Determination of the spontaneous ignition behaviour of dust accumulations

This European Standard specifies analysis and evaluation procedures for determining self-ignition temperatures (TSI) of combustible dusts or granular materials as a function of volume by hot storage experiments in ovens of constant temperature. The specified test method is applicable to any solid material for which the linear correlation of lg (V/A) versus the reciprocal self-ignition temperature 1/TSI (with TSI in K) holds (i.e. not limited to only oxidatively unstable materials).
This European Standard is not applicable to the ignition of dust layers or bulk solids under aerated conditions (e.g. as in fluid bed dryer).
This European Standard shall not be applied to dusts like recognised explosives that do not require atmospheric oxygen for combustion, nor to pyrophoric materials.
NOTE   Because of regulatory and safety reasons "recognised explosives" are not in the scope of this European Standard. In spite of that, substances which undergo thermal decomposition reactions and which are not "recognised explosives" but behave very similarly to self-ignition processes when they decompose are in the scope. If there are any doubts as to whether the dust is an explosive or not, experts should be consulted.

Bestimmung des Selbstentzündungsverhaltens von Staubschüttungen

Dieses Dokument legt Prüf- und Auswerteverfahren zur Bestimmung der Selbstentzündungstemperaturen (TSI) brennbarer Stäube oder Schüttgüter als Funktion des Schüttvolumens fest. Das geschieht durch Warmlagerungsuntersuchungen in Öfen bei konstanter Ofentemperatur. Das spezifische Prüfverfahren ist auf jeden Feststoff anwendbar, für den die Theorie der Wärmeexplosion nach Anhang A.2 gilt (d. h. nicht begrenzt auf ausschließlich oxidativ instabile Stoffe).
Die spezifische Prüfung ist auf jeden Staub oder jedes Schüttgut anwendbar, das primär mit Luftsauerstoff reagiert. Aus Sicherheitsgründen darf diese Prüfung nicht mit Stoffen durchgeführt werden, die mit festen/flüssigen Oxidantien gemischt sind (z. B. Schießpulver, Thermit, mit flüssigem Sauerstoff imprägniertes Holz) oder mit Stoffen, bei denen heftige nicht oxidative Reaktionen entstehen könnten (z. B. Peroxide, Explosivstoffe). Jedoch dürfen im Einzelfall einige Arten von Stoffen geprüft werden, bei denen nicht oxidative Reaktionen entstehen können (z. B. nicht heftige exotherme Zersetzungsreaktionen), vorausgesetzt, dass zusätzliche Sicherheitsvorkehrungen getroffen werden. Bei Zweifeln über Gefahren aufgrund der Eigenschaften des zu untersuchenden Stoffes (z. B. ob er toxisch oder explosiv ist), sollte der Rat eines Experten eingeholt werden.
Dieses Dokument gilt nicht für die Entzündung von Staubablagerungen oder Feststoffansammlungen unter belüfteten Bedingungen (wie z. B. in einem Fließbett-Trockner).

Détermination de l'aptitude à l'auto-inflammation des accumulations de poussières

Le présent document spécifie des modes opératoires d’analyse et d’évaluation permettant de déterminer les températures d’auto-inflammation (TAI) de poussières combustibles ou de matériaux granulaires en fonction de leur volume par des essais en étuve isotherme dans des étuves à température constante. La méthode d’essai spécifiée s’applique à tout matériau solide pour lequel la théorie de l’explosion thermique, selon l’Article A.2, se vérifie (c’est-à-dire que son applicabilité ne se limite pas aux seuls matériaux instables par oxydation).
L’essai spécifié s’applique à toute poussière ou tout matériau granulaire réagissant principalement avec l’oxygène de l’air. Pour des raisons de sécurité, cet essai ne doit pas être utilisé avec des matériaux mélangés à des oxydants solides/liquides (tels que de la poudre noire, des thermites ou du bois imprégné d’oxygène liquide) ou des matériaux pouvant subir de violentes réactions non oxydantes (par exemple, peroxydes, explosifs). Certains types de matériaux subissant des réactions non oxydantes (telles que des réactions de décomposition exothermiques non violentes) peuvent toutefois être soumis à essai au cas par cas, à condition de prendre des mesures de sécurité supplémentaires. En cas de doute concernant l’existence d’un danger lié aux propriétés du matériau d’essai (toxiques ou explosives, par exemple), il convient de consulter l’avis d’experts.
Le présent document n’est pas applicable à l’inflammation des couches de poussière ou des solides en vrac dans des conditions aérées (par exemple, dans un sécheur en lit fluidisé).

Določanje lastnosti samovžiga usedlih plasti prahu

General Information

Status
Published
Public Enquiry End Date
11-Jul-2019
Publication Date
26-Jan-2021
Current Stage
6060 - National Implementation/Publication (Adopted Project)
Start Date
05-Jan-2021
Due Date
12-Mar-2021
Completion Date
27-Jan-2021

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SLOVENSKI STANDARD
SIST EN 15188:2021
01-april-2021
Nadomešča:
SIST EN 15188:2007
Določanje lastnosti samovžiga usedlih plasti prahu
Determination of the spontaneous ignition behaviour of dust accumulations
Bestimmung des Selbstentzündungsverhaltens von Staubschüttungen
Détermination de l'aptitude à l'auto-inflammation des accumulations de poussières
Ta slovenski standard je istoveten z: EN 15188:2020
ICS:
13.220.40 Sposobnost vžiga in Ignitability and burning
obnašanje materialov in behaviour of materials and
proizvodov pri gorenju products
13.230 Varstvo pred eksplozijo Explosion protection
SIST EN 15188:2021 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST EN 15188:2021

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SIST EN 15188:2021


EN 15188
EUROPEAN STANDARD

NORME EUROPÉENNE

December 2020
EUROPÄISCHE NORM
ICS 13.230 Supersedes EN 15188:2007
English Version

Determination of the spontaneous ignition behaviour of
dust accumulations
Détermination de l'aptitude à l'auto-inflammation des Bestimmung des Selbstentzündungsverhaltens von
accumulations de poussières Staubschüttungen
This European Standard was approved by CEN on 18 October 2020.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this
European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references
concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN
member.

