Astm stp 1434 2002

viii THE USE OF GLASS IN BUILDINGS Glass for Fire Safety and Security This section was developed to cover a broad spectrum of topics, including security glazing, fire rated glass and sp

STP 1434

The Use of Glass in Buildings

VaIerie L Block, editor

ASTM Stock Number: STP1434

Symposium on the Use of Glass in Buildings (1st : 2002 : Pittsburgh, Pa.)

The use of glass in buildings/[edited by] Valerie L Block

p cm. ASTM special technical publication; 1434

Includes bibliographical references and index

"ASTM stock number: STP1434."

ISBN 0-8031-3458-4

1 Glass construction Congresses 2 Glazing Congresses 3 Safety

glass Congresses I Block, Valerie L., 1951- II Title

www.copyright.com/

Peer Review Policy

Each paper published in this volume was evaluated by two peer reviewers and at least one edi- tor The authors addressed all of the reviewers' comments to the satisfaction of both the technical editor(s) and the ASTM International Committee on Publications

To make technical information available as quickly as possible, the peer-reviewed papers in this publication were prepared "camera-ready" as submitted by the authors

The quality of the papers in this publication reflects not only the obvious efforts of the authors and the technical editor(s), but also the work of the peer reviewers In keeping with long-standing publication practices, ASTM International maintains the anonymity of the peer reviewers The ASTM International Committee on Publications acknowledges with appreciation their dedication and con- tribution of time and effort on behalf of ASTM International

Printed in Bridgeport, NJ December 2002

Foreword

The Symposium on The Use of Glass in Buildings was held in Pittsburgh, Pennsylvania

on 14 April, 2002 ASTM International Committee E06 on Performance of Buildings served

as its sponsor The symposium chair of this publication was Valerie L Block

Overview vii

SESSION I: QUALITY ISSUES

ASTM C 1036: Does It Work for Field Inspections of Surface Blemishes?

TED W MAZULA AND IVAR HENNINGS

Codes and Standards Affecting Glass in Buildings: The U.S and Beyond

VALERIE L BLOCK

T h e Impact of Serf.Cleaning Glass -CHRISTOPHER J BARRY AND THOMAS O'DAY

PC.Based Stress Measuring System for On-line Quality Control of Tempered

and Heat.Strengthened GlasS -ALEX S REDNER

U n i t s - - - G E O R G E R TOROK, WERNER LICHTENBERGER, AND ALLAN MAJOR

Evaluation of the Condensation Resistance Rating as Determined Using the

NFRC 500 Progedure DAN1EL J WISE AND BIPIN V SHAH

Development of Design Methodology for Rectangular Glass Supported on

Three Sides to Resist Lateral Uniformity Distributed Loads

MOSTAFA M, EL-SHAM! AND H SCOTT NORVILLE

Wind Load Resistance of Large Trapezoidal Glass Lites H scoyr NORVILLE, MOSTAFA M EL-SHAMI, RYAN JACKSON, AND GEORGE JOHNSON

57

66

79

Window Glass Design Software STEPHEN M MORSE

A Thermal Stress Evaluation Procedure for Monolithic Annealed Glass

W LYNN BEASON AND A WILLIAM LINGNELL

90

105

SESSION IV: GLASS IN HURRICANES

Retrofitting Commercial Structures with Laminated Glass to Withstand

Hurricane E f f e c t s - - P A U L E BEERS, MARK A PILCHER, AND

JEFFREY C SCIAUDONE

Testing of Annealed Glass With Anchored-Film Glass Retention Systems for

Fallout Protection after Thermal Stress Cracking BRUCE S KASKEL,

JOHN E PEARSON, MARK K SCHMIDT, AND ROGER E PELLETIER

121

131

SESSION V: GLASS FOR FIRE SAFETY AND SECURITY The Advantages of Glazing in Overall Security Strategy MiCHAEL BETTEN

AND HENRI BERUBE

The Relationship Between Sprinkler Systems and GlasS JERRY RAZWICK

Design Procedure for Blast.Resistant Laminated Glass H SCOTT NORVILLE

AND EDWARD J CONRATH

This book represents the work of numerous authors at the first Symposium on the Use of Glass in Buildings, April 14, 2002, Pittsburgh, PA Architectural glass was the broad focus for this symposium Papers and presentations were targeted to deliver information the user may find useful related to the quality, design, use, and performance of architectural glass The symposium had a broad focus that incorporated a variety of glass-related topics Em- phasis on glass design was also a key feature to the symposium

The papers contained in this publication represent the commitment of the ASTM E-06.51 subcommittee to providing timely and comprehensive information on glass used in buildings Common themes throughout the tenure of this symposium can be found in this issue Papers discussing quality issues, performance assessments, glass design glass in hurricane-prone areas, and glass for fire safety and security were presented

Quality Issues

Quality issues were addressed from several points of view One paper focused on the problems associated with the use of ASTM C1036 for field inspections of glass Another paper examined the interrelationship between building codes and glass standards A third paper discussed an on-line quality control measuring system for tempered and heat- strengthened glass A fourth paper assessed the impact of self-cleaning glass

Performance Assessments

The intent of this section was to present developments around the performance of insu- lating glass and glass facades One paper discussed in-situ dew point testing to assess life span of insulating glass units A second presented an assessment of annual energy con- sumption of ventilated double glass facades using computer simulation A third paper focused

on the evaluation of a condensation resistance rating as determined using the National Fen- estration Rating Council (NFRC) 500 procedure

Glass Design

A series of papers were presented on glass design One paper examined the structural performance of laminated 'glass made with stiff interlayers Several papers dealt with design methodologies for glass, including rectangular window glass supported on three sides, large trapezoidal window glass lites, and window glass design software based on ASTM El300 Another paper introduced a new procedure for thermal stress evaluation of monolithic glass

Glass in Hurricanes

Glass used in hurricane-prone areas requires special design consideration In this session, one speaker addressed retrofitting commercial structures with laminated glass to withstand hurricane effects A second paper discussed testing of annealed glass with anchored-film glass retention systems

viii THE USE OF GLASS IN BUILDINGS

Glass for Fire Safety and Security

This section was developed to cover a broad spectrum of topics, including security glazing, fire rated glass and sprinklers, and a design procedure for blast resistant laminated glass

Ms Valerie Block

Narberth, PA

Ted W Mazula I and Ivar Hennings 2

ASTM C 1036: Does It Work for Field Inspections of Surface Blemishes?

References: Mazula, T.W and Hennings, I., "ASTM C 1036: Does It Work for Field Inspections of Surface Blemishes?" The Use of Glass in Buildings, ASTM STP 1434, V

Block, Ed., ASTM International, West Conshohocken, PA, 2002

Abstract: Glass can be damaged after installation, and often the home or building owner is left trying to determine if the resulting surface damage is acceptable Glass quality is addressed in ASTM C1036, Standard Specification for Flat Glass However, this standard is not intended for use in the field It is useful for the proper specification of glass quality, and in lieu of any other field inspection standards, parts of ASTM C1036 are helpful in defining acceptable scratch criteria

Keywords: damaged glass, scratched glass, glass inspection, glass specification, glass storage

1Associate Consultant, Glazing Consultants, Inc., 1325 Rotonda Point, Ste 329, Lake Mary, FL, 32746

2Vice President, Glazing Consultants, Inc., 11910 Cypress Links Drive, Fort Myers, FL,

33913

Copyright9 by ASTM International

3

www.astm.org

Table 4

Thicknesses 6.0 mm (l/4in.) or Less A

Linear Blemish Size B

Medium > 75 mm (3in.)

