SIST IEC 61241-2-1:1998
(Main)Electrical apparatus for use in the presence of combustible dust - Part 2: Test methods - Section 1: Methods for determining the minimum ignition temperatures of dust
Electrical apparatus for use in the presence of combustible dust - Part 2: Test methods - Section 1: Methods for determining the minimum ignition temperatures of dust
Specifies two test methods for determining the minimum ignition temperatures of dust.
Matériels électriques destinés à être utilisés en présence de poussières combustibles - Partie 2: Méthodes d'essai - Section 1: Méthodes de détermination de la température minimale d'inflammation de la poussière
Indique deux méthodes d'essai pour la détermination de la température minimale d'inflammation de la poussière.
Electrical apparatus for use in the presence of combustible dust - Part 2: Test methods - Section 1: Methods for determining the minimum ignition temperatures of dust
General Information
Standards Content (Sample)
SLOVENSKI STANDARD
SIST IEC 61241-2-1:1998
01-april-1998
Electrical apparatus for use in the presence of combustible dust - Part 2: Test
methods - Section 1: Methods for determining the minimum ignition temperatures
of dust
Electrical apparatus for use in the presence of combustible dust - Part 2: Test methods -
Section 1: Methods for determining the minimum ignition temperatures of dust
Matériels électriques destinés à être utilisés en présence de poussières combustibles -
Partie 2: Méthodes d'essai - Section 1: Méthodes de détermination de la température
minimale d'inflammation de la poussière
Ta slovenski standard je istoveten z: IEC 61241-2-1
ICS:
29.260.20 (OHNWULþQLDSDUDWL]D Electrical apparatus for
HNVSOR]LYQDR]UDþMD explosive atmospheres
SIST IEC 61241-2-1:1998 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
---------------------- Page: 1 ----------------------
SIST IEC 61241-2-1:1998
---------------------- Page: 2 ----------------------
SIST IEC 61241-2-1:1998
CEI
NORME
IEC
INTERNATIONALE
1241-2-1
INTERNATIONAL
Première édition
STANDARD First edition
1994-12
Matériels électriques destinés à être utilisés
en présence de poussières combustibles -
Partie 2:
Méthodes d'essai —
Section 1: Méthodes de détermination de la
température minimale d'inflammation de la poussière
Electrical apparatus for use in the presence of
combustible dust —
Part 2:
Test methods —
1: Methods for determining the minimum
Section
ignition temperatures of dust
de reproduction réservés — Copyright — all rights reserved
© CEI 1994 Droits
No part of this publication may be reproduced or utilized in
Aucune partie de cette publication ne peut être reproduite ni
any form or by any means, electronic or mechanical,
utilisée sous quelque forme que ce soit et par aucun pro-
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.
Genève, Suisse
Bureau Central de la Commission Electrotechnique Internationale 3, rue de Varembé
Commission Electrotechnique Internationale CODE PRIX "
International Electrotechnical Commission
PRICE CODE v
MemulyHapopHaa 3nenrporexHwlecnaa HOMHCCHA
IEC
Pour prix, voir catalogue en vigueur
•
For price, see current catalogue
---------------------- Page: 3 ----------------------
SIST IEC 61241-2-1:1998
– 3 –
1241-2-1 © IEC:1994
CONTENTS
Page
FOREWORD 5
INTRODUCTION 7
Clause
1 Scope 9
9
2 Normative references
11
3 Definitions
11 4 Method A: Dust layer on a heated surface at a constant temperature
11
4.1 Preparation of dust sample
13
4.2 Test apparatus
15
4.3 Procedure
19
4.4 Test acceptance criteria
21
4.5 Reporting of results
21
4.6 Application of results
23
5 Method B: Dust cloud in a furnace at a constant temperature
23 5.1 Preparation of dust sample
23
5.2 Test apparatus
23
5.3 Procedure
25
5.4 Criterion of ignition
25 5.5 Minimum ignition temperature of a dust cloud
27
5.6 Reporting of results
33
Figures
Annexes
ace and measurement of temperature distribution
Construction of a heated su rf
A
31
on heated su rface
41
Construction of a constant temperature furnace B
---------------------- Page: 4 ----------------------
SIST IEC 61241-2-1:1998
1241-2-1 ©IEC:1994 - 5 -
INTERNATIONAL ELECTROTECHNICAL COMMISSION
ELECTRICAL APPARATUS FOR USE IN THE PRESENCE
OF COMBUSTIBLE DUST —
Part 2: Test methods —
Section 1: Methods for determining the minimum
ignition temperatures of dust
FOREWORD
1) The IEC (International Electrotechnical Commission) is a worldwide organization for standardization
comprising all national electrotechnical committees (IEC 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.
onal use published in the form of standards, technical
3) They have the form of recommendations for interna ti
reports or guides and they are accepted by the National Committees in that sense.
