SIST EN 14491:2006
(Main)Dust explosion venting protective systems
Dust explosion venting protective systems
This European Standard specifies the basic requirements of design for the selection of a dust explosion venting protective system. The standard is one of a series including prEN 14797 Explosion venting device and prEN 14460 Explosion resistant equipment. The three standards together represent the concept of dust explosion venting. To avoid transfer of explosions to other communicating equipment one should also consider applying prEN 15089 Explosion isolation systems.
This European Standard covers:
- vent sizing to protect an enclosure against the internal pressure effects of a dust explosion;
- flame and pressure effects outside the enclosure;
- recoil forces;
- influence of vent ducts.
This European Standard is not intended to provide design and application rules against effects generated by detonation reactions or runaway exothermic reactions. This European Standard does not cover fire risks arising from either materials processed, used or released by the equipment or materials that make up equipment and buildings. This European Standard does not cover the design, construction, testing and certification of explosion venting devices that are used to achieve explosion venting).
Schutzsysteme zur Druckentlastung von Staubexplosionen
Diese Europäischen Norm legt die grundlegenden Anforderungen an die konstruktive Gestaltung und für die Auswahl eines Systems zur Druckentlastung von Staubexplosionen fest.
Diese Norm ist aus der Reihe, zu der die Entwürfe prEN 14460 Explosionsfeste Einrichtungen und prEN 14797 Einrichtungen zur Explosionsdruckentlastung gehören. Die drei Normen zusammen bilden das Konzept der Druckentlastung von Staubexplosionen. Zur Vermeidung der Übertragung von Explosionen auf andere in Verbindung stehende Einrichtungen sollte man auch den Entwurf prEN 15089 Explosionsentkopplungs-Systeme beachten und anwenden.
Diese Europäische Norm deckt Folgendes ab:
- Größe der Entlastungsöffnung, um gegen die inneren Druckauswirkungen einer Staubexplosion zu schützen;
- Auswirkungen von Flammen und von Druck außerhalb des Behälters;
- Rückstoßkräfte;
- Einfluss der Abblaskanäle.
Diese Europäische Norm gibt keine Gestaltungs- und Anwendungsvorschriften, durch die Auswirkungen von Detonationsreaktionen oder unkontrollierten exothermen Reaktionen vermieden werden können. Brandgefahren, die entweder von den verarbeiteten Werkstoffen, von den vom Gerät benutzten oder freigesetzten Materialien ausgehen oder durch Materialien, aus denen Geräte und Gebäude bestehen, hervorgerufen werden, werden in dieser Europäischen Norm nicht behandelt. Konstruktive Gestaltung, Fertigung, Prüfung und Zertifizierung von Einrichtungen zur Druckentlastung bei Explosionen, die für die Druckentlastung im Fall von Explosionen verwendet werden, werden in dieser Europäischen Norm ebenfalls nicht behandelt ).
Systemes de protection par évent contre les explosions de poussieres
La présente Norme européenne décrit les exigences fondamentales se rapportant a la conception et au choix d’un systeme de protection par évent contre les explosions de poussieres. Cette norme fait partie d’une série a laquelle appartiennent également le prEN 14797 Dispositifs de décharge d'explosion et le prEN 14460 Appareil résistant a l'explosion. Toutes ensemble ces trois normes illustrent le concept de protection par évent contre les explosions. Pour éviter le transfert de l’explosion dans d’autres équipements communicants, il convient également de tenir compte du prEN 15089 Systemes d'isolement d'une explosion.
La présente Norme européenne traite des aspects suivants :
- le dimensionnement des évents pour la protection contre les effets de la pression interne d’une explosion de poussieres ;
- les effets des flammes et de la pression a l’extérieur de l’enceinte ;
- les forces de recul ;
- l’influence des canalisations de décharge.