Heavy < 150 ram (6in.)

Heaw > 150 mm f~iin.)

Q3 Quality 3 Di~tribr Allowed A/lowed Allowed Allowed Allowed with a minimum separation of 600mm (24in.) None Allowed

None Allowed None Allowed Glass thicker than 6.0 mm (1/4 in.) and less than or equal to 12.0 mm (1/2 in.) may contain proportionally more and longer blemishes Table 4 does not apply to glass thicker than 12.0 ram (t/2 in.) Allowable blemishes for glass thicker than 12.0 mm (1/2 in,) shall be determined by agreement between the buyer and the seller

n See 6.1.5 for detection of linear blemishes

Table 4 Blemisll lnt~p~ty Chart (continued)

Deteetigl~ Dist~ce Blemish Intensity

Over 3.3 meters ( 132 in.) Heavy

3.3 meters (132 in.) to 1.01 meters (40 in.) Medium

1 meter (39 in.) to 0.2 meters (8 in.) Light

Less than 0.2 meters (8 in.) Faint

Figure 1 - Example of Table 4

Table 4 defaults to allow m e d i u m intensity scratches that are 75 m m (3 in.) long providing any two scratches are not less than 609 m m (24 in.) apart The inspection is to

be conducted per item 6.1.5 Detection for Linear Blemishes (Scratches, Rubs, Digs, and Other Similar Blemishes) as follows: Place samples in a vertical position to the viewer The viewer shall stand approximately 4 m (160 in.) from specimen and look through the sample at an angle o f 90 ~ (perpendicular) to the surface using daylight (without direct sunlight), or other uniform diffused b a c k g r o u n d lighting that simulates daylight, with a

MAZULA AND HENNINGS ON ASTM 1036 5

minimum illuminate of 160 foot-candles The viewer shall move towards the specimen until a blemish is detected (if any) The distance from the viewer to glass surface when the blemish is In'st detectable is defined as the Detection Distance Blemish intensity is determined by comparing the Detection Distance to the Blemish Intensity Chart at the bottom of Table 4 Blemish Length is determined by measuring the perpendicular distance between the ends of the blemish

Homeowners do not want to look through scratched glass, especially if they have paid top dollar for a condominium overlooking the ocean When the sun is setting, even a small scratch in a patio door or window can be disturbing The owner's first thought is to complain to the developer, who then calls the contractor for warranty service If there are

a large number of windows and/or doors with reported scratches, the cost of replacement may be substantial In extreme cases, the homeowner may even contact a glass expert to inspect the glass and help solve the problem The parties review the contract documents

to see if the subject of glass quality has been addressed These documents typically establish glass quality as Q3 from ASTM C 1036 or do not address the issue at all In any event, the homeowner does not want to inspect the glass at 3.3 m (132 in.) with uniform light as required by the standard He or she will probably inspect the glass from a much closer distance and in direct sunlight (Figure 2) The end result is that ASTM C1036 is found to be unsuitable and all parties may be forced to expend considerable time, effort, and expense to resolve the situation.~

Figure 2 - Typical Surface Blemish (Scratch)

Drawbacks to Using ASTM C1036 in the Field

Despite the difficulties of using ASTM C1036 in the field, it is still utilized to inspect installed glass As its title suggests, the standard provides more of a guideline for

"specifying" glass than it does for "field inspecting" glass It is recognized that the industry has used segments of the procedures outlined in the standard for inspection on glazing systems installed in the field There are, however, some inherent problems with

these guidelines

First of all, the procedures to inspect the glass allow significant latitude, which ot~en results in contradictory conclusions by separate inspectors, even on the same piece of glass For example, an inspector that is 6 t~.-4 in tall will view the glass differently than

an inspector at 5 ft.-8 in tall due to the geometry of the viewing angle Second, the natural background (trees, weather conditions, adjacent buildings, etc.) at the exterior of the specimen can either draw to or detract attention from the scratch in question These conditions will undoubtedly vary from building to building Third, existing interior conditions perpendicular to the specimen may not provide the mandatory 3.3 m (132 in.) distance required for the inspection Fourth, fixed glass specimens located on shear walls may not be accessible from the exterior, therefore, cleaning prior to inspection may not be possible Inspection without consideration of cleaning the exterior glass could skew the results Finally, requiring the inspector to view "through" the glass as defined in the standard and detect a scratch is extremely subjective and creates discord among the concerned parties

Suggested Procedures

Quality of glass and the manner in which glass is to be inspected should be specified prior to the construction process Specifiers need to avoid simply referencing the ASTM C 1036 "Standard Specification for Flat Glass" in general terms They should scrutinize the ASTM C 1036 Standard to indicate the glass classification (i.e type, class, style, form, quality, and finish) The typical 6 mm (% in.) thick clear glass product can be represented in Specifications as follows: "Type I - (Transparent Glass, Flat), Class 1 - Clear, Glazing Select Quality (Q3) - intended for architectural applications including reflective and low emissivity coated glass products, and other select glazing applications Blemishes for Type I (Transparent Glass, Flat) shall not be greater than those listed in Table 4." To achieve a higher quality on projects, specifiers should consider specifying Select Quality (Q3) adding criteria as follows: Glass surfaces with detectable linear blemishes that exceed Light Intensity will not be accepted (refer to Table 4 in the standard)

In addition to tightening the specifications, proactive steps should be taken by inspecting the glass at key points in the construction schedule to identify if glass damage

is present Implementation of a quality control program to inspect the glass during the product's life cycle from manufacturing through installation is beneficial in detecting surface damage This requires inspection upon receipt of the product from the manufacturer to the project Implementation of inspection "sign-off sheets" for the glass and glazing system should be completed and dated immediately after installation This process assists in identifying damage that can occur during delivery, storage, handling, and installation This process also establishes a post installation time-line, which can help identify the point at which damage occurred to the glass Evaluation of this data can reduce the number of trades that may have been performing work in the immediate area where damage took place The cost to include glass quality and field inspection guidelines in the project specification manual is minimal and is recommended for all

MAZULA AND HENNINGS ON ASTM 1036 7

projects The costs to setup and implement a daily glass inspection schedule may be substantial and should be considered on an individual project basis Consideration of the project size, type of glass, and access for replacing glass are key components in establishing a glass inspection program

Conclusion

ASTM C1036 is useful in specifying glass, however, it does not meet the needs of the industry for field inspections to evaluate damaged glass A new document is needed that will specifically address the field inspection of glass for damage This document should provide a clear outline with fair and consistent inspection procedures and evaluation criteria to represent all parties (developers, manufacturers, contractors and owners) Furthermore, this document should address all relevant field conditions and eliminate as much subjectivity as possible In the meantime, frequent inspections from receipt of glass to installation are important in monitoring surface damage

