BF Bulletin 010 / ESG-H a controlled and externally monitored building product to the highest safety standard

Transcription

1 ESG-H a controlled and externally monitored building product to the highest safety standard

2 ESG-H a controlled and externally monitored building product to the highest safety standard 1.0 Introduction: the idea and purpose of the guide In terms of German building inspection, three products must be distinguished in respect of toughened safety glass: thermally toughened safety glass (TSG), heat-soaked TSG according to EN and ESG-H (heat-soaked TSG according to the German Construction Products List). The delimitation between these products is in practice not always completely clear. This guide is intended to provide all groups concerned, such as: processors users planners insulating glass manufacturers and fitters with more certainty about the definitions of these products and the requirements placed on them. 2.0 The product and its manufacture Toughened safety glass Toughened safety glass (TSG) is a heattempered flat glass (made for example of float glass or ornamental glass) to which a characteristic residual stress states has been imparted by a special heat treatment of the glass. Compared with normally cooled flat glass, this so-called thermal tempering process ensures a substantially higher toughness of the glass against mechanical and thermal effects. To do so, the glass is heated in a "tempering furnace" within a defined period and uniformly to about 620 C, and then rapidly cooled. As a result, the glass receives a compressive stress on both its surfaces (in each case in an area with a thickness of 20 % of the glass thickness) and a tensile stress in its core. Compressive and tensile stresses are in equilibrium. For that reason, subsequent processing of the surfaces or edges can change the properties of the TSG for the worse or lead to direct fracture. TSG has, compared with non-tempered glass, a high bending tensile strength and temperature change resistance in addition to a fine-crumbling fracture pattern, giving the product its safety characteristics. During the manufacture of float glass, it is impossible to prevent nickel contamination of the molten glass despite taking the greatest care. As a result, occlusions of nickel sulphide can occur in the glass. These have the disagreeable propensity to increase their volume over time due to phase transformation. This process is accelerated by the effect of temperature. In normally cooled glass, this phenomenon presents no problems. If however there is an occlusion of this type in the tensile stress area in the core of a toughened safety glass, the resultant additional stresses can lead to abrupt failure of the sheet. An effective counter-measure is a renewed heat treatment of this glass in a heat-soak test. approx. 0.2 ad Compressive stress d Tensile stress (Figure 1) Tensile and compressive stress in the sheet cross-section of TSG approx. 0.2 ad Compressive stress (Fig. 1) 2

3 Heat soaking of toughened safety glass In the heat-soak test, the already thermally tempered TSG is subjected to a further temperature process. The thermally tempered glass is heated in a furnace specially provided for the purpose and under defined conditions, and after reaching the specified temperature it is stored for a defined period. As this happens, any nickel sulphide occlusions that may be present become larger: if they are inside the tension zone and have a minimum size, they lead to fracture of the TSG. When this process is properly implemented, it is possible as far as is known today to reduce the failure probability of the glass sheets to the degree required for building work. 3.0 Building authority requirements A distinction is made between productrelated and applications-related requirements. 3.1 Product-related requirements A distinction is made in Germany between heat-soaked TSG according to the European definition (EN 14179) and that according to the German Construction Products List. "ESG-H" is an independent German term documenting the particularly strict requirements of the Construction Products List A, Part 1, Serial No , Annex 11.11, which go beyond the European standard. The differences between thermally tempered soda lime toughened safety glass according to the German Construction Products List A Part 1 Serial No , in the following referred to for short as "TSG"; "heat-soaked thermally tempered soda lime toughened safety glass" according to EN 14179, in the following referred to for short as "heat-soaked TSG"; heat-soaked soda lime toughened safety glass (ESG-H) according to the German Construction Products List A Part 1 Serial No , in the following referred to for short as "ESG-H", are shown in the following table. It should be mentioned at this point that the requirements placed on heat-soaked TSG according to EN and on ESG-H according to the German Construction Products List can also be met by a single product. For an appropriate identification, see for example Fig. 3 Temperature in C max. 320 target 290 to 300 min. 280 (Figure 2) Temperature curve during heat-soaking according to Construction Products List Room temperature (Fig. 2) Heating-up phase Temperature of last glass, to reach 280 C Holding phase Cooling phase Time 3