La présente norme n’est pas destinée a fournir des regles de conception et d’application contre les effets engendrés par les réactions de détonation ou l’emballement des réactions exothermiques. Elle ne traite pas des risques d’incendie provenant soit des matériaux traités, utilisés ou émis par les appareils, soit des matériaux qui constituent les appareils et les bâtiments. Elle ne traite pas non plus de la conception, de la construction, des essais et la de certification des dispositifs de décharge d’explosion ).
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2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Dust explosion venting protective systemsSystemes de protection par évent contre les explosions de poussieresSchutzsysteme zur Druckentlastung von StaubexplosionenTa slovenski standard je istoveten z:EN 14491:2006SIST EN 14491:2006en13.230ICS:SLOVENSKI
STANDARDSIST EN 14491:200601-september-2006
EUROPEAN STANDARDNORME EUROPÉENNEEUROPÄISCHE NORMEN 14491March 2006ICS 13.230 English VersionDust explosion venting protective systemsSystèmes de protection par évent contre les explosions depoussièresSchutzsysteme zur Druckentlastung von StaubexplosionenThis European Standard was approved by CEN on 13 February 2006.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 Central Secretariat 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 Central Secretariat has the same status as the officialversions.CEN members are the national standards bodies of Austria, Belgium, 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© 2006 CENAll rights of exploitation in any form and by any means reservedworldwide for CEN national Members.Ref. No. EN 14491:2006: E
EN 14491:2006 (E) 2 Contents Page Foreword.4 1 Scope.5 2 Normative references.5 3 Terms and definitions.5 4 Venting of enclosures.7 5 Sizing of vent areas.8 5.1 General.8 5.2 Venting of isolated enclosures.8 5.3 Special dust cloud conditions.10 5.4 Protection of pipelines and interconnected enclosures.10 5.5 Protection of buildings.11 5.5.1 General.11 5.5.2 Calculating the vent area.12 5.5.3 Calculation of internal surface area.12 5.6 Influences of vent ducts.13 5.7 Hybrid mixtures.15 6 Positioning of vents.15 7 Supplementary design considerations.15 7.1 General.15 7.2 Explosion effects external to the vent.16 7.2.1 General.16 7.2.2 Flame effects.16 7.2.3 Pressure effects.17 7.2.4 Deflectors.18 7.2.5 Effects of flameless explosion venting devices.19 7.3 Deformation of the vented enclosure.19 7.3.1 Recoil forces.19 7.3.2 Vacuum breakers.20 8 Information for use.21 8.1 Marking.21 8.2 Accompanying documents.21 Annex A (informative)
Estimating the L/D ratio when calculating vent areas for elongated enclosures.22 Annex ZA (informative)
Relationship between this European Standard and the Essential Requirements of EU Directive 94/9/EC.27 Bibliography.29 Figures Figure 1 — Vent duct design to which Equations (10) to (11) apply.14 Figure 2 — Vent duct designs to which Equations (10) to (11) do not apply.14 Figure 3 — Design of a blast deflector plate.19 Figure A.1 — Cylindrical enclosure with a vent in the roof.23
EN 14491:2006 (E) 3 Figure A.2 — Cylindrical enclosure with a vent in the side.23 Figure A.3 — Cylindrical enclosure with a hopper and vented in the roof.24 Figure A.4 — Cylindrical enclosure with a hopper and vented at the side.24 Figure A.5 — Rectangular enclosure with a hopper and vented at the side.25 Figure A.6 — Rectangular enclosure with a hopper and vented at the side, close to the hopper.25 Figure A.7 — Calculation of a volume of a rectangular hopper.26 Tables Table ZA.1 — Correspondence between this European Standard and Directive 94/9/EC.27
EN 14491:2006 (E) 4 Foreword This European Standard (EN 14491:2006) 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 September 2006, and conflicting national standards shall be withdrawn at the latest by September 2006. This European Standard 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(s) 94/9/EC. For relationship with EU Directive(s), see informative Annex ZA, which is an integral part of this European Standard. According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following countries are bound to implement this European Standard: Austria, Belgium, 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.