References

[1] Gana - Glass Association of North America, 1997 Edition, Glazing Manual, p 73

Codes and Standards Affecting Glass in Buildings: The U.S and Beyond

Reference: Block, V L., "Codes and Standards Affecting Glass in Buildings: The

U.S and Beyond," The Use of Glass in Buildings, ASTM STP 1434, A.B Smith and C.D Jones, Eds., ASTM International, West Conshohocken, PA, 2002

Abstract: This paper examines the development and adoption process of building code requirements and standards related to glass in buildings in the United States Issues covered include safety glazing, skylights, handrails, and glass strength The relationship between the building codes and consensus-based standard organizations, such as the American Society for Testing and Materials (ASTM), American National Standards Institute (ANSI), American Society for Heating, Refrigerating, and Air-conditioning Engineers (ASHRAE), the National Fenestration Rating Council (NFRC), and the International Organization for Standardization (ISO) will be reviewed Specific U.S glass requirements for safety glazing performance and glass quality will be compared to existing Mexican and Canadian requirements At the international level, this paper will review the work of ISO Technical Committee 160, its working groups, current activities, and the interrelationship of national and international standards in the workplace

glazing, and glass quality

Introduction

Building codes and standards go through specific development and adoption processes in the United States In many instances, standards arc referenced or included in the building codes There arc other cases where standards have lead to federal

regulations The glass industry has developed test methods, performance and quality specifications, and practices through ASTM International and the American National Standards Institute (ANSI) Although the development process is different, the adopted standards clarify and enhance the use of glass in building construction

Over the past twenty years, other organizations have developed standards that impact glass The American Society for Heating, Refrigerating, and Air-conditioning Engineers (ASHRAE), for example, has produced ASHRAE 90.1, an energy standard that includes building envelope requirements for commercial and high-rise residential buildings The fenestration performance requirements for thermal transmission (U- factor) and Solar Heat Gain Coefficient in the 90.1 standard guide the designer's selection

of windows, doors, and skylights To verify performance, manufacturers and building

i Technical Director, Primary Glass Manufacturers Council, 2945 SW Wanamaker Drive, Suite A, Topeka,

KS 66614-5321

Copyright9 by ASTM International

8

www.astm.org

BLOCK ON CODES AND STANDARDS 9

code officials look to the National Fenestration Rating Council (NFRC), a national organization that has developed measurement standards for fenestration, as well as a certification and labeling program to assure compliance

Standards writing, testing, and certification activities have occurred in other countries and at the international level This paper will explore the interrelationship between the building codes and industry standards in order to establish their significance

in building construction

U.S Building Codes

For many years, three regional building code organizations developed and

published building codes in the United States They were the Building Officials and Code Administrators (BOCA), the International Conference of Building Officials

(ICBO), and the Southern Building Code Congress International (SBCCI) These

regional code organizations developed "model" building codes that could be adopted by a state or used as a model for a state-developed building code Because the code groups themselves recognized the duplication and, often times, confusion in building code requirements from one model code to another, the three regional code organizations united in 1994 to form the International Code Council (ICC) The ICC is a nonprofit organization dedicated to developing a single set of comprehensive and coordinated national codes that identify minimum health, safety, and general welfare standards In

1998, the ICC published its first set of construction codes that included:

9 International Building Code

9 International Residential Code

9 International Electrical Code

9 International Mechanical Code

9 International Fire Code

9 International Plumbing Code

9 International Energy Conservation Code

While the three model codes still exist, they are no longer being updated and the regional building code organizations actively promote state adoption of the new I-Codes

As part of the code development process, interested individuals may submit new code proposals and code change proposals Public hearings are held to give individuals and organizations access to the code development process At the hearings, individuals can speak for or against a proposal Committee recommendations are sent to the ICC code official members for ratification and a final vote These members consist of public building and fire officials from local communities across the country As impartial officials, they have no vested interest in any specific building product.[1]

Glass requirements are found in Chapter 24 of the International Building Code (IBC), Section R308 of the International Residential Code (IRC), and in the International Energy Conservation Code (IECC) The requirements of the IBC are diverse and focus on wind, snow, and dead loads on glass, sloped glazing and skylights, safety glazing, glass

in handrails and guards, glazing in athletic facilities, and glass in floors and sidewalks (Table 1) The IRC specifically addresses safety glazing and skylights (Table 2), and the IECC includes requirements for thermal transmission (U-factor), Solar Heat Gain Coefficient, Visible Transmittance, and air leakage

The glass and fenestration industries have a voice in the code process via their trade associations or on an individual company basis The Glazing Industry Code Committee (GICC) has represented the interests of the U.S glass and fenestration industries for many years and, through its code consultants, has actually participated in writing the chapters on glass in the codes

Federal regulations and other consensus standards are often referenced in building codes For instance, within Section 2406, Safety Glazing, of the International Building Code, the federal regulation, CPSC 16 CFR 1201, and the American National Standard, ANSI Z97 I, are referenced Both of these standards contain test methods to evaluate the safe performance of glass In Section 1609.1.4 of the International Building Code, ASTM E1886 and E1996 are referenced under Protection of Openings These ASTM standards give testing information and use parameters for fenestration and storm shelters installed in hurricane-prone areas

In some cases, parts of the standards are included verbatim in the code For example, in Section 2405 of the IBC on Sloped Glazing and Skylights, twelve non- factored load charts are reprinted from ASTM E1300, Standard Practice for Determining Load Resistance of Glass in Buildings Each chart covers a specific thickness of

monolithic annealed glass By using the charts and appropriate factors for single and insulating glasses, the building official is able to confirm the load resistance of glass The final part of the building code process is adoption through the appropriate local or state legislative and administrative processes It is important to note that until the building codes are adopted, they have no basis in law and are much like any other standards that may or may not be referenced by the designer of a building Voluntary standards that are referenced or excerpted in the code become mandatory once the code has been adopted

TABLE 1 - - 2000 International Building Code, Chapter 24 Glass and Glazing

General

Definitions

General Requirements

Wind, snow and dead loads on glass

Sloped glazing and skylights

Covers glass, light-transmitting ceramic and light-transmitting plastic panels; glazing replacement

DaUe Glass, Decorative Glass, etc

Identification (labeling), glass supports, framing, interior glazed areas, louvered windows or jalousies

Vertical glass Allowable glazing materials and limitations; screening Non-factored load charts Vertical and sloped glazing; factors

Safety Glazing Human impact loads, identification of safety glazing, multiqight

BLOCK ON CODES AND STANDARDS 11

Glass in handrails and guards

Glazing in athletic facilities

Glass in Floors and Sidewalks

assemblies, hazardous locations, fire department access panels Materials, loads, support, parking garages

Testing Design loads, laminated glass, desi~ formula

Identification

Identification of multipane assemblies

Louvered windows or jalousies

Hazardous locations

Site built windows

Skylights and sloped glazings

Permanent label required for safety glazing unless building code official approves of certificate; tempered spandrel may have removal paper label, tempered glass must have permanent label One pane fully labeled, others can have "16 CFR 1201"

