CEN/TC 238 - Test gases, test pressures and categories of appliances

This document covers the measurements of the emissions of carbon monoxide (CO) and nitrogen oxides (NOX) produced by the combustion of gaseous fuel in domestic appliances. It is also possible to adapt it to liquid fuel appliances.
It explains how to correct the measured values obtained at the testing conditions of temperature, humidity and gas used into the reference conditions, as well as their conversion to different aeration factor expressed as %O2 in the dry products of combustion.
The document also contains information on the types of sampling probes, mainly their form and their dimensions, which depend on the type of flue gas system.
It also gives detailed information on the sampling of the flue gas to be analysed, the transport / transfer lines and their components, and the materials recommended for their construction.
This document contains hints on the calculation of the uncertainties and the parameters to be considered in the whole analysis chain from the sampling probe to the analysers including the calibration gases.
The calculation of the uncertainties of the measurements of NOX and CO is not covered by this document.

This document specifies methods to calculate (dynamic) viscosity, Joule-Thomson coefficient, isentropic exponent, and speed of sound, excluding density, for use in the metering of natural gas flow.

This document gives means for ensuring that samples of natural gas and natural gas substitutes that are conveyed into transmission and distribution grids are representative of the mass to which they are allocated.
NOTE      To ensure that a particular gas is taken into account in the standard, please see Annex A.
This document is applicable for sampling at sites and locations where interchangeability criteria, energy content and network entry conditions are measured and monitored and is particularly relevant at cross border and fiscal measurement stations. It serves as an important source for control applications in natural gas processing and the measurement of trace components.
This document is applicable to natural dry gas (single phase - typically gas transiting through natural gas pipelines) sampling only. On occasion a natural gas flow can have entrained liquid hydrocarbons. Attempting to sample a wet natural gas flow introduces the possibility of extra unspecified uncertainties in the resulting flow composition analysis. Sampling a wet gas (two or three phases) flow is outside the scope of this document.
This document does not apply to the safety issues associated with gas sampling.

This document specifies a coulometric procedure for the determination of water content by the Karl Fischer method. The method is applicable to natural gas and other gases which do not react with Karl Fischer (KF) reagents.
It applies to water concentrations between 5 mg/m3 and 5 000 mg/m3. Volumes are expressed at temperature of 273,15 K (0 °C) and a pressure of 101,325 kPa (1 atm).

This document specifies general requirements for the determination of water in natural gas using the Karl Fischer method (see Reference [1]).
ISO 10101-2 and ISO 10101-3 specify two individual methods of determination, a titration procedure and a coulometric procedure, respectively.

This document specifies a volumetric procedure for the determination of water content in natural gas. Volumes are expressed in cubic metres at a temperature of 273,15 K (0 °C) and a pressure of 101,325 kPa (1 atm). It applies to water concentrations between 5 mg/m3 and 5 000 mg/m3.

This document specifies the test gases, test pressures and categories of appliances relative to the use of gaseous fuels of the first, second and third families. It serves as a reference document in the specific standards for appliances.
The document makes recommendations for the use of the gases and pressures to be applied for the tests of appliances burning gaseous fuels.
NOTE   Procedures for tests are given in the corresponding appliance standards. The test gases and the test pressures specified in this standard are in principle intended to be used with all types of appliances.
However, the use of some test gases and test pressures may not be appropriate in the following cases:
-   appliances with nominal heat input greater than 300 kW;
-   appliances constructed on site;
-   appliances in which the final design is influenced by the user;
-   appliances constructed for use with high supply pressures (notably direct use of the saturated vapour pressure).
In these cases, the specific appliance standards may specify other test conditions in order to establish compliance with their requirements.

