BS EN 14491:2012 pdf download – Dust explosion venting protective systems

BS EN 14491:2012 pdf download – Dust explosion venting protective systems NOTE 1 There is no direct guidance for estimating an endangered area for toxic or other harmful emissions, but the safe discharge area for external flames calculated according to the formulae in 6.2 gives some indication of the area required in direct line from the vent. Harmful emissions will be dispersed by air movements, however, and an extensive area in lateral directions can be required. This European Standard shall be used together with EN 14797 and EN 14460. Venting neither prevents or extinguishes an explosion; it only limits the explosion overpressure. Flame and pressure effects outside the enclosure and flying debris are to be expected and suitable precautions shall be taken. Fires inside the enclosure can also occur. NOTE 2 If burning continues inside the vented vessel after the explosion, it can cause damage to the vessel, even though it has been protected from damage caused by overpressure. The increase of the length-to-diameter ratio of an enclosure results in an increase of the rate of flame propagation. This is taken into account in the formula for vent sizing (see Clause 5). Enclosures in this European Standard are limited to L/D ≤ 20. In a system consisting of connected enclosures, a dust explosion ignited in one enclosure can propagate through the connection, generating increased turbulence, perhaps causing some pre-compression and then act as a large ignition source in a connected enclosure. This combination of effects can enhance the violence of the secondary explosion. The venting requirements of the system thus need to be increased, or the enclosures isolated (see 5.4). Internal dust explosions can endanger buildings or parts of buildings and explosion venting can be applied to protect the integrity of the building. A separate method for calculating the venting requirements for buildings is given in Annex D. The effects of internal or external obstructions on venting effectiveness shall be taken into account. Recoil forces shall be taken into account when considering the location and distribution of the vent area. Explosion venting devices shall be positioned so that the effectiveness of the venting process is not impeded. Positioning shall be such that personnel and the nearby plant will not be at risk from the venting action. If the enclosure is small and relatively symmetrical, one large vent can be as effective as several small vents of equal combined area. For...