Diagnosing Glass Breakage • Chicago Window Expert (2023)

Mark Meshulam is a glass consultant & expert witness involved with glass breakage and glass injuries. This article is available as a PDF download for your library.

Diagnosing Glass Breakage • Chicago Window Expert (1)

Sometimes it’s easy to know why glass breaks

For example, a ball on the floor combined with neighborhood kids running away generally can be considered symptoms of impact-related glass breakage.
Today we will look at four types of glass breakage:

  • Impact breakage
  • Stress cracks
  • Edge damage
  • Spontaneous breakage

Impact breakage
If you know anything about glass, you know that it can break, and when it breaks, it’s not a good thing.
Back to the ball-through-the-window example, the glass breakage pattern will vary depending on the speed and mass of the ball, and the size, thickness and post-annealing treatments that were performed on the glass prior to the ballgame.
A very well-hit hardball, or a well thrown rock squarely hitting a piece of annealed glass will produce glass breakage with a circular puncture with cracks emanating outward from the point of impact.

The resulting shards between these cracks are dangerous! Broken glass injuries can be serious, even deadly. If broken glass shards fall out on your arm (as often happens during clean-up) you will soon be in the emergency room.

Experienced glaziers often tape the shards together with duct tape, then remove the entire panel. If you must remove these shards, remove the upper ones first, then the lower ones. Use heavy rubber gloves, protect your arms, head, eyes and feet, and place the shards in a cardboard box, not a garbage bag.

Blunt or Distributed Impact on Long, Narrow Lite of Annealed Glass

In this example, we see a horizontal crack at the center of the blunt glass impact, with cracks radiating away from the impact. Due to the aspect ratio (relationship between width and height), shards are long and narrow.

(Video) Breaking Glass

If you are dealing with a glass breakage epidemic email me at mark@chicagowindowexpert.com

Small Rock High Velocity
Congratulations to this vandal who was able to select just the right sized small rock, and hurl it at a speed righteous enough to completely puncture this glass. The combination of size and speed resulted in a localized pattern of glass breakage.

This vandal chose quality over quantity. He selected a smaller stone, which he was able to accelerate to a greater velocity, sufficient to completely puncture the glass.

Larger Rock Less Velocity

This vandal’s eyes were bigger than his throwing arm. Although he scored a large area of glass damage, he failed to achieve the goal of full glass penetration. The impact was large enough, however, to break the interior lite of the insulating glass unit. In the picture below you can see two sets of impact breakage patterns. You can also see the rich source of projectiles: railroad tracks. One week after we finished installing windows in a new high school, local kids had a field day with the rocks and our new windows.

Tempered Glass Breakage

When tempered glass breaks, the energy retained in the glass due to internal tension/compression releases explosively and produces a glass breakage pattern sometimes called “cubes”.

Seeing a cubic breakage pattern does not tell you why the glass broke, it only tells you that the glass was tempered. Generally, there are three reasons tempered glass will break: impact, edge damage or inclusions. Inclusions are tiny impurities in the glass. The most well known are nickel sulfide, however there are also ferrous, silica and gaseous inclusions which look like tiny bubbles.

(Video) Nickel Sulfide Inclusion - A World Inside Glass

Normally, when tempered glass breaks, it falls down into a pile of little cubes. Only the most patient glass consultants with the most generous client would ever consider piecing the cubes together to determine the cause of breakage. That being said, I have personally spent many hours picking through broken glass looking for an important clue: a pair of adjacent hexagons, known as a butterfly pattern, that borders a nickel sulfide inclusion.

However, occasionally the pieces of broken tempered glass will stay in the opening, locked to each other like blocks in a masonry arch. And just like in a masonry arch, if you remove the keystone, the arch – or glass in this case – comes tumbling down.

This picture shows broken glass which was a part of a laminated unit. The PVB (polyvinyl butyral) interlayer held the pieces in place, giving us an opportunity to observe that impact related glass breakage can be visible, even in tempered glass.

