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

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

La présente Norme européenne prescrit 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 d’étuvage dans des étuves de séchage à température constante. La méthode spécifiée est applicable à toute matière solide (c’est à dire que son applicabilité ne se limite pas aux seules matières instables par oxydation) pour laquelle se vérifie une corrélation linéaire entre le logarithme log (V/A) et l’inverse de la température d’auto-inflammation 1/TAI ( avec TAI en Kelvins).
La présente Norme européenne n’est pas applicable à l’inflammation des couches de poussière ou des masses solides dans des conditions aérées (comme par exemple dans un sécheur en lit fluidisé).
Cette méthode ne s’applique pas aux poussières, comme les explosifs reconnus comme tels, dont la combustion ne nécessite pas d’oxygène, ou aux substances pyrophoriques.
NOTE   Pour des raisons réglementaires et de sécurité, les « substances reconnues comme explosives » sont exclues du domaine d’application de la présente norme. Malgré cela, les substances qui subissent des réactions de décomposition thermique et qui ne sont pas des « substances reconnues comme explosives » mais dont le comportement est très similaire à celui de processus d’auto-inflammation lorsqu’elles se décomposent font partie du domaine d’application. En cas de doute sur la caractérisation des poussières comme explosifs ou non, il convient de consulter des experts.

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General Information

Status
Withdrawn
Publication Date
21-Aug-2007
Current Stage
9960 - Withdrawal effective - Withdrawal
Completion Date
23-Dec-2020

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2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Bestimmung des Selbstentzündungsverhaltens von StaubschüttungenDétermination de l'aptitude a l'auto-inflammation des accumulations de poussieresDetermination of the spontaneous ignition behaviour of dust accumulations13.230Varstvo pred eksplozijoExplosion protection13.220.40Sposobnost vžiga in obnašanje materialov in proizvodov pri gorenjuIgnitability and burning behaviour of materials and productsICS:Ta slovenski standard je istoveten z:EN 15188:2007SIST EN 15188:2007en,fr,de01-oktober-2007SIST EN 15188:2007SLOVENSKI

STANDARD
SIST EN 15188:2007

EUROPEAN STANDARDNORME EUROPÉENNEEUROPÄISCHE NORMEN 15188August 2007ICS 13.230 English VersionDetermination of the spontaneous ignition behaviour of dustaccumulationsDétermination de l'aptitude à l'auto-inflammation desaccumulations de poussièresBestimmung des Selbstentzündungsverhaltens vonStaubschüttungenThis European Standard was approved by CEN on 13 July 2007.CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this EuropeanStandard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such nationalstandards may be obtained on application to the CEN 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 translationunder the responsibility of a CEN member into its own language and notified to the CEN Management Centre has the same status as theofficial versions.CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Cyprus, Czech Republic, Denmark, Estonia, Finland,France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal,Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.EUROPEAN COMMITTEE FOR STANDARDIZATIONCOMITÉ EUROPÉEN DE NORMALISATIONEUROPÄISCHES KOMITEE FÜR NORMUNGManagement Centre: rue de Stassart, 36

B-1050 Brussels© 2007 CENAll rights of exploitation in any form and by any means reservedworldwide for CEN national Members.Ref. No. EN 15188:2007: ESIST EN 15188:2007

EN 15188:2007 (E) 2 Contents Page Foreword..............................................................................................................................................................3 Introduction.........................................................................................................................................................4 1 Scope......................................................................................................................................................5 2 Terms and definitions...........................................................................................................................5 3 Test apparatus.......................................................................................................................................6 3.1 Sample baskets......................................................................................................................................6 3.2 Oven........................................................................................................................................................6 3.3 Thermocouples......................................................................................................................................6 3.4 Temperature recording equipment......................................................................................................6 4 Preparation of dust samples................................................................................................................6 5 Procedure...............................................................................................................................................8 5.1 Experimental Procedure.......................................................................................................................8 5.2 Evaluation of tests.................................................................................................................................9 5.3 Calibration of thermocouples.............................................................................................................10 6 Test report............................................................................................................................................11 Annex A (informative)

Evaluation of experimental results for self-ignition temperatures......................13 A.1 Introduction..........................................................................................................................................13 A.2 Methods based on the thermal explosion theory.............................................................................13 A.3 Numerical solution of Fourier’s equation.........................................................................................16 Annex ZA (informative)

Relationship between this European Standard and the Essential Requirements of EU Directive 94/9/EC..............................................................................................20 Bibliography......................................................................................................................................................21

SIST EN 15188:2007

EN 15188:2007 (E) 3 Foreword This document (EN 15188:2007) 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 February 2008, and conflicting national standards shall be withdrawn at the latest by February 2008. Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. CEN [and/or CENELEC] shall not be held responsible for identifying any or all such patent rights. This document has been prepared under a mandate given to CEN by the European Commission and the European Free Trade Association, and supports essential requirements of EU Directive 94/9/EC.

For relationship with EU Directive 94/9/EC, see informative Annex ZA, which is an integral part of this document.