4 ESG-H a controlled and externally monitored building product to the highest safety standard Criterion TSG Heat-soaked TSG ESG-H (according to Construction (according to EN 14179) (according to Construction Pro- Products List) ducts List A Part 1, Annex 11.11) End of heating-up phase - Reaching of 280 C surface temperature in last glass, according to Construction Products List, Annex 11.11, Section 2.1 (EN Section 5.3.2) Maximum glass temperature C, according to Construction Products List, Annex 11.11, during the heating-up phase Section 2.1 (EN Section 5.3.2) Holding time - 2 h 4 h, according to Construction (EN Section 5.3.3) Products List, Annex 11.11, Section 2.1 Maximum glass temperature C 320 C according to during the holding time (EN Section 5.3.3) Construction Products List, Annex 11.11, Section 2.1 Recording the HS process - Temperature/time curve In consultation with the Number of broken sheets certification office according (EN Annex A.3.2) to Construction Products List, Annex 11.11, Section Initial check of HS furnace - Yes, on own responsibility Yes, by external monitoring (EN Section 6.5 and according to Construction Annex A) Products List, Annex 11.11, Section 3.3 Routine monitoring of the - 1 year after initial check; Every 2 years, by external HS furnace then every 5 years, monitoring according to on own responsibility Construction Products List, (EN Annex A.3.2) Annex 11.11, Section 3.3 Basic glass Float glass according to EN Float glass or coated glass Drawn flat glass according to EN made of float glass, also Ornamental glass according to EN enamelled, according to Coated glass according to EN Construction Products List, (EN Section 4 and EN Section ) Annex 11.11, Section 1 Enamelling permissible Yes, according to Construction Products List, Annex 11.11, Section 1 (EN Section 3.4 and EN Section ) Characteristic bending tensile See EN , Section 9.4, Table 6 (EN Section 11.4) strengths Clear, tinted in the mass, 120 N/mm 2 coated float glass Enamelled float glass 75 N/mm 2 (enamelling in the tension zone) Ornamental glass, 90 N/mm 2 Not regulated by Construction Drawn flat glass Products List 4

5 Criterion TSG Heat-soaked TSG ESG-H (according to Construction (according to EN 14179) (according to Construction Pro- Products List) ducts List A Part 1, Annex 11.11) Fracture pattern See EN , Section 8, See EN , Section 10, See EN , Section 8, requirements test sheet size 360 x 1110 mm; test sheet size 360 x 1110 mm test sheet size 360 x 1110 mm; compliance in all producible compliance in all producible dimensions dimensions External monitoring No Yes, according to Construction Products List, Annex 11.11, Section 3.1 Depth of max. permissible 15 % of glass Not mentioned 5 % of glass thickness edge damage thickness (as per TRLV) according to Construction Products List, Annex 11.11, Section Edge finishing, holes 1), Permissible according to Permissible according to Permissible according to apertures, cut-outs EN , Section 7 EN , Section 9 EN , Section 7 Initial check of product Required according to Required according to Required according to EN , Section EN , Section 5.2 Construction Products List, Annex 11.11, Section 3.1 In-factory production check Required according to Required according to Required according to incl. documentation EN , Section 5.3 EN , Sections 5.3 to 5.5 Construction Products List, Annex 11.11, Section 3.2 2) Identification According to EN According to EN Required according to Section 10: Name or Section 12: Name or Construction Products List, trademark of manufacturer trademark of manufacturer Annex 11.11: Manufacturer, or Text EN Text EN manufacturer's plant, text "ESG-H", certification office according to Construction Products List, Annex 11.11, Section 2.3 Requirements on the ÜH / System 3 - / System 3 ÜZ verification of conformity EN Annex ZA.2 (EN Annex ZA.2.1) BRL / CE-Norm Monitoring of installation For point-supported and back-ventilated wall coverings made of toughened safety glass, special rules apply in many of Germany's states. 1) In applications-related technical rules (TRPV, TRLV, TRAV) there are additional restrictions, e.g. distance from drilled hole to glass edge. 2) The in-factory production check according to DIN EN is also covered due to the initial product TSG according to Construction Products List A Part 1, Serial No