No thinner than 4.76mm (3/16 inch), no longer than

1219 mm (48 inches) ; wired glass prohibited with wire exposed on longitudinal edges

Same as IBC Must comply with 2404 of IBC Definition, permitted materials, screens, screens not required, glass in greenhouses, screen

characteristics, curbs for skylights

U.S Standards

There are thousands o f voluntary standards in the United States that benefit both the manufacturer and user o f products They solve issues o f product compatibility and address consumer safety and health concerns According to Amy Marasco, "Standards also allow for the systemic elimination o f non-value-added product differences (thereby increasing a user's ability to compare competing products), reduce costs, and oRen simplify product development."[2] Two o f the most important standards organizations in the U.S are the American National Standards Institute (ANSI) and the ASTM

International

The American National Standards Institute was founded in 1918 with the purpose

o f ensuring that U.S voluntary standards minimize waste, duplication o f efforts, and conflict The ANSI process is based on determining whether a standard meets the necessary criteria to be approved as an American National Standard The approval process verifies that the principles of openness and due process have been followed and that a consensus o f all interested parties has been reached.[3] Standards consider the needs of producers, users, and other interest groups An appeals process and a

requirement for balance assure that no one interest can manipulate the process unfairly

ASTM traces its roots back to the 19th century and the driving force o f Charles Dudley, a chemist with the Pennsylvania Railroad Dudley issued standard material specifications for the company's suppliers of oil, paint, steel, and other materials To alleviate problems, he organized technical committees to discuss the specifications and testing procedures and form consensus.[4] Today there are more than 80 technical committees involved in a wide range of activities ASTM standards include material standards that cover quality of a building product, engineering standards that cover product design, and testing standards covering the product performance

In 2002, ASTM changed its name to ASTM International and its focus from that

of a national standards organization to one with an international scope According to ASTM President Jim Thomas, "ASTM's method of developing standards is based on consensus without borders Our process ensures that interested individuals and

organizations representing academia, industry, product users, and government alike all have an equal vote in determining a standard's content Participants are welcome from anywhere on the globe."[5]

International Standards

In the 1980s and 1990s, global manufacturers began to demand international standards to minimize confusion caused f~om many proprietary and regional standards These standards are beneficial because they often reduce time-to-market and lower product development costs In addition, global standards facilitate the introduction of products to abroad range of countries, including developing countries.[6] Consumers also benefit from products that are safer and of a higher quality

The glass industry is actively developing international standards through the International Organization for Standardization (ISO), a non-gnvemmental organization established in 1947 ISO is a worldwide federation of national standards bodies from some 140 countries, one from each country.J7] National bodies are characterized as Participating (P) members, Observer (O), or Liaison members "P" members are responsible for submitting votes and/or comments on all technical matters coming before the committee They send delegates to meetings, offer candidates for leadership

positions, and host meetings "O" members monitor the technical work, but do not actively participate They have no power of vote within the committee, although they may attend meetings Liaison members have no power of vote, but are able to attend meetings and receive documents They are typically other committees within ISO with related interests or other international organizations

The United States is a "P" member of many ISO Technical Committees through ANSI While there are other national standards organizations in the U.S., ANSI is responsible for submitting the U.S vote on ballots issued by ISO In addition, ANSI offers U.S participants training and support on international procedures and standards writing ANSI interfaces at the international level, regional level, and national level with

a variety of standards organizations (Fig 1)

BLOCK ON CODES AND STANDARDS 13

I

I

I

io .i Standards Bodies

American Architectural Manufacturers Association American National Standards Institute

American Society for Civil Engineering British Standards Institute

European Committee for Standardization Pan American Standards Commission European Telecommunications Standards Institute Institut Beige de Normalisation

International Electrotechnical Commission International Organization for Standardization National Fire Protection Association

Ente Nazionale Italiano di Unificazione

Glass interests are organized under ISO's Technical Committee (TC) 160, Glass

in Buildings The technical committee (TC) has two subcommittees, one on glass properties and the other on glass uses Within the subcommittees are smaller working groups consisting of national experts who collaborate on the development of intemational standards These standards may contain requirements found in other national standards, but in many cases they are totally new standards developed through the expertise of working group members

There are fifteen TC 160 working groups Under subcommittee one, there are working groups on basic glass products, toughened glass, laminated glass, insulating glass units, mirrors, coated glass, glass blocks and glass paver units, and curved/bent glass Under subcommittee two, working groups are developing standards on the design strength of glazing, light and energy transmission properties and thermal properties of glazing, airborne sound insulation, fire resistant glazed assemblies, assembly rules and structural sealant glazing, safety glazing tests, and security glazing tests

Within each group, work is underway to produce international standards One working group, for example, has produced seven draft documents on security glazing tests These drafts include test methods and classifications for destructive windstorm resistant glazing material, glazing subject to arena airblast load, explosion resistant glazing (shock tube loading), bullet resistant glass, and forced-entry resistant glazing products (tests include repetitive ball drop, repetitive axe and manual attack) Another is working on a test method for safety glazing Each of these standards must eventually go through a ballot review process in order to become a recognized ISO standard

The ISO standards development process is based on consensus This means that there is general agreement, but does not imply unanimity ISO adheres to established target dates Once a New Work item has been approved, a working draft must be approved within six months A Committee Draft is required 18 months after the working draft has been submitted for review Once a Committee Draft has been reproduced, 36 months are allowed to take the draft through the ballot process to final publication Approval of a final standard is based on acceptance by a two-thirds majority of P- members voting and not more than a quarter of the total votes cast being negative The glass industry participates and responds to ISO ballots through a Technical Advisory Group (TAG) that is administered by ASTM The TAG is recognized as Task Group C14.92 under ASTM C14 Glass and Glass Products Interested U.S companies, organizations, and individuals can become members of the U.S TAG Experts are appointed from the TAG to represent the United States at interuational Working Group, Subcommittee, and Full Committee meetings oflSO TCI60 In this way, the U.S position is heard around the world

Recognizing the Need for Codes and Standards

On August 24, 1992, Hurricane Andrew hit Dade County, Florida causing $20 billion in property damage This catastrophic weather event resulted in a change to the South Florida Building Code requiring all external glazing material to be either capable

of resisting windborne debris or to be protected by shutters.[8] Three other South Florida counties and areas along the Gulf Coast in Texas enacted similar requirements The

BLOCK ON CODES AND STANDARDS 15

building officials used Australian data supplied by the glass industry to develop these windborne debris requirements

Soon after South Florida building officials adopted requirements for windborne debris, as ASTM Working Group organized to develop a consensus test method and specification that addressed requirements for glazing subjected to the severe effects of wind events This resulted in two standards, ASTM Test Method for Performance of Exterior Windows, Curtain Walls, Doors and Storm Shutters Impacted by Missile(s) and Exposed to Cyclic Pressure Differentials (El 886) and ASTM Specification for

Performance of Exterior Windows, Curtain Walls, Doors and Storm Shutters Impacted by Windborne Debris in Hurricanes (El 996) Once these standards were adopted as

consensus standards, proponents moved them into the building code arena where they were eventually adopted into the International Building Code