This document gives details for the classification of gas appliances according to the method of supplying combustion air and of evacuating the combustion products (types). This classification refers to gas appliances that are intended to be installed within buildings and/or outside of the building .
The document classifies appliances as type A, B or C according to the basic principle for the evacuation of the combustion products and air inlet.
This document is the reference for the harmonization of product standards, for the preparation of installation standards and for the common understanding of the types of gas appliances.
This document is neither an installation standard nor a product standard.
In references to a gas appliance or gas appliances connected via "its" or "their" duct or ducts, it is intended that the air inlet duct and/or the discharge duct for carrying any combustion products are part of the gas appliance. This means that such ducts are certified together with the gas appliance. Informative Annex C identifies appliance types that are designed for connection to separate chimney products, which may be part of the construction of the building.
In terms of this document, a "single duct" is a flue duct designed and capable of discharging the combustion products and/or air inlet duct for the air supply for only one appliance.
In terms of this document, a "common duct" is a flue duct designed and capable of discharging the combustion products and/or air inlet duct for the air supply for more than one appliance.

This document gives a brief overview of each of the dynamic techniques which are described in detail in the subsequent parts of ISO 6145. This document provides basic information to support an informed choice for one or another method for the preparation of calibration gas mixtures. It also describes how these methods can be linked to national measurement standards to establish metrological traceability for the composition of the prepared gas mixtures.
Since all techniques are dynamic and rely on flow rates, this document describes the calibration process by measurement of each individual flow rate generated by the device.
Methods are also provided for assessing the composition of the generated gas mixtures by comparison with an already validated calibration gas mixture.
This document provides general requirements for the use and operation of dynamic methods for gas mixture preparation. It also includes the necessary expressions for calculating the calibration gas composition and its associated uncertainty.
Gas mixtures obtained by these dynamic methods can be used to calibrate or control gas analysers.
The storage of dynamically prepared gas mixtures into bags or cylinders is beyond the scope of this document.

This document provides the means for energy determination of natural gas by measurement or by calculation, and describes the related techniques and measures that are necessary to take. The calculation of thermal energy is based on the separate measurement of the quantity, either by mass or by volume, of gas transferred and its measured or calculated calorific value. The general means of calculating uncertainties are also given.
Only systems currently in use are described.
NOTE       Use of such systems in commercial or official trade can require the approval of national authorization agencies, and compliance with legal regulations is required.
This document applies to any gas-measuring station from domestic to very large high-pressure transmission.
New techniques are not excluded, provided their proven performance is equivalent to, or better than, that of those techniques referred to in this document.
Gas-measuring systems are not the subject of this document.

This document describes the precision that can be expected from the gas chromatographic method that is set up in accordance with ISO 6974-1. The stated precision provides values for the magnitude of variability that can be expected between test results when the method described in ISO 6974-1 is applied in one or more competent laboratories. This document also gives guidance on the assessment of bias.

This part of ISO 20765 specifies a method of calculation for the volumetric and caloric properties of natural gases, natural gases containing synthetic admixture and similar mixtures, at conditions where the mixture can exist only as a gas.
The method is applicable to pipeline-quality gases within the ranges of pressure and temperature at which transmission and distribution operations normally take place. For volumetric properties (compression factor and density), the uncertainty of calculation is about ± 0,1 % (95 % confidence interval). For caloric properties (for example enthalpy, heat capacity, Joule-Thomson coefficient, speed of sound), the uncertainty of calculation is usually greater.

ISO 20765-2:2015 specifies a method to calculate volumetric and caloric properties of natural gases, manufactured fuel gases, and similar mixtures, at conditions where the mixture may be in either the homogeneous (single-phase) gas state, the homogeneous liquid state, or the homogeneous supercritical (dense-fluid) state.

ISO 23874:2006 describes the performance requirements for analysis of treated natural gas of transmission or pipeline quality in sufficient detail so that the hydrocarbon dewpoint temperature can be calculated using an appropriate equation of state. ISO 23874:2006 can be applied to gases that have maximum dewpoint temperatures (cricondentherms) between 0 °C and - 50 °C. The pressures at which these maximum dewpoint temperatures are calculated are in the range 2 MPa (20 bar) to 5 MPa (50 bar).
The procedure given in ISO 23874:2006 covers the measurement of hydrocarbons in the range C5 to C12. n-Pentane, which is quantitatively measured using ISO 6974 (all parts), is used as a bridge component and all C6 and higher hydrocarbons are measured relative to n-pentane. Major components are measured using ISO 6974 (all parts) and the ranges of components that can be measured are as defined in ISO 6974-1.