6 ESG-H a controlled and externally monitored building product to the highest safety standard 3.2 Applications-related requirements If TSG with heat-soaking is required in building projects in Germany, it must meet the requirements of Construction Products List A, Part 1 (ESG-H with Ü symbol). If the selected product meets only the requirements of the European product standard (EN 14179), then its use in Germany requires approval on a case-by-case basis from the building inspection authority which is responsible. In the following technical rules and standards, ESG-H instead of TSG is explicitly required for certain installation situations (e.g. installation height > 4 m; pointmounted facades): Technical rules for the use of linear supported glazing (TRLV) Technical rules for the use of fall-proof glazing (TRAV) Technical rules for the use of pointmounted glazing (TRPV) DIN 18008: Glass in building design and construction rules* DIN : Back-ventilated, nonloadbearing, external enclosures of buildings, made from tempered safety glass panels requirements and testing The associated amendments in the lists of technical building regulations must be noted. *Supersedes the aforementioned rules when introduced by building inspection authorities 4.0 In-factory production check and external monitoring Documenting the manufacturing processes, in particular the heat-soak test, and assuring the required product properties are an important part of the production of heat-soaked TSG and ESG-H. The documentation is intended for verifying correct implementation of the heatsoak test in in-house and external monitoring. At the request of the customer, distribution can be agreed upon separately with the manufacturer. The documentation should contain at least the following information: manufacturing plant and furnace designation where more than one furnace is involved order number / item date of performance of heat-soak test holding time and temperature during the holding phase signature of person responsible Additional information for in-house monitoring is possible. When manufacturing ESG-H, external monitoring and certification by a monitoring and certification office named by the Deutsche Institut für Bautechnik (DIBt) is mandatory, regardless of whether the production facility is inside or outside Germany. 5.0 Identification Both EN and the Construction Products List set requirements for the identification of products in order to ensure their traceability (cf. table). According to the Construction Products List, the identification made must be "durable and visible". As a general principle, an identification visible in the installed state is recommended. This is because only in this way can it been seen at all times and by everybody that this is a toughened safety glass with special fracture properties. If the identification is completely absent, use of the toughened safety glass as a building product is not permissible in accordance with the European building products directive. Manufacturer or manufacturer's plant Certification office EN Trademark or product name Mandatory information according to Construction Products List Additional information according to EN (Fig. 3) Example of an identification for ESG-H that also meets the inspection conditions according to EN In the event of complaints or building inspection authority measures for market supervision, documentation of the manufacturing process and identification of the product ESG-H are important tools for verifying correct performance of the heatsoak test. 6

