these methods might be significantly different to those obtained by the reference method. In the case of dispute or failure to comply with the regulatory limit only the reference method is used. Annex E provides guidance on a method for determination of the excess reducing agent content of cement as used in the factory internal control system of some countries. Manufacturers using such an internal control method should assure themselves of the relevance of results in comparison with testing by the reference method. 2 Normative references The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. EN 196-1:2005, Methods of testing cement — Part 1: Determination of strength EN 196-7, Methods of testing cement — Part 7: Methods of taking and preparing samples of cement EN 45011, General requirements for bodies operating product certification systems (ISO/IEC Guide 65:1996) EN ISO/IEC 17020, General criteria for the operation of various types of bodies performing inspection (ISO/IEC 17020:1998) EN ISO/IEC 17025, General requirements for the competence of testing and calibration laboratories (ISO/IEC 17025:2005)

EN 196-10:2006 (E) 7 3 General requirements for testing 3.1 Number of tests Determination of water-soluble chromium (VI) content of cement, where the determination is not part of a series subject to statistical control, shall be carried out in duplicate. Where the determination is one of a series subject to statistical control, a single test shall be the minimum required. In the case of a dispute, the number of tests shall be two (see also 3.3). 3.2 Repeatability and reproducibility Repeatability - precision under repeatability conditions where independent test results are obtained with the same method on identical test items (material) in the same laboratory by the same operator using the same equipment within short intervals of time. Reproducibility - precision under reproducibility conditions where test results are obtained with the same method on identical test items (material) in different laboratories with different operators using different equipment. Repeatability and reproducibility in this European Standard are expressed as repeatability standard deviation and reproducibility standard deviation in percent by mass. 3.3 Expression of masses, volumes, factors and results Express masses in the extraction stage in grams to the nearest 0,1 g. Express masses in the analytical stage in grams to the nearest 0,0001 g and volumes from burettes in millilitres to the nearest 0,05 ml unless otherwise specified. Express the calculated results, where a single test result has been obtained, as a percentage of the cement as received. Express the calculated results, where two test results have been obtained, as the mean of the results, as a percentage of the cement as received. If the two test results differ by more than twice the standard deviation of repeatability, repeat the test and take the mean of the two closest test results. Express the reported water-soluble chromium (VI) content as a percentage of the cement as received, to four decimal places. Where the results of determinations with and without oxidation are to be compared results shall be considered equivalent if they do not differ by more than twice the standard deviation of repeatability. The results of all individual tests shall be recorded. 3.4 Blank determinations Carry out a blank determination without a sample following the same procedure and using the same amounts of reagents. Correct the results obtained for the analytical determination accordingly.

EN 196-10:2006 (E) 8 4 Reagents 4.0 General requirements Use only reagents of analytical quality. References to water mean distilled or deionised water with electrical conductivity ≤ 0,5 mS/m. Unless otherwise stated percent means percent by mass. Unless otherwise stated the densities of concentrated liquid reagents used in this European Standard () are on the basis of g/cm3 at 20 °C. 4.1 Concentrated hydrochloric acid (HCl),

= 1,18 to 1,19. 4.2 Dilute hydrochloric acid, 1,0 mol/l. 4.3 Dilute hydrochloric acid, 0,04 mol/l. 4.4 Acetone, (CH3.CO.CH3),

= 0,79. 4.5 Indicator solution. Dissolve 0,125 g of s-diphenylcarbazide (C6H5NHNH)2CO,