ISO 6145 is a series of documents dealing with various dynamic methods used for the preparation of calibration gas mixtures. This document specifies a method for continuous preparation of calibration gas mixtures, from nominally pure gases or gas mixtures by use of thermal mass-flow controllers. The method is applicable to preparation of mixtures of non-reacting species, i.e. those which do not react with any material of construction of the flow path in the thermal mass-flow controller or the ancillary equipment.
If this method is employed for preparation of calibration gas mixtures the optimum performance is as follows: the relative expanded measurement uncertainty U, obtained by multiplying the standard uncertainty by a coverage factor k = 2, is not greater than 2 %.
If pre-mixed gases are used instead of pure gases, mole fractions below 10−6 can be obtained. The measurement of mass flow is not absolute and the flow controller requires independent calibration.
The merits of the method are that a large quantity of the calibration gas mixture can be prepared on a continuous basis and that multi-component mixtures can be prepared as readily as binary mixtures if the appropriate number of thermal mass-flow controllers is utilized.
NOTE       Gas blending systems, based upon thermal mass-flow controllers, and some including the facility of computerization and automatic control, are commercially available.

ISO 14532:2014 establishes the terms, definitions, symbols, and abbreviations used in the field of natural gas.
The terms and definitions have been reviewed and studied in order to cover all aspects of any particular term with input from other sources such as European Standards from CEN (The European Committee for Standardization), national standards, and existing definitions in the IGU Dictionary of the Gas Industry.
The definitive intention of  ISO 14532:2014 is to incorporate the reviewed definitions into the ISO/TC 193 source standards.

ISO 6145-6:2017 specifies a method for the dynamic preparation of calibration gas mixtures containing at least two gases (usually one of them is a complementary gas) from pure gases or gas pre-mixtures using critical flow orifices systems.
The method applies principally to the preparation of mixtures of non-reactive gases that do not react with any of the materials forming the gas circuit inside the critical flow orifices system or auxiliary equipment. It has the merit of allowing multi-component mixtures to be prepared as readily as binary mixtures if an appropriate number of critical flow orifices are used.
By selecting appropriate combinations of critical flow orifices, a dilution ratio of 1 × 104 is achievable.
Although it is more particularly applicable to the preparation of gas mixtures at atmospheric pressure, the method also offers the possibility of preparing calibration gas mixtures at pressures greater than atmospheric. The upstream pressure will need to be at least two times higher than downstream pressure.
The range of flow rates covered by this document extends from 1 ml/min to 10 l/min.

ISO 16664:2017 describes factors that may influence the composition of pure gases and homogeneous gas mixtures used for calibration purposes. This document only applies to gases or gas mixtures that are within the "utilization period". It provides the following guidelines for the handling and use of calibration gas mixtures:
-      storage of calibration gas cylinders;
-      calibration gas withdrawal from cylinders;
-      transfer of calibration gas from cylinders to the point of calibration.
It also outlines a method of assessing the stability of a gas mixture, taking into account the gas composition uncertainty given on the certificate and the user's measurement uncertainty.

