EN 17077-2017 pdf download.Determination of burning behaviour of dust layers.
This EN 17077 describes a test method for the determination of the burning behaviour of dust layers under defined initial conditions of air flow, temperature and ignition.
A test result of’burning class 1” with the described method does not mean that a dust cannot be ignited when dispersed in a cloud.
This method is not suitable for use with recognized explosives, like gunpowder and dynamite, explosives which do not require oxygen for combustion, pyrophoric substances, or substances or mixtures of substances which may under some circumstances behave in a similar manner. Expert advice should be called in, when any doubt exists about the existence of hazard due to explosive properties.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are indispensable for its application. 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, the terms and definitions given in EN 13237, EN 1127-1 and the
following apply.
air flow velocity
volume of air 1m31 which flows through a defined surface 1m2J per unit time [sJ
3.2
combustion
exothermic reaction with either flames or smouldering when ignited
3.3
ignition
initiation of combustion
3.4
initial temperature
4 Principle of the test method
A representative sample of the test substance Is placed at ambient temperature on a heat insulating surface and Is attempted to Ignite. The air flow moving along the length of the dust train kept constant during the test.
Since the test result may depend on the temperature of the dust sample tests at elevated temperatures could be necessary (see Annex A).
For melting substances the sample preparation or test equipment shall be modified (see 7.4)
5 Test equipment
5.1 General
The test apparatus is placed in a laboratory fume cupboard which creates an air flow of approximately 0,2 rn/s to 0.4 rn/s in direction of the reaction next to the surface of the dust. The slight overflow with air Is necessary, since the product may produce inert gas after contact with the ignition source. The inert gas can influence the burning behaviour of the dust.
NOTE The higher air velocities and/or temperatures present In filter systems or dryers may change the burning behaviour when compared to that determined by the standard test procedure. Varying test conditions may simulate technical process conditions.
If modified test conditions lead to a different burning class then this should be mentioned in the test report along with a description of how test conditions have deviated from the standard.
5.2 Test apparatus
The burning behaviour can be determined with the following apparatus:
5.2.1 Board method:
The tests are performed on a clean, non-combustible thermal isolating board or tHe with a plane surface placed in a laboratory fume cupboard and a mould 1(20 ± 2) mm width, (10 ± 1) mm height and mm. 40 mm lengths to form a triangular powder train.
NOTE 1 Different plate materials are possible (e.g. ceramic, marble, fibre insulation board).
NOTE 2 Boards with a textile structure yield in a higher burning classes for melting dust samples (see 7.4 and Annex B).
NOTE 3 The size of the mould apart from the length corresponds to the UN-Test N.l concerning readily combustible solids
6 Dust sample Characterization of sample
The applicant shall be responsible for ensuring that the sample is representative of the material as it appears in the process operated. The sample shall be characterized by:
— particle size distribution by either an optical method or sieving;
— moisture content.
Many unit operations, such as extract systems, will separate dust into finer fractions than seen in the main processing equipment. Samples should be representative of the process, or the worst case.
If the applicant cannot ensure that the sample is representative then sample preparation shall be carried out to apply worst case conditions. Therefore the dust having passed through a sieve of 250 pm and dried to a constant weight (e.g. at 500 C, in a vacuum drying chamber) before testing. If a dust is tested at other conditions these conditions shall be specified in the test report.
Grinding may be carried out to achieve a defined particle size. All preparation procedures shall be documented in the test-report, especially when altering the grain size.
NOTE Sample preparation such as grinding and sieving, or drying can alter the material characteristics. For mixtures sample preparation can result in changes to the sample composition, which in turn can result in changes to the experimentally determined parameters.
7 Test procedure
Tests on burning behaviour with defined dusts shall be carried out according to the following procedure.
If this procedure does not give a clear result, the test shall be repeated at least once.
For melting products further tests could be necessary which are described in 7.4.
7.1 Sample preparation
7.1.1 Board method
A sample prepared as described in 5.2.1 is placed on the board or tile as an unbroken powder train. 7.1.2 Lutolf apparatus method
A prepared dust sample as described in 5.2.1 is placed in the middle of the sample holder as an unbroken powder train. Afterwards the sample holder is inserted into the glass tube which is placed on the basis.EN 17077-2017 pdf download.