Spontaneous Breakage in Tempered Glass

Glass, and especially tempered glass, sometimes breaks all by itself. This can be quite disconcerting when, as has happened in a public place which will go unnamed here in our great city, large, thick panes of tempered glass basically blew up fairly frequently. The unusual cause in this rare instance: the glazing contractor attempted to grind the edges of the glass after it was tempered, creating a series of time bombs. It is a very bad idea to modify glass after it is tempered!

A more well-known, but also quite rare cause of spontaneous glass breakage is nickel sulfide inclusions. If you read the previous post, you will already be down with the fact that glass is made from melted powders. A nickel sulfide inclusion is a tiny rock of material that remains in the glass. Below see an artists graphic representation of a nickel sulfide inclusion.

Artists representation of nickel sulfide inclusion.

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You can well imagine that a little rock embedded in a slab of glass which is under high tension/compression forces, could weaken the glass and eventually cause glass breakage. But the story gets worse. Nickel sulfide grows an additional 4% of its size over time. If it is located in the strata in the glass between tension and compression, and it grows, kaboom!

If you have a glass breakage injury email me at mark@chicagowindowexpert.com

Exploding Glass Shower Doors

One of the scariest, yet somewhat common type of tempered glass spontaneous breakage is in glass shower doors. They are exposed to banging against bumpers, heat from the shower, wrenching action of through-mounted towel bars and of course, nickel sulfide inclusions. In hotels, multiply the risk factors by the number of rooms and the lack of care typically taken by a hotel patron.

There can be a delay between impact and crack propagation in tempered glass, just like any other glass, and sometimes the time the glass finally explodes seems ironic and and Machiavellian. Quite often the perverted glass will explode while the unsuspecting victim is naked and in the shower.

Let’s count the problems:

  1. The victim is naked.
  2. There are sharp cubes of glass projectiles flying around.
  3. The victim is bare footed.
  4. The victim must walk barefooted over a field of freshly shattered glass shards.

So here’s a tip for readers who actually do take showers: If your shower door shatters, stand still for a moment and take stock of the situation. Hopefully you are not cut too badly. Without moving your feet too much, look for a towel. Try to grab it and lay it down on the glass so you can walk out. Then get the hell out and never shower again.

Stress Cracks

A “stress crack” will usually only happen in annealed or heat strengthened glass. Stress cracks emanate from the edge of the glass and meander about apparently without purpose. But there is a purpose: to relieve stress in the glass. However, the term “stress crack” can be misleading.

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If annealed glass is subjected to thermal fluctuations that create glass stress beyond its capabilities, the glass will break in a way that will relieve the stresses induced by thermal changes. This type of failure is often a design issue. Heat strengthened glass may have been a better choice for the application.
However, there can be a near-identical breakage pattern which emanates from damage in the glass edge that fails as normal stresses, such as thermal, are applied. In this case the edge damage, not the thermal stress is the culprit.

Photo of broken glass. Classic meandering pattern of heat-related stress crack, accompanied by evidence of edge damage. In this case, the building had both: edge damage and underspecified glass. Reflective blinds and a South exposure combined to create a high frequency of this type of breakage.
To tell the difference between a true glass stress crack and glass breakage due to edge damage, look at the edge of the glass for a chip, which we window linguists sometimes call an “oyster”. You might have to look hard because the oyster could be buried in the primary seal on the #2 or #3 surface.

Another clue would be the distribution of glass breakage in the building. It would be normal to find stress-like cracks on elevations with greater temperature swings. But does the breakage also coincide with the use of reflective interior blinds, especially in a partially opened position? That would be indicative of a true stress crack, rather than a crack induced by edge damage. Also, look outside. Is there something that shades the glass partially? That could be a factor.

