BS EN 1794-2:2011 BSI Standards Publication Road traffic noise reducing devices — Non-acoustic performance Part 2: General safety and environmental requirements BS EN 1794-2:2011 BRITISH STANDARD National foreword This British Standard is the UK implementation of EN 1794-2:2011 It supersedes BS EN 1794-2:2003 which is withdrawn The UK participation in its preparation was entrusted to Technical Committee B/509/6, Fences for the attenuation of noise A list of organizations represented on this committee can be obtained on request to its secretary This publication does not purport to include all the necessary provisions of a contract Users are responsible for its correct application © BSI 2011 ISBN 978 580 68335 ICS 93.080.30 Compliance with a British Standard cannot confer immunity from legal obligations This British Standard was published under the authority of the Standards Policy and Strategy Committee on 28 February 2011 Amendments issued since publication Date Text affected BS EN 1794-2:2011 EN 1794-2 EUROPEAN STANDARD NORME EUROPÉENNE EUROPÄISCHE NORM January 2011 ICS 93.080.30 Supersedes EN 1794-2:2003 English Version Road traffic noise reducing devices - Non-acoustic performance - Part 2: General safety and environmental requirements Dispositifs de réduction du bruit du trafic routier Performances non acoustiques - Partie 2: Exigences générales pour la sécurité et l'environnement Lärmschutzeinrichtungen an Straßen - Nichtakustische Eigenschaften - Teil 2: Allgemeine Sicherheits- und Umweltanforderungen This European Standard was approved by CEN on 10 December 2010 CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN member This European Standard exists in three official versions (English, French, German) A version in any other language made by translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management Centre has the same status as the official versions CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, 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 STANDARDIZATION COMITÉ EUROPÉEN DE NORMALISATION EUROPÄISCHES KOMITEE FÜR NORMUNG Management Centre: Avenue Marnix 17, B-1000 Brussels © 2011 CEN All rights of exploitation in any form and by any means reserved worldwide for CEN national Members Ref No EN 1794-2:2011: E BS EN 1794-2:2011 EN 1794-2:2011 (E) Contents page Foreword 3 Introduction 4 1 Scope 5 2 Normative references 5 3 3.1 3.2 Terms, definitions and symbols 5 Terms and definitions 5 Symbols 5 4 4.1 4.2 4.3 4.4 4.5 4.6 Requirements 6 Resistance to brush fire 6 Secondary safety (falling debris) 6 Environmental protection 6 Means of escape in emergency 6 Reflection of light 6 Transparency 7 5 Test report 7 Annex A (normative) Resistance to brushwood fire 8 Annex B (normative) Secondary safety: danger of falling debris 10 Annex C (normative) Environmental protection 14 Annex D (normative) Means of escape in emergency 15 Annex E (normative) Light reflection 16 Annex F (informative) Transparency 18 Bibliography 26 BS EN 1794-2:2011 EN 1794-2:2011 (E) Foreword This document (EN 1794-2:2011) has been prepared by Technical Committee CEN /TC 226 "Road equipment", the secretariat of which is held by AFNOR 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 July 2011, and conflicting national standards shall be withdrawn at the latest by July 2011 Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights CEN [and/or CENELEC] shall not be held responsible for identifying any or all such patent rights This document supersedes EN 1794-2:2003 This European standard consists of the following parts under the general title "Road traffic noise reducing devices — Non-acoustic performance": Part 1: Mechanical performance and stability requirements Part 2: General safety and environmental requirements The main changes compared to the previous edition are: a) the classification in Table B.1; b) the Annex E with introduction of a classification of products; c) the Annex F completely revised According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria, Croatia, 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 BS EN 1794-2:2011 EN 1794-2:2011 (E) Introduction While performing their primary function, road traffic noise reducing devices should not pose hazards to road users or other people in the vicinity or to the environment at large Noise reducing devices should not assist the spread of fire from adjacent verges or nearby land Fire resistance in accordance with particular standards can in addition be required to minimise risk to adjacent premises, or to road users in confined corridors Noise reducing devices should not reflect light in such a way as to prejudice road safety They should be made from materials which not emit noxious fumes or leachates as the result of natural or industrial processes, or as the result of fire Noise reducing devices should allow a means of escape by road users and access by operatives in the event of an emergency Noise reducing devices are not in general expected to resist the impact of vehicles, but designers can need information about the consequences of such impact load to establish the