In the area of glass quality, ISO TC 160 SC 1 Working Group 1 has reviewed the CEN, U.S and Japanese quality standards in order to dratt an ISO standard on physical and mechanical properties of soda-lime silicate float glass and stock sized and cut sizes of fiat glass Since basic glass products are sold around the world, these international standards will facilitate international trade and communication by defining clear and unambiguous provisions By allowing input from key producers, the standards will be consistent and accurate, and will represent the state of the art in float glass production capabilities

Federal Standards

In the late 1960s, there was a pattern of social activism in the United States that gave rise to a grassroots consumer rights movement Many industry standards were developed at this time One such standard is the American National Standard Z97.1 This standard was initiated by the glass industry as a means of reducing glass-related injuries Despite its adoption as an industry standard, it became clear that it would only be

effective if it were adopted as a regulation

In 1972, the Consumer Products Safety Act was passed, establishing a federal commission, the Consumer Product Safety Commission (CPSC), with the power to promulgate consumer product standards With the support of industry, labor, safety, and general interest groups, the federal commission granted a petition to develop a federal safety standard for architectural glass, and in 1977, the CPSC standard 16 CFR Part 1201 was enacted by the federal government The standard, like the voluntary ANSI standard, was designed to reduce or eliminate the unreasonable risks of injury associated with architectural glazing materials.J9] Though unlike ANSI Z97.1, CPSC 16 CFR 1201 was mandatory for all parts of the United States

Initially, the CPSC standard applied to glazing in doors and other glazed panels in hazardous locations, such as sidelites and panels adjacent to walkways However, in

1981, CPSC withdrew its glazed panel provisions to permit regulation and enforcement

of glazings in those locations by state and local building code authorities State and local building code officials were expected to impose criteria for the use of glass, subject to human impact, that were consistent with the regulations of CPSC As required by the federal preemption mandate, the three regional model code bodies enacted safety glazing provisions for all hazardous location applications conforming to CPSC standards When

the three regional codes united to produce the Intemational Building Code, these

requirements were incorporated into the new building code Today hazardous locations requiring labeled safety glazing materials in the model building codes are defined to include: [ 1 O]

* Glazing in swinging doors except jalousies

9 Glazing in fixed and sliding panels of sliding patio door assemblies and panels

in other doors, including walk-in closets and wardrobes

9 Glazing in storm doors

9 Glazing in unframed swinging doors

9 Glazing in doors and enclosures of hot tubs, whirlpools, saunas, steam rooms, bathtubs and showers

9 Glazing in any portion of a building wall enclosing these compartments

9 Glazing in an individual fixed or operable panel adjacent to a door

9 Glazing in individual fixed or operable panels where the exposed area of an individual pane is greater than nine square feet and the exposed bottom edge is less than 18 inches above the floor, the exposed top edge is greater than 36 inches above the floor, and one or more walking surface(s) are within 36 inches horizontally of the plane of glazing

9 Glazing in guards and railings, including structural baluster panels and

nonstructural in-fill panels

9 Glazing in walls and fences enclosing indoor and outdoor swimming pools and spas

9 Glazing adjacent to stairways, landings and ramps

The model codes refer to the Consumer Product Safety Commission standard 16 CFR Part 1201 for impact test parameters With the exception of polished wired glass, all safety glazing products must meet Category I or Category II requirements of the CPSC standard

Safety Glazing and Glass Quality Standards, the North American Experience

Safety glazing regulations, standards and code requirements have been in

existence for decades in the United States, but only recently has Mexico adopted a safety glazing/quality standard for glass It is an official Mexican standard, NOM-146-SCFI-

2001, Productos de vidrio - Vidrio de seguridad usado en la construcci6n-

Especificaciones y m6todos de prueba Although many parts of the Mexican standard were modeled after U.S standards, there are some notable differences For one, the scope of the Mexican standard is broader than the U.S standard It does establish a minimum level of safety in order to reduce the threat of injury to people from glass breakage caused by human impact, but it also covers physical attack, accidental and natural events, and acts of aggression and vandalism The Canadian safety glazing standard is similar to the U.S standard (Table 3)

BLOCK ON CODES AND STANDARDS 17

T A B L E 3 - - Comparison of Safety Glazing Requirements

CPSC 16 CFR 1201' CAN/CGSB 12.1" NOM-146-SCFI-2001**

PRODUCTS Safety Glazing Tempered or Laminated Tempered or Laminated

PRODUCT CLASS None Type l=Laminated Class l=Tempered

Type 2=Tempered Class 2=Laminated

Type A=PVB Type B=Resin IMPACT CLASS Cat 1=18 inch drop < 9 Cat I = 460mm (18 inch) 1 = 0.46 m (18 inch)

square feet drop < 8 square meter 2 = 1.22 m (48 inch) Cat 1I 48 inch drop Cat II = 1,220 mm (48 3-3.0m (9.8 ft)

inch) drop > 8 square 4 = 6.0 m (19.6 fl) meter (9 SQ FT) 5 = 9.0 m (29.5 t~) SIZE CLASS Largest manufactured Up to 865 x 1,930 mm 86.3 cm x 193 cm

up to 34 x 76 inch (34 x 76 inch) (34 • 76 inch) QUALITY N/A CAN/CGSB-12.2 and Included in safety

IMPACT TEST Single impact Single impact Single impact

Multiple impacts for Levels 3-5 ENVIRONMENTAL Boil, weathering Boil Boil, humidity,

CENTER PUNCH

NUMBER OF Not specified, for non- 4 Asymmetrical, 3

SPECIMENS symmetrical equal alternate impacts

number of specimens from each side

No opening>3 inch/4 lb No opening > 3 inch/4 sphere can pass lb sphere can pass

10 largest particles < 10 10 largest particles < 10

sq in sq in

Does not remain in No break frame and no break

No break Permanent label or Legibly and paper certificate: permanently marked:

Standard reference Manufacturer name or Date of manufacture logo

Place of manufacture CAN/CGSB- 12 I-M Name of manufacturer M-I for Cat I only

Classification and/or designation of the glass, level of resistance

"Made in Mexico" NOM- 106-SCFI

*Safety Glazing Testing Comparison, Glass Magazine, September 2001, pp 60-61

**Norma Oficial Mexicana NOM-146-SCFI-2001, Productos de vidrio-Vidrio de segnridad usado r la construeci6n-Especificaciones y m~odos de prueba

Certification

Product certification demonstrates compliance with standards and regulations and

is mandatory to place a product on the market in many countries Certification programs are designed to assure high quality and performance In some countries, the government regulates the certification process In other countries, manufacturers are able to self- certify or test and certify through third party, independent testing laboratories A

permanent label usually identifies program compliance

The Safety Glazing Certification Council (SGCC) offers manufacturers in the United States an opportunity to test, certify, and label products to both the federal safety glazing standard CPSC 16 CFR, Part 1201, and the voluntary ANSI Z97.1 safety

standard The SGCC is a nonprofit corporation established in 1971 by manufacturers, building code officials and others interested in public safety The Council is responsible for conducting independent routine sampling and the testing program, approving and registering the form of a Licensee's label, and withdrawing authority to use that label if products do not meet specifications.[11] Over the years, many North American

companies have participated in this certification program

The National Fenestration Rating Council (NFRC) provides a framework for testing, certification, and labeling of fenestration products While the NFRC program is broader in scope than SGCC, it essentially provides the same benefits Manufacturers test their products to determine thermal and solar performance Once testing information

is available, product performance can be determined through simulation Participants in the NFRC program are required to follow specific labeling guidelines NFRC standards are now referenced in the International Building Codes, as well as in the ASHRAE energy standards

