SIST IEC 61241-2-3:1998

Electrical apparatus for use in the presence of combustible dust - Part 2: Test methods - Section 3: Method for determining minimum ignition energy of dust/air mixtures

Specifies a method of test to determine the minimum ignition energy of a dust/air mixture by an electrically generated high-voltage d.c. spark. This test method is intended to develop data to be used in deciding whether or not combustible dust/air mixtures are considered to be ignitable with respect to electrical discharge.

Matériels électriques destinés à être utilisés en présence de poussières combustibles - Partie 2: Méthodes d'essai - Section 3: Méthode de détermination de l'énergie minimale d'inflammation des mélanges air/poussières

Indique une méthode d'essai pour la détermination de l'énergie minimale d'inflammation d'un mélange poussière/air par une étincelle d'origine électrique haute tension continue. Cette méthode d'essai a pour objectif de fournir les données à utiliser permettant de décider si des mélanges air/poussières combustibles doivent être considérés comme inflammables par une décharge électrique.

Električne naprave za uporabo v prisotnosti vnetljivega prahu - 2. del: Preskusne metode -3. oddelek: Metoda določanja najnižje energije vžiga zmesi prah/zrak.

General Information

• Status: Published
• Publication Date: 31-Mar-1998
• ICS: 29.260.20 - Electrical apparatus for explosive atmospheres
• Technical Committee: EXP - Electrical apparatus for explosive atmospheres
• Current Stage: 6060 - National Implementation/Publication (Adopted Project)
• Start Date: 01-Apr-1998
• Due Date: 01-Apr-1998
• Completion Date: 01-Apr-1998
• Ref Project: IEC 61241-2-3 - Industrial communication networks - Profiles - Part 5-2: Installation of fieldbuses - Installation profiles for CPF 2

Standards Content (Sample)

SLOVENSKI STANDARD
SIST IEC 61241-2-3:1998
01-april-1998
(OHNWULþQHQDSUDYH]DXSRUDERYSULVRWQRVWLYQHWOMLYHJDSUDKXGHO3UHVNXVQH
PHWRGHRGGHOHN0HWRGDGRORþDQMDQDMQLåMHHQHUJLMHYåLJD]PHVLSUDK]UDN
Electrical apparatus for use in the presence of combustible dust - Part 2: Test methods -
Section 3: Method for determining minimum ignition energy of dust/air mixtures
Matériels électriques destinés à être utilisés en présence de poussières combustibles -
Partie 2: Méthodes d'essai - Section 3: Méthode de détermination de l'énergie minimale
d'inflammation des mélanges air/poussières
Ta slovenski standard je istoveten z: IEC 61241-2-3
ICS:
29.260.20 (OHNWULþQLDSDUDWL]D Electrical apparatus for
HNVSOR]LYQDR]UDþMD explosive atmospheres
SIST IEC 61241-2-3:1998 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST IEC 61241-2-3:1998

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SIST IEC 61241-2-3:1998
CEI
NORME
INTERNATIONALE IEC
1241-2-3
INTERNATIONAL
Première édition
STANDARD
First edition
1994-09
Matériels électriques destinés à être utilisés
combustibles -
présence de poussières
en
Partie 2:
Méthodes d'essai -
3:
Section
détermination de l'énergie minimale
Méthode de
/poussières
d'inflammation des mélanges air
Electrical apparatus for use in the presence of
combustible dust -
Part 2:
Test methods -
3: Method for determining minimum
Section
ignition energy of dust/air mixtures
Copyright — all rights reserved
© CEI 1994 Droits de reproduction réservés —
No part of this publication may be reproduced or utilized in
Aucune partie de cette publication ne peut être reproduite ni
utilisée sous quelque forme que ce soit et par aucun pro- any form or by any means, electronic or mechanical,
including photocopying and microfilm, without permission
cédé, électronique ou mécanique, y compris la photocopie et
in writing from the publisher.
les microfilms, sans l'accord écrit de l'éditeur.
Bureau Central de la Commission Electrotechnique Internationale 3, rue de Varembe Genève, Suisse
CODE PRIX
Commission Electrotechnique Internationale
International Electrotechnical Commission
PRICE CODE
IEC Me»,ayHaponHae 3ner rporexHH4ecnaR NOMHCCHA
Pour prix, voir catalogue en vigueur •
•
For price, see current catalogue