requirements for protection of road users and passers by BS EN 1794-2:2011 EN 1794-2:2011 (E) Scope This European Standard specifies minimum requirements and other criteria for assessing the general safety and environmental performance of road traffic noise reducing devices under typical roadside conditions Requirements for more onerous conditions are a matter for consideration by the designer Appropriate test methods are provided where these are necessary, but for some aspects a declaration of material characteristics may be required for the information of designers The treatment of each topic is covered separately in Annexes A to F Normative references The following referenced documents are indispensable for the application of this document For dated references, only the edition cited applies For undated references, the latest edition of the referenced document (including any amendments) applies EN 1794-1:2011, Road traffic noise reducing devices — Non-acoustic performance — Part 1: Mechanical performance and stability requirements EN ISO 2813, Paints and varnishes — Determination of specular gloss of non-metallic paint films at 20°, 60° and 85° (ISO 2813:1994, including Technical Corrigendum 1:1997) 3.1 Terms, definitions and symbols Terms and definitions For the purposes of this document, the following terms and definitions apply 3.1.1 noise barrier noise reducing device which obstructs the direct transmission of airborne sound emanating from road traffic 3.1.2 cladding noise reducing device which is attached to a wall or other structure to reduce the amount of sound reflected 3.1.3 cover noise reducing device which either spans or overhangs the highway 3.1.4 structural element element whose primary function is to support or hold in place acoustic elements 3.1.5 acoustic element element whose primary function is to provide the acoustic performance of the device 3.2 Symbols φm angle at which reflections from the surface of the transparent material obscure the view through the material, in degrees; φ0 angle between the visual axis and the normal to the noise reducing device (see Figure F.2), in degrees; αn angle of transparency (see Figure F.2), in degrees; BS EN 1794-2:2011 EN 1794-2:2011 (E) ßn angle of opacity (see Figure F.2), in degrees; KA visual acuity factor (see Figure F.3), in degrees; LT light transmission index (as determined in accordance with EN 410 or EN 2155-5), in percent; SO area of opaque features within transparent elements, in square millimetres; ST total area of transparent elements, including horizontal features, in square millimetres; T transparency, in percent; Tr transparency looking right, in percent; Tl transparency looking left, in percent; TD dynamic transparency, in percent; TS static transparency, in percent Requirements 4.1 Resistance to brush fire The noise reducing device shall be classified in accordance with Annex A NOTE This European Standard permits specifying authorities to indicate that there is no requirement for resistance to brushwood fire 4.2 Secondary safety (falling debris) When secondary safety has to be assessed, this shall be done in accordance with Annex B NOTE safety 4.3 This European Standard permits specifying authorities to indicate that there is no requirement for secondary Environmental protection The constituent materials and their breakdown products shall be identified in accordance with Annex C 4.4 Means of escape in emergency The acoustic and mechanical performances of doors or other means of escape shall be assessed in accordance with Annex D NOTE This European Standard permits specifying authorities to indicate that there is no requirement for means of escape in emergency 4.5 Reflection of light The results of a standard test of reflectivity shall be quoted in accordance with Annex E NOTE This European Standard permits specifying authorities to indicate that there is no requirement for light reflection BS EN 1794-2:2011 EN 1794-2:2011 (E) 4.6 Transparency The results of a standard test of transparency should be quoted in accordance with Annex F NOTE 5.1 This European Standard permits specifying authorities to indicate that there is no requirement for transparency Test report Every test report on aspects of performance shall include the following information: a) number and year of this European Standard, i.e EN 1794-2:2011; b) full description of the element or system tested, including manufacturer(s), part numbers, place and date of origin; c) description of the method of sampling, if parts of manufactured elements are evaluated by testing; d) place and date of assessment, and the name of the assessor; e) sufficient description of any tests carried out, any results measured and the conclusions drawn about the product together with any illustrations or photographs, all as specified in the appropriate annex 5.2 A summary report shall be produced, identifying the aspects of performance for which detailed reports are available and the level of performance assessed, where appropriate BS EN 1794-2:2011 EN 1794-2:2011 (E) Annex A (normative) Resistance to brushwood fire A.1 General A noise reducing