Trade associations have also recognized the value of certification programs in the United States The American Architectural Manufacturers Association (AAMA) has maintained a certification program since 1962 This ANSI-accredited Certification Program has given manufacturers a way to independently demonstrate product

performance AAMA's Certification Label tells customers that products have been verified as conforming to ANSI/AAMA/NWWDA 101.I.S 2 standard The Hallmark Certification Program developed by the Window and Door Manufacturers Association (WDMA) consists of a series of inspections and tests to determine that products are being manufactured in the same way in which they were tested Products are evaluated by performance requirements in one of the WDMA standards or test methods

The European community has embraced certification of products with its

Construction Products Directive (CPD) This legislation calls for all products used in buildings to satisfy six basic criteria:

1 Mechanical Resistance and Stability

2 Safety in Case of Fire

3 Hygiene, Health and Environment

4 Safety in Use

5 Protection Against Noise

6 Energy and Heat Retention

BLOCK ON CODES AND STANDARDS 19

In order to comply with the CPD, performance tests are required to demonstrate the ability of a product to perform a particular function, such as fire resistance, as well as factory production control tests to demonstrate that the product continues to pass the required tests The CPD requires the product to have a CE mark in order to be "placed on the market."[ 12]

Conclusion

Building codes and standards rely on test methods, performance and quality specifications, and practices that define product usage Building codes provide

regulations for adoption and enforcement Industry standards provide definitions,

classifications, procedures, measurements of quality and many other important

requirements or conditions to which a product or material must conform Together, they raise the bar on quality and safety of building construction; and the quality and

performance of manufacturing in the United States As more products are sold globally, the number of international standards will increase, offering the same benefits and providing a common basis for product usage and understanding around the world

References

[I] Nickson, R., "Consensus Codes-Does It Matter?" ICC Newsletter, June 2001, p.4 [2] Morasco, A A., "Standards Development: Arc You at Risk?" ASTMStandardization News, June 2000, p.22

[3]Morasco, A A., "Standards Development: Are You at Risk?" ASTMStandardization News, June 2000, p.22

[4] "Innovation by Consensus: ASTM's First Century,"

http://208.211.80/ANNIVERJconsensus.htm

[5] "A New Name A Longstanding Commitment," ASTMStandardization News, January,

2002, p.25

[6] Sterling, J., "Going Global," ASTMStandardization News, June 2001, p.27

[7] "What is ISO?" International Organization for Standardization,

[ 10] For complete code requirements see Chapter 24 of the International Building Code

[11] Certified Products Directory, July 2001, Safety Glazing Certification Council, P.O Box 9, Henderson Harbor, New York 13651, p.7

[12] Colvin, J., "The Effects of European Standardization on the Smaller Company,"

Glass Processing Days Conference Proceedings, Tampere (Finland), 2001, pp.715-718

The Impact of Self-Cleaning Glass

Reference: Barry, C J and O'Day, T., "The Impact of Serf-Cleaning Glass," ASTM

STP 1434, Use of Glass in Buildings, V Block, Ed., ASTM International, West

Conshohocken, PA, 2002

Abstract: Today there is yet one more invisible coating available to improve the properties of window glass At first there were the nearly invisible, low-emissivity coatings, which admit daylight Some of them can also admit beneficial passive solar gain These prevent winter heat loss by reflecting, or not emitting, long-wave (10 micrometer wavelength) infrared thermal radiation These low-emissivity coatings also enhance the effectiveness of heat absorbing solar control tinted glass, and reflective coatings, by preventing absorbed solar heat from radiating towards the room side of a window Now clear, self-cleaning coatings are available for the outer surface of the window These coatings act in different ways to prevent the deposition and build-up of dirt Some can rinse inorganic dust offthe glass with rain or water by their

hydrophobic, or hydrophilic properties Some of them can break down deposited organic dirt using a catalytic action powered by the ultraviolet component of daylight

Keywords: glass, self-cleaning, hydrophobic, hydrophilic, photocatalytic

lntroduc~on

Self-cleaning glass has to deal with organic and inorganic dirt The former is composed of molecules containing a carbon atom that can be broken down by chemical reactions Inorganic dirt is found as dust and grit from fine earth or sand particles from road dust Inorganic materials are not broken down by chemical means but must be prevented from sticking to glass, or must be removed from it by breaking down the adhesive which holds it in place A third form of dirt on windows is seen when salt from sea spray, or minerals and inorganic salts from lawn sprinklers, create deposits on glass as the water evaporates

1Director of Technical Services, Pilkington North America Inc., Toledo, OH 43697

2 Sales and Marketing Dept., Pilkington North America Inc., Toledo, OH 43697

Copyright9 by ASTM International

20

www.astm.org

BARRY AND O'DAY ON SELF-CLEANING GLASS 21

Clear coatings on glass for self-cleaning or dirt-resisting properties can be

temporary, hand applied, on installed glass, or permanent; applied while the glass is being made, either by vacuum deposition or by the pyrolytic chemical vapor deposition (CVD) processes

This paper addresses only the permanent dirt resisting and self-cleaning coatings and not those hand-applied solutions which need to he reapplied periodically

Benefits of Self-Cleaning Glass

The immediately obvious benefits, besides convenience, are as follows:

Economic Benefits

For commercial buildings where professional window cleaning services are used and their cost is known, it is very easy to calculate an economic case for self-cleaning glass Under normal conditions one could expect the need for manual cleaning to he at least one half to one quarter as frequent as for plain glass

Safety

A study of"Worker Deaths by Falls" [1] over a 15-year period, was undertaken

by the Department of Health and Human Services, National Institute for Occupational Safety and Health, in September 2000 They found that in the United States there were

88 reported falling accidents involving window cleaners, of which 62 were fatalities

Aesthetic

The continuous cleaning action of the self-cleaning window means that under normal weather conditions, where rain can occasionally rinse the glass, the level of visible dirt can he expected to stabilize This is in sharp contrast to ordinary glass where the level of dirt continues to accumulate until someone decides it's time to clean the windows

Self-Cleaning Methods

Self-cleaning is partly effected by controlling the action of rain water This can

be done either by repelling water (hydrophobic), or by attracting it (hydrophilic)

Water Repelling

Automotive applications can use hydrophobic coatings which increase the wetting angle of water drops This is aided by the higher wind speeds for cars as compared to buildings, which help carry off dirt containing water drops

105~ a ~wetting

The action of solar ultraviolet light, either direct, or indirect as reflected from clouds, can charge a titanium dioxide (TiO2) coating by raising the outer electrons to a higher band In its charged state it becomes hydrophilic, with a wetting angle in the 10 degree range