This European Standard exists in three official versions (English, French, German). A version in any other language made by
translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management
Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and
United Kingdom.





EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2020 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN 15188:2020 E
worldwide for CEN national Members.

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SIST EN 15188:2021
EN 15188:2020 (E)
Contents Page
European foreword . 3
Introduction . 4
1 Scope . 5
2 Normative references . 5
3 Terms and definitions . 5
4 Test apparatus . 6
4.1 Sample baskets . 6
4.2 Determination of Basket Volume . 7
4.3 Oven and test conditions . 7
4.4 Thermocouples . 9
4.5 Temperature recording equipment . 9
5 Preparation of dust samples . 9
6 Procedure . 10
6.1 Experimental Procedure . 10
6.2 Evaluation of tests . 11
6.3 Calibration of thermocouples . 12
7 Test report . 12
8 Precision . 13
8.1 General. 13
8.2 Uncertainty of extrapolation to larger volumes . 13
8.3 Uncertainty of single-basket-test (10 cm basket) . 14
Annex A (normative) Theoretical Basis to Determinations and Extrapolations . 15
Annex B (informative) Extrapolation of induction times . 21
Annex C (informative) Extrapolation to Temperatures or Volumes of Interest by Numerical
solution of Fourier’s equation . 23
Annex D (informative) Alternative method for running tests adiabatically and interpreting
the results . 26
Annex E (normative) Safety Precautions . 30
Annex F (informative) Significant Changes between this European Standard and
EN 15188:2007 . 31
Annex ZA Annex ZA (informative) Relationship between this European Standard and the
Essential Requirements of EU Directive 2014/34/EU . 33
Bibliography . 34
2

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SIST EN 15188:2021
EN 15188:2020 (E)
European foreword
This document (EN 15188:2020) has been prepared by Technical 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 June 2021, and conflicting national standards shall be
withdrawn at the latest by December 2021.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
This document supersedes EN 15188:2007.
This document has been prepared under a standardization request given to CEN by the European
Commission and the European Free Trade Association, and supports essential requirements of EU
Directive 2014/34/EU.
For relationship with EU Directive 2014/34 EU, see informative Annex ZA, which is an integral part of
this document.
According to the CEN-CENELEC Internal Regulations, the national standards organisations of the
following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria,
Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland,
Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Republic of
North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the
United Kingdom.
3

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SIST EN 15188:2021
EN 15188:2020 (E)
Introduction
The self-ignition behaviour of dusts and granular materials and their mixtures depends on their
chemical composition as well as on related substance and bulk properties. It also depends on the size
and geometry of the body of material, and, last but not least on the ambient temperature.
The reason for self-heating (with possible self-ignition) is that the surface molecules of combustible
dust or granular materials undergo exothermic reactions with air or other oxidising atmospheres
transported into the void volume between the particles even at normal ambient temperatures. Any heat
then released will cause the temperature of the reactive system to rise, thus accelerating the reaction of
additional molecules with oxygen, etc. A heat balance involving the heat produced inside the bulk
(quantity and surface of reactive surface molecules, specific heat producing rate) and the heat loss to
the surroundings (heat conductivity and dimension of the bulk, heat transfer coefficient on the outside
surface of the bulk and the size of the latter) is decisive as to whether a steady-state temperature is
reached at a slightly higher temperature level (the heat loss terms are larger than the heat production
term), or whether temperatures in the bulk will continue to rise up to self-ignition of the material, if
heat transport away from the system is insufficient (in this case the heat production term is larger than
all heat losses).
The experimental basis in this document for describing the self-ignition behaviour of a given dust or
granular material is the determination of the self-ignition temperatures (T ) of differently sized bulk
SI
volumes by isoperibolic hot storage experiments (storage at constant oven temperatures) in
commercially available ovens. The results thus measured reflect the dependence of self-ignition
temperatures upon volume of the accumulation.
Different evaluation procedures – described in Annex A – allow interpolation and extrapolation, to
characterize the self-ignition behaviour of deposits of a different scale and of different bulk geometric
shapes. Primary method is the evaluation based on the thermal explosion theory according to Frank-
Kamenetskii (A.2) and Thomas (A.3).
Interlaboratory tests have shown, that it is necessary to provide prescribed test conditions, e.g. by
installation of a mesh wire screen into the oven, surrounding the dust samples and the thermocouples.
In this way the spread of results will be minimized. If it is possible based on suitable thermo-analytic
test procedures (adiabatic, isothermal or dynamic tests) to derive a reliable formal kinetic model, which
describes the heat production of the substance as a function of temperature, then the volume
dependency of the self-ignition temperature may be calculated according to the methods described in
Annex A.
4