(1,5-diphenylcarbohydrazide) in 25 ml of acetone (4.4) in a 50 ml volumetric flask. Make up to the mark with acetone. The indicator solution will keep for one week, if kept refrigerated. 4.6 Standard chromate solution 4.6.1 Stock solution: Dissolve 0,141 4 g dried potassium dichromate (K2Cr2O7), dried to constant mass at (140 ± 5) °C, in water in a 1 000 ml volumetric flask and make up to the mark with water. The stock solution will keep for one month. This solution contains 50 mg Cr (VI) in a litre. NOTE Ready-to-use stock solution is commercially available. 4.6.2 Standard solution: Transfer 50,0 ml stock solution (4.6.1) to a 500 ml volumetric flask and make up to the mark with water. This solution contains 5 mg Cr (VI) in a litre. The standard solution will keep for one month. 4.7 CEN standard sand, in accordance with EN 196-1. 4.8 Sodium peroxodisulfate (sodium persulfate), Na2S2O8. 4.9 Orthophosphoric acid, H3PO4, (85 %). 5 Apparatus 5.1 Balance(s), analytical balance, capable of weighing to an accuracy of ± 0,000 5 g, and a laboratory balance, capable of weighing to an accuracy of ± 1 g. 5.2 Mixer, two speed in accordance with EN 196-1. 5.3 Spectrophotometer, for measuring the absorbance of a solution at 540 nm, or filter photometer equipped with a filter giving maximum transmission at approximately 540 nm. 5.4 Cells, with a light path of 10 mm.

EN 196-10:2006 (E) 9 5.5 Volumetric glassware, 50 ml, 500 ml and 1 000 ml volumetric flasks; 1,0 ml; 2,0 ml; 5,0 ml; 10,0 ml; 15,0 ml and 50,0 ml pipettes. 5.6 pH meter, capable of measuring pH to an accuracy of ± 0,05. 5.7 Filtration system, comprising a vacuum source connected to a vacuum flask fitted with a filter crucible, Buchner funnel or other suitable equipment. 5.8 Filter media, of pore size 7 µm or less, composed of fibre, free from organic binders, or equivalent fritted glass filter. NOTE Some filter media may become contaminated during manufacture with substances that can reduce chromium (VI). A blank test should be carried out to ensure the suitability of the filter medium selected. 5.9 Filtration equipment

123456
Key 1 mortar 2 filter funnel 3 to vacuum 4 low form beaker 5 filter flask 6 sand

Figure 1 — Typical arrangement of filtration equipment Filtration equipment consisting of a Buchner funnel, (e.g. diameter 205 mm, fitted onto a 2 litre filter flask), partially full of sand, inside which is a low form beaker to collect the filtrate, placed on top of the bed of sand. The apparatus is connected to a vacuum pump (see Figure 1). 5.10

Laboratory oven, capable of maintaining a temperature of (140 ± 5) °C.

EN 196-10:2006 (E) 10 5.11 Heating plate, capable of maintaining a temperature of (280 ± 10) °C. 5.12 Timer, capable of measuring to an accuracy of ± 1 s. 6 Preparation of a test sample of cement Immediately before chemical analysis, treat the laboratory sample, taken in accordance with EN 196-7, as follows to obtain a homogeneous test sample. Take approximately 1 000 g of the laboratory sample by means of a sample divider or by quartering. Transfer this test sample to a clean dry container with an airtight closure and shake vigorously to mix it thoroughly. Carry out all operations as quickly as possible and immediately seal in an airtight. container to ensure that the test sample is exposed to ambient air only for the minimum time. 7 Extraction procedure 7.1 Principle Cement is made into a mortar using CEN standard sand and water. The mortar is mixed for a specified time and then filtered. An aliquot of filtrate is treated with s-diphenylcarbazide and acidified within a narrow range of pH. Chromium (VI) in acid solution forms a red-violet complex the absorption of which is measured spectrophotometrically at 540 nm. The water-soluble chromium (VI) content is determined from a calibration curve. 7.2 Preparation of mortar 7.2.1 Composition of mortar The proportions by mass shall be one part of cement (see Clause 6), three parts of CEN standard sand (4.7), and one half part of water (4.0) (i.e. water/cement ratio 0,50). NOTE 1 The water to be used is analytical grade (see 4.0) Each batch shall consist of (450 ± 2) g of cement, (M), (1 350 ± 5) g of sand and (225 ± 1) g of water, (V1). NOTE 2 Where cements to be tested are rapid setting, a water/cement ratio of 0,50 may not yield sufficient filtrate for analysis. In these cases it is permissible to increase the water content, and hence the water/cement ratio, until sufficient filtrate (see 7.3) is obtained. This deviation should be reported. 7.2.2 Mixing of mortar

...

Questions, Comments and Discussion

Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.