device can be exposed to fire arising from dry vegetation or other material in close proximity More severe fires from spilt fuel can arise as the result of traffic accidents Where a noise reducing device is in close proximity to property it can also be necessary to consider the need to ensure that fire is not spread from the highway Where flammable systems are used, it is recommended that firebreaks of fire-resistant materials or other design are incorporated into the noise reducing device in order to prevent the propagation of fire This annex is not applicable to such fire resistant material This annex describes a test for a representative panel of a vertical noise barrier under normal exposure to brushwood fires at the roadside It does not provide information on the results of exposure to more severe conditions e.g ignition by burning spilt fuel The test should not be used to provide information on the fire safety of claddings used for tunnels or partial covers over the highway A.2 Requirements The noise reducing device, after being tested by the method given in A.3, shall be classified as follows: class 1: if the panel has been damaged to a greater extent than as defined for classes and 3; class 2: if the damaged area above either source is less than 0,06 m2 and extends to no more than 200 mm above the base of the panel, and the panel has not been burnt through to the other side; class 3: if there is no damage other than discoloration A.3 Fire test A.3.1 Acoustic elements of at least m long by 1,5 m high shall be tested by exposure to localised sources of fire at its base next to the front and rear faces independently Panels shall be free of absorbed water before testing; in the case of timber components, the moisture content shall be reduced to 18 % by an approved drying method The mass and dimensions of the panel to be tested shall be measured and the panel shall be photographed An identical panel shall be examined to determine its construction; the dimensions of its elements, including wall thickness of hollow sections, shall be measured and noted on a sketch at 1:20 scale A.3.2 Testing shall be carried out in an enclosed fireproof and draught-free chamber having a volume of at least 150 m3 Fume extraction devices may be installed in or near the ceiling, but shall be prevented from fanning any flames during the test BS EN 1794-2:2011 EN 1794-2:2011 (E) Annex C (normative) Environmental protection C.1 General Specifiers should be aware of any components of noise reducing devices which might in time either have adverse effects on the environment, or on the other hand could be recycled into similar or other products There is, consequently, a need for suppliers to identify clearly the constituent materials, so that their breakdown products under natural exposure or if subjected to fire can be identified The extent to which they have been or can be recycled also provides helpful information to specifiers C.2 Requirements C.2.1 All materials used in the barrier system shall be declared, using chemical rather than proprietary names to describe synthetic materials C.2.2 Any physical or chemical conditions which would cause potentially toxic constituents to be released into the environment shall be declared C.2.3 If some of these materials are wholly or in part recycled, the percentage of such constituents shall be stated C.2.4 Beneficial re-use of the barrier materials may be indicated, but any limitations on reprocessing conditions shall be noted 14 BS EN 1794-2:2011 EN 1794-2:2011 (E) Annex D (normative) Means of escape in emergency D.1 General Noise barriers shall effectively restrict access to the adjacent land, either within the highway or otherwise This may be acceptable where the barrier also forms the highway boundary, but direct access may be required under certain circumstances, for example: a) for maintenance of both barrier and verge; b) for emergency services attending an accident; c) as a means of escape from the vicinity of an accident for motorists The requirements for access for maintenance and other means of access for emergency services have to be determined for each length of barrier; such accesses can also serve as means of escape Where these are far apart, it can be desirable to provide additional means of escape from the highway D.2 Requirements D.2.1 In general, any access shall have minimum dimensions as follows: height: 2,1 m (or full height of the barrier if lower); width: 0,9 m D.2.2 Access shall be provided with means to ensure that the overall effectiveness of the barrier is maintained (see note of D.2.5) D.2.3 Doors shall be fitted with a self-closing mechanism and seals to prevent excessive leakage of sound through gaps All hinges, closing mechanisms and locks shall be designed for minimum maintenance and to remain operational in adverse weather conditions D.2.4 Where access to the highway from adjacent land is not restricted by other means, doors shall only be capable of being opened from the side remote from the traffic by key or special tool Doors intended for use as a means of escape should open away from the traffic