New photos: Nickel sulfide inclusions that can spontaneously shatter tempered glass

Want to learn more about nickel sulfide inclusions that can spontaneously shatter temper glass? See this photo album: Nickel Sulfide Inclusion: A tiny speck that destroys tempered glass

Need a glass consultant to diagnose glass breakage or investigate a broken glass injury?No matter where you are,
contact me, Mark Meshulam,
the Chicago Window Expert
For the expert attention


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What should you do if a glass breakage occurs? ›

Use appropriate cut-resistant gloves to handle broken glass. Use forceps, tongs, scoops, or other mechanical devices for removing or retrieving broken glass from the work area or a fume hood. A dustpan and brush should be used to clean up shards/small pieces of broken glass, Pasteur pipettes, or shards of glass.

How do you tell if a window broke from the inside or outside? ›

How can you tell if a window was broken from the outside or the inside? Take a look to see where the shattered glass fell on the ground. Glass on the outside of the window suggests that the window was broken from the inside and vice versa.

Is spontaneous glass breakage covered by warranty? ›

Spontaneous glass breakage may be covered by manufacturers' warranties or by homeowners insurance policies, and the number of reports of breakage is small compared to the amount of tempered glass that is used in homes around the country.

What causes spontaneous glass breakage? ›

Spontaneous glass breakage is an extremely rare occurrence, however it is a possibility. There are a few reasons that glass would break without impact and the two main ones are nickel sulphide inclusions or thermal shock (also known and thermal stress).

Is it OK to keep broken glass in the house? ›

According to Vastu, Glass that has been broken within the house should never be kept there; it should always be thrown out right away. Breaking of Glass or broken glass is regarded as a Mirror Vastu Dosh in Vastu. Similar to this, any window that has cracked glass needs to be fixed right away.

Can broken glass be fixed again? ›

Instead of choosing to throw it away, you can easily fix a cracked glass using a glass repair glue, such as our Bostik Fix & Glue range. Bostik's Fix & Glue super glues are solvent-free, non-toxic, odourless, clear glues that are perfect for repairing a cracked glass, as well as many other household items.

Is window glass breakage covered by insurance? ›

What if I break my own window? Homeowners insurance typically does not cover accidental breakage you cause to your own house. If your child throws a ball through your home's window or you accidentally crack a window pane, you'll likely need to pay out of pocket for the repair.

Are glass windows covered by insurance? ›

Yes, glass damage is usually covered by your comprehensive insurance unless the damage was caused during an accident, at which point your collision coverage or the other driver's liability coverage may apply.

What does glass fall under in insurance? ›

Broken glass is generally handled under your Comprehensive Physical Damage Coverage, which is usually subject to a deductible. Log into your auto insurance policy and see if you have Comprehensive Physical Damage Coverage.

What does breaking of glass indicate? ›

Traditionally, in Indian tradition, the shattering of glass has been connected with bad luck and foreboding warnings of the impending occurrence of something dreadful. There is also a widespread belief that the soul of a person who breaks a glass becomes imprisoned inside the glass in various locations.

What causes hairline cracks in glass? ›

Here's the scientific reason for the crack: Thermal stress cracks — commonly known as “stress cracks” — typically occur in windows when a thermal gradient causes different parts of the glass to expand by different amounts.

What are the 3 causes of glass fracture? ›

The main causes of fracture of glass panes are, in no particular order: 1) Thermal stresses, 2) Impurities, 3) Impact damage and 4) Edge damage.

What is the 3R rule of glass? ›

The 3R rule states "radial fractures make right angles to the rear." By examining the radial fractures and the direction in which they form a right angle, the rear side of the pane of glass (opposite the side the force was applied) can be determined.

What is the 4R rule in glass? ›

The ridges (Wallner lines) on radial cracks nearest the point of impact are at right angles to the side opposite, or to the rear, of the impact. This phenomenon is referred to as the 4R rule, (Ridges on Radial cracks are at Right angle to the Rear.)

What type of evidence is a broken window? ›

Broken or shattered glass found at a crime scene is an important piece of forensic evidence.

What harm can broken glass cause? ›

Shattered glass from a car windshield, window, or an item in the vehicle's cab can cause a range of injuries, including deep cuts and lacerations, internal bleeding, nerve damage, and even loss of limbs. The face and scalp are the body parts most likely to be injured by broken glass, one study noted.

