EN 1839-2012 pdf download.Determination of explosion limits of gases and vapours.
4.1.2.4 Heat-resistant, chemically inert material for gaskets and adhesive mountings.
Sample containers shall be kept closed before and after sampling to avoid changes in the sample composition within the container (e.g. loss of volatile components from mixtures). If a sample container contains a mixture with both gaseous and liquid phases present, the mixture composition of the two phases will be different. Under such conditions, it is recommended that the test substance sample be removed from the liquid phase. lithe sample is taken from the gaseous phase, account must be taken of the difference in composition.
4.1.3 Apparatus
4.1.3.1 Test vessel.
The test vessel is an upright cylindrical vessel made of glass or other transparent material (e.g. polycarbonate) with an inner diameter of (80 ± 2) mm and a minimum length of 300 mm.
The vessel is equipped with an inlet pipe with a three-way valve for the test mixture, located at the bottom, and an outlet pipe and pressure vent in the upper part.
The bottom and top may be made of other material. However, the material must be free of any catalytic effect and resistant to corrosion from the test mixture or the reaction products.
4.1.3.2 Ignition source.
A series of induction sparks between two electrodes is used as the ignition source.
The electrodes shall end (60 ± 1) mm above the bottom of the test vessel.
Stainless steel is a suitable material for the electrodes. The electrodes shall be pointed roes witn a oiameter ot maximum 4 mm. The angle of the tips shall be (60 ± 3)°. The distance between the tips shall be (5 ± 0,1) mm. The electrodes shall be mounted in the vessel so that they are gas tight at the highest pressures generated during the test. The mounting shall be resistant to heat and the test mixture, and provide adequate electrical resistance from the test vessel body.
A high voltage transformer, with a root mean square of 13 kV to 16 kV and a short circuit current of 20 mA to
30 mA, shall be used for producing the ignition spark. The primary winding of the high voltage transformer shall be
connected to the mains via a timer set to the required discharge time.
The spark discharge time shall be adjusted to 0,2 s. II a spark discharge time 010,2 S does not result in the ignition of the test mixture, the test may be repeated with a spark discharge time of up to 0,5 s.
The power of the induction sparks is dependent on the gas mixture and its pressure. In air at atmospheric conditions, according to calorimetric and electric measurements, such a source gives a spark with a power of approximately 10W.
When evaporating liquid samples, it is important to remember that the mixture composition of the gaseous phase in equilibrium with a liquid phase (vapour) generally differs from the mixture composition of the liquid phase itself. Furthermore, the mixture compositions of the liquid and the vapour phases may change when removing material from the vapour phase, Allowance for this is necessary when determining explosion limits for flammable liquids. when handling liquid samples and when preparing test mixtures by evaporating liquid samples. To avoid error, the method of dynamic total evaporation is used. An example of a suitable evaporator set up is described In Annex C. When liquids are metered, It has to be ensured that bubbles are not formed In any component carrying the liquid (e.g. pipes). To achieve complete homogenization, the test mixture flows through a mixing vessel, preferably made of glass. For a mixing vessel with no built-in elements, a volume of at least 600 ml is recommended. It Is expedient to introduce the test mixture tangentially. The mixing vessel is not necessary if homogenization is effectively achieved by the metering device. The temperature of the mixing vessel and of all parts carrying the test mixture is kept constant to prevent the test substance from condensing. It is recommended that the components carrying the test mixture are heated along with the test vessel.
4.1.5 Procedure
If the explosion limits are to be determined at elevated temperature, preheat the test vessel and all parts carrying the test mixture to the required temperature. For liquid samples, the temperature of the test mixture shall be at least 25 K higher than the condensation temperature. Prior to each ignition attempt, it has to be ensured that the temperature in the test vessel differs by no more than 5 K from the required value.
The determination of the explosion limits consists of a series of ignition tests which are carned out with test mixtures whose test substance content is varied.
For safety reasons, the initial ignition tests are carried out using a test mixture with test substance content which, if possible, lies outside the expected explosion range.
For organic substances which consist exclusively of carbon, hydrogen and oxygen (with the exception of peroxides), the LEL can be roughly estimated. At 20 °C, the LEL. in many cases, is approximately half the test substance content of the stoichiometric composition. The temperature dependence of the LEL has to be taken into account Up to 200 C, the LEL decreases more or less linearly between 30 % and 50 % of the value estimated for
20’C.
There is currently no method which readily estimates the UEL,
Prior to each ignition attempt, the test vessel is purged with the test mixture. The purging volume has to be at least ten times the volume of the test vessel. When purging Is complete, the inlet to the test vessel is sealed. The test mixture then by-passes the test vessel and flows directly into the exhaust system. An ignition is attempted using the induction spark under quiescent conditions (i.e. after a 6 s to 10 s delay). It is observed whether a flame detaches from the ignition source (see Annex B).
It Is recommended that the ignition testing is carried out without interruption of the production of the test mixture. If restarting. it will take a finite time to produce a test mixture of constant composition even if the adjustment has not been changed.EN 1839-2012 pdf download.
EN 1839-2012 pdf download
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