and be fitted with panic bolts and latches D.2.5 The location of means of escape shall be clearly indicated by signs NOTE Account should be taken of special needs where access for vehicles can be required NOTE Acoustic integrity may be achieved by: a) stepping sections of barrier out of line, with sufficient overlap or other means to prevent sound escaping through the gap; b) providing doors set into the line of the barrier and constructed to an appropriate acoustic specification NOTE If access onto the road from the far side of the barrier is restricted, a notice should be placed on the traffic side warning that return can be prevented Provision should be made for safe exit under adverse conditions, especially if the road is raised above the level of the surrounding land 15 BS EN 1794-2:2011 EN 1794-2:2011 (E) Annex E (normative) Light reflection E.1 General Light is reflected from any flat surface The amount of reflection depends on the angle of incidence At large angles of incidence, reflections of the sun, or headlights at night, can be strong enough to confuse or dazzle drivers and also affect road safety Problems are likely to be specific to the interaction of products and site conditions This annex provides a classification system for light reflection to authorities, engineers and designers, in order to better define and assess the level of possible risks to drivers E.2 Requirements E.2.1 General Values of reflectivity measured in accordance with the test method described in E.3 shall be provided together with the resulting classification according to the table in E.2.2 E.2.2 Classification Four classes are considered (see Table E.1) The highest gloss value out of the three obtained at the three angles of incidence of 20°, 60° and 85° shall determine the resulting class Table E.1 — Classification Classification Gloss value Class Not tested Class Gloss higher than 80 Class Gloss from 40 to 80 (included) Class Gloss lower than 40 E.3 Test method E.3.1 The test apparatus described in EN ISO 2813 requires a flat surface of sufficient area to allow it to stand in several different positions E.3.2 A flat sample of the surface finish at least 150 mm by 300 mm shall be provided NOTE This can be defined on the face of a full size panel, or part of such, or a specially prepared flat test piece of the same material with the surface finish applied in the same way as on a non-flat product 16 BS EN 1794-2:2011 EN 1794-2:2011 (E) E.3.3 The apparatus shall be used in accordance with EN ISO 2813; 10 measurements of reflectivity at three angles of incidence (20°, 60° and 85°) shall be taken with different positions of the apparatus chosen at random NOTE The following precautions shall be adopted with transparent materials (light transmission higher than 10 %): a) application of a black opaque scotch all around the edges of specimens if the cutting surface is bright; b) adoption of an environmental light, natural or artificial, at a normal (not intense) level of illuminance during measurements; c) supporting of the test specimens supported on a black opaque plane surface E.4 Test report E.4.1 The test sample shall be described, in particular indicating whether it was part of a panel as used or a specially prepared test piece having the same surface coating treatment The resulting values of gloss (mean and standard deviation) at each angle of incidence (20°, 60° and 85°) shall be listed in the test report E.4.2 E.4.3 The test report shall report the classification according to E.2.2 17 BS EN 1794-2:2011 EN 1794-2:2011 (E) Annex F (informative) Transparency F.1 General This annex is intended to enable designers to establish the effective transparency of noise reducing devices A harmonised method of assessment is provided in order that different products and arrangements may be compared objectively The effective transparency has to be defined for a person viewing it at a certain angle, taking into account the variation in the visual acuity of the eye and loss of transmitted light at oblique angles As a noise reducing device is generally much longer than its height, only the variation of transparency in the horizontal plane is considered Two aspects of transparency have to be considered separately: a) transparency for people living behind the noise reducing device (static transparency); b) transparency for road users (dynamic transparency) Static transparency is important for people who are protected by a noise reducing device As they look along it, their view becomes more restricted by opaque elements Dynamic transparency affects the view for road users of the scene behind a noise reducing device and may be important for traffic safety, for example where drivers need an advance view of traffic merging from behind it The driver will often only be able to view the scene through a noise reducing device at an oblique angle, or grazing incidence The method for assessing overall effective transparency allows for the relative transparency of different materials and for losses associated with oblique views through the transparent elements as well as opaque elements in