According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and the United Kingdom. SIST EN 15188:2007

EN 15188:2007 (E) 4 Introduction The self-ignition behaviour of combustible dusts 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 behind self-heating (or possibly self-ignition) is that the surface molecules of combustible dust particles undergo exothermic reactions with the oxygen in air transported into the void volume between the particles even at normal temperatures. Any heat then released will cause the temperature of the reactive dust-air system to rise, thus accelerating the reaction of additional dust 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 dust, 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 is the determination of the self-ignition temperatures (TSI) of differently-sized bulk volumes of the dust by isoperibol hot storage experiments (storage at constant oven temperatures) in commercially available ovens. The results thus measured reflect the dependence of self-ignition temperatures upon dust volume. Plotting the logarithms of the volume/surface ratios [lg (V/A)] of differently sized dust deposits versus the reciprocal values of the respective self-ignition temperatures [1/TSI in K-1] or following other evaluation procedures – described in Annex A – one produces straight lines, allowing interpolation, to characterise the self-ignition behaviour of dust deposits of a different scale and of a different bulk geometric shapes (see 5.1). Experience has shown that the spread of slopes of such straight lines determined by different laboratories using differently constructed ovens is fairly large. This is the reason why scale up of those results to industrial scale will lead to non-negligible errors in TSI. Experience has shown, that it seems necessary to prescribe the installation of a unique inner chamber into the oven, surrounding the dust samples and the thermocouples, with an also prescribed air flow through this chamber. In this way the spread of results should be minimised. Decisions on the design of this inner chamber and on the amount of air flow respectively other test setups leading to comparable results have to be carried out later on. 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. SIST EN 15188:2007

EN 15188:2007 (E) 5 1 Scope 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 should 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. 2 Terms and definitions For the purposes of this document, the following terms and definitions apply. 2.1 self-ignition temperature TSI highest temperature at which a given volume of dust just does not ignite NOTE Self-ignition temperature is expressed in °C. 2.2 oven temperature arithmetic mean of the measured values of two thermocouples, both freely installed in an oven at half the distance between the wall and the surface of the dust sample NOTE Oven temperature is expressed in °C. 2.3 sample temperature temperature measured at the centre of the dust sample using a thermocouple NOTE Sample temperature is expressed in °C. 2.4 induction time interval of time between reaching the storage temperature and an ignition NOTE Induction time is expressed in h. 2.5 ignition initiation of combustion [EN 13478:2001, 3.20] SIST EN 15188:2007

EN 15188:2007 (E) 6 3 Test apparatus 3.1 Sample baskets The samples have to be loosely filled into mesh wire baskets of different volumes. The baskets have to be open at the top and closed at the bottom. They consist of a narrow-meshed wire net, made of e.g. stainless steel. The width of the mesh has to be chosen in such a way that the dust cannot fall through the mesh, but the diffusion of oxygen from the oven air into the dust sample is not hindered. Recommended shapes of the mesh wire baskets are that of a cylinder with a height to diameter ratio of 1 or that of a cube. To allow an assessment of the self-ignition behaviour of dust accumulations of larger sizes than the laboratory-scale at least three mesh wire baskets of different volumes have to be used for the tests. NOTE 1 A higher level of certainty is achieved with four different sample volumes. The smallest volume should normally be in the order of 10 cm3 and the largest should normally not be smaller than approximately 1 l. If only a limited amount of sample material is available, even smaller baskets may be used. However it has to be assured that the volume of the basket following in a series exceeds that of the previous one by a factor of 2 at a minimum. 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-ignition temperature for a basket of 400 cm3 or 1 000 cm3 is sufficient. 3.2 Oven Commercially available ovens can be used. They shall have an air inlet opening in the lower section and an air outlet opening in the upper section (see schematic drawing in Figure 1). They should have a useful volume of about 120 l (enabling the installation of an inner chamber into the oven, surrounding the dust samples and the thermocouples, being equipped with an upstream heat exchanger consisting of copper tube coils) and be controllable in a temperature range from 35 °C to 300 °C. This construction enables a prescribed air flow through this chamber. The oven temperature shall be stable within a range of ± 1 % of the respective oven temperature. Alternative test arrangements can be used to provide the specified test conditions. For example, the test basket can be shielded by placing it inside an additional mesh wire basket.

Mechanically ventilated ovens can also be used provided the test basket is shielded (e.g. by using an inner chamber or an additional mesh wire basket). 3.3 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. 3.4 Temperature recording equipment Appropriate data acquisition may be used for measuring and recording signals of the thermocouples. 4 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 dust for each experiment is determined by weighing the baskets as well as the moisture content of the dust before and after filling. SIST EN 15188:2007

EN 15188:2007 (E) 7

Key 1 heating oven 5 thermocouple for measuring sample temperature 2 inner chamber (volume ≈ 50 l) 6 wire gauze cylinder with dust sample 3 air outlet, diameter ≈ 10 mm 7 deflector 4 thermocouple for measuring oven temperature 8 air inlet (preheated air, adjustable flow rate),

diameter ≈ 8 mm Figure 1 — Suggested experimental setup for hot storage tests If the results are required to compare different dusts with each other (for the purpose of tabular data compilations), tests shall to be carried out with the dust having passed through a sieve of 250 µm mesh aperture and dried to constant weight at 50° C in a vacuum drying chamber. If necessary, the substance may be ground and/or sieved. All preparation procedures shall be recorded and included in the report, especially when altering the grain size, quoting the grain size distribution of the sample tested. SIST EN 15188:2007

EN 15188:2007 (E) 8 5 Procedure 5.1 Experimental Procedure The test basket shall be filled with the dust sample by tapping it several times. Then remove any surplus dust from the upper margin and position the basket at the centre of the oven that has been preheated to the test temperature. The thermocouple for measuring the sample temperature is to be positioned with its hot junct

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