Does broken glass decay? ›

Glass takes a very, very long time to break down. In fact, it can take a glass bottle one million years to decompose in the environment, possibly even more if it's in a landfill.

Why should you not pick up broken glass? ›

Trying to catch it may result in glassware to be broken in your hand. While handling broken glass, wear cut-resistant gloves whenever possible. Disposal nitrile or latex gloves should never be worn. Glass will cut through those gloves.

Why did my double pane window crack? ›

Insulating glass — windows with two panes of glass that have air inside them — may get pressure cracks if they are installed at too high or too low of an elevation level or if there are drastic pressure system changes in the weather.

How do you fix a cracked window without replacing it? ›

If you only need a temporary fix, you can fix cracked glass at home by securing the glass with heavy-duty tape, glass adhesive, clear nail polish, super glue, or plastic bracing. For a longer-term solution and a cleaner finish, an epoxy mixture is recommended.

How do you fix a crack in a double pane window? ›

Whether your window was broken by a weather event or somebody practicing baseball in the backyard, you cannot repair the glass in a double pane window. When glass in a double-pane window is broken, both panes of glass need to be replaced to maintain your window's efficiency.

Which coverage form covers glass breakage? ›

A comprehensive policy provides coverage whether the glass was damaged accidentally or deliberately. The policy covers windows, doors, decorative glass displays, and signs.

Is glass breakage usually covered under peril? ›

Yes, your homeowners insurance covers the cost to repair or replace a broken window if it was broken by a covered peril. Covered perils are things like hurricanes, tornadoes, hail, a falling tree or vandalism.

What type of coverage pays for things like broken glass? ›

Comprehensive insurance coverage is defined as an optional coverage that protects against damage to your vehicle caused by non-collision events that are outside of your control. This includes theft, vandalism, glass and windshield damage, fire, accidents with animals, weather, or other acts of nature.

Can I insure my windows? ›

Window glazing protection, in the context of home insurance, relates to having insurance cover to protect you against damage to the windows in your home, from unforeseen events. This should protect your double glazed windows against damage resulting from unforeseen natural disasters, like extreme winds or storm damage.

What is a covered peril? ›

A covered peril is an event that your insurance will cover. When you file a claim for a covered peril — such as a lightning strike, fire, theft, vandalism, wind, or hail damage — your insurance company will reimburse you for the damage less your homeowners insurance deductible.

What does open peril mean? ›

Open perils coverage is a form of commercial property insurance that provides protection against nearly every type of loss except those specifically excluded in the policy. Open perils property insurance is different from named perils insurance, which only provides coverage for losses specifically listed in the policy.

What is a glass only claim? ›

How does it work. If your car has glass damage only, you can file an insurance claim to get that glass fixed at no cost to you. This means any chipped, cracked, or broken windshields or windows can be repaired or replaced without you paying a deductible.

What property does glass belong to? ›

Glass is an amorphous solid. Although the atomic-scale structure of glass shares characteristics of the structure of a supercooled liquid, glass exhibits all the mechanical properties of a solid.

What is glass or safety glazing material coverage? ›

The Glass or Safety Glazing Material additional coverage, like the peril it replaces, does not require that a specific cause the breakage, but instead covers breakage of glass that is a part of the building, including glass in storm doors and windows, from any cause and is only limited by the amount of insurance.

When should I be worried about cracks on my windows? ›

When you should worry about window frame cracks. Hairline cracks aren't a larger indicator of a foundation issue. However, if you can put a quarter into a crack like an older slot machine, that is a serious issue. Larger cracks aren't something you want to leave unaddressed.

Should I be worried about cracks around my windows? ›

The rule of thumb: If a crack is a quarter-inch wide or wider, then there's concern. Inside the home, drywall can crack as well. “A drywall crack that starts at any corner of a window or the upper corner of any door, at about a 45-degree angle, indicates settlement in the home,” Fenimore says.