the barrier, such as posts, stripes (to protect flying birds) etc., which reduce the overall impression of transparency The effects of surface treatments and soiling of transparent elements are not included It is recommended that transparent noise reducing devices should be installed in such a way that soiling due to traffic is minimized in order to avoid the need for frequent cleaning F.2 Definition of transparency F.2.1 The transparency of the elements LT is defined for normal incidence, measured for a sample of the material with thickness t LT’ may be calculated for a different material thickness t’ using the relationship t' ( 1+ µ2 100 k LT t LT ' = where k = 2µ k 100 ) in terms of the refractive index µ (F.1) (The refractive index of transparent materials used in noise reducing devices may be taken as approximately 1,5 for this purpose) F.2.2 The effective transparency of a noise reducing device is affected by the degree to which the view is in peripheral vision The acuity of the eye at different angles is given in Figure F.1 Effective transparency is defined from the viewpoint of an observer at P looking towards a distant point as shown in Figure F.2 The visual axis intersects the barrier at point O The coordinates of P relative to the barrier, with origin at the point of normal incidence are (-D,-L) 18 BS EN 1794-2:2011 EN 1794-2:2011 (E) The effective transparency T comprises the sum of effective transparency to the left and the right of the normal But in certain cases, the contribution of one or other side may be negligible n (S − S ) T= T O × ST ∑[L (θ ).α K i=1 ∑[ α K γi = δi = i i i A φ − γi ] (F.2) n i=1 where T A φ − γi + βi KA φ − δi ] φ = tan-1(L/D) and α0 + αi α0 + βi i −1 + ∑ [α j + β j ] (F.3) j=1 i + ∑ [ α j + β j−1 ] (F.4) j=1 The effect of visual acuity at different angles is taken into account by KA , which can be calculated from the equation given in Figure F.1, noting that for angles less than 0,1 radian, KA = For a single layer transparent material having a refractive index between 1,5, LT(φ(i)) and normal transparency between 70 % and 90 %, KA may be calculated from LT t θ where t θ is a function of the angle of incidence θ (in radians, from the normal to the surface of the transparent element) In the case of transparent elements in the plane of the noise reducing device, φ(i) = γ(i), as shown in Figure F.2 Where the transparent elements are set at an angle η, as shown in Figure F.3, φ(i) = γ (i) + η t θ = 1+ a(LT) θ + b(LT) θ + c(LT) θ + d(LT) θ + e(LT) θ (F.5) in which the coefficients are quadratic functions of LT/100, defined in Table F.1 Table F.1 — Coefficients a b c d e Const 0,614 2,809 -6,115 4,474 -1,109 (LT/100) -0,722 -12,881 27,013 -20,865 5,285 0,0 11,374 -23,883 19,266 -5,208 (LT/100) In case where transparency is provided by gaps between louvres as shown in Figure F.3, LT = for all angles of incidence F.3 Static transparency Static transparency is calculated for the visual axis at normal incidence TS = T r = T I (F.6) where T r and T I are calculated from Equation (F.1) for views to the left or right of the normal PN 19 BS EN 1794-2:2011 EN 1794-2:2011 (E) F.4 Dynamic transparency Dynamic transparency is calculated in a similar manner from Equation (F.2), but where the driver is looking ahead, only one component of transparency, to the left or right needs to be taken into account, as shown in Figure F.3 This figure also illustrates that where opaque panels are at an angle ε to the plane of the device, they may overlap and still provide dynamic transparency If the panels of transparent material are set at an angle η to the plane of the noise reducing device, this improves light transmission at oblique angles of incidence TD = T I (barrier on the right of the vehicle) TD = Tr (barrier on the left of the vehicle) F.5 Requirements F.5.1 The basic parameter LT of the transparent material shall be measured in accordance with the appropriate harmonized standard The effect of using a different thickness of transparent material from that tested may be calculated by the adjustment given in F.2.1 The effect of oblique view through the transparent material shall be taken into account using Equation (F.5) and the effect of visual acuity using the equation in Figure F.1, as described in F.2.3 F.5.2 Static and dynamic transparency shall be calculated for a given position of the observer on the normal through the midline of a transparent panel, for a specified direction of the visual axis PO The following positions and directions are recommended for the purposes of comparison: Static transparency: distance D = 10 × L, PO normal and at 45° to the plane of the device Dynamic transparency: distance D = L, PO at 15° and 30° to the plane of the device 20 BS EN 1794-2:2011 EN 1794-2:2011 (E) Key A visual axis B curve fitted to Ka C KA = 0,358 8x – 1,780 8x + 2,793 6x – 0,727 3x – 1,772 9x + 1,184 4, for angles of less than 0,1 rad, KA = D angle radians Figure F.1 — Variation of visual acuity over field of view 21 BS EN 1794-2:2011 EN 1794-2:2011 (E) Key visual axis Figure F.2 — Calculation of transparency to the left of the normal