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SIST EN 15188:2021
EN 15188:2020 (E)
1 Scope
This document specifies analysis and evaluation procedures for determining self-ignition temperatures
(T ) of combustible dusts or granular materials as a function of volume by hot storage experiments in
SI
ovens of constant temperature. The specified test method is applicable to any solid material for which
the thermal explosion theory according to A.2 holds (i.e. not limited to only oxidatively unstable
materials).
The specified test is applicable to any dust or granular material that reacts primarily with oxygen from
the air. For safety reasons, this test is not used with materials mixed with solid/liquid oxidant (e.g.
gunpowder, thermites, wood impregnated with liquid oxygen) or materials that could undergo violent
non-oxidative reactions (e.g. peroxides, explosives). On a case by case basis, some types of materials
undergoing non-oxidative reactions (e.g. non-violent exothermic decomposition reactions) may be
however tested provided that additional safety precautions are taken. Where any doubt exists about the
existence of hazard due to the properties of the test material (e.g. toxic or explosive), expert advice is
sought.
This document is not applicable to the ignition of dust layers or bulk solids under aerated conditions
(e.g. as in fluid bed dryer).
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements 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 1127-1:2019, Explosive atmospheres - Explosion prevention and protection - Part 1: Basic concepts
and methodology
EN 13237:2012, Potentially explosive atmospheres - Terms and definitions for equipment and protective
systems intended for use in potentially explosive atmospheres
3 Terms and definitions
For the purposes of this document, the following terms and definitions given in EN 13237:2012,
EN 1127-1:2019 and the following apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at https://www.iso.org/obp
3.1
self-ignition temperature
T
SI
highest temperature at which a given volume of dust just does not ignite
Note 1 to entry: Self-ignition temperature is expressed in °C.
3.2
oven temperature
arithmetic mean of the measured values of two thermocouples, both freely installed in an oven at a
distance of 5 cm to the surface of the dust sample
Note 1 to entry: Oven temperature is expressed in °C.
5

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SIST EN 15188:2021
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3.3
sample temperature
temperature measured at the centre of the dust sample using a thermocouple
Note 1 to entry: Sample temperature is expressed in °C.
3.4
induction time
interval of time between reaching the storage temperature and start of ignition (defined by the
inflection point, see Figure 3 case C)
Note 1 to entry: Induction time is expressed in h.
3.5
ignition
initiation of combustion
[SOURCE: EN ISO 19353:2019, 3.20]
3.6
bulk density
sample mass divided by the determined volume of the basket
3.7
dust
finely divided solid particles, up to 500 µm in nominal size
3.8
granules
discrete particles larger than 500 µm
4 Test apparatus
4.1 Sample baskets
The samples have to be filled into mesh wire baskets of different volumes. The baskets have to be open
at the top and closed at the bottom. They shall consist of two layers of narrow-meshed wire net, made of
e.g. stainless steel. The width of the mesh for the inner sample container has to be chosen in such a way
that the dust cannot fall through the mesh, but the diffusion of the oven air into the dust sample is not
hindered (e.g. mesh opening of 0,05 mm). The outer basket should be made from coarser mesh wire
(e.g. mesh opening of 0,5 mm). The outer basket defines the test volume therefore the inner basket
should be tightly fitting within, such that it does not distort when inserted. Recommended shapes of the
mesh wire baskets are that of a cube, or that of a cylinder with a height to diameter ratio of 1.
To allow an assessment of the self-ignition behaviour of larger sizes of dust accumulations than the
laboratory-scale, by extrapolation, at least four mesh wire baskets of different volumes have to be used
for the tests.
3
The smallest volume should normally be in the order of 100 cm and the largest should normally not be
3
smaller than approximately 1 000 cm . The volume ratio of the baskets should be approx. 1 : 1,7 : 5: 8;
e.g. cubes with edge length of 5 cm, 6 cm, 8,5 cm and 10 cm.
NOTE 1 Larger baskets are acceptable when sufficient material is available.
If only a limited amount of sample material is available, even smaller baskets may be used.
6

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NOTE 2 For the sake of comparing products with respect to their self-ignition behaviour in devices or
apparatus, where the sizes of the dust accumulations are limited for the reason of a specific design, often the
3 3
determination of the self-ignition temperature for a basket of 400 cm or 1 000 cm is sufficient.
4.2 Determination of Basket Volume
The volume of the sample baskets shall be determined by using suitable material consisting of
sufficiently small particles of spherical shape having a smooth surface and therefore of a known and
stable bulk density, e.g. glass beads with a diameter of approx. 0,3 mm. The baskets are filled with the
suitable material; any surplus material from the upper margin has to be removed. The basket is
weighed before and after filling. The volume results from the weight of the filled in material with known
bulk density (mean value of at least two measurements).
4.3 Oven and test conditions
Commercially available ovens (natural and forced convection) can be used. They shall have an air inlet
opening in the lower section and an air outlet opening in the upper section and should be controllable
in a temperature range from 35 °C to 300 °C. After reaching the test temperature the oven temperature
shall be stable over time within a range of ± 1 K.
The temperature field surrounding the sample shall exhibit maximum spatial temperature differences
of 4 K at an oven temperature of 120 °C. To determine the differences the temperature shall be
measured on 6 sides of a 10 cm sample cube in a distance of 5 cm, respectively. This measurement shall
be performed after installing the set-up and if the set-up (including hot storage oven) is changed. The
measurement shall be repeated once a year. Radiative heat transfer across the sample surfaces should
be minimized.
To achieve these conditions a mesh wire screen shall be installed into the oven. The minimum distance
between the screen and the oven walls shall be 5 cm. The screen consists of mesh wire with mesh
opening of e.g. 0,5 mm. The screen shall be equipped with a front door and a sample holder, see
Figure 1. The sample baskets shall freely hang in the oven. Additional metal sheets (thickness 0,25 mm
to 0,5 mm) can be installed at half height and on top to achieve the above conditions. The width of the
sheets shall be chosen in such a way, that the largest sample basket, hanging in the screen, is covered.
For measuring the oven temperature two thermocouples have to be installed on opposite sides at a
distance of 5 cm to the sample. The thermocouples have to be re-positioned for sample baskets of
differing sizes. The minimum distance between the thermocouples and the wall of the screen is 2,5 cm,
see Figure 2.
7

