1、BRITISH STANDARDBS EN 14756:2006Determination of the limiting oxygen concentration (LOC) for flammable gases and vapoursThe European Standard EN 14756:2006 has the status of a British StandardICS 13.230g49g50g3g38g50g51g60g44g49g42g3g58g44g55g43g50g56g55g3g37g54g44g3g51g40g53g48g44g54g54g44g50g49g3g
2、40g59g38g40g51g55g3g36g54g3g51g40g53g48g44g55g55g40g39g3g37g60g3g38g50g51g60g53g44g42g43g55g3g47g36g58BS EN 14756:2006This British Standard was published under the authority of the Standards Policy and Strategy Committee on 31 January 2007 BSI 2007ISBN 978 0 580 50109 8National forewordThis British
3、Standard was published by BSI. It is the UK implementation of EN 14756:2006.The UK participation in its preparation was entrusted to Technical Committee FSH/23, Fire precautions in industrial and chemical plant.A list of organizations represented on FSH/23 can be obtained on request to its secretary
4、.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 obligations.Amendments issued since publicationAmd. No. Date CommentsEUROPEAN STANDARDNORME
5、 EUROPENNEEUROPISCHE NORMEN 14756November 2006ICS 13.230English VersionDetermination of the limiting oxygen concentration (LOC) forflammable gases and vapoursDtermination de la concentration limite en oxygne (CLO)des gaz et des vapeurs inflammableBestimmung der Sauerstoffgrenzkonzentration (SGK) frb
6、rennbare Gase und DmpfeThis European Standard was approved by CEN on 2 October 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
7、 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
8、 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, L
9、atvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania,Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.EUROPEAN COMMITTEE FOR STANDARDIZATIONCOMIT EUROPEN DE NORMALISATIONEUROPISCHES KOMITEE FR NORMUNGManagement Centre: rue de Stassart, 36 B-1050 Brusse
10、ls 2006 CEN All rights of exploitation in any form and by any means reservedworldwide for CEN national Members.Ref. No. EN 14756:2006: EEN 14756:2006 (E) 2 Contents Page Foreword3 Introduction .4 1 Scope 5 2 Normative references 5 3 Terms and definitions .5 4 Test apparatus .7 5 Reagents and materia
11、ls 8 6 Test method8 6.1 Principle8 6.2 Procedures .8 6.2.1 General8 6.2.2 Short procedure.9 6.2.3 Extended procedure 11 6.3 Oxygen analysis.12 7 Verification of the test apparatus.12 8 Safety precautions.12 9 Test report 12 Annex A (informative) Examples of the determination of the LOC 13 A.1 Exampl
12、e 1: Determination of the LOC short procedure .13 A.2 Example 2: Determination of the LOC extended procedure 14 Annex ZA (informative) Relationship between this European Standard and the Essential Requirements of EU Directive 94/9/EC 15 Bibliography 16 Figures Figure 1 Explosion area for a ternary s
13、ystem of test substance, air and inert gas . 7 Figure 2 Short procedure scheme for the determination of the LAC 10 Figure 3 Extended procedure scheme for the determination of the LAC . 11 Figure A.1 Determination of the LAC of a ternary system of n-hexane, air and nitrogen at 100 C and ambient press
14、ure 13 Figure A.2 Determination of the LAC of a ternary system of hydrogen, air and nitrogen at 20 C and ambient pressure 14 Tables Table ZA.1 Correspondence between this European Standard and Directive 94/9/EC 15 EN 14756:2006 (E) 3 Foreword This document (EN 14756:2006) has been prepared by Techni
15、cal Committee CEN/TC 305 “Potentially explosive atmospheres - Explosion prevention and protection”, the secretariat of which is held by DIN. 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 May 200
16、7, and conflicting national standards shall be withdrawn at the latest by May 2007. This document has been prepared under a mandate given to CEN by the European Commission and the European Free Trade Association, and supports essential requirements of EU Directive(s). For relationship with EU Direct
17、ive(s), see informative Annex ZA, which is an integral part of this document. 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,
18、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 14756:2006 (E) 4 Introduction This European Standard describes a method for
19、the experimental determination of the limiting oxygen concentration (LOC) of mixtures consisting of flammable gas or vapour, air and inert gas. The LOC is the maximum concentration of oxygen in a mixture at which an explosion cannot occur at any fuel concentration. Explosion protection by “inerting“