In order to promote international unification, IEC National Committees undertake to apply IEC International
4)
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.
International Standard IEC 1241-2-1 has been prepared by sub-committee 31H: Apparatus
for use in the presence of ignitable 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
31H(CO)9 31 H(CO)14
Full information on the voting for the approval of this standard can be found in the report
on voting indicated in the above table.
Annexes A and B form an integral part of this standard.
---------------------- Page: 5 ----------------------
SIST IEC 61241-2-1:1998
- 7 -
1241-2-1 © IEC:1994
INTRODUCTION
This section of IEC 1241-2 describes methods for determining the minimum ignition
temperature of dust which are:
- method A: Dust layer on a heated surface at a constant temperature (clause 4);
- method B: Dust cloud in a furnace at a constant temperature (clause 5).
Method A determines the minimum ignition temperature of a dust layer on a prescribed
heated surface.
Method B determines the minimum ignition temperature of a dust cloud within a prescribed
heated furnace.
The test methods are of a general nature, and may be used for purposes of comparison,
but in certain industrial situations further tests may be necessary.
The methods for determining the minimum ignition temperatures are not suitable for use
with recognized explosives, for example, gunpowder, dynamite, or mixtures of substances
which may, under some circumstances, behave similarly.
Where there is doubt, an indication of the existence of a hazard due to explosive pro-
perties may be obtained by testing a very small quantity of the dust on a surface at 400 °C
or higher, located remotely from the operator.
---------------------- Page: 6 ----------------------
SIST IEC 61241-2-1:1998
1241-2-1 ©IEC:1994 - 9 -
ELECTRICAL APPARATUS FOR USE IN THE PRESENCE
OF COMBUSTIBLE DUST —
Part 2: Test methods —
Section 1: Methods for determining the minimum
ignition temperatures of dust
1 Scope
This section of IEC 1241-2 specifies two test methods for determining the minimum
ignition temperatures of dust.
The methods are not suitable for use with substances having explosive properties.
Method A (clause 4) is applicable to the determination of the minimum temperature of a
ace which will result in the decomposition and/or ignition of a layer of
prescribed hot su rf
dust of a specified thickness deposited on it. The method is particularly relevant to
industrial equipment with which dust is present on hot su rfaces in thin layers exposed to
the atmosphere.
Method B (clause 5) is applicable to the determination of the minimum temperature of a
ace which will result in the ignition of a cloud of a given sample of dust
prescribed hot su rf
or other particulate solid. The test is intended to be carried out as a complementary test
after determining the minimum ignition temperature of a dust layer by method A of this
standard.
NOTES concerning method B
1 Because the method of operation of the furnace gives short residence times for dust particles within it,
this method of test is applicable to industrial equipment where dust is present as a cloud for a short time.
This method of test is of small scale and the results are not necessarily representative of all industrial
conditions.
2 The method is not applicable to dusts which may, over a longer period of time than provided for in the
test method, produce from deposits gases generated during pyrolysis or smouldering.
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 parties
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.
ISO 565: 1990, Test sieves - Metal wire cloth, perforated metal plate and electroformed
sheet - Nominal sizes of opening
ISO 4225: 1980: Air quality - General aspects - Vocabulary
---------------------- Page: 7 ----------------------
SIST IEC 61241-2-1:1998
- 11 -
1241-2-1 © IEC:1994
3 Definitions
For the purpose of this section of IEC 1241-2, the following definitions apply:
Small solid particles in the atmosphere which settle out under their own
3.1 dust:
weight, but which may remain suspended in air for some time (includes dust and grit as
defined in ISO 4225).
Ignition is considered to have occurred if glowing or
3.2 ignition of a dust layer:
flaming is initiated in the material, or a temperature of 450 °C or more, or a temperature
ace, is measured in
rise of 250 K or more above the temperature of the prescribed hot su rf
the test.
3.3 minimum ignition temperature of a dust layer: Lowest temperature of a hot
ace at which ignition occurs in a dust layer of specified thickness on this hot su rface.
su rf
NOTES
1 Because of the wide range of processes in industry, the ignition of dust layers may be dependent upon
local conditions. This method of test is not necessarily representative of all industrial conditions, where
account may need to be taken of such factors as the presence of thick layers of dust and of the distribution
of temperature in the environment.
2 When carrying out this test, it is essential that all necessary precautions be taken to safeguard the
health of personnel, for example, against the risk of fire, explosion, inhalation of smoke and any toxic
products of combustion.