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SIST EN 15188:2021
EN 15188:2020 (E)

Key
1 front door
2 metal sheets (optional)
3 mesh wire
4 sample holder
5 thermocouples for measuring oven temperature
6 thermocouple for measuring sample temperature
7 mesh wire container with dust sample
Figure 1 — Mesh wire screen to be installed into the heating oven
8

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EN 15188:2020 (E)

Figure 2 — Position of sample and thermocouples
Alternative test arrangements can be used to provide the specified test conditions. In this case, the
uncertainty specified in Clause 8 may be not applicable.
4.4 Thermocouples
Both for measuring the sample temperature as well as for measuring the oven temperature, sheathed
thermocouples with an external diameter of e.g. 1 mm are recommended.
4.5 Temperature recording equipment
Appropriate data acquisition may be used for measuring and recording signals of the thermocouples.
5 Preparation of dust samples
To investigate situations occurring in practice a representative sample should be used (produced by the
operating conditions of the process). The sample characteristics shall be recorded in the test report.
The bulk density of the sample should be adjusted to the respective practical conditions (if known).
The bulk density shall be determined in the baskets and shall not vary by more than ± 2 % in the test
series.
Due to the limited size of the sample baskets used, it may be necessary to remove larger particles from
the sample (e.g. fraction > 20 mm)
9

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6 Procedure
6.1 Experimental Procedure
The test basket shall be filled with the dust sample with the settled bulk density. Any surplus dust from
the upper margin has to be removed. It shall be checked by weighting if the settled bulk density is
reached with an accuracy of ± 2 %. Position the basket at the centre of the oven (see Figure 1) that has
been preheated to the test temperature.
NOTE It is also possible to position the basket at the centre of cold oven if the target oven temperature is
reached and is stable within 30 min.
The thermocouple for measuring the sample temperature is to be positioned with its hot junction
directly at the centre of the sample. The hot junctions of two additional thermocouples on opposite
sides will be freely installed in the air space at a distance of 5 cm to the sample (see Figure 2). These
two thermocouples are used to measure the oven temperature, corresponding to, in critical cases, the
T . The temperatures of these three thermocouples shall be recorded continuously over time.
SI
In cases where the sample ignites the oven temperature may increase due to the heat released by the
burning sample. To prevent misinterpretation the oven temperature shall be taken at the crossing point
(where the temperature of the sample first reaches, and is equal to, the oven temperature) for the
evaluation of the test.
The temperature difference of both thermocouples measuring the oven temperature shall not exceed
2 K. If a larger temperature difference is observed the adjustment of the thermocouples and, if
necessary, the spatial temperature differences around the sample shall be checked.
The air inlet and air outlet openings of the oven shall be left open during the test to enable fresh air to
enter and combustion gases to leave the oven. A sufficient number of hot storage tests – with a fresh
dust sample for each test – shall be carried out to determine the highest oven temperature at which no
ignition occurs, as well as the lowest oven temperature at which the dust sample showed an ignition for
each sample volume chosen. Normally the test can be stopped if the temperature in the sample falls (see
case B in Figure 3) or if a situation like case C in Figure 3 occurs. Striking features during testing (e.g.
production of gases, physical changes to the sample) and the mass loss from samples shall be written
down.
Figure 3 is an idealised one. In some cases, the type B curve is followed by a steep increase of sample
temperature after the temperature drop has occurred. Attention should be paid to the fact that this may
happen after significantly long periods of time. In such cases, such modified type B curves have to be
evaluated as type C ones. This situation may also occur with type A curves.
10

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Key
ϑ temperature of surrounding environment (for tests this is the oven temperature): shown by dashed lines
t duration of the test
P inflection point
t induction time (for Curve C): delineated by lines with dashes and dots. Starts at the time the sample
i
temperature crosses the oven temperature (ϑC) and finishes at the inflection point
A hot storage test type A
B hot storage test type B
C hot storage test type C
Figure 3 — Idealised temperature courses over time in dust samples of the same volume at hot
storage temperatures ϑ to ϑ
A C
6.2 Evaluation of tests
Figure 3 shows idealised temperature curves over time in samples from three hot storage tests of the
same volume and the same dust, but at different oven temperatures. The dashed horizontal lines show
the oven temperatures (ϑ to ϑ ) of the respective hot storage tests (A, B and C) where sample
A C
temperatures are shown by thick continuous lines.
If one works at temperatures significantly lower than the T the sample temperature will
SI
asymptotically approach the oven temperature (curve A).
Higher oven temperatures show noticeable reactions with oxygen in the body of dust. Then sample
temperatures temporarily will be higher than oven temperatures. This indicates the beginning of the
self-heating processes, without self-ignition of the sample (curve B).
A test is evaluated as having ignited if one of two criteria is fulfilled:
a) when the temperature-time-curve, measured at the centre of the sample, shows an inflection point
during the heating phase at a temperature above the oven temperature
or
11