I

Figure 2 - Hydrophilic Wetting Angle

The build-up of salt deposits from sea water spray, or mineral deposits from hard water in lawn sprinklers on a hydrophilic coating will not be different from ordinary glass because of the salts' inorganic nature But it is expected that the hydrophilic action of an activated coating will make it much easier to rinse off salt deposits with a hose Mineral deposits from hard water should be prevented from building up If it is necessary to rinse glass with hard water then a few drops of liquid dish washing detergent can be added as a surfactant to prevent droplet formation The best method is

to rinse off dust with a portable, 1 or 2 gallon, hand-pump pressurized, garden spray bottle with plain distilled water from a hardware store

BARRY AND O'DAY ON BEEF-CLEANING GLASS 23

Photocatalyfic Breakdown

A titanium dioxide (TiO2) coating acts, in a simplified description, by first having

its electrons raised to a higher level where they react with water vapor molecules to create OH radicals The direct or indirect, reflected UV light from the sun, present in all outdoor daylight, performs the charging action on the electrons The created OH radicals react with organic dirt on the glass, breaking it down into carbon dioxide (CO2) and water vapor (H20) gases in an accelerated version of naturally occurring

decomposition

One manufacturer of self-cleaning glass calls their product "PhotoActiv rM'' to illustrate this action It should be noted that indirect UV reflected from clouds and buildings is sufficient to activate the'coating Fully activated coatings have been seen

on north elevations, behind insect screens and under roof eaves

Figure 3 - CVD Pyrolytic Process

A reactive gas mixture is presented to the freshly formed hot glass ribbon while it

is still in the float bath The higher temperature of the glass causes a reaction to occur forming a TiO2 coating on the glass

Manufacturing by Vacuum Deposition Process

Sputter coating various materials on glass, in a vacuum chamber, can also create dirt resistant coatings But the nature of the vacuum deposition process appears to give these coatings only hydrophilic (or hydrophobic) properties, without any effective photocataiytic activity

Applications of Self-Cleaning Glass in Buildings

An invisible self-cleaning coating is now added to the list of available glass

options to control window appearance, heat loss and heat gain, amongst other design characteristics This new coating must be properly fabricated and installed to achieve the desired results

Glazing Details

Self-cleaning glass must be protected from contaminants which could smother or otherwise inhibit the catalytic and hydrophilic actions Such contaminants include metal oxide run down from copper or lead roofing and silicone oils which can be leached out, by water, from silicone sealants

Fabrication and Glazing Tools

It is obviously vitally important that the coating is correctly installed in a window Placing the coating incorrectly on the room side surface would not only deny it most of the UV radiation needed to activate the TiO2, but there would also be no rinsing action available from rain to remove inorganic dirt

Handheld portable detectors are available to correctly identify the photocatalytic coating These work by emitting and detecting the reflection of UV light from the TiO2 coating Such light would not be reflected as strongly from clear glass

Handheld tools are also available to detect low-emissivity coatings by measuring their electrical conductivity but unfortunately they do not detect the self-cleaning coatings

The Impact of Self-Cleaning Glass

The new self-cleaning coating offers yet one more option to the window designer

By intelligent selection of products, a window can now be designed and manufactured that is strong enough to resist hurricane winds and the associated debris, it can keep out unwanted solar heat gain, it can reduce winter nighttime heat loss, admit sufficient daylight, provide acoustic insulation, have a color and appearance selected from a wide range of tints and reflectivities, and finally have an exterior self-cleaning surface Self-cleaning glass significantly reduces the labor needed to maintain the exterior surface of windows and represents a considerable cost saving to a building owner over its useful life, but it also offers reduced accident potential in an area where OSHA has reported many accidents and fatalities from falls

The self-cleaning coatings available today do not mean that windows will never have to be cleaned again The coatings work with daylight and rain In dry areas a light hosing will be needed to remove dust Where large deposits of organic dirt, such

as bird droppings, are involved the coating is overwhelmed by the amount of material

to be broken down Such deposits are quickly loosened by the coating and can normally

be removed by hosing, but the organic breakdown of the complete deposit by the coating alone will typically take an unreasonably long time

Finally, it has been seen that most silicone sealants can release silicone oils which are not organic and do not take part in the photocatalytic self-cleaning reaction These oils can cover the sell-cleaning coating for a band a few centimeters wide all around the window and permanently inhibit photocatalytic reaction

BARRY AND O'DAY ON SELF-CLEANING GLASS 25

The window fabricators and installers now have an added complication to their work When the typical double-glazed window includes a clear low-emissivity and a clear self-cleaning coating, there are up to 8 or 12 different assembly combinations for positioning the coatings: only one is correct; the others are all wrong While this

problem may appear to be trivial, its occurrence has already been seen in the field There is now a requirement upon the window fabrication and glazing industries to recognize the availability of these significant glass improvements and to promote,

fabricate and install them correctly

Conclusion

It is less than 20 years since clear and essentially colorless low-emissivity glass coatings have been readily available The benefits of such coatings are now universally recognized and they can be found on commercial and residential windows in the cold north and the warm south where they give improved comfort and energy savings by day and by night, in both summer and winter When the performance and benefits of the clear and colorless self-cleaning coatings are recognized, it is suggested by the authors that in less than 20 years these coatings too will become similarly ubiquitous and will

be used in windows as readily as the low-emissivity coatings

References

[1] "Worker Deaths by Falls," Department of Health and Human Services, National Institute for Occupational Safety and Health, September 2000

PC-Based Stress-Measuring System for On-Line Quality Control of Tempered and Heat-Strengthened Glass

Reference: Redner, A S., "PC-Based Stress-Measuring System for On-Line Quality Control of Tempered and Heat-Strengthened Glass," Use of Glass

hocken, PA 2002

Abstract: A new PC-based stress measuring system was developed for measuring edge-stress in tempered glass The system is based on the Spectral-Contents Analysis method, modified to permit the very high-speed data acquisition needed for measuring stress in a moving item, within a region where the stress gradient is high

Keywords: Stress, tempered glass, quality control

Introduction

Heat-strengthened and fully tempered glass can be as much as 3 and 7 times as strong as annealed glass, depending upon aspect ratio and other factors such as the ac- tual residual surface compression present [1] The additional strength is due to the presence of residual compressive stress in the surface and edge layers, offsetting tension due to handling, impact and service loads Because the increased strength is the prod- uct's main characteristic, there is an obvious need to implement systematic Quality Control stress testing programs to assure conformance to US and foreign specifications [2]

Quality Control procedures are designed to assure the producer and the user that the product meets material specifications, has the desired strength and that test documenta- tion supporting the test data is available In addition, the testing should help the manu- facturer maintain uniformity and production economy

ASTM C1048-97b, "Specification for Heat Treated Flat Glass - Kind HS, Kind

FT Coated and Uncoated Glass," clearly defines the surface and edge pre-stress levels that must be met to satisfy "Fully Tempered" (FT) or "Heat-Strengthened" (HS) glass specifications In addition, the C1048-9To specification includes a reference to ASTM

C 1279-94, "Test Method for Non-Destructive Photoelastic Measurement of Edge and Surface Stresses in Annealed, Heat-Strengthened, and Fully Tempered Flat Glass," for measuring surface and edge compression stresses Historically, the specification changes have been closely related to development of new stress measuring instruments