ISO 6976:2016 specifies methods for the calculation of gross calorific value, net calorific value, density, relative density, gross Wobbe index and net Wobbe index of natural gases, natural gas substitutes and other combustible gaseous fuels, when the composition of the gas by mole fraction is known. The methods specified provide the means of calculating the properties of the gas mixture at commonly used reference conditions.
Mole fractions by definition sum to unity. Guidance on the achievement of this requirement by chromatographic analysis is available in ISO 6974‑1 and ISO 6974‑2.
The methods of calculation require values for various physical properties of the pure components; these values, together with associated uncertainties, are provided in tables and their sources are identified.
Methods are given for estimating the standard uncertainties of calculated properties.
The methods of calculation of the values of properties on either a molar, mass or volume basis are applicable to any natural gas, natural gas substitute or other combustible fuel that is normally gaseous, except that for properties on the volume basis the method is restricted to mixtures for which the compression factor at reference conditions is greater than 0,9.
Example calculations are given in Annex D for the recommended methods of calculation.
NOTE 1       The qualifiers "superior", "higher", "upper" and "total" are, for the purposes of this document, synonymous with "gross"; likewise, "inferior" and "lower" are synonymous with "net". The term "heating value" is synonymous with "calorific value"; "mass density" and "specific density" are synonymous with "density"; "specific gravity" is synonymous with "relative density"; "Wobbe number" is synonymous with "Wobbe index"; "compressibility factor" is synonymous with "compression factor". The dimensionless quantity molecular weight is numerically equal to the molar mass in kg·kmol−1.
NOTE 2       There are no explicit limits of composition to which the methods described in this document are applicable. However, the restriction of volume-basis calculations to mixtures with a compression factor greater than 0,9 at reference conditions sets implicit limits on composition.
NOTE 3       Because the mole fraction of any water present is not normally available from chromatographic analysis, it is common practice to calculate the physical properties on a dry gas basis and to allow for the effects of water vapour in a separate procedure. However, if the mole fraction of water vapour is known then the property calculations can be carried out completely in accordance with the procedures described herein. The effects of water vapour on calorific value, whether the latter is directly measured or calculated, are discussed in ISO/TR 29922.
NOTE 4       For aliphatic hydrocarbons of carbon number 7 or above, any isomer present is included with the normal isomer of the same carbon number.
NOTE 5       If the user's requirement includes the replacement of, for example, a C6+ or C7+ grouping of analytically unresolved components by a single pseudo-component, then it is the user's own task to set the mole fraction composition, and hence properties, of this pseudo-component so as to be fit for purpose in the particular application. Any so-called "spectator water" and "non-combustible hydrogen sulfide" are treated as pseudo-components by setting the appropriate enthalpy of combustion values to zero.

ISO corr

ISO 6142-1:2015 specifies a gravimetric method for the preparation of calibration gas mixtures in cylinders with traceable values for the amount-of-substance fraction (amount fraction) of one or more components. This part of ISO 6142 describes a method for calculating the uncertainty associated with the amount fraction of each component. This uncertainty calculation requires the evaluation of the contributions to the uncertainty due to factors including the weighing process, the purity of the components, the stability of the mixture, and the verification of the final mixture.
ISO 6142-1:2015 is only applicable to mixtures of gaseous or totally vaporized components, which may be introduced into the cylinder in the gaseous or liquid state. Both binary and multi-component gas mixtures (including natural-gas type mixtures) are covered by this part of ISO 6142. Methods for the batch production of more than one mixture in a single process are not included in this part of ISO 6142.
ISO 6142-1:2015 requires estimation of the stability of the mixture for its intended life time (maximum storage life), but it is not for use with components that react with each other unintentionally. This part of ISO 6142 also requires the impurities in each parent gas or liquid used in the preparation of the mixture to be assessed and quantified.

ISO 6141:2015 specifies minimum requirements for the contents of certificates for homogeneous gas mixtures in gas cylinders to be used as calibration gas mixtures. Pure gases, when used as calibration gas mixtures, are also covered by this International Standard. Gases and gas mixtures produced for other purposes are not considered.
The requirements in ISO 6141:2015 deal with the metrological aspects of calibration gas mixtures. Other aspects, such as safety and legislative aspects, are not covered.
Furthermore, it specifies additional information (optional data) recommended for describing a homogeneous gas mixture, supplied under pressure in a cylinder or other container. It does not cover the field of safety-relevant data and related labelling.