For uniform panel length s Viewed from a distance D = n.s Proportion of span opaque = p th Angle to normal through centre of r panel = γr th Angle to normal through centre of r support = δr D = n.s = r.s ( r + 0.5).s = tan(γ r ) tan(δ r ) th Angular view of r panel = αr + βr (F.7) where 2r − (1− p) 2r + (1− p) − tan−1 2n 2n 2r + (1+ p) 2r − (1− p) − tan−1 βr = tan−1 2n 2n αr = tan−1 (F.8) -1 th If the visual axis is at φ to the normal, where φ = tan (L/D), visual acuity looking through r panel is KA|φ - γr| (F.9) th effective transparency of the r panel is KA|φ - γr| LT(γr) αr 22 (F.10) BS EN 1794-2:2011 EN 1794-2:2011 (E) Key direction of motion – visual axis merging traffic Figure F.3 — Dynamic transparency for merging traffic F.6 Uncertainty in calculation of effective transparency The combined uncertainty of a calculated function can be estimated by taking the square root of the weighted sum of the squares of the uncertainties in the measured parameters: 23 BS EN 1794-2:2011 EN 1794-2:2011 (E) ∑ (w u ) uT = i i (F.11) i where the weights wi are the partial derivatives of the calculated function with respect to the relevant variable We have two functions to consider: Normal transparency L T ’, if thickness t’ of the product is different from that of the sample for which L T was measured: t' 100 k LT t LT ' = k 100 k= where (1 + µ ) (F.12) 2µ The overall transparency of a noise reducing device with transparent panels and opaque supports is given by: n (S − S ) T= T O × ST ∑[L (θ ).α K i =1 T i =1 i i A φ − γi ] (F.13) n ∑[ α K i A φ − γi + βi KA φ − δi ] Ignoring the influence of approximations in the geometric terms which are used in the calculation, the potential sources of error occur in measurements of ST, SO, LT, t, µ The partial derivatives are as follows: In F.13: ∂L'T ∂L'T L'T t ' µ − t '−t = L'T ⋅ ⋅ and = ⋅ µ kt ∂µ ∂LT LT t ∂L'T L'T k L = ⋅ ln T ; t ∂t ' 100 In F.12: S ∂T T = ⋅ o and ∂S T ( S T − S o ) S T ∂T −T = ; ∂S o ( S T − S o ) (F.14) ∂T T = ∂LT LT (F.15) The square of the uncertainty in T is obtained by summing variances of contributing terms: 2 uT ∂T ∂T ∂T =u + u LT ⋅ + uSo ∂LT ∂S T ∂S o 2 ST (F.16) and if LT is determined indirectly as in Equation (F.1), additional terms will expand the third term above: 2 ' ' ∂ L' ∂L ∂L + u t T + u µ T + u LT T ∂t ' ∂µ ∂LT 2 ∂T ⋅ ∂LT (F.17) Substituting and simplifying 2 2 u LT t '.L'T uT S o uST uSo ⋅ + + = ⋅ T S T − S o S T S o LT t ⋅ LT ( ) u + µ L T + t ⋅ ln t 200 24 uµ + µ µ − t '−t L'T ⋅ ⋅ ⋅ 2 1 + µ t LT 2 (F.18) BS EN 1794-2:2011 EN 1794-2:2011 (E) Assuming errors in dimensions ST and So will be similar, for example of order mm, we can use typical values for other parameters in order to estimate uncertainty in the overall transparency So take ST and So to be m and 200 mm respectively Assuming typical values LT’ ≈ LT = 90 % and µ = 1,5 allows further simplification for estimating the overall uncertainty of the calculation: 2 2 2 2 u LT t ' u t 2,925 × 90 uµ 1,25 t '−t uT [ ] 1,01 ln ⋅ + ⋅ + ⋅ ⋅ + ⋅ = (F.19) 1800 LT t t 200 1.5 3,25 t T The range of optical parameters is as follows: LT (for clear materials): 87 % to 93 %; µ: 1,49 to 1,52 Taking the range of optical parameters as being standard deviations on either side of the mean value (99 % confidence interval), the uncertainty associated with these parameters is: uLT = 0,01; uµ = 0,005 so u LT LT = 0,011 and uµ µ = 0,033 The estimated uncertainty in measuring t is %, i.e ut = 0,05 t And so for t’ = 2t; uncertainty in overall transparency uT = 0,03.T , i.e % (F.20) 25 BS EN 1794-2:2011 EN 1794-2:2011 (E) Bibliography [1] EN 410, Glass in building — Determination of luminous and solar characteristics of glazing [2] EN 1793-1, Road traffic noise reducing devices — Test method for determining the acoustic performance — Part 1: Intrinsic characteristics of sound absorption [3] EN 1793-2, Road traffic noise reducing devices — Test method for determining the acoustic performance — Part 2: Intrinsic characteristics of airborne sound insulation [4] EN 2155-5, Aerospace series — Test methods for transparent materials for aircraft glazing — Part 5: Determination of visible light transmission 26 This page deliberately left blank NO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAW British Standards Institution (BSI) BSI is the national body responsible for preparing British Standards and other standards-related publications, information and services BSI is incorporated by Royal Charter British Standards and other standardization products are published by BSI Standards Limited About us Revisions We bring together business, industry, government, consumers, innovators and others to shape their combined experience and expertise into standards -based solutions Our British Standards and other publications are updated by amendment or revision The knowledge embodied in our standards has been carefully assembled in a dependable format and refined through our open consultation process Organizations of all sizes and across all sectors choose standards to help them achieve their goals Information on 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