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SIST EN 15188:2021
EN 15188:2020 (E)
b) when the temperature at the centre of the sample rises at least 60 K above its oven temperature.
Curve B relates to an oven temperature ϑ , slightly below the T . At its maximum, the sample
SI
B
temperature surpasses the oven temperature by an amount Δϑ (to be less than 60 K). Thereafter the
sample temperature decreases to oven temperature.
Curve C relates to the oven temperature ϑ , a value just above the T . Heat production in the sample
SI
C
has now reached a point at which it continuously surpasses the heat loss (by heat conduction,
convection and radiation). Stationary conditions are no longer possible. After an induction time the
temperature of the sample raises rapidly, until self-ignition occurs.
The self-ignition temperature lies between the oven temperatures of curves B and C.
The selection of the hot storage temperatures for the decisive final two tests shall be made in such a
way that the oven temperatures of the test just producing ignition (curve C) and that of the test not
producing an ignition (curve B) differ by not more than 2 K. The decisive test not producing an ignition
shall be repeated. The T is the highest oven temperature at which a given volume of dust just did not
SI
ignite.
Besides the temperature recordings, the time interval between the positioning of a sample in the oven
and the achieving of the storage temperature as well as the complete storage period should be recorded
for every test. Additionally, the time interval between reaching the storage temperature and the ignition
(i.e. induction time: case C), or the time from exceeding the storage temperature until the maximum
sample temperature has been reached (case B), should be recorded.
Different methods allow extrapolation of the laboratory test results to larger storage volumes, see
Annex A. Primary method is the evaluation based on the thermal explosion theory according to Frank-
Kamenetskii (A.2) or Thomas (A.3). These methods also allow derivation of reaction kinetic data of the
self-ignition process.
A simplified, empirical method is described in A.5 (Pseudo-Arrhenius plot).
The results of these tests are documented in a table, comparing sample volumes tested, the respective
T values, and induction times. Further, results are represented in graphs, such as Figure A.1 and
SI
Figure A.3.
6.3 Calibration of thermocouples
The whole measuring chain (thermocouples, compensating cables, A/D-converter, data acquisition
system) shall be calibrated at intervals according to internal fixed rules.
At least annually a function test and if necessary an adjustment shall be done.
7 Test report
The test report shall include at least the following details:
a) reference to this document (EN 15188:2020);
b) name and address of the test institute which carried out the tests;
c) name and address of the client;
d) characterization of the sample:
1) sample description (including when known particle size distribution and moisture content);
2) name or chemical composition of the sample;
12

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SIST EN 15188:2021
EN 15188:2020 (E)
3) bulk density;
4) sample preparation (if done e.g. for comparison of different dusts);
e) any changes to the test equipment or test procedures specified in this standard, the reasons
...

SLOVENSKI STANDARD
oSIST prEN 15188:2019
01-julij-2019
Določanje lastnosti samovžiga usedlih plasti prahu
Determination of the spontaneous ignition behaviour of dust accumulations
Bestimmung des Selbstentzündungsverhaltens von Staubschüttungen
Détermination de l'aptitude à l'auto-inflammation des accumulations de poussières
Ta slovenski standard je istoveten z: prEN 15188
ICS:
13.220.40 Sposobnost vžiga in Ignitability and burning
obnašanje materialov in behaviour of materials and
proizvodov pri gorenju products
13.230 Varstvo pred eksplozijo Explosion protection
oSIST prEN 15188:2019 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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oSIST prEN 15188:2019

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oSIST prEN 15188:2019


DRAFT
EUROPEAN STANDARD
prEN 15188
NORME EUROPÉENNE

EUROPÄISCHE NORM

April 2019
ICS 13.230 Will supersede EN 15188:2007
English Version

Determination of the spontaneous ignition behaviour of
dust accumulations
Détermination de l'aptitude à l'auto-inflammation des Bestimmung des Selbstentzündungsverhaltens von
accumulations de poussières Staubschüttungen
This draft European Standard is submitted to CEN members for enquiry. It has been drawn up by the Technical Committee
CEN/TC 305.

If this draft becomes a European Standard, CEN members are bound to comply with the CEN/CENELEC Internal Regulations
which stipulate the conditions for giving this European Standard the status of a national standard without any alteration.

This draft European Standard was established by CEN in three official versions (English, French, German). A version in any other
language made by translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC
Management Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,
Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey and United Kingdom.

Recipients of this draft are invited to submit, with their comments, notification of any relevant patent rights of which they are
aware and to provide supporting documentation.

Warning : This document is not a European Standard. It is distributed for review and comments. It is subject to change without
notice and shall not be referred to as a European Standard.


EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2019 CEN All rights of exploitation in any form and by any means reserved Ref. No. prEN 15188:2019 E
worldwide for CEN national Members.

