ISO IEC 80079-20-1:2017 pdf free download.Explosive atmospheres — Part 20-1: Material characteristics for gas and vapour classification — Test methods and data.
1 Scope
This part of ISOIIEC 80079 provides gwdance on classifIcation 01 gases and vapours. It describes a test method Intended for the measurement of the maximum experimental safe gaps (MESO) for gas-air mixtures or vapour-air mixtures under normal conditions of temperature and pressure (20 C, 101.3 kPa) so as to permit the selection of an appropriate group of equipment. ISO IEC 80079-20-1 also describes a test method intended for use in the determination oP the auto-ignition temperature (AlT) of a vapour-air mixture or gas-air mixture at atmospheric pressure, so as to permit the selection of an appropriate temperature class ol equipment.
Values of chemical properties of materials are provided to assist in the selection of equipment to be used In hazardous areas. Further data may be added as the results of validated tests become available.
The materials and the characteristics included in a table (see Annex B) have been selected with particular reference to the use of equipment In hazardous areas, The data In this document have been taken from a number of references which are given In the bibliography.
These methods for determining the MESG or the Alt may also be used for gas-air-Inert mixtures or vapour-air-inert mixtures. However, data on air-inert mixtures are not tabulated.
2 Normative references
The following documents are referred to In the text In such a way that some or all at their content constitutes requirements of ISO IEC 80079-20-1. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
IEC 60050-426, nternatvonal E?ectrotechnicat Vocabulary – Part 426.’ Electrical apparatus lot explosive atmospheres (available at http:i!www.elecfropedia.org/)
IEC 60079-11, Explosive atmospheres — Part ii: Equipment protection by lntnnsic salary r
IEC 60079-14, Explosive atmospheres — Part 1 4: Electrical installations design. selection and
erection
3 Terms and defInItions
For the purposes of this document, the terms and definitions given in IEC 60050-426 and the following apply,
ISO and IEC maintain tei’mrnological databases for use in standardization at the following addresses:
• lEG Electropedia: available at httpilwww.electropedia.orgl
• ISO Online browsing platform: available at hlep:llwww.iso.orgtobp
NOTE 1 The standard method for delermming MESO is desctbed in 8.2, but aeere determination, have been undertaken only In an S I spherical vessel with ignition close to the flange gap these can be accepted provisionally
NOTE 2 Thu design of lii. te$t apparatus for 5fe gap deteimination, other ihn that iied ir selecting the appropriate .qulpment group of enclogur. ho, a perticuta, gas. may need to be diii .r.nl to th, on. cIe.cnb.d in this document. For exampte, the volume or the enclosure. flange width, gas conceehrsbons and the distance between the flange, and any eelernal a-aS or ottetruction nay have to be varied. As the design depend. on the particular investigation which Is to be undertakan. it I. impracticable to recommend spadric design requirements. but for most applications the general pnmciples and precautions indicated in this document will illS apply.
NOTE 3 In IEC 6007914 minimum distances of obstruction from the flamptwoof flange joints related to the equipment group of the hazardous area are given
For the purpose of classification the MESG limits are
Equipment Group hA: MESG  0,90 mm.
Equipment Group IIB: 0,50 mm <MESG <0.90 mm.
Equipment Group tiC: MESG 0.50 mm.
DetermInation 01 both the MESG and MIC ratio is required when 0.50 c MESG < 0.55. Then the equipment group is determined by MIC ratio,
NOTE 4 For gases and highly volatile liquids. lii. MESO is determined at 20 C.
NOTE S lilt was necessary to do the MESO determination Cl temperatures higher than ambient temperature a temperature 5 K above that ne.ded to giv, the necessary vapour pressure or SO K above the lash point is osed and firs value of MESG ‘a given in the tabl, and the classification of the equipment group is based on this result
4.3 ClassiIlcatIon according to the minimum Igniting current ratio (MIC ratio)
Gases and vapours may be classified according to the ratio of their minimum Igniting currents
(MIC) to the ignition current of Laboratory methane Into Equipment Groups hA. hIB or IIC The
purity of laboratory methane shall be not less than 99.9 % by volume.