ISO 16960:2014 specifies a method for the determination of total sulfur in the range from 1 mg/m3 to 200 mg/m3 in pipeline natural gas by oxidative microcoulometry. Natural gas with sulfur contents above 200 mg/m3 can be analysed after dilution with a suitable sulfur-free solvent.

ISO 15970:2008 gives requirements and procedures for the measurement of the properties of natural gas that are used mainly for volume calculation and volume conversion: density at reference and at operating conditions, pressure, temperature and compression factor.
Only those methods and instruments are considered that are suitable for field operation under the conditions of natural gas transmission and distribution, installed either in-line or on-line, and that do not involve the determination of the gas composition.
ISO 15970:2008 gives examples for currently used instruments that are available commercially and of interest to the natural gas industry.
The density at reference conditions (sometimes referred to as normal, standard or even base density) is required for conversion of volume data and can be used for other physical properties.
Density at operating conditions is measured for mass-flow measurement and volume conversion using the observed line density and can be used for other physical properties. ISO 15970:2008 covers density transducers based on vibrating elements, normally suitable for measuring ranges of 5 kg/m3 to 250 kg/m3.
Pressure measurement deals with differential, gauge and absolute pressure transmitters. It considers both analogue and smart transmitters (i.e. microprocessor based instruments) and, if not specified otherwise, the corresponding paragraphs refer to differential, absolute and gauge pressure transmitters without distinction.
Temperature measurements in natural gas are performed within the range of conditions under which transmission and distribution are normally carried out (253 K < T < 338 K). In this field of application, resistance thermometer detectors (RTD) are generally used.
The compression factor (also known as the compressibility factor or the real gas factor and given the symbol Z) appears, in particular, in equations governing volumetric metering. Moreover, the conversion of volume at metering conditions to volume at defined reference conditions can properly proceed with an accurate knowledge of Z at both relevant pressure and relevant temperature conditions.

ISO 15971:2008 concerns the measurement of calorific value of natural gas and natural gas substitutes by non‑separative methods, i.e. methods that do not involve the determination of the gas composition, nor calculations from it. ISO 15971:2008 describes the principles of operation of a variety of instruments in use for this purpose, and provides guidelines for the selection, evaluation, performance assessment, installation and operation of these.
Calorific values can be expressed on a mass basis, a molar basis or, more commonly, a volume basis. The working range for superior calorific value of natural gas, on the volume basis, is usually between 30 MJ/m3 and 45 MJ/m3 at standard reference conditions (see ISO 13443). The corresponding range for the Wobbe index is usually between 40 MJ/m3 and 60 MJ/m3.
ISO 15971:2008 neither endorses nor disputes the claims of any commercial manufacturer for the performance of an instrument. Its central thesis is that fitness-for-purpose in any particular application (defined in terms of a set of specific operational requirements) can be assessed only by means of a well-designed programme of experimental tests. Guidelines are provided for the proper content of these tests.

ISO 6974-5:2014 describes a gas chromatographic method for the quantitative determination of the content of nitrogen, carbon dioxide and C1 to C5 hydrocarbons individually and a composite C6+ measurement, which represents all hydrocarbons of carbon number 6 and above in natural gas samples.

ISO 13734;2013 specifies requirements and test methods for organic compounds suitable for odorization of natural gas and natural gas substitutes for public gas supply, hereafter referred to as odorants.

ISO 13686:2013 specifies the parameters required to describe finally processed and, where required, blended natural gas.
The main text of ISO 13686:2013 contains a list of these parameters, their units and references to measurement standards. Informative annexes give examples of typical values for these parameters, with the main emphasis on health and safety.

ISO 10723:2012 specifies a method of determining whether an analytical system for natural gas analysis is fit for purpose. It can be used either to determine a range of gas compositions to which the method can be applied, using a specified calibration gas, while satisfying previously defined criteria for the maximum errors and uncertainties on the composition or property or both, or to evaluate the range of errors and uncertainties on the composition or property (calculable from composition) or both when analysing gases within a defined range of composition, using a specified calibration gas.