EN 14491:2006 (E) 5 1 Scope This European Standard specifies the basic requirements of design for the selection of a dust explosion venting protective system. The standard is one of a series including prEN 14797 Explosion venting devices and prEN 14460 Explosion resistant equipment. The three standards together represent the concept of dust explosion venting. To avoid transfer of explosions to other communicating equipment one should also consider applying prEN 15089 Explosion Isolation Systems. This European Standard covers: vent sizing to protect an enclosure against the internal pressure effects of a dust explosion; flame and pressure effects outside the enclosure; recoil forces; influence of vent ducts. This European Standard is not intended to provide design and application rules against effects generated by detonation reactions or runaway exothermic reactions. This European Standard does not cover fire risks arising from either materials processed, used or released by the equipment or materials that make up equipment and buildings. This European Standard does not cover the design, construction, testing and certification of explosion venting devices that are used to achieve explosion venting1). 2 Normative references These following referenced documents are indispensable for the application of this European Standard. For dated references, only the edition cited applies. For undated references the latest edition of the referenced document (including any amendments) applies. EN 1127-1:1997, Explosive atmospheres — Explosion prevention and protection — Part 1: Basic concepts and methodology EN 13237:2003, 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 European Standard, the terms and definitions given in EN 1127-1:1997 and EN 13237:2003 and the following apply. 3.1 building enclosed, roofed space that contains a working environment that may include process plant, offices and personnel, either separately or together, but is not, in itself, an item of process plant 3.2 enclosure vessel that forms a distinct and identifiable part of a process plant and to which explosion protection by explosion venting can be applied as described in this European Standard
1) This is covered in the European Standard prEN 14797.
EN 14491:2006 (E) 6 3.3 design pressure p design strength of the vessel/enclosure (explosion resistance) 3.4 hybrid mixture mixture of flammable (combustible) substances with air in different physical states NOTE An example for hybrid mixtures is a mixture of methane, coal dust and air. [EN 1127-1:1997; 3.20] 3.5 Kst value parameter, specific to the dust, that characterises the explosibility of a dust and which is calculated according to the cubic law NOTE The KSt value is numerically equal to the value for the maximum rate of explosion pressure rise, (dp/dt)max, measured in the 1 m3 vessel under specified test conditions. 3.6 vent area A geometric vent area of vent NOTE It is the minimum cross-sectional flow area of the vent opening taking into consideration the possible reduction of the cross section, e.g. by back pressure supports, retaining devices and parts of the explosion venting device which remain after bursting or venting. 3.7 cross sectional area Ac area of cross section of rectangular enclosure normal to longest dimension of this enclosure 3.8 required vent area Av quotient of the geometric vent area A and the venting efficiency Ef for the venting device NOTE The required vent area is used in making up the vent area for explosion venting. 3.9 effective enclosure area Aeff ratio of the total free volume of an enclosure and its height 3.10 maximum explosure overpressure pmax maximum overpressure occurring in a closed vessel during the explosion of an explosive atmosphere and determined under specified test conditions [EN 1127-1:1997; 3.27]
EN 14491:2006 (E) 7 3.11 pipeline connection, which is at least 20 times longer than the diameter, carrying process material between two or more enclosures in a process plant and which cannot be explosion protected by the explosion venting methods for enclosures described in this European Standard 3.12 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 3.13 maximum reduced explosion overpressure pred, max maximum overpressure generated by an explosion of an explosive atmosphere in a vessel, protected by either explosion relief (venting) or explosion suppression 3.14 maximum rate of explosion pressure rise (dp/dt)max maximum value of the pressure rise per unit time during explosions of all explosive atmospheres in the explosion range of a combustible substance in a closed vessel determined under specified test conditions NOTE This parameter measured in a 1 m3 vessel is numerically identical with the parameter KSt, if the test vessel is 1 m3 in volume, but the unit of the latter is bar m s–1 whereas the unit of the (dp/dt)max is bar s–1. 3.15 maximum value of the peak overpressure pext external maximum value of the peak overpressure generated by vented dust explosion NOTE This maximum occurs at a distance RS from the vent opening. 3.16 static activation overpressure pstat overpressure that activates a rupture disk or an explosion door when a slow rate of pressure rise (≤ 0,1 bar min–1) is applied 4 Venting of enclosures Explosion venting is a protective measure for enclosures by which unacceptably high internal explosion overpressures are prevented. Weak areas in the walls of the enclosure open at an early stage of the explosion, burning and/or un-burnt material and combustion products are released and the overpressure inside the enclosure is reduced. The vent area is the most important factor in determining the value of pred, max, the maximum reduced explosion overpressure generated inside the enclosure by the vented explosion. Information required for calculation of the vent area includes the design pressure 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 of 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 the immediate environment. If there is no alternative to explosion venting an endangered area shall be specified. NOTE There is no direct guidance for estimating an endangered area for toxic or other harmful emissions, but the safe discharge area for flame calculated in 7.2 gives some indication of the area required in direct line from the vent.