7 6.0 Safety standard All building materials are subject to high demands on their dependability. In this connection, limit values for failure probability are defined. According to DIN "Actions on structures Basis of design, safety concept and design rules", Annex B, and EN 1990 "Eurocode: Basis of structural design", Annex C, the "permitted" failure probability of components whose failure poses a risk to life and limb is 1:1,000,000 per year (dependability index ß > 4.7 for reference period of 1 year). New findings have shown that properly produced ESG-H meets this requirement. This higher safety standard compared with heat-soaked TSG according to EN 14179, which assumes a maximum of one fracture for 400 tonnes of glass, is achieved on the basis of a holding time prolonged by two hours during the heat-soak test. 7.0 Fracture causes in toughened safety glass Thanks to the thermal tempering process, toughened safety glass is mechanically and thermally stronger than non-tempered glass. As a brittle material, it can nevertheless fracture when overloaded and incorrectly handled, with the cause often not being obvious. A nickel-sulphide occlusion is often prematurely assumed to be the cause of the fracture in this case. However there are a number of other possible factors that can create a fracture, such as for example: edge damage, incorrect block setting, unplanned restraints during fitting, exceeding of the temperature change resistance, structural settling, contact of glass with hard materials, subsequent glass finishing, vandalism. To pinpoint the nickel-sulphide occlusion as the cause of fracture, the following features must be verified in line with the current state of scientific research: 1. Butterfly fracture pattern (only visible if the sheet remains inside the frame or if large connected sheet fragments are found) 2. Spherical, usually metallic-sheen occlusion on the fracture level of the fracture's origin 3. Characteristic rough surface structure ("elephant skin") and brass colour of the occlusion in the light-optical microscope (in reflected light) 4. Diameter of occlusion approx to 0.5 mm 5. Position of occlusion in tensile stress area of the sheet cross-section 6. Evidence of the characteristic composition of nickel and sulphur, e.g. by EDX (Energy-Dispersive X-ray spectroscopy) 7. Fracture level analysis All seven features must be confirmed by analysis. The presence of one of these features on its own is insufficient as evidence for nickel sulphide as the cause of the fracture. 8.0 Information on ordering and processing of orders with ESG-H Customer and manufacturer should agree unequivocally whether TSG, heat-soaked TSG or ESG-H according to the definitions set forth in this guideline is the subject matter of the contract. In cases of doubt, it must be clarified which requirements apply for the product to be supplied (safety standard, installation location...). The directions from the manufacturer must be followed. If the customer requests passing on of the documentation of the manufacturing processes, in particular of the heat-soak test, this must be agreed upon separately (cf. Chapter 4). In view of the current legislation, the manufacturers are in some cases compelled to state in writing their reservations about the use of TSG, heat-soaked TSG or ESG-H for the implementation of construction projects when these products are ordered, in order to safeguard their legal position. In the event of complaints about alleged spontaneous fractures, the many other possible causes of damage (cf. Chapter 7) should be considered. 7

8 9.0 Literature / Associated documents EN 1990: Eurocode: basis of structural design. TRPV: Technical rules for the use of pointmounted glazing. Construction Products List A, Construction Products List B and List C, DIBt information, special issue, ISSN DIN : Actions on structures basis of design, safety concept and design rules. DIN 18008: Glass in building design and construction rules. DIN : Back-ventilated, non-loadbearing, external enclosures of buildings, made from tempered safety glass panels. EN 12150, Glass in building thermally tempered soda lime toughened safety glass. EN 14179, Glass in building heatsoaked thermally tempered soda lime toughened safety glass. TRLV: Technical rules for the use of linear supported glazing. TRAV: Technical rules for the use of fallproof glazing. Technical guideline No. 3: "Block setting of glazing units" and No. 17 "Glazing of insulating glass" of the glazier trade, Technical Competence Center of the Glazier Trade, Hadamar. VFF Guideline V.05: Recommendations for use of safety glass in building of Verband Fenster und Fassade e. V., (Association of Window and Facade Manufacturers) Frankfurt a. M. This bulletin was produced by: The Safety glass working group at Bundesverband Flachglas e.v. Mülheimer Straße 1 D Troisdorf With the cooperation of: Flachglas MarkenKreis GmbH, Gelsenkirchen Saint-Gobain Glass Deutschland GmbH, Aachen Semcoglas Holding GmbH, Westerstede and Prof. Dr. Jens Schneider of TU Darmstadt. Bundesverband Flachglas e. V. Approval for reprinting will gladly be given on request. However, reprinting or reproducing the document or parts thereof is not permitted without our express approval. No claims can be derived from the publication. Bundesverband Flachglas e.v. Mülheimer Straße Troisdorf