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SIST IEC 61241-2-3:1998
1241-2-3 IEC:1994 – 3 –
CONTENTS
Page
5
FOREWORD
Clause
1 Scope 7
2 Normative references 7
3 Definitions 9
4 Test apparatus 9
4.1 Spark generation circuit 9
11
4.2 Test vessel
11
5 Test sample
11
6 Procedure
11
6.1 Brief description
15 6.2 Calibration
15
6.3 Test repo rt
Annexes
17 A Examples of spark-generating systems
33 B Significance of minimum ignition energy
C Bibliography 38

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SIST IEC 61241-2-3:1998
1241-2-3 IEC:1994 - 5 -
INTERNATIONAL ELECTROTECHNICAL COMMISSION
ELECTRICAL APPARATUS FOR USE IN THE PRESENCE OF
COMBUSTIBLE DUST -
Part 2: Test methods -
Section 3: Method for determining minimum
ignition energy of dust/air mixtures
FOREWORD
1) The IEC (International Electrotechnical Commission) is a worldwide organization for standardization
comprising all national electrotechnical committees (lEC National Committees). The object of the IEC is to
promote international cooperation on all questions concerning standardization in the electrical and
electronic fields. To this end and in addition to other activities, the IEC publishes International Standards.
Their preparation is entrusted to technical committees; any IEC National Committee interested in
the subject dealt with may participate in this preparatory work. International, governmental and
non-governmental organizations liaising with the IEC also participate in this preparation. The IEC
collaborates closely with the International Organization for Standardization (ISO) in accordance with
conditions determined by agreement between the two organizations.
2) The formal decisions or agreements of the IEC on technical matters, prepared by technical committees on
which all the National Committees having a special interest therein are represented, express, as nearly as
possible, an international consensus of opinion on the subjects dealt with.
3) They have the form of recommendations for international use published in the form of standards, technical
reports or guides and they are accepted by the National Committees in that sense.
4) In order to promote international unification, IEC National Committees undertake to apply lEC International
Standards transparently to the maximum extent possible in their national and regional standards. Any
divergence between the IEC Standard and the corresponding national or regional standard shall be clearly
indicated in the latter.
5) The IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any
equipment declared to be in conformity with one of its standards.
International Standard IEC 1241-2-3 has been prepared by sub-committee 31H: Apparatus
for use in the presence of combustible dust, of IEC technical committee 31: Electrical
apparatus for explosive atmospheres.
The text of this standard is based on the following documents:
DIS Report on voting
31 H(CO)19
31H(CO)17
Full information on the voting for the approval of this standard can be found in the report
on voting indicated in the above table.
IEC 1241 consists of the following parts, under the general title: Electrical apparatus for
use in the presence of combustible dust:
- Part 1: Electrical apparatus protected by enclosures
- Part 2: Test methods
Annexes A, B and C are for information only.

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SIST IEC 61241-2-3:1998
1241-2-3
IEC:1994 - 7 -
ELECTRICAL APPARATUS FOR USE IN THE PRESENCE OF
COMBUSTIBLE DUST -
Part 2: Test methods -
Section 3: Method for determining minimum
ignition energy of dust/air mixtures
1 Scope
This section of IEC 1241-2 specifies a method of test to determine the minimum ignition
energy of a dust/air mixture by an electrically generated high-voltage d.c. spark. This test
method is intended to develop data to be used in deciding whether or not combustible
dust/air mixtures are considered to be ignitable with respect to electrical discharge. It is
intended that the dust be tested in a form (particle size, moisture content, etc.) represent-
ing conditions of actual use so that assessment of the hazard present can be made.
Ignition energies determined by this method would be compared with ignition energies of
other dusts to assess the relative hazard with regard to ignition by an electrical or electro-
static discharge, thereby permitting decisions to be made on the suitability of electrical
apparatus for installation in areas where combustible dust is present.
The test method is not suitable for use with recognized explosives, gunpowder, dynamite,
explosives which do not require oxygen for combustion; pyrophoric substances, or
substances or mixtures of substances which may under some circumstances behave in a
similar manner. Where any doubt exists about the existence of a hazard due to explosive
properties, an indication may be obtained by placing a very small quantity of the dust in
question on the heated surface of the apparatus described in section 1 of the IEC 1241-2-1,
heated to 400 °C.
NOTE – Precautions should be taken to safeguard the health of personnel conducting the tests against
the risk of fire, explosion and/or the effects, including toxic effects, of combustion. Compliance with this inter-
national standard does not itself confer immunity from legal obligations.
Annex B of this section includes guidance on the significance of minimum ignition energy
with respect to electrostatic discharges.
2 Normative references
The following normative documents contain provisions which, through reference in this
text, constitute provisions of this section of IEC 1241-2. At the time of publication,
the editions indicated were valid. All normative documents are subject to revision, and pa rties
to agreements based on this section of IEC 1241-2 are encouraged to investigate the
possibility of applying the most recent editions of the normative documents indicated
below. Members of IEC and ISO maintain registers of currently valid International Standards.
IEC 50(301, 302, 303): 1983, International Electrotechnical Vocabulary
- Chapter 301: General terms on measurements in electricity
- Chapter 302: Electrical measuring instruments
- Chapter 303: Electronic measuring instruments
ISO 4225: 1980, Air Quality - General aspects - Vocabulary