Initiation of an explosion by the transfer of energy to a
3.4 ignition of a dust cloud:
dust cloud in air.
3.5 ignition temperature of a dust cloud: Lowest temperature of the hot inner wall of
a furnace at which ignition occurs in a dust cloud in air contained therein.
NOTE - When carrying out this test, it is essential that all necessary precautions be taken to safeguard
the health of personnel, for example, against the risk of fire, explosion, inhalation of smoke and any toxic
products of combustion.
4 Method A: Dust layer on a heated surface at a constant temperature
4.1 Preparation of dust sample
The sample shall be prepared so as to be homogeneous and representative of the dust
received for consideration.
The dust sample to be tested shall, in general, be able to pass through a woven metal wire
cloth or a square hole perforated plate test sieve with a nominal size of aperture of 200 gm
(for supplementary sizes, see ISO 565). If it is necessary to test a coarser dust, passing a
ure up to 500 gm, the fact shall be stated in the test
test sieve with a nominal size of ape rt
repo rt .
---------------------- Page: 8 ----------------------
SIST IEC 61241-2-1:1998
1241-2-1 ©IEC:1994 - 13 -
Any apparent changes noted in the properties of the dust during preparation of the
sample, for example, by sieving or owing to temperature or humidity conditions, shall be
stated in the test report.
4.2
Test apparatus
The apparatus is shown schematically in figure A.1. Essential details and pe rformance
requirements are given in the following subclauses. Methods of construction to enable
these requirements to be met are described in annex A.
4.2.1 Heated surface
The heated su rface shall consist of a circular metal plate and shall provide a working area
of at least 200 mm in diameter and be not less than 20 mm in thickness. The plate shall be
heated electrically and its temperature shall be controlled by a device for which the
sensing element is a thermocouple mounted in the plate near the centre and with its
junction within 1 mm ± 0,5 mm of the upper su rface and in good thermal contact with the
plate.
A similar thermocouple shall be mounted near the control thermocouple in a similar
manner, and shall be connected to a temperature recorder to record the temperature of
the su rface during a test. The heated surface and its control device shall satisfy the
following pe
rformance requirements:
a) the heated su rface shall be capable of attaining a maximum temperature of 400 °C
without a dust layer in position;
±5
K throughout
b) the temperature of the heated su rface shall be constant to within
the period of a test;
c) when the heated su rface has reached a steady state, the temperature across the
surface shall be uniform to within ±5 K when measured across two diameters at right
angles, by the procedure described in annex B. This requirement shall be satisfied at
nominal su ace temperatures of 200 °C and 350 °C;
rf
d) the temperature control shall be such that the recorded surface temperature does
not change by more than ±5 K during the placing of the dust layer, and it shall be
restored to within ±2 K of the previous value within 5 min of placing the dust layer;
e) temperature control and measurement devices shall be calibrated and shall have
±3
limits of inaccuracy of K.
4.2.2
Dust layer thermocouple
A fine thermocouple (0,20 mm to 0,25 mm diameter) of chromel-alumel or other suitable
material shall be stretched across the heated su rface, and parallel to it, at a height of
between 2 mm and 3 mm from it with the junction over the centre of the plate. This thermo-
couple shall be connected to a temperature recorder in order to determine the behaviour
of the dust layer during the test.
4.2.3 Temperature measurements
Temperature measurements using thermocouples shall be made either relative to a fixed
reference junction or with automatic cold junction compensation. In either case, calibration
shall satisfy the requirements of 4.2.1 e).
---------------------- Page: 9 ----------------------
SIST IEC 61241-2-1:1998
1241-2-1 © IEC:1994 - 15 -
4.2.4 Ambient temperature measurements
The ambient temperature shall be measured by a thermometer placed not more than 1 m
ace, but shielded from heat convection and radiation from the surface.
from the heated su rf
The ambient temperature shall be within the range 15 °C to 35 °C.
4.2.5 Dust layers
Dust layers shall be prepared by filling the cavity formed by placing a metal ring of appro-
priate height on the heated su rface and levelling the layer to the top of the ring. The ring
shall have an internal diameter of nominally 100 mm and shall have slots at opposite ends
of a diameter to clear the test thermocouple (figure A.2). The ring shall be left in place
during a test.
A given dust shall be tested in a layer of 5,0 mm ± 0,1 mm depth. For predictive purposes
(see 4.6) a second depth (such as 12,5 mm ± 0,1 mm or 15,0 mm ± 1 mm) is useful.
Rings of appropriate depths will be required.