EN 14491:2006 (E) 8 Harmful emissions will be dispersed by air movements, however, and an extensive area in lateral directions may be required. This European Standard shall be used together with prEN 14797 and prEN 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. 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 equation 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 acting as a large ignition source in a connected enclosure. This combination of effects can enhance the violence of the secondary explosion and 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 venting may be applied to protect the integrity of the building. A separate method for calculating the venting requirements is given in 5.5. 5 Sizing of vent areas 5.1 General Accurate sizing of vents is the most important aspect of vent design. The size of the vent depends on the explosion characteristics of the dust, the state of the dust cloud (concentration, turbulence and distribution), the geometry of the enclosure and the design of the venting device. The two principal explosion characteristics of the dust are the maximum overpressure pmax and the dust explosion constant KSt. These are measured by standard test procedures that establish representative conditions of fuel concentration and dust cloud homogeneity and turbulence considered to encompass those in the majority of practical applications. For cubical enclosures, pmax and KSt are essentially independent of enclosure volume. The volume of the enclosure and the length-to-diameter ratio L/D relevant to the shape of the enclosure and the position of the explosion vent are required for sizing vents. The design pressure of the enclosure pred, max is also required for vent sizing. All parts of the enclosure, e.g. valves, sight-glasses, man-holes and ducts, that are exposed to the explosion pressure shall be taken into account and the design pressure of the weakest part shall be taken as the design pressure for the enclosure. The two principal vent device parameters are the static activation overpressure pstat and the weight per unit area of the venting element. The maximum value of the tolerance range of the static activation overpressure shall be used when sizing vents. The weight per unit area of the venting element determines its venting effectiveness factor. 5.2 Venting of isolated enclosures The following equation shall apply to single enclosures where appropriate measures (explosion isolation) have been taken to prevent flame propagation between enclosures.