NOTE The standard method of determining MIC ratios a with the apparatus described In IEC 6007911. but where
determinations have been undertahe In Other apparatus these can be accepted provisionally.
For the purpose of classification the MIC ratios are:
Equipment Group hA: MIC 080.
Equipment Group hiB: 0,45 s MIC  0.80.
Equipment Group tIC: MIC <0,45.
Determination 01 both the MESG and MIC ratio is required when 0.70 < MIC < 0.90 or 0,40 c MIC <0,50. Then the equipment group Is determined by MESG.
4.4 Classification according to the similarity of chemical structure
When a gas or vapour es a member of a homologous series of compounds, the classification of the gas or vapour can provisionally be inferred from the data of the neighbouring members of the SeriSs.
The classification according to the similarity of chemical structure Is not allowed if the classification of one of the neighbouring members Is based on MESO and the other on MIC ratio.
4.5 ClassIfication of mixtures of gases
Mixtures of gases should generally be allocated to an equipment group only after a specIal determination or MESG or MIC ratio. One method to estimate the equipment group is to determine the MESG of the mixture by applying a form of La Chtehiers principle:
If the auto.ignitiorl temperature is to be determined in mixture with air/Inert gas. purge the test vessel with the air/inert gas mixture after cleaning (with aw) so that the atmosphere inside the Erlenmeyer flask is completely changed, or clean the test vessel with the airmen gas mixture betore each injection
7.4.2 Sample Injection
7.4.2.1 LiquId samples
When testing samples with boiling points at or near room temperature, care shall be taken to maintain the temperature of the sample injection system at a value whIch will ensure that no change of state occurs before the sample is injected Into the test flask.
The required volume of the sample to be tested shall be injected as droplets (see 7.2.5) Into the centre ol the flask at a rate 01 1 to 2 droplets per second. The metering device shall then be quickly withdrawn Care shalt be taken to avoid wetting the walls of the fLask during injection.
7.4.2.2 Gaseous samples
The metering device and the connected filling tube are purged sufficiently (at least 10 tImes the volume) and then tilled with the gas. The filling tube is lntroducd into the centre oh the flask so that the outlet of the tube has a distance of (10 ± 2) mm to the bottom. The required volume shall then be injected into the test flask in portions 01(10 ± 1) ml at a rate ol about 25 ml per second keeping the rate of Injection as constant as possible. The filling tube shall then be quickly withdrawn from the flask.
7.4.3 DeterminatIon of the auto-Ignition temperature (AlT)
7.4.3.1 IgnItion criterion
Any flame detected withIn 5 mm via the mirror or the photo-diode shall be taken as ignition.
Within 5 mm a rapid temperature rise of at least 200 K with a rate of 10 los shall be met when using thermocouple(s) to detect an Ignition.
NOTE With this cnrenon, normally hot lames at. ob..rv.d. Even El they ar, very pal. ones eg hyêog.n, methanol, these are ho flames. Some 5ietances or miziures ot luhetances are aItta to iorm cool llamas, For such cool flame phenomena a.. Annex C.
7.4.3.2 Testing procedure
The testing procedure to determine the auto-Ignition temperature given In 7.4.3.3 to 7.4.3.8
shall be used.
7.4.3.3 StartIng Iemp.rature
Starting from 80 C the test vessel Is heated up with a temperature rate of (5 ± 1) Ks’rnin. Whilst heating up inject every 20 K, (50 ± 5) ml in case of a gas or five droplets in case of a liquid till an ignition occurs. The test vessel shall be flushed completely by air before each Injection. The temperature of the vessel at which this ignItIon occurs Is the starting temperature.
The starling temperature shall be higher than the auto-ignition temperature.
7.4.3.4 Variation of temperature
Heat the lest vessel to the starling temperature. lnect (50 * 5) ml in the case of a gas or five droplets in the case of a liquid. If an ignition occurs within 5 mm, lower the temperature of the lest vessel In Intervals of (5 ± 1) IC till no ignition occurs within 5 mm after Introducing the.