BS EN 14491:2012 pdf download

BS EN 14491:2012 pdf download.Dust explosion venting protective systems.
3.10
pipe
connection between two or more enclosures
Note 1 to entry: A pipe cannot be explosion protected by the explosion venting methods for enclosures described In this European Standard.
3.11
explosive atmosphere
mixture with air, under atmospheric conditions, of flammable (combustible) substances in the form of gases, vapours, mists or dusts, in which, after ignition has occurred, combustion spreads to the entire unburned mixture
3.12
maximum reduced explosion overpressure
Pr.d.Ina.
resulting maximum overpressure generated by an explosion of an explosive atmosphere in a vessel at optimum fuel concentration, after effective explosion venting or explosion suppression
3.13
maximum rate of explosion pressure rise (dpk),
maxwnum value 01 the pressure rise per unit time during explosions of all explosive atmospheres ii the explosion range of a combustible substance in a dosed vessel determined under specified test conditions
Note 1 to entry This parameter is numerically idenbcal with the parameter Ks,, W the test vessel is 1 m3 in volume, but the unit 01 the latter is bar-rn-s ‘whereas the unit of the (dp/dd,,.. is bar-s
Note 2 to entry; See EN 14034-2.
3.14
maximum external overpressure
external maximum value of the overpressure generated by vented dust explosion
3.15
static activation overpressure
differential pressure at which the retainmg element activates such that the venting element is able to open
(SOURCE: EN 14797:2006. 3.111
3.16
vacuum breaker
device which prevents damage to a vessel when the internal pressure falls below atmospheric pressure
4 Venting of enclosures
Explosion venting is a protective measure for enclosures by which unacceptably high internal explosion overpressures are prevented- Weak areas ii the walls of the enclosure open at an early stage of the explosion, burning aridiot- unbumt material and combustion products are released and the overpressure inside the enclosure is reduced. Information required for calculation of the vent area includes the explosion resistance of the enclosure, the explosion characteristics of the dust, the shape and size of the enclosure, the static activation overpressure and other characteristics of the vent closure, and the condition of the dust cloud inside the enclosure.
Explosion venting shall not be performed if unacceptable amounts at materials that are classified as poisonous, corrosive, irritant, carcinogenic. teratogenic or mutagenic can be released. Either the dust or the combustion products can present a hazard to lhe immediate environment, If there is no altemative to explosion venting, an endangered area shall be specified
NOTE 1 There Is no chrect guidance for estimating an endangered area for toxic or other hanWul emissions, but the safe discharge area for external flames catutated acoordeig to the fonnulae wi 6.2 gives some lnchcatlon 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 directons can be required.
This European Standard shall be used together with EN 14797 and EN 1446O
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 It burrwng continues rnside the vented vessel alter 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 lithe formula for vent sizing (see Clause 5). Enclosures ii this European Standard are limited to LID  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 extemal obstructions on venting effectiveness shall be taken into account. Recoil forces shall be taken into account when consldenng 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 large enclosures, the location of multiple vents to achieve uniform coverage of the enclosure surface to the greatest extent practicable Is recommended.
NOTE 3 In the formulae presented in this standard, 4 is important to use the correct wits, which are not always SI- units. The units are indicated for every parameter used in the hnits of app*cation, Where log is used in the meant.