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Contents Page
European foreword . 4
Introduction . 5
1 Scope . 6
2 Normative References . 6
3 Terms and definitions . 6
4 Test apparatus. 7
4.1 Sample baskets. 7
4.2 Oven and test conditions . 8
4.3 Thermocouples . 9
4.4 Temperature recording equipment . 9
5 Preparation of dust samples . 9
6 Procedure. 10
6.1 Experimental Procedure . 10
6.2 Evaluation of tests . 11
6.3 Calibration of thermocouples . 12
7 Test report . 12
8 Precision . 13
8.1 General . 13
8.2 Extrapolation of results . 13
8.3 Single-basket-test (10 cm basket) . 14
Annex A (normative) Theoretical Basis to Determinations and Extrapolations. 15
A.1 Introduction . 15
A.2 Methods based on the thermal explosion theory . 15
A.3 Modification to theory for realistic boundary conditions . 17
A.4 Limitations to Analysis by Thermal Explosion Theory . 19
A.5 Scaling Plot (Pseudo-Arrhenius plot) . 19
Annex B (informative) Extrapolation of induction times . 21
Annex C (informative) Extrapolation to Temperatures or Volumes of Interest by Numerical
solution of Fourier’s equation . 23
C.1 Numerical solution of Fourier’s equation . 23
Annex D (informative) Alternative method for running tests adiabatically and interpreting the
results . 26
D.1 Summary and justification . 26
D.2 Experimental Set-up . 26
D.3 Experimental procedure . 26
D.4 Evaluation of tests . 27
Annex E (normative) Safety Precautions . 30
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E.1 General . 30
E.2 General precautions: . 30
Annex F (informative) Significant Changes between this European Standard and EN 15188:2007
. 31
(informative) Relationship between this European Standard and the essential requirements of
Directive 2014/34/EU aimed to be covered . 33
Bibliography . 34
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European foreword
This document (prEN 15188:2019) has been prepared by Technical Committee CEN/TC 305 “Potentially
explosive atmospheres – Explosion prevention and protection”, the secretariat of which is held by DIN.
This document is currently submitted to the CEN Enquiry.
This document will supersede EN 15188:2007.
This document has been prepared under a standardization request given to CEN by the European Commission
and the European Free Trade Association, and supports essential requirements of EU Directive 2014/34/EU.
For relationship with EU Directive 2014/34 EU, see informative Annex ZA, which is an integral part of this
document.
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Introduction
The self-ignition behaviour of dusts and granular materials and their mixtures depends on their chemical
composition as well as on related substance properties. It also depends on the size and geometry of the body of
material, and, last but not least on the ambient temperature.
The reason for self-heating (or possibly self-ignition) is that the surface molecules of combustible dust or
granular materials undergo exothermic reactions with air or other oxidising atmospheres transported into the
void volume between the particles even at normal temperatures. Any heat then released will cause the
temperature of the reactive system to rise, thus accelerating the reaction of additional molecules with oxygen,
etc. A heat balance involving the heat produced inside the bulk (quantity and surface of reactive surface
molecules, specific heat producing rate) and the heat loss to the surroundings (heat conductivity and
dimension of the bulk, heat transfer coefficient on the outside surface of the bulk and the size of the latter) is
decisive as to whether a steady-state temperature is reached at a slightly higher temperature level (the heat
loss terms are larger than the heat production term), or whether temperatures in the bulk will continue to rise
up to self-ignition of the material, if heat transport away from the system is insufficient (in this case the heat
production term is larger than all heat losses).
The experimental basis for describing the self-ignition behaviour of a given dust or granular material is the
determination of the self-ignition temperatures (T ) of differently-sized bulk volumes by isoperibolic hot
SI
storage experiments (storage at constant oven temperatures) in commercially available ovens. The results thus
measured reflect the dependence of self-ignition temperatures upon volume of the accumulation.
Different evaluation procedures – described in Annex A –allow interpolation and extrapolation, to characterize
the self-ignition behaviour of deposits of a different scale and of a different bulk geometric shapes. Primary
method is the evaluation based on the thermal explosion theory according to Frank-Kamenetskii (Annex A.2)
and Thomas (Clause A.3).
Interlaboratory tests have shown, that it is necessary to provide prescribed test conditions, e.g. by installation
of a mesh wire screen into the oven, surrounding the dust samples and the thermocouples. In this way the
spread of results will be minimized. If it is possible based on suitable thermo-analytic test procedures
(adiabatic, isothermal or dynamic tests) to derive a reliable formal kinetic model, which describes the heat
production of the substance as a function of temperature, then the volume dependency of the self-ignition
temperature may be calculated according to the methods described in Annex A.
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1 Scope
This document specifies analysis and evaluation procedures for determining self-ignition temperatures (T ) of
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combustible dusts or granular materials as a function of volume by hot storage experiments in ovens of
constant temperature. The specified test method is applicable to any solid material for which the thermal
explosion theory according to Annex A.2 holds (i.e. not limited to only oxidatively unstable materials).
The specified test is applicable to any dust or granular material that reacts primarily with oxygen from the air.
For safety reasons, this test shall not be used with materials mixed with solid/liquid oxidant (e.g. gunpowder,
thermites, wood impregnated with liquid oxygen) or materials that could undergo violent non-oxidative
reactions (e.g. peroxides, explosives). On a case by case basis, some types of materials undergoing non-