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SIST IEC 61241-2-3:1998
1241-2-3 IEC:1994 - 9 -
3 Definitions
For the purposes of this section of IEC 1241-2, the definitions in IEC 50(301, 302, 303)
and also the following apply.
3.1 dust: Small solid particles that settle out under their own weight but that may remain
suspended in air for some time.
NOTE - This definition includes what are defined in ISO 4225 as "dust" and "grit".
Dust that is ignitable in mixtures with air.
3.2 combustible dust:
NOTES
ain concentration limits.
1 Mixtures of combustible dust in air are ignitable only between cert
2 Combustible dusts are capable of being ignited by external ignition sources and will continue to burn at
atmospheric temperatures but they will only spontaneously ignite above their minimum ignition temperatures.
3.3 spark discharge: Transient electric discharge which takes place between two
conductors which are at different potentials. A spark is a discrete discharge that bridges
the gap between the conductors in the form of a single ionization channel.
3.4 minimum ignition energy (of a combustible dust/air mixture): Lowest energy of
spark (as measured by the procedure in this standard) that is capable of igniting the most
sensitive dust/air mixture with sustained combustion.
3.5 ignition: In the test, ignition is considered to have occurred when:
- a pressure rise of at least 0,2 bar above any pressure introduced by the igniting
spark is measured in a closed vessel (e.g. 20 I sphere); or
- a flame which propagates at least 6 cm away from the spark position is observed in
an open tube (e.g. Hartmann tube).
Time between dispersion of the dust and the occurrence of the
3.6 ignition delay time:
spark discharge.
4 Test apparatus
4.1 Spark generation circuit
Annex A describes some suitable forms of circuit, all of which shall have the following
characteristics. What follows deals only with the circuit:
- inductance of discharge circuit: 1 mH to 2 mH except when the data is to be used
for the assessment of electrostatic hazards when the inductance of the discharge
circuit shall not exceed 25 µH;
- ohmic resistance of discharge circuit: as low as possible and not more than 5 S2;
electrode material: stainless steel, brass, copper or tungsten;
-
- electrode diameter and shape: 2,0 mm ± 0,5 mm. Electrodes with rounded tips can
be used to reduce corona effects that can occur with pointed electrodes, and which
may give incorrect values of spark energy. If pointed electrodes are used, corona
effects should be carefully considered;

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SIST IEC 61241-2-3:1998
1241-2-3 IEC:1994 -11 -
- electrode gap: 6 mm (minimum);
- capacitors: low-inductance type, resistant to surge current;
- capacitance of electrode arrangement: as low as possible;
prevent leakage
- insulation resistance between electrodes: sufficiently high to
currents.
S2 is required for a minimum
NOTE — Typically, a minimum resistance between the electrodes of 10 12
ignition energy of 1 mJ, and 10 10 S2 for a minimum ignition energy of 100 mJ.
4.2 Test vessel
rtmann tube. These
The recommended vessels are the 20 I sphere apparatus and the Ha
vessels are described in references [6] and [7]*. Other vessels can be used, provided that
the calibration requirements in 6.2 are met.
5 Test sample
Tests shall be performed on samples in a state of preparation corresponding to that found
in practice under plant conditions.
Minimum ignition energy decreases with decreasing particle size. Tests shall be carried
out on samples having particle sizes that are consistent with, or finer than, the finest
material that can be present in the intended use.
For comparative tests the samples shall be prepared by a constant method with the object
of fixing particle size distribution and moisture content.
NOTE — Where the particle sizes of the material are not known, tests should be carried out on particle sizes
less than 63 µm.
Minimum ignition energy decreases with decreasing particle size. It should be checked
that the particle sizes of the sample are representative of the finest material that can
be present in the plant. Tests should be carried out on material of particle size less
than 63 pm.
6 Procedure
6.1 Brief description
The combustible dust to be tested is uniformly dispersed in air at atmospheric pressure
and temperature in a suitable apparatus, and the dust/air mixture is subjected to a spark
discharge from a charged capacitor.
The energy value of the discharge is calculated from the formula:
W = 0,5 C x Uz
where
Wis the stored energy in joules (J);
C is the total discharge capacitance, in farads (F);
U is the voltage of the charged capacitor in volts (V).
Figures in square brackets refer to the bibliography, annex C.