20、 is based on the LOC. EN 14756:2006 (E) 5 1 Scope This European Standard specifies the method for determining the LOC of mixtures consisting of flammable gas or vapour, air and inert gas at atmospheric pressure and temperatures from ambient temperature to 200 C. 2 Normative references The following
21、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 1839:2003, Determination of explosion limits of gases and va
22、pours 3 Terms and definitions For the purposes of this document, the following terms and definitions apply. 3.1 limiting air concentration LAC maximum air concentration in a mixture of a flammable substance, air and an inert gas, in which an explosion will not occur, determined under specified test
23、conditions NOTE 1 LAC is usually expressed as molar fraction in % or volume fraction in % (for conversion of units see EN 1839:2003, Annex F). NOTE 2 The LAC does not depend only on the flammable gas or vapour, but also on the inert gas used. 3.2 limiting oxygen concentration LOC maximum oxygen conc
24、entration in a mixture of a flammable substance, air and an inert gas, in which an explosion will not occur NOTE 1 LOC is usually expressed as molar fraction in % or volume fraction in % (for conversion of units see EN 1839:2003, Annex F) NOTE 2 The LOC does not depend only on the flammable gas or v
25、apour, but also on the inert gas used. 3.3 test substance substance or mixture of substances for which the LOC is to be determined NOTE The test substance is usually a flammable gas or the vapour generated by the complete evaporation of a flammable liquid. 3.4 test mixture mixture of test substance,
26、 air and inert gas EN 14756:2006 (E) 6 3.5 inert gas gas that does not react with the test substance or oxygen 3.6 explosion range range of concentration of a flammable substance or mixture of substances in air within which an explosion can occur 3.7 explosion limit limit of the explosion range or o
27、f the explosion area NOTE 1 Explosion limits (lower explosion limits, LEL, and upper explosion limits, UEL) are determined according to EN 1839. At the explosion limits flame propagation does not occur. The explosion limits are not part of the explosion range or explosion area. NOTE 2 Explosion limi
28、ts means also the limits where the test mixture contains additional fractions of inert gas. 3.8 explosion area area inside the boundary curve formed by the explosion limits of a flammable substance in various mixtures with air and inert gas NOTE 1 See Figure 1. NOTE 2 In many cases the boundary curv
29、e has an apex, which corresponds to the limiting air concentration, LAC. EN 14756:2006 (E) 7 Key 1 explosion area 2 apex 3 stoichiometric line x molar fraction in % IN inert gas TS test substance a air Figure 1 Explosion area for a ternary system of test substance, air and inert gas 4 Test apparatus
30、 The standard test apparatuses for determination of the LOC are described in EN 1839. For practical reasons there are two methods for the determination of the explosion limits, a tube method (T) and a bomb method (B). A specific apparatus is specified for each method, both of which are suitable for
31、the determination of the LOC. It shall be clearly stated which of the two methods was used, as the apparatus and test procedure may influence the LOC value. For the purposes of this European Standard the oxygen concentration shall be measured by means of a calibrated oxygen analyser with a precision
32、 of a molar fraction of 0,1 % oxygen (e.g. paramagnetic analyser, gas chromatography etc.). EN 14756:2006 (E) 8 5 Reagents and materials Air: the air shall be free of water and oil. If synthetic air is used, it shall be stated in the report; inert gases: the purity of the inert, or the mixture of in
33、erts, shall be a molar fraction of 99,8 % or better. If a mixture of inerts is used, the composition of the mixture shall be stated in the test report; flammable substance: the flammable substance may be: a single substance or a defined mixture of substances; a process sample (of known or unknown co
34、mposition). When a single substance or a mixture of substances is used, the purity of each substance shall be a molar fraction of 99,8 % or better. In the case of a mixture of substances or a process sample of known composition, the precision of the composition shall be stated in the test report. In
35、 the case of a process sample of unknown composition, the sample shall be defined as well as possible (e.g. process conditions, lower explosion limit). If the flammable gas is derived from a liquid containing more than one component, the gas phase composition can differ from the composition of the l