An example of this influence can be seen in the specification C1048-97b where the residual stress range allowed in Heat-strengthened glass was narrowed as a result of the availability of more accurate test methods described in C1279-94

Copyright9 by ASTM International

26

www.astm.org

REDNER ON HEAT-STRENGTHENED GLASS 27

These surface and edge stress levels are not explicitly stated in the European Norms prEN1863, part 1 and part 2, and prEN 12120, part 1 and part 2, [2] where only the strength is specified, and correlation between the measured surface compression and the strength is the user's burden Assuming, however, that the surface compression increases the strength due to service loads, the European standards are nearly identical

to ASTM C1048-97b

Product specifications published by automotive industries define an additional test parameter: the maximum average tensile stress occurring near the edges In automotive glass, edge stress testing has higher emphasis, justified by the frequency of installation and service failures In both architectural and automotive applications, conformance verification requires an accurate and economical stress measuring test procedure

Testing Procedures

The fragmentation test is suitable only for "safety" glass This is a destructive test seldom practiced in strict accordance with the test method The European standard [2] also includes the required frequency of fragmentation testing and documentation

Measuring surface compression using surface polarimetry [3] [4] and edge stress using transmitted light are described in the ASTM C1279 test method The Grazing Angle Surface Polarimeter (GASP*) is a non-destructive test instrument extensively used in architectural, automotive and "IV glass industries [4], [5] While the GASP is extremely valuable for Quality Control, the method requires glass contact and is not adaptable to an "On-Line" process control Measurement of edge stress offers a viable solution for this purpose The new method described below permits "On-Line" meas- urements, assuring 100% quality control

Edge Stresses in Heat-Strengthened and Tempered Glass

As shown in Figure 1, the edge of tempered glass is, in reality, just another free surface (E) The glass edge is exposed to air quenching in the tempering process [6] and develops edge-surface stress related to the temperature gradient developed during the quenching process in the layers adjacent to the edge-surface (E)

Figure 1 - Development of Residual Stresses on Edge-Surfaces

Surface compression (-) is balanced by tensile (+) stresses in the mid-layers

In regions distant from the edges, a typical parabolic distribution develops

Figure 2 - Average Stress Measured in Transmitted Light

Similarly, the edge surface compression (-) is balanced by tensile (+) stress in the region adjacent to the edge The tensile stresses balancing the surface-compression add

to the edge-balancing tension, creating a region where the average or integrated stress is tensile (+) As a result, tempered and heat-strengthened glass is substantially weakened near the edge [7] This weakened region is of concern to the automotive industry and maximum tensile average stress is stated in automotive glass specifications The edge stress also reveals the strength and service performance of the product

Edge stresses are routinely measured in transmitted light As result of edge finish geometry, edges are not transparent and an extrapolation method is needed to obtain the

"real edge" stress A simple, (but not necessarily most accurate), linear extrapolation technique using results of measurements at 2 points, xl and x2 (Figure 2) is included in the ASTM C1279-94 test method These calculations make the procedure cumber- some The PC-based SCA method [8] automates the test and eliminates the

difficulties of manual extrapolation The speed of data acquisition of the SCA method makes it possible to implement On-Line edge stress measurements

Automated On-Line Production Control of Prestress

The edge stress gradient is very high in a very narrow region The average stress, measured in transmission, decreases rapidly as the distance from the edge increases The Figure 2 shows experimental results acquired using several samples [6] It should

be noted that a 4 th degree polynomial provides an excellent fit to experimentally ac- quired data points A minimum of 10 points are needed to fit the polynomial with

a suitable confidence level within the critical region 2 to 5 mm from the edge In addi- tion, glass exiting the tempering furnace moves with a linear velocity ranging between

100 and 500 ram/see Combining the linear speed and the length of the measured re-

REDNER ON HEAT-STRENGTHENED GLASS 29

gion, one finds that data acquisition near an edge must be completed in less than 0.01 second, requiring a measuring speed of 1000 data points/second

The SCA sensor described below, installed at the exit of a tempering furnace, meas- ures stress at a speed in excess of 2000 points/see The system yields an over-abundant number o f data points to accurately establish the leading and trailing edge-stress, as well

as the maximum average tensile stress in the near-edge region

SCA Measuring Method [8]

When polarized light crosses a sheet of glass exiting a tempering furnace, the

transmitted light intensity is modified The light source (Figure 3) projects polarized light of intensity Io on the glass The transmitted light acquires a retardation 8, related

The basic principles and applications of this method are extensively documented in several publications This SCA method has been used extensively during the last 10 years for On-Line stress measurement in float glass The system schematic (Figure 3) illustrates the components used to implement this method On-Line

An SCA based edge-stress scanning system used to measure edge stress in automo- tive glass is shown in Figure 4 A light-weight sensor is used to scan the edge of auto- motive glass, yielding 1000 data points/sec and a spacial resolution of 0.1 mm, demon- strating the method capability The selection the spectral range determines the speed of

Figure 3 - Schematic of the SCA Measuring System

Figure 4 - Portable Stress Scanner using PC-Based SCA Method

REDNER ON HEAT-STRENGTHENED GLASS 31

data-acquisition, resolution and maximum retardation measuring range The SCA sys- tern designed for measuring edge stress was evaluated up to 8,000 nm, capable of meas- uring 150 MPa stresses in glass thickness up to 20 mm thick The measuring sensitivity

of the SCA sensor shown in Figure 4 was 1 nm (0.02 MPa in 2.5 mm thick glass)

On the other hand, in a 2 mm thick heat-strengthened glass (stress is 30-40 MPa),

the retardation to be measured is less than 200 nm, requiring a resolution of I nm At

a small distance from the edge, the average stress measured in transmission decreases

to zero

A typical edge scan result is shown in Figure 5 The software permits automated calibration, eurve fitting, verification of"zero" and performs a scan based on selected scan length and scan speed

Figure 5 - Stress Scan Graph

Conclusions

A new stress measuring system was developed The speed and spatial resolution of the method permits On-Line monitoring of tempered and heat-strengthened glass The system is PC based allowing 100% inspection and documentation, not possible to obtain using present Quality Control methods

Guillemet, C and Acloque, P., "New Optical Method for Determination of Stresses Near the Surface," 2nd GAMAC Conference, pp 157-163, Paris, 1962 Redner, A.S and Bhat, G.K., "Precision of Surface Stress Measurement Test Methods and Their Correlation to Properties," Proceedings, GPD, pp 169-171, June 1999

Redner, A.S., "Stress Measurement in TV Production," GLASS, 74 (6), pp 218-219, June 1997

Redner, A.S and Voloshin, A.S., "Surface and Edge Stress in Tempered Glass," Proceedings, 9th International Conference on Experimental Mechanics, Copenhagen, 1990

Gulati, S.T., et al, "Delayed Cracking in Automotive Windshields," Material Science Forum 210-213, pp 415-424, 1996

Redner, A.S., "Photoelastic Measurements by Means of Computer-Assisted Spectral Contents Analysis," Experimental Mechanics 25(2) pp 148-153, ffune 1985

PERFORMANCE ASSESSMENTS