4.2.6
Formation of dust layer
The dust layer shall be formed without compressing it unduly. That is to say, the dust shall
be put into the ring with a spatula and distributed mainly with sideways movement of the
spatula until the ring is slightly overfilled. The layer shall then be levelled by drawing a
straight edge across the top of the ring. Any excess should be swept away.
For each type of dust, a layer shall be formed in the above manner on a sheet of paper
whose weight is known and weighed. The density shall be calculated from the mass of the
dust and the filled volume of the ring, and shall be reported.
4.3 Procedure
4.3.1
General
Ignition in particulate or porous solids exposed to elevated temperatures is generally
preceded by a more or less protracted period of self-heating (usually due to atmospheric
oxidation). Depending on the temperature of exposure, self-heating may result in no more
than a transient, though sometimes substantial, rise in temperature within the solid which
does not lead to propagation of combustion. Further, the "induction period" for ignition, at
temperatures near to the minimum required for ignition is usually many times greater than
for ignition in dust clouds or in gases and vapours (minutes or hours rather than seconds).
For both reasons the recognition of the minimum ignition temperature of dust layers is less
straightforward than for dust clouds or for gases and vapours. It is necessary especially to
be ce ain that failure to ignite at a given temperature is not merely because a test was
rt
terminated prematurely.
---------------------- Page: 10 ----------------------
SIST IEC 61241-2-1:1998
-17 -
1241-2-1 © IEC:1994
The occurrence of ignition in a layer of dust on a surface at a given temperature depends
critically on the balance between the rate of heat generation ("self-heating") in the layer
and the rate of heat loss to the surroundings. The temperature at which ignition of a given
material occurs depends, therefore, on the thickness of the layer. Values determined for
two or more thicknesses of a given dust may be used for predictive purposes (see 4.6).
Following the recommended procedure, ignition shall be considered to have occurred if:
a) visible glowing or flaming is observed (figure 3a), or
a temperature of 450 °C, is measured or
b)
a temperature rise of 250 K above the temperature of the heated plate (figure 3c), is
c)
measured.
With regard to items b and c above, ignition shall not be considered to have occurred if it
can be shown that the reaction does not propagate to glowing or flaming. The temperature
shall be measured by thermocouple (see 4.2.2) It will usually be found that, provided the
temperature of the heated surface is high enough, the temperature in the layer will slowly
increase to a maximum value which may be in excess of the temperature of the heated
surface and then slowly fall to a steady value below the temperature of the heated surface
(figure 3b). This behaviour is evidence of self-heating in the dust layer and it may often be
accompanied by a discoloration of the dust but without active and visible combustion of
the layer. If the temperature of the heated surface is slightly higher, the temperature
measured in the dust layer will continue to rise instead of passing through a maximum.
Some materials exhibit more than one stage of self-heating, and it may sometimes be
necessary to prolong the test in order to fully explore this possibility. With organic dust,
combustion will usually take the form of charring followed by the appearance of
smouldering with glowing which will progress through the layer and leave a residue of ash.
With dust layers composed of certain divided metals, ignition may be characterized by the
relatively sudden appearance of highly incandescent smouldering combustion progressing
rapidly through the layer.
In the determination of the minimum ignition temperature for a layer of given thickness,
repeated trials are carried out, using a fresh layer of dust each time and with up-and-down
adjustments to the temperature of the heated surface until a temperature is found which is
high enough to cause ignition in the layer but which is no more than 10 K higher than a
temperature which fails to cause ignition. The highest temperature at which ignition fails to
occur shall be confirmed by continuing the test long enough to establish that any self-
heating is decreasing in rate; that is, the temperature at the point of measurement in the
layer is decreasing to a steady value lower than the temperature of the heated surface.
4.3.2 Method
The apparatus shall be set up in a position free from draughts, and preferably under a
hood capable of extracting smoke and fumes.
---------------------- Page: 11 ----------------------
SIST IEC 61241-2-1:1998
1241-2-1 © IEC:1994 -
19 -
The temperature of the heated surface shall be adjusted to the desired value and shall be
allowed to become steady within the prescribed limits of 4.2.1 b). A metal ring of the
required height shall be placed centrally on the heated surface and this ring shall be filled
with the dust to be tested and levelled off within a period of 2 min. The recorder for the
dust layer thermocouple shall then be started.
The test shall be continued until it is ascertained either that the layer has ignited, either
visually or by the thermocouple recording, or has self-heated without igniting and is sub-
sequently cooling down.
If, after a period of 30 min, no self-heating is apparent the test should be terminated and
repeated at a higher temperature. If ignition or self-heating occurs the test shall be
repeated at a lower temperature, if necessary, prolonging the test beyond 30 min. Test
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.