EN 14491:2006 (E) 9
For enclosures the following equations allow the calculation of the required vent area Av. The required vent area can, in practical applications, be divided into several smaller areas as long as the total area equals the required vent area: a) 0,1 bar overpressure ≤ pred, max < 1,5 bar overpressure ()D/LlogCBA×+=1in m2 (1) with ()[]753,05,0maxred,stat569,0maxred,Stmax51,027,010264,3VpppKpB××−×+××××=−−− (2) ()758,0log305,4maxred,+×−=pC fEAAv/=
(Ef: venting efficiency) (3) b) 1,5 bar overpressure ≤ pred, max ≤ 2,0 bar overpressure BA= fvE/AA=
(Ef: venting efficiency) (4) The equations are valid for: enclosures volume 0,1 m3 ≤ V ≤ 10 000 m3 ; static activation overpressure of the venting device 0,1 bar ≤ pstat ≤ 1 bar; for pstat < 0,1 bar, use pstat = 0,1 bar; maximum reduced explosion overpressure pstat ≤ pred, max ≤ 2 bar. It is recommended that pred, max shall at least be 0,12 bar; maximum explosion overpressure 5 bar ≤ pmax ≤ 10 bar for a dust specific parameter of 10 bar m s–1 ≤ KSt ≤ 300 bar m s–1; maximum explosion overpressure 5 bar ≤ pmax ≤ 12 bar for a dust specific parameter of 300 bar m s–1 < KSt ≤ 800 bar m s–1; atmospheric conditions conditions of the surrounding medium where the atmospheric pressure can vary between 80 kPa and 110 kPa, the temperature between – 20 °C and 60 °C (the variation of temperature being less then 0,5 °C/min), the relative humidity between 5 % volume fraction and 85 % volume fraction and oxygen content (20,9 ± 0,2) % volume fraction; length-to-diameter ratio 1 ≤ L/D ≤ 20 (Examples for calculating L/D are given in Annex A). If one or more of the above conditions are not fulfilled the applicability of the above equation shall be proven. A is the venting area that shall be fitted to the enclosure assuming the venting efficiency factor of the venting device is 1 and thus the effective venting area is equal to the physical venting area. Some venting devices have a venting efficiency factor less than 1, and the effective venting area is thus less than the geometric
EN 14491:2006 (E) 10 venting area. To compensate for the lower efficiency of the venting device the required venting area Av shall be larger than the geometric vent area A. 5.3 Special dust cloud conditions The equations in 5.2 are designed to calculate vent areas for most practical applications – an enclosure completely full of a turbulent dust cloud of optimum dust concentration. In some practical applications, however, the test procedures specified in accepted European Standards may overstate or understate the explosion intensity compared to the actual processing environment. In conditions of moderate and low turbulence, and in conditions where a non-homogeneous fuel-air mixture or low dust concentration is the norm, the procedure specified in accepted European Standards is likely to overstate the explosion hazard. In such circumstances a reduced vent area can be used but shall be based on either published or experimental data that has been obtained from representative explosion venting trials. In conditions of particularly severe turbulence (e.g. in enclosures with turbulence inducing obstructions) there is a possibility that the explosion intensity is understated. In some plants there can be conditions that may generate severe turbulence, and in these cases the equations in 5.2 can underestimate the necessary vent area. In such specific circumstances an increased vent area shall be based on either published or experimental data that has been obtained from representative explosion venting trials. 5.4 Protection of pipelines and interconnected enclosures The vent sizing methods in 5.2 are suitable for enclosures that are isolated and can be treated as single units. If an explosion can propagate from one enclosure to another through a connecting pipeline, increased turbulence, a relatively large flame jet and pressure piling effects may combine to give an explosion of increased violence. Interconnected enclosure systems shall normally be protected by isolating each separate enclosure so that an explosion in one protected enclosure is stopped from propagating into a second one. Isolation methods have been discussed in prEN 15089. The basis of safety for pipelines and interconnected enclosures rests on a combination of the strength of the pipeline, isolation of the explosion effect and explosion protection of the enclosures. If the explosion begins following an ignition in a protected enclosure and the maximum reduced explosion overpressure pred, max does not exceed 0,5 bar the distance along a straight pipeline, L, at which a specified overpressure pL will occur can be estimated from the equations: for KSt ≤ 100 bar m s–1 ()[]L1072,0e18,324pDL×−−××=, applicable to (L/D) ratios no greater than 100; (5) for 100 < KSt ≤ 200 bar m s–1 ()L640,1e99,8157,88pDL×−×−×=, applicable to (L/D) ratios no greater than 50; (6) for 200 < KSt ≤ 300 bar m s–1 ()L1484,0e42,6276,63pDL×−×−×=, applicable to (L/D) ratios no greater than 50. (7) where D is the pipeline diameter between 0,2 m to 0,6 m. No guidance is available for other pipeline diameters.