Is it normal to have cracks around windows? ›

Have you noticed hairline cracks over doors and windows? This is likely due to what we call “settling” in the industry. No matter the age of your home or structure, movement and shifting over time is fairly normal. These cracks tend to occur in the weakest part of the wall.

What does a stress fracture in glass look like? ›

If you have a crack in your window, you can tell if it's a stress crack by looking for some tell-tale signs: Stress cracks run perpendicular to the edge of the glass. They tend to extend in a straight line about half an inch or more from the window's edge.

What are the two types of glass fracture cracks? ›

When a projectile i.e. a bullet or rock hits the glass, it will form two distinct types of fractures: Radial and Concentric.

What are the two most often used methods of glass analysis? ›

The projects focus on the two elemental analysis techniques X-Ray Fluorescence (XRF) and Laser Ablation Inductively Coupled Mass Spectrometry (LA-ICP-MS) that are commonly used by forensic glass analysts.

Can auto glass spontaneously break? ›

Driving vibrations, heat transfer from the vehicle frame, and excess frame pressure can all damage the edges of the glass and contribute to spontaneous breakage.

What damages are not covered under warranty? ›

A description of damage not covered by the warranty is provided on the The most frequent causes for exclusion of liability under the warranty include: moisture or liquid penetration, mechanical damage — i.e. damage to the device as a result of a fall, impact, etc.

What is the spontaneous glass breakage rate? ›

How Often Does Spontaneous Breakage of Tempered Glass Occur? According to the US Glass Industry, glass breakage rates may be as high as 1%. That's a ridiculously high failure rate. Put differently, 1 in every 100 panes of glass in your building could just randomly shatter.

Can tempered glass break randomly? ›

Spontaneous breakage of tempered glass is most commonly caused by chipped or nicked edges during installation, stress caused by binding in the frame, internal defects such as nickel sulfide inclusions, thermal stresses in the glass, and inadequate thickness to resist high wind loads.

Can car windows shatter from heat? ›

The simple answer is that, barring previous damage to the integrity of the vehicle or the glass, no, the glass in your car will not shatter due to the heat.

Can a window shatter from cold? ›

For a start, the answer to the first question we mentioned is, “Yes, glass can break in the winter.” If a pane of glass is very cold or frozen, it will be unlikely to break, but easier to break than normal.

Which type of damages are not recoverable? ›

Direct damages are the easiest to foresee. For this reason, special damages are not usually recoverable. Special damages are meant to compensate the innocent party for injury or loss that is indirectly related to the breach. Even special damages must be foreseeable to be recoverable.

Which voids the warranty? ›

The warranty period has expired. The defect or part is not covered. The product failure is due to misuse or lack of proper maintenance. You have made significant alterations to the product, affecting its performance.

What is a defense to breach of warranty claim? ›

Defenses to Breach of Warranty

The simplest defense is to show that no warranty exists, whether it's an oral or implied warranty. If the seller made comments about the product, the defense can claim that it was mere “puffery” and not a promise.

What are the different types of glass breaking? ›

Below are four types of glass breakage and how to identify them, in both commercial and residential settings.
  • Stress Cracks. Stress cracks start out near the edge of the window and spread from there. ...
  • Impact Breakage. ...
  • Spontaneous Breakage. ...
  • Edge Damage.
Apr 20, 2020

What kind of property is breaking glass? ›

Definition of Physical Changes – Transformation that DO NOT change the chemical composition of the substance. NOTE: They are usually reversible, but consider shattering the glass in a window. Breaking is a physical change because the shards are still glass, but it can't be easily made whole again.

What glass is the biggest hazard when broken? ›

This toughness gives tempered glass a far higher load and breakage resistance. Toughened glass needs to be hit a lot harder than other safety glass in order to break. Whereas laminated glass holds in place when shattered, toughened glass breaks up into hundreds of tiny pieces.

What is the toughest glass to break? ›

If you're interested in unbreakable glass that truly lives up to its name, polycarbonate panels are the type you want. Polycarbonate panels are significantly more difficult to break than both standard glass windows and laminated glass mentioned above.


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