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SIST IEC 61241-2-3:1998
1241-2-3 IEC:1994 -13 -
NOTES
1 At spark energies above 100 mJ, the spark resistance can become so small that the circuit resistance is
no longer negligible compared with the spark resistance, particularly when the circuit contains an inductance
coil of the order of 1 mH. In such cases the net spark energy can be obtained from the equation:
w= f 1(t) U(t)dt
where
is the spark current, and
1(t)
U(t) the spark voltage; both of which are obtained by measurement.
2 Further information relative to the calculation of spark energies is contained in annex A.
It is necessary to take account of the following possible influences on the test:
dust/air mixture aerodynamics (e.g. ignition delay time, dispersing pressure);
-
- dust concentration;
- voltage to which the capacitor is charged;
- capacitance of the capacitor;
- inductance of the discharge circuit;
ohmic resistance of the discharge circuit;
-
materials and dimensions of the electrodes and the gap between the electrodes.
-
To limit the expense of testing, every apparatus uses electrodes composed of a specific
material with standardized dimensions and minimum electrode gap. The ohmic resistance
of the discharge circuit shall be kept as low as possible (see clause 4).
Starting with a spark energy that will reliably cause ignition of the dust being tested, the
dust concentration and dust dispersion parameters (e.g. ignition delay time and dispersion
pressure) are adjusted to establish the most ignitable dust cloud. Using the optimal
conditions for ignition, the spark energy is successively halved, by adjusting the capa-
citance of the capacitor and/or the voltage to which it is charged, until no ignition occurs
in 20 successive tests.
NOTE - When tests are carried out using the 20 I sphere apparatus, the ignition delay time should be 120 ms.
, at which ignition
lies between the highest energy, W 1
The minimum ignition energy,
Wmin,
fails to occur in 20 successive attempts to ignite the dust/air mixture, and the lowest
at which ignition occurs within 20 successive attempts.
energy, W2,
1
W < Wmin < W2

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SIST IEC 61241-2-3:1998
1241-2-3 IEC:1994 - 15 -
6.2 Calibration
Calibration tests should be carried out on three reference dusts which shall have been
dried under atmospheric pressure at 50 °C for 24 h prior to the measurements.
The results shall be within the following ranges:
Wmin = 5 to 15 mJ, mean particle diameter 31 µm;
lycopodium:
anthraquinone: Wmin = 2 to 6 mJ, mean particle diameter 18 µm;
min = 2 to 6 mJ, mean particle diameter 27 µm.
polyacrylonitrile:
W
The dust dispersion parameters, including ignition delay time, for each sample shall be
noted.
6.3 Test report
rt shall
Where the test has been carried out in accordance with this standard, the test repo
provide the information listed in 6.3.1, 6.3.2 and 6.3.3. Although the dust concentration
values associated with the limits of the range of minimum ignition energy should be
recorded by the test laboratory, the values, expressed in terms of the amount of dust which
is weighed, divided by the volume of the explosion vessel, are not usually included in the
test report.
6.3.1 Product characteristics
sample designation (name and chemical description if not implicit in the name);
-
sample origin or source;
- sample pre-treatment;
characteristics data for particle size distribution and moisture content if available
-
and not already given by pre-treatment procedures.
Characteristics of the test apparatus
6.3.2
- triggering;
explosion vessel;
-
- dust-dispersion system;
total inductance of the discharge circuit;
-
charging voltage, electrode material and length of gap of the optimized discharge
-
circuit.
6.3.3 Results
- highest energy W1 at which ignition does not occur;
at which ignition is obtained.
- lowest energy W2
rt form
6.3.4 Repo
An example of a suitable form is given in figure A.1.

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SIST IEC 61241-2-3:1998
1241-2-3 IEC:1994 – 17 –
Annex A
(informative)
Examples of spark-generating systems
A.1 General
Clauses A.2, A.3, A.4 and A.5 contain descriptions of four designs of spark-generating
circuit suitable for use in this test. With any of these examples it is possible to use different
explosion vessels, provided that the dust dispersion is optimized and that suitable pre-
cautions are taken in order to prevent side-effects occurring in comparatively large vessels
from electrostatic charging phenomena during the dispersion of the dust. These phenomena
include additional chargi
...