2011-04-08 EMA: Draft for // final vote received in ISO/CS (see notification of 2011-04-06 in dataservice).

This part of ISO 6974 gives methods for calculating component mole fractions of natural gas and specifies the data processing requirements for determining component mole fractions. This part of ISO 6974 provides for both single and multiple operation methods and either multi-point calibration or a performance evaluation of
the analyser followed by single-point calibration. This part of ISO 6974 gives procedures for the calculation of the raw and processed (e.g. normalized) mole fractions, and their associated uncertainties, for all components. The procedures given in this part of ISO 6974 are applicable to the handling of data obtained from replicate or
single analyses of a natural gas sample.

This part of ISO 6974 describes the process required to determine the uncertainty associated with the mole
fraction for each component from a natural gas analysis in accordance with ISO 6974‑1.

ISO 6145-9:2009 is one of a series of International Standards dealing with various dynamic volumetric methods used for the preparation of calibration gas mixtures. This part specifies a method for continuous production of calibration gas mixtures containing one or more readily condensable components. A relative expanded uncertainty of measurement, U, obtained by multiplying the relative combined standard uncertainty by a coverage factor k = 2, of not greater than ±1 %, can be obtained using this method.
Unlike the methods presented in the other parts of ISO 6145, the method described in this part does not require accurate measurement of flow rates since flow rates do not appear in the equations for calculation of the volume fraction.
Readily condensable gases and vapours commonly become adsorbed on surfaces, and it is therefore difficult to prepare stable calibration gas mixtures of accurately known composition, containing such components, by means of static methods. In addition, these calibration gas mixtures cannot be maintained under a pressure near the saturation limit without the occurrence of condensation. The saturation method can be employed to prepare mixtures of this type.

ISO 6145-5:2009 is one of a series of International Standards dealing with the various dynamic volumetric techniques used for the preparation of calibration gas mixtures. This part specifies a method for the continuous production of calibration gas mixtures from pure gases or gas mixtures using capillary calibration devices in single or multiple combinations (gas dividers).
Single capillary systems can be used to provide gas mixtures where the minor component is in the range of volume fractions from 10-8 to 0,5.
The relative expanded uncertainty of this technique is less than ±2 % (k = 2) relative. This application is used in industrial gas mixing panels for the production of specific gas atmospheres.
Gas dividers can be used to divide gas mixtures prepared from gases or gas mixtures into controlled proportions by volume. These devices are capable of dilutions in the range of volume fractions from 0,000 5 to 0,9 of the primary gas concentration with a relative repeatability of better than 0,5 %.
Traceability of the gas mixtures produced by a gas divider is achieved by comparison of a mixture with gas mixtures related to national or international gas standards. An example is given in Annex A.

ISO 12213 specifies methods for the calculation of compression factors of natural gases, natural gases containing a synthetic admixture and similar mixtures at conditions under which the mixture can exist only as a gas.
It is divided into three parts: this part, ISO 12213-3:2006, specifies a method for the calculation of compression factors when the superior calorific value, relative density and carbon dioxide content are known, together with the relevant pressures and temperatures. If hydrogen is present, as is often the case for gases with a synthetic admixture, the hydrogen content also needs to be known.
The method is primarily applicable to pipeline quality gases within the ranges of pressure p and temperature T at which transmission and distribution operations normally take place, with an uncertainty of about +/-0,1 %. For wider-ranging applications the uncertainty of the results increases.

ISO 12213 specifies methods for the calculation of compression factors of natural gases, natural gases containing a synthetic admixture and similar mixtures at conditions under which the mixture can exist only as a gas.
It is divided into three parts: this part, ISO 12213-1:2006, gives an introduction and provides guidelines for the methods of calculation described in Parts 2 and 3.