EN 14491:2006 (E) 11 Experimental data indicate that this guidance covers the range of flow velocities typical of pneumatic conveying systems. If conditions in pipelines connected to a protected enclosure where ignition occurs are such that the pressure in the pipeline will reach 10 bar, then PN10 construction shall be used. When the plant design is such that high pressures are not likely, then PN6 or PN3 pipeline construction can be used, depending on the pressures likely to arise. If the diameter of the pipeline is ≤ 0,5 m and KSt ≤ 100 bar m s–1 and the length-to-diameter ratio of the pipeline exceeds L/D = 20 at least 3 bar shock resistant construction shall be used. Additional venting of straight pipelines constructed as described above is not necessary. However, if pipelines have bends or obstructions, venting at or near to the bends or obstructions shall be applied. If enclosures are not isolated, interconnected systems require explosion protection either by containment (explosion resistant design for the maximum explosion pressure) or other means. For determination of the venting requirements of interconnected enclosures the Equations (1) to (4) shall not be used. In systems of interconnected enclosures where only one of the vessels can be vented: a) When the larger of the enclosures cannot be vented, then the entire system shall be designed for full containment, or, alternatively, the use of explosion suppression shall be considered. b) When the smaller of the enclosures cannot be vented, then it shall be designed for containment or, alternatively, explosion suppression shall be applied and the vent area of the larger vessel shall be based on either published or experimental data that has been obtained from representative explosion venting trials. c) When the enclosures are of equal size, and one enclosure cannot be vented, b) applies. When both enclosures can be vented the venting requirement shall be based on either published or experimental data that has been obtained from representative explosion venting trials. In case such information is not available, the following simple rules shall be applied when enclosure volumes are ≤ 20 m3: d) For KSt values of 150 bar m s–1 or less, dimensionless vent areas of greater than 0,25 will limit the maximum reduced explosion overpressure to 0,5 bar. e) For KSt values between 150 bar m s–1 and 250 bar m s–1, dimensionless vent areas of 0,4 will limit the maximum reduced explosion overpressure to 0,5 bar. The dimensionless vent area is defined as Av/V2/3 where Av is the vent area and V is the enclosure volume. The total vent area shall be divided between the enclosures so that the dimensionless vent area has the same value in each enclosure. When venting a system of interconnected enclosures, the venting devices shall be designed for a low static activation overpressure, pstat ≤ 0,1 bar. 5.5 Protection of buildings 5.5.1 General For buildings pred, max shall always exceed pstat by at least 0,02 bar. The vent area shall be distributed as symmetrically and as evenly as possible over the available surface. The course of an explosion in buildings will be affected by several parameters such as the shape of the building, the presence of equipment and structural elements, the possibility of propagation from room to room and the presence of flammable dust left to lie on surfaces such as window sills, pipework and floors etc. The dust explosion may be limited to a small part of the total volume. Pressure development will vary according to circumstances and a wide range of dust explosion loads can be expected. Vent areas on buildings shall be distributed uniformly over the wall and roof areas. In estimating pred, max care shall be taken to ensure that the weakest structural element, as well as any equipment or other devices that
EN 14491:2006 (E) 12 can be supported by structural elements, is identified. All structural elements and supports shall be considered. For example, floors and roofs are not usually designed to be loaded from beneath. However, a lightweight roof can be considered sacrificial, provided its movement can be tolerated and provided ice or snow does not hinder its movement. 5.5.2 Calculating the vent area The recommended venting equation for buildings is as follows: 5,0maxred,−××=pACAS (8) where A is the geometric vent area, in square-metres (m²); Av is the required vent area Av = A/Ef, in square-metres (m²); Ef is the venting efficiency; C is the venting equation constant: 0 < KSt ≤ 100:
C = 0,018 0,5 bar; 100 < KSt ≤ 200: C = 0,026 0,5 bar;
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