oxidative reactions (e.g. non-violent exothermic decomposition reactions) may be however tested provided
that additional safety precautions are taken. Where any doubt exists about the existence of hazard due to the
properties of the test material (e.g. toxic or explosive), expert advice should be sought.
This document is not applicable to the ignition of dust layers or bulk solids under aerated conditions (e.g. as in
fluid bed dryer).
2 Normative References
The following documents are referred to in the text in such a way that some or all of their content constitutes
requirements 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 1127-1, Explosive atmospheres - Explosion prevention and protection - Part 1: Basic concepts and
methodology
EN 13237, Potentially explosive atmospheres - Terms and definitions for equipment and protective systems
intended for use in potentially explosive atmospheres
3 Terms and definitions
For the purposes of this document, for the purposes of this document, the terms and definitions given in
EN 13237, EN 1127-1 and the following apply.
3.1
self-ignition temperature
T
SI
highest temperature at which a given volume of dust just does not ignite
NOTE Self-ignition temperature is expressed in °C.
3.2
oven temperature
arithmetic mean of the measured values of two thermocouples, both freely-installed in an oven at a distance of
5 cm to the surface of the dust sample
NOTE Oven temperature is expressed in °C.
3.3
sample temperature
temperature measured at the centre of the dust sample using a thermocouple
NOTE Sample temperature is expressed in °C.
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3.4
induction time
interval of time between reaching the storage temperature and start of ignition (defined by the inflection point,
see Figure 3 case C)
NOTE Induction time is expressed in h.
3.5
ignition
initiation of combustion
[EN ISO 19353:2016, 3.20]
3.6
bulk density
sample mass divided by the determined volume of the basket
3.7
dust
finely divided solid particles, up to 500 µm in nominal size
3.8
granules
discrete particles larger than 500 µm
4 Test apparatus
4.1 Sample baskets
The samples shall be loosely filled into mesh wire baskets of different volumes. The baskets shall be open at the
top and closed at the bottom. They shall consist of two layers of narrow-meshed wire net, made of e.g. stainless
steel. The width of the mesh for the inner sample container shall be chosen in such a way that the dust cannot
fall through the mesh, but the diffusion of the oven air into the dust sample is not hindered (e.g. mesh opening
of 0.05 mm). The outer basket should be made from coarser mesh wire (e.g. mesh opening of 0,5 mm). The
outer basket defines the test volume therefore the inner basket should be tightly fitting within, such that it does
not distort when inserted. Recommended shapes of the mesh wire baskets are that of a cube, or that of a
cylinder with a height to diameter ratio of 1.
To allow an assessment of the self-ignition behaviour of larger sizes of dust accumulations than the laboratory-
scale, by extrapolation, at least four mesh wire baskets of different volumes shall be used for the tests.
3
The smallest volume should normally be in the order of 100 cm and the largest should normally not be smaller
3
than approximately 1 000 cm . The volume ratio of the baskets should be approx. 1:1.7:5:8; e.g. cubes with edge
length of 5 cm, 6 cm, 8,5 cm and 10 cm.
NOTE 1 Larger baskets are acceptable when sufficient material is available.
If only a limited amount of sample material is available, even smaller baskets may be used.
NOTE 2 For the sake of comparing products with respect to their self-ignition behaviour in devices or apparatus, where
the sizes of the dust accumulations are limited for the reason of a specific design, often the determination of the self-
3 3
ignition temperature for a basket of 400 cm or 1 000 cm is sufficient.
The volume of the sample baskets shall be determined by using suitable material consisting of sufficiently small
particles of spherical shape having a smooth surface and therefore of a known and stable bulk density, e.g. glass
beads with a diameter of approx. 0,3 mm. The baskets are filled with the suitable material; any surplus material
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from the upper margin shall be removed. The basket is weighted before and after filling. The volume results
from the weight of the filled in material with known bulk density (mean value of at least two measurements).
4.2 Oven and test conditions
Commercially available ovens (natural and forced convection) can be used. They shall have an air inlet opening
in the lower section and an air outlet opening in the upper section and should be controllable in a temperature
range from 35 °C to 300 °C. After reaching the test temperature the oven temperature shall be stable over time
within a range of ± 1 K.
The temperature field surrounding the sample shall exhibit maximum spatial temperature differences of 4 K at
an oven temperature of 120 °C. To determine the differences the temperature shall be measured on 6 sides of a
10 cm sample cube in a distance of 5 cm, respectively. This measurement shall be performed after installing the
set-up and if the set-up (including hot storage oven) is changed. The measurement shall be repeated once a
year.
To achieve these conditions a mesh wire screen shall be installed into the oven. The minimum distance
between the screen and the oven walls shall be 5 cm. The screen consists of mesh wire with mesh opening of
e.g. 0,5 mm. The screen shall be equipped with a front door and a sample holder, see Figure 1. The sample
baskets shall freely hang in the oven. Additional metal sheets (thickness 0,25 mm to 0,5 mm) can be installed at
half height and on top to protect the sample from radiation. The width of the sheets shall be chosen in such a
way, that the largest sample basket, hanging in the screen, is covered.
For measuring the oven temperature two thermocouples have to be installed on opposite sides at a distance of
5 cm to the sample. The thermocouples have to be re-positioned for sample baskets of differing sizes. The
minimum distance between the thermocouples and the wall of the screen is 2,5 cm, see Figure 2.