ISO 12213 specifies methods for the calculation of compression factors of natural gases, natural gases containing a synthetic admixture and similar mixtures at conditions under which the mixture can exist only as a gas.
It is divided into three parts: this part, ISO 12213-2:2006, specifies a method for the calculation of compression factors when the detailed composition of the gas by mole fractions is known, together with the relevant pressures and temperatures.
The method is applicable to pipeline quality gases within the ranges of pressure p and temperature T at which transmission and distribution operations normally take place, with an uncertainty of about +/- 0,1 %. It can be applied, with greater uncertainty, to wider ranges of gas composition, pressure and temperature.

ISO - Taking over of an ISO Technical Corrigendum

ISO 6145-11:2005 specifies a method for the preparation of calibration gas mixtures by using electrochemical generation of a calibration component and introduction into a complementary gas flow. By alteration of the gas flow or the charge passed through the cell electrolyte, it is possible to change the composition of the gas mixture. The relative expanded uncertainty of the calibration gas content, U, obtained by multiplying the relative combined standard uncertainties by a coverage factor, k = 2, is not greater than 5 %.
The method described in ISO 6145-11:2005 is intended to be applied to the preparation of calibration gas mixtures in the volume fraction ranges (0,1 to 250) x 10-6.

ISO 15796:2005 specifies generic methods for detecting and correcting bias (systematic errors) of analytical procedures for the analysis of gases, using reference gas mixtures or reference analytical procedures, as well as for estimating the correction uncertainty.
The main sources of (and parameters affecting) bias of analytical procedures are instrumental drift (time) and matrix interferences (matrix composition). Moreover, bias normally varies with analyte concentration. ISO 15796:2005 therefore establishes protocols for detecting and correcting drift for an analytical system of limited stability, and for investigating and handling bias of a stable analytical system for a specified range of sample composition. These protocols are intended to be used in method development and method validation studies, either separately or sequentially.
ISO 15796:2005 specifies procedures for two options, applicable to systematic effects, as follows:
1) tracing the observed pattern of deviations and correcting for their effect,
2) averaging over their effects and increasing the uncertainty,
where normally the first option entails lower uncertainty at the expense of higher effort.
For the convenience of the user, the methods specified in ISO 15796:2005 are described for procedures of composition analysis, i.e. procedures for measuring the concentration of a specified analyte in a gas mixture. However, they are equally applicable to measurements of physico-chemical properties of a gas or gas mixture relevant to gas analysis, and translation into this subject field is straightforward.

ISO 6145-8:2005 specifies a dynamic method using diffusion for the preparation of calibration gas mixtures containing component mole fractions ranging from 10-9 to 10-3. A relative expanded uncertainty of measurement, U, obtained by multiplying the relative combined standard uncertainty by a coverage factor k = 2, of not greater than ± 2 % can be achieved by using this method.
By keeping the path between the diffusion source and place of use as short as possible, the method can be applied for the generation of low-concentration calibration gases of organic components that are liquid at room temperature, with boiling points ranging from about 40 °C to 160 °C.
ISO 6145-8:2005 is applicable not only for the generation of calibration gas mixtures of a wide range of hydrocarbons at ambient and indoor air concentration levels, but also for the generation of low-concentration gas mixtures of water.

ISO 6145-4:2004 specifies a method for continuous production of calibration gas mixtures, containing two or more components, from pure gases or other gas mixtures by continuous injection of the calibration component(s) into a complementary gas stream by means of a syringe.
If pre-mixed gases are used instead of pure gases (see Annex A), much lower volume fractions can be obtained. The volume flow rates, from which the volume fractions are determined, can be calculated from the individual flow rates and can be independently measured by a suitable method given in ISO 6145-1.
The merits of the method are that a substantial quantity of the gas mixture can be prepared on a continuous basis and that multi-component mixtures can be prepared almost as readily as binary mixtures if the appropriate number of syringes is utilized, or if the syringe already contains a multi-component mixture of known composition. This method also provides a convenient means for increasing the volume fraction of the calibration component in the mixture in small steps. It is therefore a useful method for evaluation of other characteristics of gas analysers, such as minimum detection limit and dead zone, as well as accuracy. The relative expanded uncertainty in the volume fraction obtainable for a binary mixture (at a coverage factor of 2) is 5 % and the range of applicability is 10-5 to 10-2.