36、iquid phase. When large quantities of the gas are drawn off, the composition of both the liquid and gas phases can change with time. For these reasons, the test sample shall be taken from the liquid phase. 6 Test method 6.1 Principle Ignition trials with defined test mixtures according to EN 1839 (m
37、ethod (T) or (B) are carried out in order to obtain the explosion area or a part of the explosion area for a ternary system of test substance, air and inert gas. By increasing incrementally the fraction of inert gas in the test mixtures the limiting air concentration, LAC, is obtained. From the meas
38、ured LAC the LOC is calculated according to the following equation: LACLOC 209,0= (1) 6.2 Procedures 6.2.1 General Two different methods are described for the determination of the LAC, an extended procedure and a short procedure. The short procedure may be applied if the LAC is at the apex of the ex
39、plosion area, which is mostly the case. The extended procedure shall be applied if the LAC is given by a tangent on the UEL branch. The criterion for the decision “short procedure“ or “extended procedure“ is given by Equation (2). ()Lair,xUEL 1008,0 (2) where Lair,xis the air fraction at the explosi
40、on limit, as molar fraction in %, measured according to step 2. EN 14756:2006 (E) 9 To determine UEL, if unknown, and xair,Lthe following two steps have to be carried out: 1) If LEL and UEL are unknown, it is first necessary to determine the explosion limits according to EN 1839, without any inert g
41、as added. The LEL and UEL shall be measured at the same temperature. 2) The explosion limit along the stoichiometric line nearby the apex shall be determined. If nitrogen is the inert component and if the stoichiometric line is unknown, the test substance concentration shall be fixed with xTS= 1,2 L
42、EL. The explosion limit shall be obtained by varying the air and inert fractions. To start with, the inert fraction shall be a molar fraction of 50 %. The first increment shall be a molar fraction of 5 %. Near the explosion limit the increment of the air fraction shall be lowered to at least a molar
43、 fraction of 0,5 %. The inert fraction of this explosion limit is xIN,Land the air fraction xair,L. If the stoichiometric line is unknown and the heat capacity of the inert component deviates considerably from that of air the extended procedure shall be used. NOTE Violent reactions can occur in some
44、 cases for near stoichiometric mixtures with a molar fraction of 50 % inert gas. For the purposes of this European Standard it is sufficient to carry out only one repeat test for the determination of the explosion limits. Four repeat tests, in accordance with EN 1839, are required for the determinat
45、ion of the LAC according to 6.2.2 and 6.2.3. 6.2.2 Short procedure If Equation (2) is satisfied the short procedure may be applied. In this case only the area around the apex needs to be investigated (see Figure 2). EN 14756:2006 (E) 10 Key 1 explosion area 2 line of xTS= 1,2 LEL 3 stoichiometric li
46、ne x molar fraction in % IN inert gas TS test substance a air Figure 2 Short procedure scheme for the determination of the LAC After first undertaking steps 1 and 2 the following two further steps shall be carried out: 3a) Four additional tests by varying the content of test substance at the constan
47、t air fraction xair, L (see Figure 2) shall be carried out. The step size for these tests shall be: a molar fraction of 0,2 %, for test substance fractions less than a molar fraction of 5 % and a molar fraction of 0,5 % for test substance fractions equal to or more than a molar fraction of 5 %. Two
48、of the additional tests shall be carried out below the probable apex point and two above. If ignition is observed during these additional tests, steps 2 and 3 of procedure shall be repeated at the corresponding test substance fraction, until the position of the apex is determined. 4a) To confirm tha
49、t the LAC does lie at the apex of the explosion area, the explosion limits of a mixture with an inert fraction of 0,8 xIN, Lshall be determined. no explosion (see EN 1839) explosion (see EN 1839) additional tests at xair,L EN 14756:2006 (E) 11 6.2.3 Extended procedure If Equation (2) is not fulfilled (the LAC does not lie at the apex) the full explosion area, near the UEL branch, shall be investigated using the following procedures (after carrying out steps 1 and 2) (see Figure 3): Key 1 explosion area 2 line of xTS= 1,2 LEL x molar fraction