Key
1 front door 5 thermocouples for measuring oven temperature
2 metal sheets (optional) 6 thermocouples for measuring sample temperature
3 mesh wire 7 mesh wire container with dust sample
4 sample holder
Figure 1 — Mesh wire screen to be installed into the heating oven
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Figure 2 — Position of sample and thermocouples
Alternative test arrangements can be used to provide the specified test conditions.
4.3 Thermocouples
Both for measuring the sample temperature as well as for measuring the oven temperature, sheathed
thermocouples with an external diameter of e.g. 1 mm are recommended.
4.4 Temperature recording equipment
Appropriate data acquisition may be used for measuring and recording signals of the thermocouples.
5 Preparation of dust samples
To investigate situations occurring in practice a representative sample should be used (produced by the
operating conditions of the process). The sample characteristics shall be recorded in the test report.
The bulk density of the sample should be adjusted to the respective practical conditions (if known).
The bulk density shall be determined in the baskets and shall not vary by more than ± 2 % in the test series.
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6 Procedure
6.1 Experimental Procedure
The test basket shall be filled with the dust sample with the settled bulk density. Any surplus dust from the
upper margin shall be removed. It shall be checked by weighting if the settled bulk density is reached with an
accuracy of ± 2 %. Position the basket at the centre of the oven (see Figure 1) that has been preheated to the
test temperature.
NOTE It is also possible to position the basket at the centre of cold oven if the target oven temperature is reached and
is stable within 30 min.
The thermocouple for measuring the sample temperature is to be positioned with its hot junction directly at
the centre of the sample. The hot junctions of two additional thermocouples on opposite sides will be freely
installed in the air space at a distance of 5 cm to the sample (see Figure 2). These two thermocouples are used
to measure the oven temperature, corresponding to, in critical cases, the T . The temperatures of these three
SI
thermocouples shall be recorded continuously over time.
In cases where the sample ignites the oven temperature may increase due to the heat released by the burning
sample. To prevent misinterpretation the oven temperature shall be taken at the crossing point (where the
temperature of the sample first reaches, and is equal to, the oven temperature) for the evaluation of the test.
The temperature difference of both thermocouples measuring the oven temperature shall not exceed 2 K. If a
larger temperature difference is observed the calibration of thermocouples and, if necessary, the spatial
temperature differences around the sample shall be checked.
The air inlet and air outlet openings of the oven shall be left open during the test to enable fresh air to enter and
combustion gases to leave the oven. A sufficient number of hot storage tests – with a fresh dust sample for each
test – shall be carried out to determine the highest oven temperature at which no ignition occurs, as well as the
lowest oven temperature at which the dust sample showed an ignition for each sample volume chosen.
Normally the test can be stopped if the temperature in the sample falls (see case B in Figure 3) or if a situation
like case C in Figure 3 occurs. Striking features during testing (e.g. production of gases, physical changes to the
sample) and the mass loss from samples shall be written down.
Figure 3 is an idealised one. In some cases, the type B curve is followed by a steep increase of sample
temperature after the temperature drop has occurred. Attention should be paid to the fact that this may happen
after significantly long periods of time. In such cases, such modified type B curves shall be evaluated as type C
ones. This situation may also occur with type A curves.
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Key
ϑ temperature of surrounding environment (for tests this is the oven temperature)
t duration of the test
P inflection point
t induction time (Curve C)
i
Figure 3 — Idealised temperature courses over time in dust samples of the same volume at hot storage
temperatures ϑ to ϑ
A C
6.2 Evaluation of tests
Figure 3 shows idealised temperature curves over time in samples from three hot storage tests of the same
volume and the same dust, but at different oven temperatures. The dashed horizontal lines show the oven
temperatures ( to ) of the respective hot storage tests (A, B and C).
ϑ ϑ
A C
If one works at temperatures significantly lower than the T the sample temperature will asymptotically
SI
approach the oven temperature (curve A).
Higher oven temperatures show noticeable reactions with oxygen in the body of dust. Then sample
temperatures temporarily will be higher than oven temperatures. This indicates the beginning of the self-
heating processes, without self-ignition of the sample (curve B).
A test is evaluated as having ignited if one of two criteria is fulfilled:
a) when the temperature-time-curve, measured at the centre of the sample, shows an inflection point during
the heating phase at a temperature above the oven temperature;
or
b) when the temperature at the centre of the sample rises at least 60 K above its oven temperature.
Curve B relates to an oven temperature , slightly below the T . At its maximum, the sample temperature
ϑ SI
B
surpasses the oven temperature by an amount ∆ϑ (to be less than 60 K). Thereafter the sample temperature
decreases to oven temperature.
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Curve C relates to the oven temperature ϑ , a value just above the T . Heat production in the sample has now
SI
C
reached a point at which it continuously surpasses the heat loss (by heat conduction, convection and radiation).
Stationary conditions are no longer possible. After an induction time the temperature of the sample raises
rapidly, until self-ignition occurs.
The self-ignition temperature lies between the oven temperatures of curves B and C.
The selection of the hot storage temperatures for the decisive final two tests shall be made in such a way that
the oven temperatures of the test just producing ignition (curve C) and that of the test not producing an
ignition (curve B) differ by not more than 2 K. The decisive test not producing an ignition shall be repeated. The
T is the highest oven temperature at which a given volume of dust just did not ignite.
SI
Besides the temperature recordings, the time interval between the positioning of a sample in the oven and the
achieving of the storage temperature as well as the complete storage period should be recorded for every test.
Additionally, the time interval between the achieving of the storage temperature and the ignition (induction
time, case C), i.e. the achieving of the maximum temperature (case B) should be recorded.
Different methods allow extrapolation of the laboratory test results to larger storage volumes, see Annex A.
Primary method is the evaluation based on the thermal explosion theory according to Frank-Kamenetskii
(Annex A.2) or Thomas (Annex A.3). These methods also allow derivation of reaction kinetic data of the self-
ignition process.
A simplified, empirical method is described in Annex A.5 (Pseudo-Arrhenius plot).
The results of these tests are documented in a table, comparing sample volumes tested, the respective T
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values, and induction times. Further, results are represented in graphs, such as Figure A.1 and Figure A.2.
6.3 Calibration of thermocouples
The whole measuring chain (thermocouples, compensating cables, A/D- converter, data acquisition system)
shall be calibrated at intervals according to internal fixed rules, at least annually.
7 Test report
The test report shall include at least the following details:
a) reference to this document (EN 15188:201x);
b) name and address of the test institute which carried out the tests;
c) name and address of the client;
d) characterization of the sample:
1) sample description (including when known particle size distribution and moisture content);
2) name or chemical composition of the sample;
3) bulk density;
4) sample preparation (if done e.g. for comparison of different dusts);
e) any changes to the test equipment or t
...

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