This part of ISO 6145 specifies a dynamic method using permeation membranes for the preparation of calibration
gas mixtures containing component mole fractions ranging from 10−9 and 10−6. A relative expanded uncertainty of
2,5 % of the component mole fraction can be achieved using this method. In the mole fraction range considered, it
is difficult to maintain some gas mixtures, for example in cylinders, in a stable state. It is therefore desirable to
prepare the calibration gas immediately before use, and to transfer it by the shortest possible path to the place
where it is to be used. This technique has been successfully applied in generating low content calibration gas
mixtures of, for example, sulfur dioxide (SO2), nitrogen dioxide (NO2) and benzene (C6H6) in air.
If the carrier gas flow is measured as a gas mass-flow, the preparation of calibration gas mixtures using permeation
tubes is a dynamic-gravimetric method which gives contents in mole fractions.

The aim of ISO 15403-1:2006 is to provide manufacturers, vehicle operators, fuelling station operators and others involved in the compressed-natural-gas vehicle industry with information on the fuel quality for natural gas vehicles (NGVs) required to develop and operate compressed-natural-gas vehicle equipment successfully.
Fuel meeting the requirements of ISO 15403-1:2006 should provide for the safe operation of the vehicle and associated equipment needed for its fuelling and maintenance, protect the fuel system from the detrimental effects of corrosion, poisoning, and liquid or solid deposition and provide satisfactory vehicle performance under any and all conditions of climate and driving demands.
Some aspects of ISO 15403-1:2006 may also be applicable for the use of natural gas in stationary combustion engines.

Describes hygrometers which determine the water content of a gas by detecting water vapour condensation occurring on a cooled surface or by checking the stability of the condensation on this surface. The hygrometers considered here may be used for determining water vapour pressure, without requiring calibration, in a system operating under total pressures greater than or equal to atmospheric pressure.

ISO - Taking over of an ISO Technical Corrigendum

ISO/TR 24094:2006 describes the validation of the calorific value and density calculated from current practice natural gas analysis by statistical comparison with values obtained by measurement using a reference calorimeter and a density balance.

ISO 14912:2003 defines the following quantities commonly used to express the composition of gas mixtures: mole fraction, mass fraction and volume fraction, as well as mole concentration, mass concentration and volume concentration.
Relating to these quantities of composition, ISO 14912:2003 provides methods for the conversion between different quantities and the conversion between different state conditions. Conversion between different quantities means calculating the numerical value of an analyte content in terms of one of the quantities listed above from the numerical value of the same analyte content, at the same pressure and temperature of the gas mixture, given in terms of another of these quantities. Conversion between different state conditions means calculating the numerical value of an analyte content, in terms of one of the quantities listed above, under one set of state conditions from the numerical value of the same quantity under another set of state conditions, i.e. pressure and temperature, of the gas mixture. Gas mixture composition can be converted simultaneously between different quantities of composition and different state conditions by combination of the two types of conversion.
ISO 14912:2003 is only applicable to homogeneous and stable gas mixtures. Therefore any state conditions (pressure and temperature) considered need to be well outside from the condensation region of the gas mixture and that of each of the specified analytes.

ISO 6144:2003 specifies a method for the preparation of calibration gas mixtures by a static volumetric method and provides a procedure for calculating the volumetric composition of the mixture. It can be used either with binary gas mixtures (containing one calibration component in a complementary gas, which is usually nitrogen or air) or with mixtures containing more than one component in the complementary gas. This International Standard also specifies how the expanded uncertainty in the volume fraction of each calibration component in the mixture is determined by a rigorous evaluation of all the measurement uncertainties involved, including those associated with the apparatus used for the preparation of the gas mixture and those associated with the experimental procedure itself.