Mark Meshulam is an expert witness and exterior facade consultant located in Chicago, IL, USA

Glass can be dangerous or deadly. Here are some legal matters I have been involved with as an expert witness:

Woman trips and falls through glass. In an accident, the victim's life can go from normal to disastrous in an instant

• A large bathroom mirror became detached from the wall, broke and injured the occupant who was unclothed
• A storm window blew off a building and impacted and injured a city worker
• A hotel guest was injured when a glass shower door shattered while she showered
• A bicyclist fell through an untempered storefront window and died from his injuries
• A woman fell against untempered storefront glass and was lacerated badly when the glass broke
• Glass in a sports facility broke, presenting a danger to crowds below
• A woman died when she fell through glass in a hotel window-wall

In many of these cases, glass failed due to a pre-existing damage that expressed itself into a full blown failure in barely an instant. There is precious little research on this subject. How much does a bullet hole weaken the glass? How much more easily will a pane of glass break if an edge is chipped? Nobody really knows.

I intend to find out.

Join me and Quast Consulting & Testing of Mosinee, WI in this important study:

Research Proposal
Study to Determine the Effect of Pre-Existing Damage
to Annealed Glass on Breakage Resistance

Introduction
Each year hundreds of people are injured or killed by broken glass, whether by falling through a sheet of glass, or by having glass fall on them, even while they shower when a glass shower door suddenly shatters. This glass may have been in windows, doors or storefronts near where people live, work and walk. In some of these instances, witnesses have reported that a seemingly intact lite of glass seemingly “gave way”, bringing about a dangerous condition.

The author of this study, Mark Meshulam, has been involved as an expert witness and exterior facade consultant in legal matters involving two deaths and one severe injury due to glass breakage. In each of these cases, the glass broke suddenly without much force having been applied to it.

Co-author Tim Quast of Quast Consulting and Testing says, “the importance of this study can not be understated. Glass can be very strong, yet sometimes it just simply gives way bringing about serious injury or even death. We are proud to work with Mark to develop a test method that will get at the root of this problem, and to generate data that will be of real value to our industry and community.” Quast’s window testing laboratory in Mosinee, WI will be the site of the glass testing.

Deep scratch in storefront glass. The pane next to this one broke under minor pressure, severely lacerating a woman

Equally known to those in the glazing industry is the propensity for glass to break if damaged at the edge. For this reason, almost universally, rubber setting blocks are placed beneath glass when it is installed. This avoids any chance that the glass edge will come in contact with a harder material that might chip the glass edge, thereby weakening the glass.

Pressures which may be applied to the glass, whether by wind, impact, human contact or thermal variations, appear to greatly accelerate the propagation of cracks through glass. The purpose of this study is to determine if, and to what extent, pre-existing damage to glass reduces the ability of the glass to withstand pressure.

To accomplish this, pressures will be applied to damaged and undamaged glass. Failure pressures will be observed, collected and compared.

Methods for Testing Glass in Laboratory

Bullet hole in glass - conchoidal fracture

Three damage types, found often in real life will be simulated:

1. A low caliber bullet hole
2. A chip at the glass edge
3. A scratch on the glass surface

Bullet holes will be simulated by dropping a steel ball from a height that will produce the familiar cone-shaped spall known as a Hertzian cone crack, a type of conchoidal fracture. This method of is known as the Hertzian fracture test. A clear opening of 1/8” diameter at the impact side will be created.

Edge damage will be caused by using a spring-loaded hardened steel punch applied to the edge at a depth of approximately ¼ the overall glass thickness. This will produce a familiar chip fracture known to the trades as an “oyster”.

Glass edge damage - oyster shaped chip fracture

The scratch damage will be simulated by scratching a uniform X on the glass face.

In order to apply pressure the glass, it will be placed horizontally on the top of a test chamber. Using a regulated air blower, air will be extracted from the chamber. This will induce a downward load on the glass. A manometer will be used to measure the differential pressure that is applied to the glass. Undamaged and pre-damaged glass specimens will be brought to destruction through increasing chamber pressure. The pressure at which the failure occurs will be recorded.

There are three additional variables that are of interest to this study:

1. Deflection of the glass under load
2. The side of the glass that has preexisting damage compared with the direction of pressure
3. Speed of crack propagation.

Glass deflection is important because if a relationship can be established between deflection and failure, there may be an opportunity to communicate to the public that excessive deflection of a glass lite may be a precursor to a dangerous condition.

The direction of pressure is important because of tension/compression in the glass under bending. Glass cutting practice involves bending the glass away from the score mark. There may be a difference in breakage behavior if the bending is toward the score mark.

Excerpt from glass cutting manual. The manufacturer points out that even annealed glass has internal tensions that aid in breakage. A fissure depth of only 8-10% is needed to break the glass by bending it. 8% of 1/4" typical glass thickness is only 20/1000 of an inch

In order to quantify deflection, during the glass testing a dial indicator will be used at the center of the glass. Maximum deflection before failure will be recorded.

In order to quantify the speed of crack propagation, a high-speed video camera will be utilized. With a known frame rate and glass dimensions, speed of propagation can be calculated by studying the videotapes after the testing.

To reduce the variables, all damage applied to the test specimens will be located at centerlines of the glass. Bullet holes will be located as close to the glass center as possible. Edge damage will be located at the longitudinal center of the edge.

The Pitch
We are seeking individual, corporate and government sponsors for this research.
Minimum sponsorship is $1000. Sponsors will be invited to attend the glass testing in the laboratory and will be recognized when the research paper is released. If you or your organization are interested in participating, please call or write now.

Please join this project if you can allocate resources for this life-safety cause.

Thank you!
Mark Meshulam
Chicago Window Expert
Expert witness and exterior facade consultant

Want to be a research sponsor?

Mark Meshulam, Chicago Window Expert invites you to join his research team

Even if you are in ,
call me, Mark Meshulam,

the Chicago Window Expert

to talk about joining our research team!

My phone: 847-878-8922

My email: Mark@ChicagoWindowExpert.com

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